The Ever Popular TH1. My Fiero @ Ocean. Moon. com. There are a bunch of things about the TH1. This is a collection of the issues asked about in the forum. It’s by no means a complete list of things. It does however cover some obscure things needed by customizers. Shift Problems. Do the Torque Converter tests in the TC article.
What feels like a shift in TH1. TC locking or unlocking. If there is a problem with the TC lock then it can feel like you’ve lost a gear. Does the problem happen with the TC lock plug disconnected? If the TC lockup is working correctly you usually don’t notice it at all but do the test anyway.) When does the problem happen? If it is only one shift/gear then you very likely need a shop to work on it. You can try the stuff below but don’t be surprised if nothing helps.
If the problem is with all gears, it could be something dumb or major. Check the easy stuff before panicking.
First of all make sure that the transmission fluid is at the right level. Over or under fill will both cause shift problems. What condition is the fluid in?
The ever popular TH125. There are a bunch of things about the TH125c transmission that need to be kept in mind when working on it. This is a collection of the issues. Find great deals on eBay for TH125 Transmission in Complete Auto Transmissions. Shop with confidence. List of GM transmissions General Motors is. 1980–1999 TH125/TH125C/3T40 — 3-speed light-duty. Muncie SM420 - 4 speed manual used up to 1967.
If it’s turned light or even clear then it’s old, likely oxidized, and you might want to try changing the fluid and filter before taking it for repairs. If it’s brown to black or smells different from new fluid then the transmission may have fried a clutch. You could try changing fluid but you should probably take it to a shop to be checked out. The next item to check is the Throttle Valve Cable, which runs from the throttle linkage on the engine to the top of the transmission. If this cable is binding or out of adjustment you will have shift problems. Another thing that happens is the Governor or a passage inside the valve body gets blocked with a flake of dirt or sludge. This can affect one shift or the whole transmission.
You can try one of the cleaning products that you add to the fluid. Some people have reported good luck with these. Depends on just what’s blocking the passage if it will work or not. If this fixes your problem then do a fluid and filter change to get the rest of the dirt out.
Types of Transmission Manuals We Sell: transmission rebuild manuals, automatic transmission repair manual, automatic transmission repair manual download, transmission. The Ever Popular TH125. By blogadmin, on April 23rd, 2009. There are a bunch of things about the TH125c transmission that need to be kept in mind when working on it. ATSG Transmission Repair Manuals. 4L80E ATSG Transmission Repair Manual, TH125 ATSG Transmission Repair Manual, 440T4 ATSG Transmission Repair Manual.
Another possibility, although rare, is that the filter has failed or come unsealed inside the tranny. The result is that the fluid is picked up higher in the transmission. This can have the same result as low fluid. Notes. Shift Kits: These kits WILL NOT fix a transmission with problems. Worse they could hide some problems.
Be sure that your transmission is good before adding the kit. Source of parts and manuals besides GM dealer: Transmission Exchange Co. They have loose parts, full rebuild kits, Trans- Go shift kits, TC lock delay modules and various other things. The red dye in the fluid will fade over time. It doesn’t automatically mean the fluid is bad, just old. Throttle Valve Cable.
What does the TV cable do? The purpose of the TV cable is to tell the transmission what the actual throttle setting is at any given time. TH1. 25c doesn’t use a modulator valve so this is the only way it can get some clue about engine load. This cable IS NOT a “kick down” cable/linkage like many people are familiar with. It works with an internal governor to control all transmission shift points. The TV cable is always synchronized to the throttle butterfly and NEVER the gas pedal position.
The transmission doesn’t give a rat’s ass about the gas pedal. If it is adjusted properly, the car will shift correctly even with a severely stretched cable/linkage between the motor and pedal. You’d think the gas pedal movement would always equal the same action at the throttle but this isn’t always true.
Wear and cable stretch often mean the gas pedal movement doesn’t match the movement of the throttle butterfly. This is especially the case with the 7- 8 foot long accelerator cables used in Fiero. Adjustment. WARNING!!! DO NOT EVER step on the gas pedal to do this!!!!!
Not on Fiero or any other car. It takes considerable effort to make the TV cable adjuster move. Do Not press the accelerator pedal to make the adjustment or you’ll likely damage the throttle cable or other parts in the system, especially in Fiero with it’s snake of a cable…. You could even snap the cable. If you try to do the TV cable adjustment by mashing the pedal it will not be right most of the time.
The adjustment procedure for the TV cable is in the Haynes book and is correct for all years. Note however that the location of the adjuster moved on the DIS (8. It is now on the transmission end of the cable. Also, You turn the black pulley the cables are connected to and not the throttle wheel on the TB/TBI. Once you make sure the TV adjuster isn’t stuck etc… Pull the slide part of the adjuster about 1/4- 3/8 of an inch. Be careful how far out you pull the adjuster slide. The adjustment button is normally slightly below the edge of the shell.
The button MUST NOT be crooked or pop up higher than the shell. If it does then the slide has been pulled out too far. If you try to adjust the cable with the button messed up you’ll break something. For 8. 7 and later L4… Rotate the idler pulley by hand until the TBI unit reaches WOT. There is a mechanical stop on the 7. TBI at WOT. This is much easier ifyou hold the TBI quarter pulley against the WOT stop then turn the idler pulley until the slack is gone from the small bit of cable between the two pulleys.
As you rotate the idler, the TV cable will ratchet into the tranny. Wherever it stops you are done. Mine ended up with the fat sliding part about even with the adjuster hole.)Once the cable has been adjusted, it is possible you may still need to fine- tune it a little by hand. You should not need to adjust the cable more than a couple teeth. If the transmission will not shift correctly after TV adjustment either you did it wrong or there are internal problems. L4 note: The idler pulley is bloody hard to turn by hand to make the TV cable adjustment. If you look at the idler pulley you’ll see three holes in it.
You can make a tool to fit two of the holes or you can go to a bicycle shop and see about getting a special wrench, shown left, that is used for working on the gear packs of 1. The ends of the bike tool fit the idler perfectly. T6. 0 (4. 40- T4) Note.
Warning! These transmissions use both a TV cable and a Modulator Valve. Both items must work and be adjusted properly or the transmission will not shift correctly if at all. The modulator must connect to a Manifold Vacuum source. Proper adjustment of the 4. T6. 0 requires a pressure gauge and should be done only by qualified transmission mechanics. Engine Conversion Note. The TV cable IS NOT optional.
These transmissions WILL NOT shift right unless the cable is connected and working properly. On the 4. T6. 0 you must connect the modulator to a Manifold Vacuum source.
Again, this cable IS NOT a “kick down” cable! It is used full time to control all shifting. It must move in sync with the throttle butterfly. If you connect it like a “kick down” that only moves at/near WOT then the TH1. T6. 0 transmissions will not shift right if at all. Adjusting the cable correctly on the TH1.
You should not trust the built in adjuster to work by itself for many conversions. Governor. The Governor Valve is part of the assembly that runs the VSS (Vehicle Speed Sensor) and is used with the TV cable to control shifting. If you’ve correctly adjusted the TV cable and still have late/no up shifts then this device may be dirty. If you attempt to repair this yourself be extremely careful! Damaging any part of the governor will screw up shifting. If you damage the springs in any way they MUST be replaced. The springs are calibrated items and the transmission will not shift right if they are out of whack.
If you continue to have shifting problems after cleaning out the governor then you’ve got internal problems that will require tearing down the transmission. Fluid & Filter changes. There is a way to significantly reduce the mess associated with this job as well as get the maximum amount of old oil out of the transmission. I’ve used it a number of times and it works well. The transmission will stay oiled well enough to prevent damage but don’t take chances. Follow the warnings.
This method will get a good amount of the oil normally held in the Torque Converter. The most oil I’ve gotten out of the Fiero using this method is 6. Many people say you need to flush out the rest of the old oil. My feeling is that you only need to do that if the old fluid is burnt. If the old fluid is burnt then you likely need other major work done.
Flushing is extremely wasteful for most situations. WARNING! The following procedure can be dangerous. It should not be performed on a hot transmission. Use of properblocking and jack stands is a must. Do not allow transmission oil to run onto hot exhaust parts.
This is not a GM approved method. There is the remote possibility you can damage the transmission.
DO NOT shift the car from park during this operation! DO NOT allow the engine to run once oil flow has stopped. DO NOT GET UNDER THE CAR WHILE IT IS RUNNING! If you are uncomfortable with this then you could suck the oil out thru the dipstick tube. That will empty the pan but won’t get near the same amount of oil out.
K- Mart Wal- Mart and others sell a small pump kit for about $1. It will also make coolant work much less messy.) At K- mart they are in the auto section. With the car raised on jack stands and the front wheels blocked.
Disconnect the bottom cooler line from the transmission. Install a temporary piece of line long enough to reach a catch basin under the car. Make sure the line is aimed so oil can’t spray out of the pan. The oil will flow at a small amount of pressure. Anchor the line in the pan so it won’t jump out.
Set the parking brake. If the hand brake doesn’t work then someone should stay in the car and hold the pedal tight. Start the car and let it idle until oil flow stops.
Shut off the car as soon as oil flow stops. DO NOT SHIFT THE CAR! DO NOT GET UNDER THE CAR WHILE IT IS RUNNING!
Let the car stand 5- 1. Disconnect the top cooler hose and put the bottom line in a jar.
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