The following details the procedure for replacing stripped nylon gears used in the Toyota Power Seat mechanism. The instructions here are for the Toyota Supra 93 although the same mechanism may be used in other Toyota models. Check the dimensions of the parts before ordering (see below) and attempting a repair.
Problem: When the power seat is operated the seat base does not move laterally forward or back at all (both gears stripped) or only moves on one side and starts to twist (one gear stripped). Complete failure could be due to the motor or an electrical fault which is not covered here.
Components: Gearbox constructed of plastic with a nylon helical gear driven by a steel screw gear at right angles.
Solution 1: Replace complete gearbox unit. The cost of the complete left hand side gearbox unit is expensive at approx $174 (£112 UK purchase). The cost of the right hand side gearbox may be similar.
Solution 2: Replace the individual gear within the gearbox approx $19. The following procedure is for option 2.
Dismantling the seat mechanism will take some head scratching, but persevere.
On disassembly of the gearbox you will most likely find the nylon gear has stripped and the driving steel screw gear is intact.
The dimensions of the white nylon gear in this case are:
- Inside diameter 14.5 mm
- Outside diameter 22.5 mm
- Width 10.0 mm
The nylon gear is press fitted onto a splined steel shaft. To remove the gear from the shaft you will need a piece of wood drilled with a five eighths of an inch (16 mm) diameter hole and at least three quarters inch (19mm) deep.
Remove the stripped gear
Center the shoulder of the the nylon gear over the hole and use a piece of wood to protect the steel shaft whilst carefully using a hammer to tap the steel shaft out of the nylon gear. Before removal it may be useful to cut right through the gear both sides, close to and parallel to the splines. The nylon gear is somewhat brittle and there may be traces of glue on one one side.
After the gear is removed, clean any trace of grease and glue from the steel shaft. The rubbery glue on the authors piece did not respond to mineral spirit so had to be scraped off.
Insert the new gear
Check the root dimension of the splines on the steel shaft matches the inside diameter of the nylon gear. Offer the gear to the shaft using the side of the gear which may have a slight taper on the edge of the hole. The splines have no leading taper either end. The angle of the gear teeth is correct which ever way round it is fitted.
Position the gear centrally over the hole in the wood. Using a small hammer carefully tap the steel shaft into the gear. Alternatively use a press. The steel is hard so careful light tapping with a hammer should not cause any deformation of the shaft, but the use of a small protective buffer or soft faced hammer when tapping is advised. You will need to tap around the periphery of the shaft to straighten it as it will tend to go in at an angle initially but become more aligned the further it enters. A number of small increments is better than large incrementas as this may cause jamming and damage to, or breakage of the gear. Tap or press the shaft in until it covers the splines equally on both sides. There will be some nylon particles ejected from the gear as the splilnes bit into it.
Reassemble the gearbox using lithium LM grease, or equivalent, on the gears. Glue may be required on the surface of the shaft if it passes through a roller bearing? Refit the gearbox. Before and during re-assembly of the seat mechansim you will need to ensure the two seat rails are at the same part of their travel so the seat does not try and skew at the end of the travel. The long thread screw which the seat runs along can be turned using a wrench on the bolt head under the plastic covers at the front of the seat. Note you may only be able to turn this one way – force in the wrong direction may damage the nylon gears.
If the gearbox on one side has failed and the seat has been operated to maximum, the seat runners may be distorted. Check for smooth running of the seat runners and that the two steel rollers are not twisting sideway in the slot and jamming at any point of travel. This could indicate a deformed runner track. You will need to straighten any deformation before continuing. Due to the design and spring of the metal you may find it difficult to return the runners to a good state, such that free travel exists at all points of the track.
Unimpeded running and good lubrication is essential to ensure the gears are not damaged during operation. There should be little resistance, at any part of the travel, when turning long seat runner screws manually when the runners are off the seat and gearboxes are not in place. Clean out all the accumulated dirt on the runners and mechanism and use plenty of grease at appropriate points on reassembly.
Nylon gears with dimensions as above are available from http://www.cruiserparts.net Description: Front Power Seat Track Gear only 93-97