TPI-RS

iTrader: (6)

Okay... Let me start off by explaining what I have done to my car...

I bought the car 3 years ago. It is a 1991 RS with the 6 cyl in it. At the same time I bought this car, I also picked up an 1987 IROC parts car. This car had a 305 TPI motor with 700R4 tranny. After a LOT of headaches, I put the 305 TPI into the RS car. I finally got the car running last year, but didn't really drive it until this past summer...

Here is a list of the car / what I have done...

Car = 1991 RS (original 6 cyl)
Motor = 1987 IROC 305 TPI (rebuilt with all 1991 Z28 sensors etc)
Tranny = 1987 IROC 305 TPI - 700R4
Wiring Harness in car now is from a 1991 Z28 (speed density)
ECM & Prom = new from GM for 1991 Z28 with 305 TPI

I think that covers all my bases...

So. Once I really started driving the car it was very obvious that my transmission was slipping like crazy. It doesn't like to shift down into 1st gear all that often, unless I manually do it. I've changed the fluid, changed the filter, and changed the kick down cable. (all during the rebuild of the motor when it was out of the car...)

For the whole summer i drove around with the tranny slipping, just dealing with it, because I can't afford a new one right now, or a rebuild...

So, yesterday, I met up with a bunch of car guys that restore antique cars of all sorts for fun. I got talking to them about how I need a new transmission and what i have done to my car.

One of them, who seems very knowledgeable informed me that my issue may not be my transmission... it may be my computer. He said that if the computer wasn't programed properly for the new motor / tranny, then it wont run correctly. So I guess my question is this: is a 1987 - 700R4 different than a 1991 - 700R4. Now... I know the tailshaft is different, because of the mechanical to the electric speedo, but besides that, is it different? I'm wondering if my new GM 1991 computer and prom are sending signals to the tranny that it can't read, because it is from an 87...


I think that all makes sense. It makes sense in my head but i'm not sure if I wrote it all correctly! Any help would be great so I know if i'm dealing with a new computer (or tune) or if i still need a new tranny, as thought before...

Thanks in advance!!

RBob

iTrader: (1)

The only transmission item that the ECM controls is the torque converter clutch (TCC) lockup. No line pressure, no shifting, no anything else.

If anything the TV cable (the 700R4 doesn't have a kickdown cable) can cause the issues you are having. At the same time there is little difference between an '87 and a '91 700R4 transmission. Some odds & ends but otherwise the same tranny.

I would definitely double check the TV cable adjustment as it is critical on a 700R4 trans.

RBob.

TPI-RS

iTrader: (6)

Thanks for your response. In regards to your comment, what would the ECM do to the TCC. is this something that i would need the 87 programs from? or should it work the same for the 91.

I meant the TV cable, I'm not sure why I called it a kickdown cable. thats my mistake. It is adjusted properly though, i've had 2 different mechanics check it to ensure its correct.

SO... Just to clarify, you are reinforcing my original thought... that I need a new tranny?

RBob

iTrader: (1)

The ECM locks & unlocks the TCC. Based on low gear/high gear, MPH & TPS.

For the trans, if it is slipping then it does need to be rebuilt. As having it slip will glaze the clutch packs. You didn't mention whether is slips in all gears, or just on the 2-3 shift, or when? Fluid level OK?

RBob.

TPI-RS

iTrader: (6)

It slips bad just about in every gear. It sat for over 2 years before I put it into my car, and I dont know if it worked before that... it came with the doner car. I wanted to rebuild it anyways so it doesn't bother me much, I just got concerned when I was told it may not be the tranny that is the issue...

Thanks for your help!