Trans Swap Issues

[GMCYukonDriver]

Hey guys.

I've got a 1995 Yukon that lost 3rd gear a while ago. The bands just finally wore out. Anyways, since this thing is supercharged, I wanted to swap in a 4L80e. I bought one from a yard, had it completely cleaned up and rebuilt. Took it to a shop and had them modify the crossmember mounts, wiring, and put the trans in.

Problem is, it runs like poop.

I got the tune and wiring schematics from Wester's Garage. I've triple checked them, and all the wiring matches up with how they say it should be. I took a datalog today and here's what's going on.

First, the trans is in limp mode. Takes off in 2nd gear. Reverse works fine, but drive has issues. I was letting it idle, to pick up speed, and at about 8 mph, the slip RPM's for the torque converter suddenly went from 200 RPM to NEGATIVE 500?! The truck shook pretty bad and almost died, so I stopped. I threw it in Reverse and backed it into the driveway. Don't want to break anything.

Anyone have any ideas? I've sent all the info and that datalog to Wester's, so we'll see what they say, just wanted to send this out and try to get some ideas. I appreciate the help, I can't wait to get this thing running.

 

[Nak]

I'm not completeley sure about this trans, but here's my guess. If you have a 4L80E with a TCM, it probably needs to talk to your ECM. If your ECM hasn't been reprogrammed, it might not know how to talk to a 4L80E if it came with a 4L60E. You need to verify that the ECM and the TCM can talk to each other. You have TBI, so I'd start by talking to somebody that programs chips for that. Also, what year is your TCM? Is it receiving compatible data from the wheel speed sensors? 1995 is a bastard year, still TBI but new interior. Things changed besides TBI to Vortech. ABS for one. I have no idea if you have the 1992-1994 ABS or the later ABS. That can matter for your trans. Ideally, get a complete factory shop manual for your 1995 and figure out exactly how your trans works. What inputs does it get? What outputs does it put out? What systems does the TCM interact with? AllDIY.com will be a big help if you can't locate a shop manual.

When you swap components that are computer controlled, or even get a minor input from a computer, or put out a minor input to a computer, you have to know and understand all of the interactions to get the swap to work. For instance, my current swap vehicle came with a 700R4, not computer controlled at all. Whoops! Except for the lockup torque converter. And the transmission does send an analog signal to my ABS. SO, I have to figure out exactly how that torque converter interacts with my ABS if I want the ABS to continue to work properly. Your swap has a TCM, ABS, wheel speed sensors, and an ECM. All of those components have to interact properly.

Try finding a thread about an identical swap. If you can't find one, talk to a TBI programmer. The fix may be something as simple as a chip reprogram. You may need a TCM from 1995.

Good luck and report back so the next guy knows what to do!

---------- Post added at 10:12 PM ---------- Previous post was at 10:06 PM ----------

Found these:
http://www.ebay.com/itm/1995-Chevro...Set-/251775373466?hash=item3a9efb509a&vxp=mtr

http://www.ebay.com/itm/1995-Chevy-...oks-/161600057826?hash=item25a01d31e2&vxp=mtr

http://www.ebay.com/itm/1995-Chevro...:1995|Model:Yukon&hash=item1e7e9964d8&vxp=mtr

I don't know anything about these items, just did a search on ebay.

 

[GMCYukonDriver]

Awesome, I'll look into that. Thanks.

I'm pretty sure it has something to do with the tune or wiring, just not sure what. I have posted this pretty much everywhere, but I'll see if I can get my hands on a shop manual for it. That would help with making sure the wiring is absolutely right.


On a 95, to my knowledge, the trans is completely ECM controlled, so it shouldn't have a TCM. Also, all 4L80e's were electronically the same after 1994, so that shouldn't matter either. Unless it's possible that my ECM is not capable of controlling a 4L80e for some reason, but I don't think that is the case.

I have some more research to do.