Fiero Auto Transmission TH125c Shift Kit Installation
Stock transmissions are built to provide long, smooth shifts between gears, for the comfort of the consumer. However these delayed shifts actually reduce the life expectancy of the transmission. And, of course, what Fiero owner wants a performance car with soft shifts?! A shift kit will produce crisper shifts, at more efficient places. Installing a kit will NOT fix an old/worn transmission, and may aggravate any problems - so be sure your transmission is in good working order before buying a kit! The difference is very nice, and I am very pleased with the results.
However, this job is not for everyone! Besides the usual mechanics work involved, there are a LOT of small parts, and fine details that must be attended to. If you aren't good with puzzles, I would suggest you take it to a transmission shop that will know exactly what to do with all the little springs and balls ;)
Transmission Shift Kit - Transtar Model Number: K51908
TH125c Valve Body Cover Gasket - Available from GM dealer
TH125c Piston Housing gasket - I re-used the old one, but get one in case yours is brittle.
Transmission Filter & Gasket Kit- Most parts stores will stock this
4-5 bottles of cheap ATF
4-5 bottles of good ATF
2 oil eater boxes
3.5 foot 5/16th Trans Cooler Hose
Brake Cleaner
Big baking pan
Gasket Scraper / Razor Blade
Clean lintless cloth
Specialty Tools
T-40 Torx Bit
Metric set of wrenches / drivers
Anti-Drainback Valve Intallation
Raise car on jackstands
Remove wheel
Remove wheel well housing
Take note of the two pipes coming out of trans with tubes attached. The short hose comes from the bottom pipe and attaches to a vertical metal line on the side of the engine compartment. The long hose goes from the top pipe, and loops around through a bracket and into a horizontal metal line.
Follow procedure in the Ogre's Cave to drain maximum amount of ATF, without the usual "pan drop" mess.
Remove cooler line pipes for increased access & top fitting
Install Anti-Drainback valve in the top fitting. Valve consists of an aluminum sleeve and an unpainted spring.
Re-install fitting
Valve Body Removal / Modifications
Unbolt Valve Body Cover, let excess ATF drain into bake pan
The cover is tricky to remove, but i was able to wiggle it out through the wheel well - through the gap between the cradle and the A-arm.
You now have a full view of the valve body, TCC Solenoid and TV Cable hookup
You will now need to unbolt a whole bunch of 10mm bolts, 2 13mm bolts and one T-40 torx bolt. Do not unbolt ALL of the bolts, as you don't need to remove the part I colored green. I studied the pictures in the instruction sheet to determine which bolts go all way through the VB and actually hold it on. My circled bolts are from memory, so please refer to the instructions, as I did
Unclip the black electrical connector at the top left of the VB housing- its quite hard to get your hand in there.
The Valve Body (VB) should now pull off from the transmission. There is a shaft that goes from inside the trans into the VB, but it should come off the VB with a bit of wiggling. Be careful not to squash a finger- the VB is quite heavy. Also, keep an eye out for check balls that might fall out while you are removing the VB.
Note the locations of check balls, and put them somewhere safe.
From this point on, follow the detailed instructions that come with your shift kit.
You will probably need to remove several springs and parts from inside the VB. Most of the valves etc are kept in the housing of the VB by retaining pins. Push on one side of the pin and it will pop out the other side of the VB. The parts will now slide out of the VB.
Follow instructions on which springs, etc to replace/modify.
Remove separator plate and gasket from VB / trans. Use gasket scraper to remove old residue.
Use brake cleaner to clean the VB and trans. Even small particles can prevent trans from operating correctly.
To put things back together, use some ATF to hold the gasket/plate to VB/trans. A little bit of ATF also helps keep the check balls in their holes.
Slip a few bolts in to hold the VB in place. The Kit may specify which bolts to tighten first.
Bend tab on TV Belcrank as instructed, then attach TV Valve cable to the TV Belcrank.
Install Belcrank, insuring tab goes UNDER the vertical plastic valve
Tighten down VB bolts - I didn't have any torque specs, but just made sure they were tight without risking breaking bolts.
I would recommend replacing the transmission cooler hose to avoid future leaks from aging hose
Fill up with cheap ATF as detailed in Haynes or Chiltons. I drove the car at this point to get the ATF circulating, and any gunk/particles to get caught in the old filter. This should eliminate a maximum amount of debris before installing a new filter
Servo Piston / Filter Removal & Modifications
Drain ATF again as described above. Unbolt Transmission pan. Do one end first so fluid can be "poured" into baking pan. Remove pan. Remove old filter.
Unbolt Servo Piston housing - 4 10mm bolts.
Carefully remove piston assembly, taking take not to damage gasket
There is a valve that might drop out at this point, take note of how it is supposed to go into the piston housing!
Remove E-clip
Install Shift Kit components.
The spacer which goes under the large spring makes it hard to put back together, but with a bit of elbow grease you can get the E-clip back on by hand after. If you have trouble, careful use of a clamp might work.
Re-install piston and housing. Don't forget to reinstall the accumulator valve that might drop out!
Install the boot that comes with the filter first, then press the new filter in - make sure it is supported by the metal tab
Before you put the pan back on, you may want to consider adding a drain valve/bolt. B&M sells one, and makes it much easier to drain the pan in the future. Be careful to install in a location where there is enough spacec for the valve!
At this point, you can bolt the pan on. Clean it thoroughly, and put back the magnet if one was in there. I found if I put the gasket on the dropped pan off the car, and pushed the bolts through the gasket, then the bolts would hold the gasket in place when bolting the pan back on.
Governor Removal & Modifications
Unbolt governor on passenger side of transmission. Pull out governor.
Replace spring with spring included with kit.
Now fill up with good ATF as detailed in Haynes or Chiltons. You're done!
Created 11/02, Last modified 4/04. Email comments / questions to pimmel@hawaii.edu
Hawaii Fiero Owner's Club information should addressed to me also. All enthusiasts welcome!
