How bad is my tranny?

[big61fourby]

Background:
Bought this truck last July; have put 10,000 miles on it since, now at 132K. Tranny fluid was burnt pretty bad when I bought it--very brown, smelled horrible. Did two drain and refills with filter last fall, getting ready to do another. Truck was previously equiped with 5th wheel rails, and currently has a GN hitch.

Symptoms:
While driving along level ground trying to maintain constant speed, TC will unlock, give her a tad more pedal, and it locks back up. This is most pronounced between 45-55 mph (typ. lockup speed), but will also occure at higher speeds (driving solo). Happens while using cruise as well. Haven't noticed a direct correlation to ambient temp, but a tranny temp gauge is comming soon.

Problem is, I just flat out don't have the money right now to fix it. If it can hold on till this summer, I'll be ok.

So, how bad is it, and what will it do when she goes? Any additive I could add to help it along for a while? Like I said, I can deal with it this summer, so I just need another 6-8K out of this poor trans. Thoughts?

Also, recommendations on replacements that are reasonably priced?

[john8662]

4L80E's are a mystery to me, but others have had luck patching them.

Do you have any codes?

Perhaps it's a matter of a TCC solenoid on the valve body that is failing causing the problem. I know the other shift solenoids in the pan have been suspect for some folks. Some have changed them as preventative maintenance, but too much work, I like changing engines better :rolleyes: j/k

Those in the know are sure to put their .02 in soon!

[JohnC]

If there are no codes than I'd look at the brake light switch. Otherwise, follow the codes...

[BobND]

If there are no codes than I'd look at the brake light switch. Otherwise, follow the codes...

Don't forget to check for damaged tailight wiring, or a damaged or filled with conductive green corrosion trailer light socket.

[charliepeterson]

These 4L-80's are very good and can take alot of abuse.

[big61fourby]

With the condition of the fluid, I have been leaning towards failing internal hard parts, but there will be some other things to check first.

First, I don't own a scanner, and I do not have an SES light showing (light works on bulb check). Will any of the basic OBD II scanners read tranny codes?

Also, how does tail light wiring work into the equation? I would guess a short to ground in the brake wire would cause the TCC to unlock???? Haven't looked at the brake switch real close, but are there any easy tests for that?

How hard are the solenoids to change? If thats all it is, I'd be thrilled.

Thanks for the ideas!!

[DA BIG ONE]

When you do get into trans, install a TransGo shift kit "off road-towing" one. Get the kevlar clutches and premium steels, do all the updates that solve misc problems relating to your year trans, use only synthetic fluid. If you tow, or go for extra performance a multi disk lockup converter will help too.

This site I found is best for transmission updates information and parts, http://www.transhardparts.com/

I would further check for junk (road dirt) blocking trans cooler, cond, radiator and clean it out from the inside out. Pressurized air blown from back of each item towards front of truck works best here.

[Scooby]

My 96 does not unlock the torque converter when the brake pedal is depressed. I have seen others say the same thing on here too. I use the brake pedal method on other vehicles to check for converter lockup, but on the 6.5 with 4L080E that doesnt work.

[JohnC]

If it's slipping internally it'll set a code. The only time it won't is if it thinks it's supposed to unlock.

Mine always unlocked as soon as you started pressing on the brake pedal.

[big61fourby]

[SIZE=3][FONT=Arial]Scooby, that

[JohnC]

Do tranny codes set the SES light?

Not necessarily.


Will the small generic OBDII scanners read tranny codes?

Should!

[dano6.5]

I have some similiar things going on. My tranny kicks out of gear in OD while coasting down hill. Mechanic scanned and found no problems with solienods or shifters. GM tech diagnosis is the over run clutches used in OD. Going to pull tranny next week and possible rebuild. I use this unit for only towing. Let me know how you solved your trouble. Thanks.

[big61fourby]

Never pursued the issue any farther. It was doing this when I bought it, and I've racked up 40k in a little less than 2 years and it's still doing the same thing; TC unlocking under light throttle cruising in the 40-50 mph range. Moderate to heavy throttle--she runs out great. Also, this only occurs when there is very little load on the engine. These symptoms are reduced greatly when towing.

Are you experiencing the same symptoms, or are you saying that the motor returns to idle when coasting? If the engine returns to idle under zero throttle coasting down a hill, I'd say that's normal. That's the way they're programed, I believe.

I'd probably take a hard look at DA BIG ONE's recommendations above if you go ahead with the rebuild...

[JohnC]

...My tranny kicks out of gear in OD while coasting down hill. ....

I may be misunderstanding what you're saying, but that sounds normal to me. That's what an overrunning clutch does...

[bcbigfoot]

I have some similiar things going on. My tranny kicks out of gear in OD while coasting down hill. Mechanic scanned and found no problems with solienods or shifters. GM tech diagnosis is the over run clutches used in OD. Going to pull tranny next week and possible rebuild. I use this unit for only towing. Let me know how you solved your trouble. Thanks.


My suggestion is tell everyone you know not to use the GM dealer/garage, and then tell that dealer they are either unethical crooks or idiots. That is how your 4l80e was intended to operate from factory (unfortunetly). The older OBDI 4l80e could be fooled into engine braking but the newer OBDII like your truck, there are no good fixes that I am aware of, the computer controls to much.