Transmission Shifting Problems

[ksteak]

Hey! I have a 2003 Yukon XL Denali with 118k. 2 years ago (at ~85k), I had the transmission rebuilt. Now it is having issues again. In both first and second gear, the RPM's will rev up all the way to redline (and not shift) until you let up on the gas... only then will it shift to the next gear. It does this in gears 1-2 and 2-3, but beyond that, it's fine. If you let up on the throttle, it will shift fine... but if you keep on the throttle, it will just rev up higher and higher without shifting.

Any ideas? I'm hoping not to do ANOTHER rebuild, but I'm not optimistic. Front diff is going too... so the repair bill is gonna be big.

Another question: Can you still get *brand new* trannies for these vehicles? I've never had much luck with rebuild longevity.

Thanks!

 

[blueflamed03]

Kamin, sounds like a 4l60e issue for sure. For a stronger unit, please check
one of these great companies:

http://www.finishlinetrans.com/

http://www.performabuilt.com/

 

[ksteak]

Thanks Tracy. Is there a way to easily know if I have the 4l60e or the 4l80e?? It's an '03 Denali XL (6.0L).

I'm guessing it would be stamped somewhere on it, but I have not crawled under to check yet.

 

[Jay]

You will have a 4L65E behind the 6.0.

Sounds like there are multiple leaks. Could be a damaged separator plate gasket, leaking accumulator piston (builders don't always replace the plastic ones during rebuild! Go with the aluminum pistons next time), o-ring, or the PWM circuit wasn't addressed during rebuild and that's usually the biggest cause of low line pressure.

The PCM is most likely commanding the shift at the right time... around 2000rpm at light throttle... but if the line pressure isn't where it's needed to be to complete the shift, the shift won't happen until you rev the engine up higher like stated above, where the pump is spinning faster and producing more output to overcome the leaks. Even a simple $1 o-ring seal can cause this while the rest of the trans is perfectly fine.

In some cases a gear won't happen at all. I've seen a few that did the rev limit then shift under immediate return to light throttle, completely skipping 2nd or 3rd gear. When i tore it down, it was nothing more than a ruptured seal, gasket, or the 2-3 accumulator check valve was leaking. But the trans had to be torn apart to find it.

The problem with these transmissions is it's either a really simple fix with a pan drop or the whole thing needs to be torn down to inspect. At that point it only makes sense to install new clutches, seals, band, etc (or total overhaul) while you're in there. The clutch parts are actually quite cheap... lo/roller clutch, forward clutch, overrun clutch, 2-4 band, and 3-4 clutch pack can all be purchased for under $200. It's the labor that gets you at some $80-100 per hour plus machine work if any is needed on the valve body.

At 118k miles you may want to have a performance build done by a reputable company. I've only heard good things about the two listed above.