Transmission issues

[Ttchutch]

I'm not sure if this is the place to post this issue.I've got a '91 GMC Suburban V2500 4x4 with a military 6.2l diesel. This Suburban has the 4l80E transmission in it. The transmission went out a few months ago so I pulled it, had it rebuilt and reinstalled it. Then about 3 weeks ago the transmission went out again so I dropped the vehicle off at the transmission shop that originally rebuilt it. The wiring from the TCM had been melted and damaged at some point. The shop is telling me that they will have a very hard time diagnosing the problem that is causing this transmission to go out and they are hesitant to even try. There is something going on with either the TCM or the wiring or both. I am not getting any real advise from them on what to do. I am thinking of ordering a new factory TCM but the main harness from the fire wall to the transmission is no longer available. Or should I have the shop install the Quick 1 trans controller? Has anyone installed the Quick 1 transmission controller? How many hours of labor would it take to install? I am on a very tight budget and I need to keep the price around $1000 or less.

 

[Tinstar]

I'm not sure if this is the place to post this issue.I've got a '91 GMC Suburban V2500 4x4 with a military 6.2l diesel. This Suburban has the 4l80E transmission in it. The transmission went out a few months ago so I pulled it, had it rebuilt and reinstalled it. Then about 3 weeks ago the transmission went out again so I dropped the vehicle off at the transmission shop that originally rebuilt it. The wiring from the TCM had been melted and damaged at some point. The shop is telling me that they will have a very hard time diagnosing the problem that is causing this transmission to go out and they are hesitant to even try. There is something going on with either the TCM or the wiring or both. I am not getting any real advise from them on what to do. I am thinking of ordering a new factory TCM but the main harness from the fire wall to the transmission is no longer available. Or should I have the shop install the Quick 1 trans controller? Has anyone installed the Quick 1 transmission controller? How many hours of labor would it take to install? I am on a very tight budget and I need to keep the price around $1000 or less.

$1000 or less and transmission usually don't go together in the same sentence.

Have you taken it to a different shop for a second opinion?

 

[Ttchutch]

I meant $1000 or less for the controller with installation.

 

[Ttchutch]

They are going to warranty the transmission. I have thought about taking the truck to another shop but, the truck is 2 hours away from me. I'm in a small town.

 

[rustystud]

At this point I would go with the after-market controller. There is something seriously wrong with your present controller or wiring to cause such damage (like a direct short). You could spend weeks trying to find the culprit in the wiring and in the end being forced to go after-market anyway. I have found almost all of the newer generation controllers to be fine products, so I would not hesitate to let them install this one for you.

 

[muddobber40]

The quick 1 and 4 controllers are both great. The quick 1 would probably be just fine for your application. They both only take a couple hours to install and that includes programming it on the computer before you hook it up. Have to have a Windows based computer for the software to program it. Very easy to do even with limited mechanical and computer knowledge.

When you or whomever installed the 6.2, was the TPS swapped over?

What exactly is your trans doing? Does it just engage in reverse and 2nd? Missing a gear? No OD? Or is it not engaging period?

 

[Barrman]

I agree that a different controller and wiring harness is a must. However, a hidden cost here is your year transmission. The early 4L80E years had a different wiring harness plug and such inside the transmission than all the later years. Talk to the shop about that.

 

[Ttchutch]

I bought the Suburban with a bad 6.2 already in it. So I ordered a used military 6.2 from White Owl and swapped them out. I installed the TPS from the old motor and changed everything from 24v to 12v.
I drove the Suburban for about 3 years and then I started having what I thought was engine related power issues. I went from going 50 up mountain passes to 20-25 and horrible mpg, it felt like I was pulling a trailer. About a couple weeks later I lost first gear. The fluid was black. The other gears worked fine. If I tried to manually shift it into 1st it would bind up real bad and not move. That's when I pulled the transmission and had it rebuilt. I reinstalled it and I had all my power back. Mountain passes were then pulled at 50 mph again. Then all of a sudden the I lost power again (like before it felt like I was pulling around a heavy trailer). Shortly after that I lost reverse and overdrive and now the entire truck is at the shop.

 

[Ttchutch]

The wire harness has already been changed out to the '94 on harness.

 

[muddobber40]

Loss of power is usually a TCC issue. It can be an issue in the converter itself, worn bushings etc. No reverse can be many things( nothing electronic though), but usually incorrect band installation. Sounds to me like they didn't do a good job on the rebuild on top of electrical issues possibly.

Were all internal electronics replaced? Was there any fluid in the pins of the pass through connector? 94 and up harness can still leak

 

[Ttchutch]

Loss of power is usually a TCC issue. It can be an issue in the converter itself, worn bushings etc. No reverse can be many things( nothing electronic though), but usually incorrect band installation. Sounds to me like they didn't do a good job on the rebuild on top of electrical issues possibly.

Were all internal electronics replaced? Was there any fluid in the pins of the pass through connector? 94 and up harness can still leak

When I originally pulled the transmission out a few months ago the plug has some fluid in it. It was the original plug.
I have no idea if the new plug was leaking or not because I dropped the truck off at the shop as I lost reverse and overdrive.
Apparently they're going to warranty the transmission but they don't want to get into diagnosing the electrical or TCM issues. This is why I'm looking into the Quick 1 or Quick 4 controller.

 

[rustystud]

Loss of power is usually a TCC issue. It can be an issue in the converter itself, worn bushings etc. No reverse can be many things( nothing electronic though), but usually incorrect band installation. Sounds to me like they didn't do a good job on the rebuild on top of electrical issues possibly.

Were all internal electronics replaced? Was there any fluid in the pins of the pass through connector? 94 and up harness can still leak

Actually reverse is controlled electronically in this transmission since your using the direct clutch. If it was the band at installation it would have been bad from the beginning not later. I agree with the shop here. There is something in the wiring or control module that is bad.

 

[muddobber40]

Ah yes, forgot about the DC.Been a decade or so since i actually had to diagnose one. Guess I better get the service manual back out and refresh my memory. As for the band, I was referring to checking apply pin length. Short pins will have reverse for a little bit, but fail fast.

AS for the Quick Shift, nice set ups. Have two QS 1s on the shelf for swaps coming up in October. Have used a the QS 4s on two 6.0/4l80 swaps. Not worth spending the extra money on your application Jake and Kevin are great to work with.