quote:

Originally posted by PorterN:
So, are you telling your family and friends that you blew a tranny?

Good luck - I hope it works out in your (cheapest) favor!

I don’t think today is the day for this. Five threads already locked.

Looked into this a while back with a similar transmission.

Drive requires about 85 PSI to function properly. Reverse needs more like 145 PSI.

There aren't that many internal components that function during both operations. Guessing the fluid (level and/or temperature), then the pump, valve body, bands, and lastly the clutch pack(s).

Bands, packs and the valve body would likely have presented themselves with a hesitant 2-3 shift.

Heat is the enemy of automatic transmissions, so have the lines flushed and consider an external transmission cooler if one can be had for your ride.
The hydraulic capabilities of the fluid is a primary function, but also the volume of fluid and its heat dissipation capabilities is crucial for long transmission life.

Here was my most recent rebuild. Fun times!

Any chance these overpasses were in Michigan, or someplace with freezing temps?

quote:

Originally posted by holdem:
...I was on the interstate, cruise control set at 82mph and I went over an overpass, the truck shifted and the motor quickly revved to nearly 6,000 rpm before I could tap the brake to disengage the cruise.

At the next overpass I was ready, with my foot hovering over the brake, and the problem repeated itself.

transfer case or rear diff maybe?

quote:

Originally posted by dynorat:
Any chance these overpasses were in Michigan, or someplace with freezing temps?

Florida. It was 65-70 degrees at the time.

Can I have your headliner?

Not to be a downer, but... We just had to have out transmission rebuilt on our Equinox. The shop that did it told us that the Yukon, Tahoe, Suburban transmissions are not very good. He did not specify which years but definitely newer models. I hope that is not your case as it is not an inexpensive repair bill.

It sounds to me like it's either the pump failing (my guess) or a blockage/clogged filter. I had this issue on a transmission where it worked perfectly when cold, then once the fluid got hot (and thinned out) it started slipping and it turned out to be the pump.


Typically if you have bad bands/clutches they slip all of the time.

I've heard that if prior owners don't flush and then new owner flushes somewhere around 100k or more this happens. Something about all the dirt and pieces holding everything together.

quote:

Originally posted by Scuba Steve Sig:
I've heard that if prior owners don't flush and then new owner flushes somewhere around 100k or more this happens. Something about all the dirt and pieces holding everything together.

I have heard the same thing quite a lot. Last week I had the vocational school flush my coolant. I could have done it myself but the ground would be a mess, and why do it when the shop teacher will do it? Anyway, he asked what is next for my Silverado with 83,000 on it. I asked him about the transmission flush and he said no problem. I asked him about what you said in your post and he said in older vehicles possibly, but he wouldn't be concerned doing a flush on my 2010.

quote:

Originally posted by Scuba Steve Sig:
I've heard that if prior owners don't flush and then new owner flushes somewhere around 100k or more this happens. Something about all the dirt and pieces holding everything together.

It has to do with sludge being loosened up and then clogging up the valve body. New transmission fluid is a great cleaner.

I've always followed the advice on a neglected transmission to only do a pump out and refill, several times, over the course of a few months. This only replaces around 40-50% of the fluid at a time. Logic being to more slowly allow the deposits to be dissolved instead of the scouring of all new fluid.