Possible 4L80 problem

[JHB3]

Hello guys, I have 94 gmc 6.5 3500 with a 4L80. My problem is that I can put it in reverse. And push the accelerator sometimes it moves and sometimes it doesn't. There is no strange noises and the fun part is when I mash peddle to the floor with it in gear the engine does rev up. Shifting it to drive does the same thing but not as frequent. Any suggestions would appreciated.

 

[NickTransmissions]

Hello guys, I have 94 gmc 6.5 3500 with a 4L80. My problem is that I can put it in reverse. And push the accelerator sometimes it moves and sometimes it doesn't. There is no strange noises and the fun part is when I mash peddle to the floor with it in gear the engine does rev up. Shifting it to drive does the same thing but not as frequent. Any suggestions would appreciated.

Do you have third gear when in D or D3? When did this start happening? Any recent transmission work?

If so, drop the pan and check the seals on the low reverse servo piston to see if they are worn or hardened (sometimes this happens, esp if the vehicle goes through a long period of disuse...

Whatever you do, don't keep revving it up like that in reverse unless you want to destroy your low reverse band and have to yank the unit out, overhaul it.

 

[JHB3]

Do you have third gear when in D or D3? When did this start happening? Any recent transmission work?

If so, drop the pan and check the seals on the low reverse servo piston to see if they are worn or hardened (sometimes this happens, esp if the vehicle goes through a long period of disuse...

Whatever you do, don't keep revving it up like that in reverse unless you want to destroy your low reverse band and have to yank the unit out, overhaul it.

Yes I have drive. The truck will go down the & shift through all the gears, but seems sluggish. The truck was shifting hard at one point but it was not the last time. I took it down the road.
All this just started happening recently. I just started back working on the truck. No transmission work has been done since I have had it.

 

[NickTransmissions]

Yes I have drive. The truck will go down the & shift through all the gears, but seems sluggish. The truck was shifting hard at one point but it was not the last time. I took it down the road.
All this just started happening recently. I just started back working on the truck. No transmission work has been done since I have had it.

Drop the pan and see what's on the bottom. If you see a whole lot of clutch material, put the pan back on with a few bolts and yank it out for overhaul. Otherwise follow my suggestion above. Check/continuity test the wiring harness and solenoids (i have a video that shows you how, if not sure). Also check the case connector for leaks - common issue with 4L80s

Also replace the filter as it may be partially clogged.

Let us know what you find...

 

[JHB3]

Are your videos on YouTube?
I appreciate your help!

 

[NickTransmissions]

Are your videos on YouTube?
I appreciate your help!

You're welcome.

Here's my Youtube video on testing 4L80E electronic components using a multimeter

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[JHB3]

Giving a update, I dropped the pan. There was not that much flake in it. Tested the pressure switch, it passed. But I did notice a little bit of fluid in the plug. And when I unplugged the connector from the pressure switch. I broke the secure tabs. So I'm going to put a new harness & filter in it and hopefully that will fix it. Now my question is what type fluid do I put in it?

 

[NickTransmissions]

Giving a update, I dropped the pan. There was not that much flake in it. Tested the pressure switch, it passed. But I did notice a little bit of fluid in the plug. And when I unplugged the connector from the pressure switch. I broke the secure tabs. So I'm going to put a new harness & filter in it and hopefully that will fix it. Now my question is what type fluid do I put in it?

Dex3 / Dex-Merc

Fluid looks dark...What is that stuff at the bottom of the pan? Looks like flakes of burnt clutch...If so, that thing may need to come out...

 

[JHB3]

There is some flake.

 

[NickTransmissions]

There is some flake.

Fyi- please Quote my post or mention me if you would like me to respond as i dont get notifications (just happened to notice you replied)

Keep driving it if it works but Id keep an eye on it and be prepared to yank it out pretty much at any time going forward. That stuff is typical of what I see when they come in for rebuild