4l80e Problems

[yammerhammer]

Hello, new to site and have a 4L80E question.

 

First off, the vehical is as follows:

1991 Suburban V2500

5.7L 4L80E

4X4

All stock with 170k miles.

 

I had some trouble a few months ago that when I was driving at highway speeds at

any lenght of time and come to a stop, the transmission wouldn't shift out of first gear

until I stopped, turned the key off for a minute and restarted. It did this a couple times

then quite doing it all together. I wrote this off a a sitting problem since it sat for weeks

previous to this.

 

The other is, and I'm not sure if they are related, when I drive at highway speed, let off the throttle and get right back into it, it seems the converter unlocks momentarily and then locks back up ( I get high RPM then "slips" back into gear). I also notice that when

I let off from higher speeds and use engine braking to slow the vehical it surges as if, again, the converter is locking and unlocking. Once I get to a lower speed it unlocks all together. I come off a few steep hills in 4x4 low and get no engine braking, it just seems to "free wheel".

 

I know it's very difficult to diagnose a tranny problem, esspecially a E tranny, over a keyboard but just wonder if I'm looking at a $2500 tranny for a $500 vehical or may it be something simple?

 

Thanks in advance

Jim in Colorado.

[green 788]

Well... first of all I think your vehicle is worth more than 500 dollars.

 

I just rebuilt my 4l80e for a cost of just over 1800 dollars, using all new GM parts.

 

Very possibly, however, your tranny is not needing a rebuilt.

 

Check to see if there is transmission fluid leaking into the plug junction where the computer connects to the transmission. That was actually what the main problem with my transmission was, and I could have probably just replaced that seal in that plug and stopped the leak... and been okay. But my truck has 203,000+ miles on it, and I had the money handy, so I went for a total rebuild.

 

You can disconnect the speed sensor on the transfer case (which will render your speedometer inop)... and see how the truck shifts. It will go to default shift points and parameters without input from the speedometer, and your shifts will be a bit firm (like you've got a shift kit installed)...

 

If it shifts alright with the speed sensor unplugged (the speed sensor on the transfer case), then I would suspect electrical problems, possibly related to the aforementioned electrical plug seal leaking. When this plug gets full of transmission fluid, the signals being sent to and from the transmission to the main computer get muddled, and can cause problems.

 

Transmission shops can diagnose your problem for you, but remember that they make money rebuilding transmissions. They don't make a lot if your problem ends up being a bad sensor, plug seal, or wiring harness getting brittle. These guys are good at giving your "dooms-day" scenarios. So get two or three different opinions, and see if the stories match.

 

Just because you're getting that slipping going from 3rd to overdrive doesn't mean the clutches are shot. If the clutches are actually shot, that slipping will be random, and last for different amounts of time (1 second one time, 2 to 3 seconds the next, and get worse when the tranny gets hotter). If the slipping (revving up) between 3rd and OD is consistent in the amount of time being taken, that would lead me to believe it's an electrical issue rather than a bad clutch or two...

 

Good luck, and let us know what you discover. Sometimes just getting the tranny serviced (new filter and fluid, don't pay for a rip-off flushing) will improve things as well.

 

Dan

[yammerhammer]

Well... first of all I think your vehicle is worth more than 500 dollars.

I've got $310 to date. Bought it from a gal whom just wanted it out of her newly

aquired, covinent controlled neighborhood for $250.

 

Thanks for the info Dan. As soon as the sun comes out, I'll give that a try.

[green 788]

nice truck... you got a great deal.

 

Even if you have to put a used tranny in it (about 600 dollars most places) you're way ahead of the game.

 

Dan

[ColoradoSkiCountry]

I have to agree!! Sweet ride!

[yammerhammer]

Here she is after some bucket seats and a $40 set of wheels. I'm building a cargo rack

for the roof and installing KC lights front and rear along with CB radio, cd player, high lift jack and plethora of other parts that will compliment the off road/trail/hunting rig I'm looking for.

[grampadirt]

Here she is after some bucket seats and a $40 set of wheels. I'm building a cargo rack

for the roof and installing KC lights front and rear along with CB radio, cd player, high lift jack and plethora of other parts that will compliment the off road/trail/hunting rig I'm looking for.

 

 

Here ya go Jim,you might like what I've done to my '95 Burb...you've got a real good start on a bitchin' Burb

 

 

this will give you an idea what's possible with these behomiths

 

gramps..... I screwed up the picture posting,sorry,my FAIL

[pennzoil29]

Have you serviced the tranny? Fluid and filter change. I had a similar problem with my '99, it turned out to be the TPS.