Transmission Problems

[99 GMC Yukon]

First post here! I have a 1999 GMC Yukon SLT 4wd with autotrac and ltd slip.

I was driving down the highway the other say at about 70 mph and notice my rpms changing erractily. Well since then it has gotten worse. The truck now wont go over about 45 and that is with the gear selector in 2nd... Most of the time I have to put it in 1st to get it rolling. Reverse still works fine but the other day after continuing to drive it messed up i almost completly lost every gear. truck would barly do anything. On trans shop said it needs a rebuild other said the transfer case is locking up. Been reading forums and im thinking it may be other things now but i havent found someone with an identical problem... But I hope you guys can help me and maybe I can get this thing running right again. thanks in advance.

 

[96ProCompTahoe]

sounds like you fried the 2-3 and 3-4 clutch packs. what color is your trans fluid?

 

[99 GMC Yukon]

suprisingly its still pretty read and shows no signs of any kinds of composites in the fluids.

 

[96ProCompTahoe]

it could also be an electrical problem.

not sure how the T-case could be causing it unless you fried the T-case. but it would still go into gear.

 

[99 GMC Yukon]

yea. by time i got it to that guy i had put some miles on it so it was binding up and i think he just thought it mght be that. but I wasnt to suuure. it was almost like it was stuck in 4 lo.

 

[tracey-canada]

does your transmission fluid have a burnt smell to it at all?

 

[99 GMC Yukon]

Not that I could smell. its really weird.

 

[tracey-canada]

don't know if you are in a cooler climate area or not but I know in my old Explorer (yicky ford...) my transmission was slipping out of gear, somedays would work, some not - on the colder days it seemed to work good but as soon as it heated up (the transmission) or the temperature was above freezing it would slip.

It didn't have a smell in the fluid either. It wasn't until we finally took it apart we saw all the damage to the gears.

 

[georgehulse]

You guys with Tranney problems: My '97 Tahoe in OD, when cruising sometimes feels/sounds like I'm running over rumple strips on the side of the highway. Foot off gas, or increase speed, it goes away. Then, "check engine" light went on for a couple of days, then out. Some think its the torque converter jumping in and out quickly(might required a new converter - expensive). Others think its just an actuator in the shifter (just needs actuator - couple of hundred $). Otherwise, both engine and transmission smooth and quiet.

Any suggestions?

Thanks. [email protected]

 

[PotentialTahoe]

Gentlemen, I too am having similar problems, Truck starts in 4th gear while in drive, very difficult to accelerate. I was reading a post in technincal and a gentlemen said he had the problem and had to replace the speed sensor gm part#15547452 on the tranny and the problem went away, I think I will try the replacement of that. It can be purchased from GM Parts direct for $90. If you can find it cheaper, please advise. Thanks

 

[NYrr496]

I'm having similar issues. Here's what I found... The computer tells the trans to increase line pressure from 60 psi to 150. I had a corroded connection on my truck's ECM plug and it wasted my 3-4 clutchpack. My friend who owns a very reputable trans shop rebuilt the 4L60E and cleaned the connections and dielectric greased them. Truck was fine for 28,000 miles when the exact same failure happened again. He warranteed it, but I was without a car for two weeks.
Anyone have any input on this? I'm going to install an Autometer guage on the trans to monitor line pressure and he's suggesting I swap the ECM..

 

[badbear82]

i'm kinda having the same problem so if anyone can give me any suggestions about what i can do let me know. my '02 tahoe seems like its not shifting in to fourth gear my rpm is like at 3000 doing 65mph. just started doing this and when i give it gas seems like it wont shift and the peddle could be all the way to the floor

 

[spooled]

Whenever you have a condition where the shift is delayed, neutrals, or soft.

1st thing is to always check fluid w/ engine running in neutral, check the dipstick 2-3 times for proper reading & @ operating temp.

Transmissions will shift better when cold sometimes because composition of the fluid is a bit thicker & when warm it expands therefore causing blow-by, pressure loss, fluid leaks, etc.

To the poster above, it sounds like you may have a tcc issue @ that speed. Do you have check engine light on?

 

[spooled]

Meant to say if fluid is pink, red, & shows no signs of metal flakes/shavings it could be something that can be resolved without removing the trans.

Also, smell is important as well, it can be red, well darker red & smell burnt, which is almost as bad as brown, black. Alot of people don't really know how clear trans. fluid is when it is new.

But when there is a lag between shifts, neutrals, skips gears, these are signs of clutch failure & best bet is to find a reputable re-builder & get a reman. unit.