On vehicle Poppet Adjustment
Contents
1. TRW Automotive Commercial Steering Systems Service Bulletin TAS 101 On Vehicle Poppet Readjustment for TAS This TRW Commercial Steering Systems service 3 bulletin has been written to help you repair commer THP and PCF Steering Gears cial vehicles more efficiently This bulletin should not replace your manuals you should use them Revised August 2003 together These materials are intended for use by properly trained professional mechanics NOT Do it yourselfers You should not try to diagnose or repair steering problems unless you have been trained and have the right equipment tools and know how to perform the work correctly and safely What are poppets Poppets are pressure unloading valves set to trip just before full turn is reached in each direction When this proce dure is completed correctly system pressure will be reduced before the axle stop screw contacts the axle stop in both directions To determine if the poppets require readjustment or if they are performing properly install a Power Steering System Analyzer PSSA between the power steering pump and the steering gear If poppet readjustment is necessary you can leave the PSSA in the system to verify that the following procedure is completed properly Why might poppets need to be readjusted e Changing to larger tires e Reduced vehicle wheelcut e Pitman arm mistimed condition corrected e Steering gear being installed on a different truck e Ste2. put 30 Ibs rim pull on a 20 dia steering wheel c Release the steering wheel and shut off the engine Back out adjusting 9 Loosen the sealing nut and back out the adjusting screw screw until 1 is past the nut Tighten the sealing nut against the housing A CAUTION Do not hold the steering wheel at full turn for more than 10 seconds at a time the heat build up at pump relief pressure may damage components Set lower poppet 10 a Start the engine and let it idle b Turn the steering wheel in the original direction end of timing mark toward adjusting screw until axle stop contact Is made c Hold the steering wheel in this position with 30 los rim pull for 10 seconds then release Repeat this hold and release process as many times as necessary while completing step 11 gt Position adjusting 11 a With steering wheel held at full turn loosen the screw jam nut and hold it in place with a wrench b Turn the adjusting screw in clockwise using finger pressure only don t use a ratchet until the Allen wrench comes to a stop Do not attempt to turn it in farther Pause the turning in process each time the driver releases the steering wheel Continue turning only while the wheel is held at full turn c Back off the adjusting screw 3 turns and tighten the sealing nut Torque the sealing nut to 35 ftelb The procedure is 12 The poppets have now been completely reset complete Lower the vehicle
3. Check the reservoir and fill if required The length of the adjusting screw beyond the nut must be no more than 1 46 for proper thread engagement NOTE The length of adjusting screw beyond the sealing nut may be different for each vehicle TRW Commercial Steering Systems P O Box 60 Lafayette IN 47902 Phone 765 423 5377 Fax 765 429 1868
4. em Turn the adjusting screw and sealing nut assembly without rotating the nut on the screw into the housing until the nut is firmly against the housing using a 7 2 allen wrench TAS Series THP PCF 60 series or a 6mm allen wrench THP PCF 45 Series Tighten the sealing nut against the housing CAUTION ifthe drive end of the screw is below the face of the nut the poppet seat flange will break during step 7d Refill system reservoir with approved hydraulic fluid A CAUTION Do not mix fluid types Mixing of transmission fluid motor oil or other hydraulic fluids will cause seals to deteriorate faster Jack up vehicle 6 Place a jack under the center of the front axle and jack up the front end of the vehicle so the steer axle tires are off the ground Push upper poppet 7 a Start the engine and let it run at idle speed out to prepare it for b Note which output shaft timing mark is nearest setting the housing piston bore c Turn the steering wheel in the direction that makes this timing mark move toward the adjusting screw just Installed Turn in this direction until axle stop contact is made d Pull hard on the steering wheel put 30 Ibs rim pull on a 20 dia steering wheel after the axle stop is contacted Set upper poppet 8 a Turn the steering wheel in the opposite direction end of timing mark away from adjusting screw until the other axle stop is contacted b Pull hard on the steering wheel
5. er axle stop bolt s were bent or broken e Steer axle u bolt s were bent or broken NOTE This resetting procedure will work in most cases with at least 134 hand wheel turns from each side of center If you re making a large reduction in wheelcut and this procedure does not work you may have to internally reset the poppets using the procedure described in the TAS Service Manual Set axle stops warm up system Assemble adjusting screw into nut Remove poppet stop bolt Turn adjusting screw assembly into housing Refill reservoir 1 Set the axle stops to vehicle manufacturer s wheelcut or clearance specifications Start the engine and allow the vehicle to idle for 5 10 minutes to warm the hydraulic fluid Shut off the engine If anew poppet adjusting screw and nut are being used turn the screw into the non sealing end of the jam nut until the drive end of screw is flush with the nut Your steering gear will have either a fixed stop bolt or an adjusting screw If the adjusting screw is already part of the steering gear back the nut off of the adjusting screw until it is flush with the end of the adjusting screw Make sure the engine is off and the road wheels are in straight ahead position Remove and discard the poppet fixed stop bolt if equipped and washer if equipped from the lower end of housing If the unit has a poppet adjusting screw and sealing nut that need to be replaced remove and discard th
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