1997 Tahoe transission failure @ 135K

[glenncof]

I believe this vehilce has the 4L60 tranny and has had light use, no towing or off-road. Transmission, I believe, is orginal as I got the truck at 36K.

It is at the transmission shop and I would like to know how it failed. Any comments are welcome.

I was on a camping trip, loaded with wood and gear the day of the problem. The Tahoe had done about 1500' climb up hill on a 100 degree day in heavy traffic. (Route 17, San Jose to Santa Cruz California). When pulling into over night parking I heard stuttering.

Next morning, from cold start it would operate normally but within a minute or more I could hear a quiet werring sound, then erractic (down) shifting.

Then it would act like it was in neutral. No power transmitted even in reverse. Rev engine = nothing. No indicator lights on dash.

History: Fuild/filter were changed at 100K, no flush.



Any ideas ?

[2000CAYukon]

You have the 4L60E. The Sun Shell is a weak point on the 4L60E/4L60. When is goes, you will lose Reverse, 2nd and 4th. At this point, a rebuild or crate transmission is your only choice. There is an upgraded Sun Shell called the "Beast" that is much stronger than the stock one.

By the way, I live in San Jose. If you went over the "hill" (as we call it) on Saturday July 22nd it was very hot that weekend. Well over 100 (I think the high was 107). I doubt the heat did you in but a weak cooling system can cause the tranny to fail sooner.

//2000CAYukon

[glenncof]

Your right, I was going over that "hill" but on the 23rd. I monitored the engine temperature and it never rose.

It was all gears that did not work so the Sun gear not likely from what I read.

[2000CAYukon]

Originally Posted by glenncof

Your right, I was going over that "hill" but on the 23rd. I monitored the engine temperature and it never rose.

It was all gears that did not work so the Sun gear not likely from what I read.

Well the 23rd was pretty hot too! Are you sure it shifts into 2nd and 4th?

You only lost reverse and the noise?

//2000CAYukon

[glenncof]

I was actually rolling along at about 35 mph on a flat road, probably in 4th, and it slowly lost power. Revving engine did nothing.

Slowly came to a stop and no response in any gear/reverse.

I have studied the GM shop manual and I'm guessing I lost line pressure.

[2000CAYukon]

Originally Posted by glenncof

I was actually rolling along at about 35 mph on a flat road, probably in 4th, and it slowly lost power. Revving engine did nothing.

Slowly came to a stop and no response in any gear/reverse.

I have studied the GM shop manual and I'm guessing I lost line pressure.

Yeah, you probably lost the pump or torque converter (which drives the pump).

Have you pulled the pan to take a look at what is in there?

//2000CAYukon

[glenncof]

I took the vehicle to Morimoto's Transmission in Wattsonville, CA. He diagnosed it as Torque Convertor failure. After pulling tranny apart we inspected the internal components. (Morimoto's came highly regarded from a few people.)

There was some metal but not very much. Sludge was there, more than when I pulled pan at 100K for cleaning.The gears were all in good shape except the high drive. The clutches were not bad but a few were replaced. (none of these items were cause of failure).

Interesting items were; No MIL codes after failure! Lack of metal given deterioration of the drive gear. The drive gear was deteriorated but the corresponding sun shell was not (?). Actually I was surprised it looked so good.

My diagnosis was something in the pressure regulator circuit was causing the pressure to high/low compared to what it should be. This sets a code but not the MIL indicator and shuts down the pressure. No control signal to torque convertor would cause it to disengage. Morimoto did not do the pressure test.

There did not appear to be sufficient sludge/metal to close off the regulator solenoid. The solenoid was pressure tested and found ok.

It's back together and running fine but I'm still wondering about the old torque convertor.; was it really the problem.

Anyone have similiar experience ?

[maxwedge]

May not be related here but the valve bodies are an issue , the tcc control valve bore wears causing a pressure loss to the tcc, this usually sets code p1870, there is a sleeve fix to the vb that most trans shops do on any trans repair on the fwd and rwd units with the aluminum vb. This will not cause a catastrophic trans failure, as it causes the pcm to raise line pressure to the max to compensate for the press. loss on tcc apply.