1991 V2500 4l80e 1st Gear Issue

[trav2210]

Hey all,

New to Square Body's and the forum.

I picked up this 91 Suburban and love it. It does however have an issue with 1st Gear.

Let me start by saying that after trying to diagnose this issue, I eventually decided to stop trying to fix it where I bought it and drive it back home.

Problem was that it was 1900 miles away.....yes, I live in Florida and bought it out of Colorado....more on that later

Anyways, Suburban drove great all the way down, with one exception. It feels like it starts out in 2nd gear every time, yet shifts all the way into lockup....got 16mpg on the way home.

The major problem I see is when put in 1st gear on the selector, It feels like it is stuck. you can feel it wants to go forwards or backwards, and cant make up its mind. If I put it in Reverse, it slams in hard but works just fine.

Checked codes and its showing code 86. Makes sense as 1st would be the low gear reference. Its obviously in limp mode and thats why its starting in 2nd and applying so much force when commanding reverse (max pressure), but i am confused on the forward and backward movement when in first gear. It is obviously the culprit, but where to start.

I have replaced both shift solenoids, both speed sensors (front and rear, not tcase) with no Joy. I cleaned all connectors, have good voltage at Pin E, and good ground. Throttle position sensor is good to go. Fluid was a little burnt, but not too bad for high miles. Other than missing first this transmission works great, which leads me to believe that it should be a simple fix. I assume maybe wear causing leakage in the 1st reverse band somewhere...

Any suggestions would be greatly appreciated!!!

 

[trav2210]

You must be registered for see images attach

You must be registered for see images attach

You must be registered for see images attach

You must be registered for see images attach

Oh and did I mention, Factory installed Sidewinder Winch....

You must be registered for see images attach

 

[foamypirate]

That's a pretty sweet rig! Hopefully we can get the trans gurus in here.


@HotRodPC,

Any ideas on this issue? Not sure if you have any 4L80E experience, but you are the resident trans guru, so I figured I'd page.

 

[trav2210]

Thanks, I could only be so lucky to hear from them. I've done many engines and a few trans, but this is my first venture into a 4l80e.

by the way, $1300 bought the suburban!!!

 

[trav2210]

some odd things I've noticed so far, it is a 91 trans for sure, and has the original old style electrical connector with the bolt in the center of it.

The solenoids that were in it prior to me changing them were the newer style with the screens in them...Also, the pan had an odd style bolt in it which tells me someone has been in this thing.

It was a government vehicle, so I don't doubt that it was constantly being serviced, the question I'm looking at now is, could someone have tried to swap in a newer valve body and thats why the new solenoids are in it, or is it because someone tried to troubleshoot this problem already and put new ones in...

 

[yevgenievich]

I would start with a new electrical connector and the harness as that was the main issue for 91. But binding on 1st gear would indicate a crossleak somewhere. Verify with a meter that correct solenoids are on when first is selected.

 

[HotRodPC]

I was going to suggest same as Victor. A crossleak in the valvebody somewhere. Maybe a bad valve body gasket. However, being it's the electonic trans, I am not as experienced. I've seen this happen in Th350's after guys installed their own shift kits in Th350's and I asked if they torqued the valve body and they said no, just tightened everything back up. One of them the guy missed 2 bolts on the valve body, that for sure caused a crossleak. The other, I don't recall exactly what he did, seems maybe he left the wrong check ball out according to instructions.

It could even be a stuck valve. A valve that is not letting something apply that needs to be. I don't have a diagnostic flow chart for 4L80-E, so not much help.

 

[yevgenievich]

Unfortunately seals on the input drum can cause the issues as well and require a full dissasembly to inspect.
And as seeing new style solenoids, last time when i had 4l60e binding in first I put new solenoids in as well. Was a waste of time as a teflon seal was a culprit.

 

[HotRodPC]

Unfortunately seals on the input drum can cause the issues as well and require a full dissasembly to inspect.
And as seeing new style solenoids, last time when i had 4l60e binding in first I put new solenoids in as well. Was a waste of time as a teflon seal was a culprit.

You actually mean the seals on the input shaft right? I can see how that can certainly cause a crossleak also. Though it would require R&R of the transmission, it's not all that hard to remove the pump just to inspect those, and they can be replaced right there and the pump put back on.

 

[yevgenievich]

You actually mean the seals on the input shaft right? I can see how that can certainly cause a crossleak also. Though it would require R&R of the transmission, it's not all that hard to remove the pump just to inspect those, and they can be replaced right there and the pump put back on.

Seals on the shaft are the ones I am referring to, trying to indicate where the shaft goes and too long to type out
4l80e has a number of other weak areas that show up with high miles, the wore out bore for tcc apply, reverse boost valve issue and couple of other items. Mostly related to bores getting wore out in the valve body. Good overall transmission, but parts do get wore after many miles

 

[HotRodPC]

It just take too long to type it out, but yes, the seals on the shaft.

Figured so. That brings the thought to my mind too, could it even be a crossleak in the pump rings? If he chooses to go that route, I'd sure replace the pump rings too while in there.

 

[trav2210]

Thats kind of where I'm at. I assume cross leak in the valve body, as being that when I pulled the pan, it had new style solenoids as if someone had been in it before.

Along those lines, to try for an easy fix, I'm going to pick up a new valve body. Expense is right around 150, and If I end up buildin the trans at the end of all of this, A new valve body is in the mix anyways as like you said, High miles causes wear.

That way I'm not out 150 if it doesnt work.

Before I go to those lengths though, I will start with inspecting the VB. I'm going to pull it down and go through to look for stuck valves, leaking seals etc.

Anything you guys would make sure I check besides the obvious? Fingers crossed

 

[HotRodPC]

Be sure to use NEW valve body gaskets, be sure they are the correct year model gaskets because there is changes and I do believe VB is certainly one of those. And torque the bolts and be sure not to miss any. Probably what's more important than the actual torque spec is consistency. If you can get them all equally torqued within a foot lb call it good. Maybe even 2 foot lbs being a cast iron and not an aluminum valve body.

 

[trav2210]

Still doing research, and ran across this....

Usually when I experience a bind up in reverse, it is because the forward clutches failed. The forward clutch is on in all forward gears only. When the forward clutches fail they go metal to metal and what you have is too much clearance in the drum causing the forward apply piston to come out of its bore. When this happens, the forward apply piston will not return to the release position and the clutches stay applied no matter what gear you put it in including reverse or neutral. MikeL

 

[HotRodPC]

hmmm, kinda find that hard to believe the way that's expalined about the piston travel.

I guess it is certianly possible the forward clutches have overheated and welded themselves together with the steels. I have seen that happen. And it would act the same way.