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Publication Number: FHWA-HRT-05-153
Date: December 2006

Long-Term Pavement Performance Program Falling Weight Deflectometer Maintenance Manual

Chapter 3. Subassembly

The subassembly is a rigid component that bolts directly to the trailer frame with four bolts and nylon lock nuts to secure the bolts. The top of the subassembly, or tower bridge, is bolted into place using eight bolts and washers. Use thread locker (medium-strength blue Loctite® or equivalent) to prevent loosening. Every 3 to 6 months, examine all eight bolts, tighten, and replace any missing bolts).

Figure 25 shows the subassembly and figure 26 shows the subassembly mounted on the trailer.

Figure 25. Freshly painted subassembly with joints reinforced.

Photograph shows a subassembly that has been freshly painted and had its joints reinforced. Arrows indicate the locations of the oil pump mounting location, hydraulic oil fill neck, hydraulic oil sight glass, top of subassembly open parenthesis tower bridge close parenthesis, raise and lower guide rails that attach to strike plate, base of subassembly, and the four bolt locations open parenthesis two on each side close parenthesis to attach subassembly to the trailer.

Figure 26. Subassembly mounted on trailer.

Photograph shows a subassembly mounted on a trailer. Arrows indicate the locations of the channel iron and the hydraulic tank.

SUBASSEMBLY MAINTENANCE

Conduct a visual examination monthly to ensure no cracks develop. The most common points where cracks may develop are the welds between the channel iron and the hydraulic tank (both sides) and at the opposite ends of the channel. Cracking can be caused if only one side of the channel is welded, rather than both sides. This was a common problem on older units.

If cracks develop, a reputable welding shop needs to make the repairs, observing the following four steps:

  1. Disconnect the charging plug, light plug, safety chain, and breakaway cable from the tow vehicle (figure 27).

    Figure 27. FWD attached to tow vehicle.

    Photograph shows a F W D attached to a tow vehicle. Arrows indicate the locations of the breakaway cable, light plug, chains, and power plug.
     
  2. Raise the trailer hitch completely off the tow vehicle.
  3. Disconnect the positive (+) and negative (-) battery terminals (figure 28).
  4. Disconnect the multisignal cable from the power control box (figure 29).

Figure 28. Disconnect battery terminals.

Photograph shows connected battery terminals. Arrows indicate the locations of the positive and negative terminals that need to be disconnected.

Figure 29. Multisignal connection to control box.

Photograph shows a multisignal connection to a control box. Arrow indicates the location of the multisignal cable terminal that must be disconnected.
 

Disconnect all electrical components during the welding to reduce the chance of electrical current flowing through the trailer, which might damage sensitive electronics.

After the repairs are made, the affected area can be cleaned and painted. Figures 30 and 31 show the reinforced welds on the subassembly.

Figure 30. Reinforced weld on top of subassembly.

Photograph shows reinforced welds on the top the subassembly. Arrow indicates the location of the reinforced top joint and the reinforced bottom joint.

Figure 31. Reinforced weld on bottom of subassembly.

Photograph shows reinforced weld on bottom of subassembly. Arrow indicates subassembly bottom joint reinforced weld.

Guide Profiles

Annual maintenance is recommended on the guide profiles including shimming the rollers for correct alignment. Rails should be checked every 6 months. They may need to be shimmed periodically, depending on the amount of use. Yearly, apply a liberal amount of grease to the guide roller post (figure 32). This requires removing the guide profile rails as seen in figure 25.

Figure 32. Guide locations on a subassembly.

Photograph show a subassembly mounted on a trailer. Arrows indicate the locations of the four mounting bolts to attach the subassembly to the trailer, guide roller, and shims.
 

Although the subassembly frame does not require any specific maintenance, it is recommended that all associated fasteners be checked for tightness every 3 to 6 months. Other components also may require periodic maintenance and repair:

  • Main cylinder.
  • Hydraulic motor.
  • Upper catch assembly.
  • Hydraulic pump.
  • Side cylinders (two).
  • Flow control valves and pressure switches.

Drop Weight Assembly

Minimal maintenance is required on the drop weight assembly:

  1. Replace the lift collar semiannually. Unscrew the collar and replace, but do not apply thread locker. Use the setscrew to secure the lift collar. Rotate the upper catch daily to ensure equal wear on the collar (figure 33).

    Figure 33. Drop weight assembly.

    Photograph shows a drop weight assembly. Arrows indicate the locations of the lift collar, buffer stem slots, and dowel pins for the F W D weights.
     
  2. Install the glide ring on the drop weight assembly (a new feature not found on older models). This glide ring prevents metal chaffing from occurring between drop weight package and the main cylinder. After disassembly and during assembly, apply a small amount of grease to the glide ring (figures 34 and 35). Thereafter, lubricate weekly with a spray silicone.

    Figure 34. Placement of glide ring, bottom view of weight package.

    Photograph is a bottom view of a weight package showing the placement of a glide ring.

    Figure 35. Closeup view of glide ring.

    Photograph shows a closeup view of the guide ring location. Note: later model designs have a groove machined in the bottom base for a glide ring. Lubricate weekly with spray silicone.
     
  3. Place four adjustable drop height targets (activators) in a vertical rail on the drop weight.These targets, which are adjustable to various loads, can be selected to determine weight-height target locations (figure 36).

    Figure 36. Roller guides mounted to drop plate.

    Photograph shows roller guides mounted to a drop plate. Arrows indicate the locations of the roller bearing guide bar, original lift collar, set screw, adjustable drop height targets, and dowel pins.
     
  4. Check buffer pads for proper seating and any cracks or splitting (figure 37).

    Figure 37. Buffer pads and drop plate in position.

    Photograph shows the buffer pads and drop plate in position. Arrows indicate the locations of the buffer pads open parenthesis 110 millimeters close parenthesis, transport lock, drop plate, and stop bolt open parenthesis check annually close parenthesis.
     
  5. Place the lift collar on the drop plate (figure 38).

    Figure 38. Lift collar.

    Photograph shows a lift collar. Arrows indicate the locations of the lift collar open parenthesis make sure setscrew is secure and use medium strength thread sealer close parenthesis and the center cylinder flange.
     
  6. Stack the weights over the buffer plates on the drop plate and tighten securely (figure 39).

    Figure 39. Weights on the drop weight assembly.

    Photograph shows weights on the drop weight assembly. Arrows indicate the locations of the guide roller open parenthesis lubricate weekly close parenthesis, tightening handle and screw open parenthesis check daily close parenthesis, weights, buffer pads open parenthesis make sure buffers are seated correctly in the drop weight assembly and check for cracks or splitting close parenthesis, weight high open parenthesis W H close parenthesis proximity switch, target open parenthesis lower to increase load and raise to decrease load close parenthesis, and spacer open parenthesis length varies by weight configuration used close parenthesis.

HYDRAULIC SYSTEM

The hydraulic system is one of the most important parts on the FWD. It can also be the most complicated to assemble and troubleshoot. The following paragraphs describe and illustrate various components of the hydraulic system.

The hydraulic system incorporates the following main items:

  • A hydraulic cylinder ("main cylinder") for raising and lowering the weight catch.
  • Two parallel connected cylinders ("side cylinders") for raising and lowering the falling weight subassembly.
  • A hydraulic pump (figures 40 and 41) including an adjustable excess pressure valve operated by:
    – A 12 volt (V) direct current motor.
    – A directional control ("DC") valve (also called the "A/B valve") with two-12V direct current coils, denoted "A" and "B."
    – A normally open solenoid valve with a 12 V direct current coil, denoted "C."
    – A normally closed solenoid valve with a 12 V direct current coil denoted "D."
    – A hydraulic oil reservoir (tank), which is an integral part of the falling weight subassembly frame.
    – Two pressure sensitive switches (one normally closed contact and one normally open contact) used in the electronic control circuits.
 

The modes of operation of the hydraulic system are to raise and lower the load plate, as well as raise and drop the weights. The modes of operation are best explained in a "truth table," as shown in table 1. It is also useful to install a hydraulic pressure gauge to assist in troubleshooting.

Table 1. Truth Table for Hydraulic System Operation.
Mode A B C D M1  
Raise weight (lower plate) OFF ON OFF OFF ON (Notes 1, 2, 3)
Drop weight (lower plate) OFF ON ON OFF ON (Notes 1, 3)
Lower catch ON OFF ON OFF ON (Note 4)
Raise plate ON OFF ON ON ON
1M is the coil of the motor starting relay.
Note 1: "Plate" means falling weight subassembly.
Note 2: If the weight has dropped, then this will be a "raise catch" mode.
Note 3: This mode will also cause lowering of the plate and will not be fully active until both shafts of the two "raise
plate" cylinders (side cylinders) have been pressed out completely to their bottom position.
Note 4: This mode also lowers the catch.

The hydraulic pump is mounted to the top of the hydraulic fluid tank (figures 40 and 41). A single bolt, which runs through the bottom of the tank, holds the pump in place. An O-ring is used to seal the pump to the tank. The pump has proven very reliable. Yearly, remove the hydraulic motor and lubricate the drive coupler with high quality moly-type grease. The only other routine monthly maintenance needed are changing oil and filter, tightening motor to pump bolts, and checking for excess pressure and adjusting if necessary (as explained in the Dynatest Owner’s Manual). A drain plug for replacing or adjusting hydraulic fluid is located on the bottom of the hydraulic tank.

Figure 40. Hydraulic pump, motor, and fluid tank.

Photograph shows a hydraulic pump, motor, and fluid tank. Arrows indicate the locations of the hydraulic motor, hydraulic hoses and connections, oil filter, manifold block, A/B valve, hydraulic line, hydraulic pressure gauge, filler cap, and hydraulic fluid tank.

Figure 41. Hydraulic pump.

Photograph shows a hydraulic pump. Arrows indicate the locations of the hydraulic fill, hydraulic pump with excess pressure bypass valve location open parenthesis not installed in picture close parenthesis, steel hydraulic line clamp, hydraulic drive coupler open parenthesis lubricate yearly close parenthesis, and rubber O-ring under pump housing.

Semiannually check all steel line clamps. These clamps are used to keep the steel lines from rubbing against each other and from contacting areas where a hole could result. Check the clamps every 6 months and apply a medium-strength thread locker to fasteners.

The hydraulic motor mounts directly to the pump (figure 42). The 12 V-motor is a brand that is equipped with inspection covers, and it has replaceable brushes and brush retainers. Brushes and retainers (figure 43) should be checked every 3 months.

Figure 42. Hydraulic motor.

Photograph shows a hydraulic motor. Arrows indicate the locations of the hydraulic motor, hydraulic manifold block bolts, cover plate for the hydraulic motor brushes, hydraulic pump, and oil ports.

Figure 43. Brushes and retainer.

Photograph shows brushes and retainer. An arrow indicates the location of the retaining clip open parenthesis brushes are located behind clip close parenthesis.

The manifold block is attached to the pump housing (figure 44). A gauge helps in troubleshooting pressure-related problems. If one is not installed, it is recommended to install one.

Figure 44. Manifold block and A/B valve mounted to hydraulic pump.

Photograph shows a manifold block and A/B valve mounted to a hydraulic pump. Arrows indicate the locations of the hydraulic motor, manifold block, oil filter open parenthesis replace yearly close parenthesis, A valve, B valve, C valve, D valve, and hydraulic pressure gauge open parenthesis optional, but recommended close parenthesis.

NOTE: Rubber O-rings are used to seal the manifold block to the pump and the A/B valve to the manifold (figure 45).

Figure 45. Components of the A/B valve and manifold block.

Photograph shows components of the A/B valve and manifold block. Arrows indicate the locations of the pressure sensitive switch P S2 open parenthesis yellow or green dot on the end of the switch close parenthesis, A/B valve, C valve, D valve, manifold block, hydraulic line fitting, pressure sensitive switch P S1 open parenthesis red dot on the end of the switch close parenthesis.

PS1 and PS2 are pressure sensitive switches (figures 46 and 47). PS1 is a pressure sensitive switch with a normally closed contact that opens when the pump outlet pressure exceeds approximately 40 bar (34.47 to 4,136.85 kPa (5–600 psi)). PS1 is used for excess pressure detection; thus, the (red) PS1 light emitting diodes (LED )must turn off at excess pressure.

PS2 is a pressure sensitive switch with a normally open contact, which closes from the pressure in the return oil during catch lowering (setting approximate 2 bar (25–30 psi)). PS2 must stay on while the catch is moving downward, and it must come off when the catch stops at its bottom position. If any of these operations fail, check to see if oil is leaking from the end of the switch. A leak is a good indication the switch has failed.

NOTE: If PS1 or PS2 must be replaced, use Teflon® tape on the threads to ensure a secure, leak-free seal. Take care to not over tighten to the point of breaking the fitting or causing thread damage. Over tightening may also damage the manifold block.

Figure 46. PS1 and PS2 switches.

Photograph shows pressure sensitive P S1 open parenthesis marked with a green dot close parenthesis and PS2 open parenthesis marked with a red dot close parenthesis switches.

Figure 47. Threads on the PS1/PS2 switch.

Photograph shows threads on the P S1/P S2 switch. An arrow indicates the location of the threads wrapped with Teflon-brand tape.

The hydraulic motor solenoid switch requires no routine maintenance (figure 48). Periodically check to make sure the connections are tight.

Figure 48. Solenoid mounted to hydraulic motor.

Photograph shows a solenoid mounted to a hydraulic motor. An arrow indicates the location of the hydraulic motor solenoid.

Periodically check the wiring carefully for loose connections (figures 49 and 50). Be careful not to over tighten connections, as damage can occur to terminal lugs. As part of the monthly maintenance, remove A/B wiring plugs and clean with contact cleaner. Also, remove and clean coils on each end of the A/B valve. Remove and clean the stems on C/D valve assembly.

Figure 49. Wiring for Motor and Solenoid.

Photograph shows wiring for a motor and solenoid. Arrows indicate the locations of the positive connection open parenthesis from hydraulic motor close parenthesis, negative connection open parenthesis ground for the motor close parenthesis, excessive pressure adjustment location, positive connection to the manual control box, the ground from the manual control box open parenthesis check periodically to ensure it is tight close parenthesis, and the pump.

Figure 50. Electrical wiring for the hydraulic motor.

Photograph shows electrical wiring for the hydraulic motor. Arrows indicate the locations of the negative terminal, positive terminal, C valve, D valve, and A/B wiring open parenthesis remove annually and clean with contact cleaner close parenthesis. Note: check connections periodically to ensure they are tight, but do not overtighten open parenthesis damage can occur to terminal lugs close parenthesis.

Main Cylinder

The main cylinder is made up of four major components:

  • Center cylinder.
  • Main cylinder gland.
  • Catch flange and release piston.
  • Outer tube.

Figure 51shows the main cylinder partially disassembled. Damaged seals could result in leaking hydraulic fluid or loss of hydraulic pressure.

Figure 51. Main cylinder components.

Photograph shows main cylinder components. Arrows indicate the locations of the O-ring open parenthesis inside at the base of tube close parenthesis, main cylinder nut open parenthesis high-strength thread locker close parenthesis, beveled edge to the bottom, piston with seals installed, main cylinder outer tube, inner tube open parenthesis note: holes to the top close parenthesis, main cylinder gland with outer O-ring installed, and center cylinder tube.

Center Cylinder

The center cylinder shaft is used to raise and lower the weight package catch assembly. The shaft is composed of a piston, two O-rings, seal, guide and wiper seals, and three attaching bolts. The main cylinder gland guides the shaft. The piston moves up and down inside the inner tube Figure 52. Center cylinder and components. The shaft should be straight and free of nicks and pitting. The piston, shaft, seals, and O-rings should (figure 52).

Figure 52. Center cylinder and components.

Photograph shows center cylinder and components. Arrows indicate the locations of the center cylinder, O-rings, guide seal, seal, and attaching bolts open parenthesis use high-strength thread locker when assembling close parenthesis.

The shaft should be straight and free of nicks and pitting. The piston, shaft, seals, and O-rings should be examined if there is a problem with piston operation. Figure 53 shows a completed center cylinder after all seals and O-rings have been replaced. Figure 54 shows the oil hole port through which the hydraulic fluid flows to into the cylinder.

Figure 53. Center cylinder.

Photograph shows center cylinder. Arrows indicate the locations of the piston, guide seal, center cylinder, and shaft. Note: check for nicks, pitting, or excessive wear such as chrome peeling or flaking and replace if necessary.

Figure 54. Oil hole port.

This is a closeup photograph of the oil hole port at the end of the center cylinder. The oil hole port activates the catch flange plunger.

Main Cylinder Gland

The main cylinder gland is screwed into the main cylinder tube to guide the center cylinder. It is also equipped with a bleed screw to bleed the hydraulics of excess air. Numerous O-rings and seals may need replacement

Figure 55 shows the main cylinder gland and all necessary seals used in this component. Replacement of these seals is relatively simple. First, remove the old seals. Second, install the O -ring (A), then the internal seals (B) at the same location. Third, install the glide ring seal. (It may be necessary to form this seal first.) Fourth, put the outer O-ring into place. Fifth, install the dust seal. Finally, install the bleed screw and sealing ball (figure 56).

Figure 55. Main cylinder gland and components.

Photograph shows a main cylinder gland and its components. Arrows indicate the locations of the internal O-rings open parenthesis A close parenthesis, glide ring seal, internal seal wiper open parenthesis B close parenthesis open parenthesis same location as each O-ring close parenthesis, main cylinder gland, outer O-ring, bleed screw, sealing ball, and dust seal.

Figure 56. Assembled main cylinder gland.

Photograph shows an assembled main cylinder gland. Arrows indicate the locations of the glide ring; O-ring installed then internal seal open parenthesis set one close parenthesis, wiper seal, O-ring under internal seal open parenthesis set two close parenthesis, and bleeder set screw open parenthesis when bleeding hydraulics, do not overtighten close parenthesis.

Catch Flange and Plunger Piston

The catch flange is screwed into the center cylinder and the release plunger freely floats until hydraulic pressure builds up to the release pressure. The upper catch assembly attaches to the catch flange. After the weight package is raised to the target height, the release plunger is forced up and releases the inner catch collar. Figure 57 shows the O-rings and seals required for this component. Figures 58 through 60 show various views of the catch flange.

Figure 57. Catch flange, release piston, and plunger shaft.

Photograph shows a catch flange, release piston, and plunger shaft. Arrows indicate the locations of the release plunger shaft, bleed screw location for catch flange, catch flange, release piston, outer O-ring, inner glide seal, bleed screw, seal ball, inner O-ring, inner seal, and locking set screws open parenthesis use medium strength thread locker close parenthesis.

Figure 58. Top view of catch flange.

Photograph shows the top view of a catch flange and two set screws. Arrows indicate the locations of the two set screws open parenthesis use medium-strength thread locker when installing close parenthesis.

Figure 59. Assembled catch flange and release piston (bottom view).

Photograph shows an assembled catch flange and release piston. The view of the component is from the bottom.

Figure 60. Assembled catch flange and release piston (top view).

Photograph shows an assembled catch flange and release piston. The view of the component is from the top, and arrows indicate the locations of the set screws open parenthesis use medium-strength thread locker close parenthesis.

When installing this component, do not use a thread locker. Setscrews are used to secure this flange. A pipe wrench can be used to tighten flange to the center cylinder; however, great care should be used to avoid marring or damaging the outer surface. This component does not require excess force to tighten.

NOTE: Always install a new outer O-ring if this component has been removed. Also, before reinstalling this component, a fine metal file should be used to remove any dimples caused by the setscrews on the cylinder. This will help ensure a flush surface and reduce the chance of hydraulic leaks.

Bench Assembly Method

To bench-assemble the main cylinder components, follow these steps:

  1. Slide the gland over the center cylinder shaft (figure 61).

    Figure 61. Center cylinder and gland.

    Photograph shows a center cylinder and gland. Arrows indicate the locations of the top and bottom of the component.
     
  2. Carefully slide the shaft piston into the center tube. Lower both components into the outer tube housing (see figure 51 above and figure 62).

    Figure 62. Inner tube.

    Photograph shows an inner tube. An arrow indicates the location of the holes to the top of the component.
     
  3. Insert the center cylinder and gland into the inner tube, piston first. After this has been done, these two components can be inserted into the main cylinder (figure 63).

    Figure 63. Assembled main cylinder.

    Photograph shows an assembled main cylinder. Arrows indicate the locations of the main cylinder nut, pressure or inlet port, main cylinder gland, catch flange, return or discharge port, main cylinder, center cylinder, and catch release piston.
     
  4. Insert the inner tube with attached center cylinder and gland into the main cylinder tube. Make sure the O-ring is installed around the hub inside the main cylinder (figure 64). This O-ring is not installed on replacement tubes from the manufacturer.

    Figure 64. O-ring installed in the main cylinder.

    Photograph shows an O-ring installed in the main cylinder. An arrow indicates thelocation of the O-ring installed on the hub inside the main cylinder. Note: Replacement tubes from the manufacturer do not have this O-ring installed.
     

To assemble the main cylinder on the unit, follow these steps, which are similar to those when assembled on a bench:

  1. Install inner tube (figure 62) on to the center cylinder tube, beveled to the bottom and holes to the top.
  2. Slide the center cylinder shaft piston into the inner tube (figure 63). Slide the shaft down onto the tube until the gland threads are in contact with the outer tube threads.
  3. Use a spanner wrench to tighten the gland.
  4. Secure the main cylinder to the strike plate by using the main cylinder nut (figure 65). Check the nut annually and torque to 190-230 N-m (140-170 lbf-ft). Apply a high-strength thread locker.

Figure 65. Main cylinder attached to strike plate.

Photograph shows a main cylinder attached to a strike plate. Arrows indicate the locations of the main cylinder, hydraulic lines, catch flange, center cylinder, weight height open parenthesis W H close parenthesis proximity switch, subassembly, trigger open parenthesis T R G close parenthesis proximity switch, and strike plate. Note the wear on the outer tube. Newer units use a glide ring to prevent such wear.
Notice the wear on the outer tube. Newer units use a glide ring to prevent such wear.

Upper Catch Assembly

The upper catch assembly grabs the weight package lift collar so that the weight package can be raised and dropped. The upper catch is equipped with numerous moving components that will wear with use. (figures 66 and 67). It is important to keep all parts lubricated and free of debris, which could cause binding or excessive wear. Clean and inspect the moving components annually. Replace worn components.

NOTE: This repair can be made on the FWD without removing the cylinder shaft.

Figure 66. Upper catch shell and interior components.

Photograph shows an upper catch shell and its interior components. Arrows indicate the locations of the inner ring open parenthesis designed to wear out close parenthesis, catch top cover, ball bearings open parenthesis requires 6 close parenthesis, compression springs, heavy duty spring, spring retainer for heavy spring, plunger guide open parenthesis inner close parenthesis for heavy spring flange, hex bolt open parenthesis M5 by 12 millimeters close parenthesis, hex bolt open parenthesis M5 by 35 millimeters close parenthesis, hex bolt open parenthesis M6 by 20 millimeters close parenthesis, catch shell top cover, outer shell open parenthesis designed to wear out close parenthesis, guide pin, and hex bolt open parenthesis M6 by 60 millimeters close parenthesis.

Figure 67. Upper catch shell.

Photograph shows an upper catch shell. Arrows indicate the locations of the inner body shell, inner catch top cover, outer shell, and catch shell top cover.

After all components are clean, begin reassembly. Following are the steps to assemble the upper catch:

  1. Place the inner shell top down on a workbench (figure 68). Make sure the guide pins are tight. If they are loose, clean pin threads and use a high-strength thread locker (figure 69).

    Figure 68. Inner body.

    Photograph shows an inner body.

    Figure 69. Placement of the guide pins.

    Photograph shows the placement of the three guide pins in the inner body.
     
  2. Put ball bearings in position by placing the outer shell top down on the workbench and turn the inner body top up. Place the six ball bearings in the correct locations, making sure to grease each bearing with a liberal amount of light all-purpose grease. Lower the inner shell into the outer catch shell (figures 70 and 71).

    Figure 70. Ball bearings in place on the inner body.

    Photograph shows ball bearings in place on the inner body. Arrows indicate the locations of the six ball bearings in place, holes for the hex bolts open parenthesis M6 by 60 millimeters close parenthesis, and inner body set into position. Use all-purpose white lubricating grease on the ball bearings. An aerosol can of lubricant is shown in the photograph.

    Figure 71. Inner body set in place.

    The photograph shows the inner body set into place and the position of the four M6 by 60 millimeters hex bolts.
     
  3. Place four M6 × 60 mm hex bolts in the four holes on the top of the inner body (figure 72). These secure the upper catch assembly to the top of the main cylinder.

    Figure 72. Inner body and hex bolts.

    Photograph shows an inner body with two hex bolts placed in position to be tightened into the holes.
     
  4. Place the inner catch top cover on the outer shell. Use a medium-strength thread locker on all six M5 × 12 mm hex bolts (figure 73).

    Figure 73. Inner catch top cover installed.

    Photograph shows inner catch top cover installed on an inner body component.
     
  5. After the cover is installed, turn the assembly over so the top rests on the workbench (figure 74).

    Figure 74. Outer shell, top down, with interior components exposed.

    Photograph shows an outer shell top down with its interior components exposed. Arrows indicate the location of the M6 by 60 millimeter hex bolts, M5 by 35 millimeter hex bolt holes for securing the upper catch assembly to the guide flange, six ball bearings, and guide pins.
     
  6. Put the three compression springs over the guide pins (figure 75).

    Figure 75. Interior of catch assembly with compression springs.

    Photograph shows the interior of a catch assembly with three compression springs placed over the guide pins.
     
  7. Place the inner ring (figure 76) on the three springs. The inner ring has two sets of holes used to rotate the inner ring after it shows signs of wear. Rather than replace the inner ring, it can be rotated to the previously unused set of holes for extended life.

    Figure 76. Inner ring.

    Photograph shows an inner ring. Arrows indicate the locations of one of two sets of three holes, and two areas showing signs of wear.
     
  8. Slide the inner ring in position over the springs by picking up the assembly and turning it upside down. This allows the ball bearings to release the inner rings and slide over the compression springs. The collar then can move to the bottom of the outer shell, allowing the ball bearings to retract enough for the inner ring to reach its lowest possible position (figures 77 and 78).

    Figure 77. Outer shell with inner ring in position.

    Photograph shows an outer shell with the inner ring in position. Note: Photo shows the inner collar facing up toward the outer catch shell top. This is the correct orientation.

    Figure 78. Inner ring in position inside the outer shell.

    Photograph shows an inner ring that has been placed in position inside the outer shell by picking up the assembly and turning it upside down, allowing the ball bearings and compression springs to slide into place.
     
  9. Insert the outer spring retainer over the four M6 × 60 mm hex bolts (figure 79).

    Figure 79. Insert outer flange.

    Photograph shows an outer flange inserted into the outer shell above the inner ring. An arrow indicates the location of the flange
     
  10. Attach the upper catch to the main cylinder; it takes time and practice to accomplish this. With the plunger shaft extended, place the spring guide on top of the plunger. Next, put the plunger spring on top of the spring guide (figure 80). In this picture, the main cylinder is not attached to the FWD to show how the upper catch is attached.

    Figure 80. Guide flange and spring.

    Photograph shows a guide flange and spring. Arrows indicate the locations of the release piston, four holes for attaching bolts below, heavy spring, and spring guide. In this picture, the main cylinder is not attached to the F W D in an effort to better show how the upper catch is attached.
     
  11. Hold the upper catch in your hands and carefully place your fingers at the base of the outer flange and inner ring (figure 81). Turn the assembly so the top faces up and the outer flange and inner ring slide down. Hold in place until the inner ring is resting on the guide flange with the outer catch shell.

    Figure 81. Upper catch.

    Photograph shows an upper catch held by a technician. Arrows indicate the locations of the inner collar and four bolts that attach to four holes above open parenthesis use medium-strength thread locker close parenthesis.
     
  12. Place the upper catch over the guide flange and spring. The inner collar should help guide the catch over the spring and onto the catch flange.
  13. Tighten the four M6 × 60 mm hex bolts on the catch flange and rotate the upper catch until the bolts line up with the threads on the catch flange (figure 82). Do not tighten the bolts completely. Next, reach under the catch and collapse it by pushing upward on the collar, which contains the ball bearings.

    Figure 82. Attach the upper catch.

    Photograph shows how to attach the upper catch over the guide flange and spring onto the catch flange using a hex wrench. Arrows indicate the correct position for the wrench.
     
  14. Using an O-ring pick or similar tool, align the two center holes on the inner catch cover with the holes on the spring guide (figure 83). Use two M5 × 35 mm hex bolts and medium-strength thread locker to secure the top (figure 84). After tightening these two bolts, go back and tighten the four M6 x 60 mm hex bolts.

    Figure 83. Align top cover.

    Photograph shows correctly aligned top cover. Arrows indicate how to position the top cover so that the connecting bolts can be tightened.
     

    Figure 84. Tighten all bolts.

    Photograph shows bolts positioned to tighten the top cover to upper catch assembly. Note: It may be necessary to rotate the catch assembly to properly align. Lubricate catch assembly weekly.
     
  15. Place the top cover on the upper catch assembly and secure with two M6 × 20 mm hex bolts, then use medium-strength thread locker (figure 85).

    Figure 85. Complete upper catch assembly with cover.

    Photograph shows a complete upper catch assembly with top cover tightened into position.

SIDE CYLINDERS

Two side cylinders (front and rear) raise and lower the load/strike plate (figure 86). They are assembled similar to the main cylinder; therefore, a detailed description of assembly is not necessary.

Figure 86. Side cylinder and components.

Photograph shows a side cylinder and its components. Arrows indicate the locations of the flange O-rings and seals, piston, fluid port open parenthesis lower close parenthesis, side cylinder pin location, flange, lock collar, shaft, fluid port open parenthesis raise close parenthesis, outer housing, fluid direction, and the direction of the oil that pushes the piston downward.
 

To install the side cylinders after they have been assembled, follow these steps:

  1. Attach hydraulic lines to the fluid ports. The longer line goes to the top fluid port (lower plate) and the shorter line attaches to the bottom fluid port (raise plate) (figure 87).

    Figure 87. Mounted side cylinder.

    Photograph shows a mounted side cylinder. Arrows indicate the locations of the guide roller shafts, side cylinder pin open parenthesis lubricate monthly, check bolts monthly to make sure they are tight close parenthesis, side cylinder, and side cylinder shaft open parenthesis extended close parenthesis. A hydraulic line supplies the lower mode oil flow, and another hydraulic line supplies the upper mode oil flow.
     
  2. Put the cylinder into position on the subassembly frame. The top of the cylinder has a hole for the pin to anchor it to the subassembly. Install anchor bolts and apply medium-strength thread locker.
  3. Attach the flexible hydraulic lines to the rigid mounted hydraulic lines already in place on the subassembly frame.
  4. Put the side cylinder shaft through the strike plate and attach it with a washer and bolt that secures it to the strike plate (figures 88 and 89). Use medium-strength thread locker.

    Figure 88. Front side cylinder, looking up, from under FWD.

    Photograph shows the front side of the cylinder from underneath the F W D. Arrows indicate the locations of the hydraulic lines, bolt, washer for the front side cylinder open parenthesis apply medium-strength thread locker close parenthesis, and raise/lower pulley and cable open parenthesis lubricate monthly close parenthesis.

    Figure 89. Rear side cylinder looking up from under FWD.

    Photograph shows the rear side of the cylinder from underneath the F W D. Arrows indicate the locations of the large washer, plate low proximity switch, and bolt open parenthesis threads into side cylinder shaft, use medium-strength thread locker close parenthesis.
     

    NOTE: The rear-stepped washer is designed to have no contact with the plate low-proximity switch when the cylinder is fully retracted.

  5. Attach hydraulic lines.
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The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT).
The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT). Provide leadership and technology for the delivery of long life pavements that meet our customers needs and are safe, cost effective, and can be effectively maintained. Federal Highway Administration's (FHWA) R&T Web site portal, which provides access to or information about the Agency’s R&T program, projects, partnerships, publications, and results.
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United States Department of Transportation - Federal Highway Administration