What are the differences between the '86 auto trans and the '90 auto trans?

I put an '86 model trans in a '90 model car and the trans will not shift out of first (checked the detent cable/valve and govoner and they are fine). I talked to the guy that rebuilt the trans for me and he said that he totally overlooked that fact that the '86 trans was going into a '90 model and that there are some differences with the electronics that is most likely causing the problem. Apparently there is a way to make it work that he has done before and he is going to look it up and find out for me, but I wanted to ask you guys here as well. Only other thing it could be according to the Helms manual is the 1-2 shift valve sticking, which I find unlikely.

Can anyone shed some light on what exactly is the problem, because my transmission guy does favors for me for free (or beer) so I have to wait on him to get time away from his shop, which sometimes takes a while.

 

They are both non-electrinic transmissions. They are are physically, 100%, interchangeable. I can't imagine why one wouldn't shift out of first gear in the other application. Where is Pete K?

RACE ON!!!

 

Checked the banana shaped thing where ur shifter hooked, may be the spring fell off under tranny pan or not hooked right, if this is case than an easy fix, take the pan out and see. Hope iam right and sure u need to pm pete k or let him chime in to confirm my statement, i might be wrong but its only an suggestion what i went throug in past. sami

 

There was a small upgrade internally in '88, but that shouldnt cause this problem, they are interchangeable.

 

Ther are enough differences internally to write a small book. They are completely interchangable from 84-92 though.
The short version is:
82-84 sucked. Especially 82
30 spline input shaft became standard in 85, although rumored to have been installed in later 84's, I have not stumbled upon any 84's that have (yet)
87 was the beginning of a much better trans. The forward sprag and lo-roller clutch(rear sprag) were beefed up in 87. In the case of sprags, bigger is better.
87 also was the first year for the 10 vane pump.
If the tv is correct and the governor is working properly, I am at a loss as to what your problem may be. I will stick my nose in the reference chart later and see if I can figure something out.

 

Thanks because I'm at a loss when it comes to transmissions, and I don't want to have to drop the valve body to inspect the 1-2 valve as the Helms manual suggests for the '90 model when this happens (is there anyway to check to see if it is stuck without removing the valve body?).


Could a slightly out of adjustment tv cable cause this? I adjusted it per the GM instructions, and then again per instructions from people on this board (very similar instructions btw), both times with the same results, and the plunger looking thing that it controls in the valve body is moving freely in and out with spring tension on it when pressed in.

 

I would put a guage on it. They factory readings will apply if the pump regulator spring and boost valve are both stock. If either(or both) of these are changed, it changes the pressures on the high and low sides.
Any time a trans suffers for shift quality or shift timing issues, suspect tv 1st. Then governor. I would drop the valve body last.

 

The valve body is stock, transmission internals were beefed up a bit though, something about better clutches and a kevlar band, sorry I know I'm not much help. How do I check to see if the tv plunger thingy (what is this called so I can quite calling it that) is working properly? I don't see anyway to take it apart without dropping the valve body, unless the lever that depresses it will come off and it can be pulled out that way?

 

The plunger for the tv valve is removable without dropping the v/b. However, the actual tv valve is behind it. This valve(and all others) has a roll pin holding it in. The v/b must come down to access it.
I am going to make a guess as to what your problem is.

During a trans failure, alot of trash is generated. It is forced through every port and crevice in the trans. This trash typically gathers in the valve body as well. Most production trans shops do dot completely disassemble the v/b and spit shine each and every valve or it's bores.
The v/b is the first part removed, and normally gets tossed in the solvent tank while the overhaul occurs. When the time comes, it is shaken out, and torqued up. Now, the fresh fluid(which is like a detergent) gets pumped through and dislodges the remaining trash. Valves hang up and shifting problems occur.
The moral of my story is:
If the v/b comes down, disassemble, spit shine, and reinstall. No such thing as too clean. I spend as much as 3 hrs on a valve body during an overhaul.
Also, check to see that the later style(double yellow stripe) v/b gaskets were used and the one marked with a "c" is on the top of the seperator plate. Also that the one marked v is on the bottom.
If the check ***** were retained with anything other than vaseline, it too could be hung up. Some guys use wheel bearing grease. That is a no no.
Hope this info helps

 

Just a shot in the dark, but you could have a stuck govenor or a sheared gear on the govenor. It's rare but it happens.

 

Already took the govenor off and inspected it, its ok, thanks though.

 

Going to bring this thread back up because I still have not solved the problem. I have taken that valve body off and inspected for any stuck valves. 1-2 shift valve was sticking, took care of that but still won't shift out of first. Govenor was also check and was good

I then turned to the tv cable. I noticed that for the '86 and the '90 there are two different part numbers, and one is called a kickdown ('86) and the '90 is refered to as a throttle valve or detent cable and they are completely different part numbers.

I have the cable for my '90 on the car but its an '86 trans, could this be the culprit?

 

I know you can't mix separator plates, ask me, I would think that there are differences between the valve body channels which would cause problems when mixed.
What've you got to lose? Put the right parts back together.
The cable length may be different, I know the throttle bodies are different mounting styles.

 

Nope.
The length of the cable and the end that attaches to the throttle body are what seperates them.
The pre aux valve body transmissions (82- early 87) use the same seperator plate. There are dozens of different plates available for the aux valve body units. The correct plate must match the correct case.