Time for a tranny?

gmc
2500
transmissions

#1

I have a 97 GMC Truck, 4x4, automatic, with about 140k on it. Lately, it started ‘slipping’ under acceleration, as if the tires were spinning. Happens in 2x and 4x so I know it’s not a traction issue, AND I’m now hearing a sort of scuffing/squealing noise from the tranny area when I accelerate harder.

Is there anything besides needing a new tranny that would cause this? Second, am I better off getting a) a used trans from a salvage yard, b) rebuilding this one, or c) buying a new GM factory one, similar to the crate motors?

Last, if and when it is out, is there anything I should do to the t-case as preventative maintenance?

THANKS!


#2

Forgot a couple details! I have no idea what the maintenance history of the truck is, and I’ve only had it a few months. The trans fluid (checked hot, running,etc) is full, pink, clean-looking and no burnt odor.


#3

Make sure you’re not being fooled by a siezed or siezing fan clutch. A transmission cannot slip much at all without destroying the friction element that slips. There’s no mistaking the smell and color. If a sprag clutch slips at all, its life is over and you’d really know it. The converter clutch may slip w/o much evidence but you can disable that to confirm. Sources for a rebuilt??? hit or miss…someone else here knows better than I.


#4

What would the fan clutch have to do wiith the transmission? By converter clutch you mean the lockup? I’ve read conflicting opinions about disabling that, told it can cause damage?


#5

The roar and (sometimes) sqeal feels just like a slipping transmission. There’s hurricane going on under the hood when that siezes and it robs a decent percentage of power (I’d guess 25HP or so at 3500 RPM). I hear one most every day in normal travels. Particularly on trucks that has been misinterpreted many times as a trans slip. I’ve made many a customer happy by fixing the slipping transmission with a $60.00 fan clutch.


#6

Except it would do it when the truck is parked and being revved up, whcih it doesn’t. But it happens as soon as I’m going down the road. Plus, the noise comes from below, not in front. I wish it was that simple though!


#7

Yes. This is the typical way this type of info gets dispensed–through dialogue such this. Of course the best conveyance would be via a test drive…but then the $100/hr shop rate starts to change nonchalant candor of things. Anyhow, the fluid shuold and will stink like hell if a friction clutch is really slipping (there are no critical bands in GM rear drive transmissions). A clogged catalytic converter can also exibit the same roaring, stressed engine and reduced power as described by the patient. This is pretty good info for what we’re doing here…check the cat too.


#8

I never said there was a roaring noise. There is also no reduced power, or stressed engine. That would not lead to the engine revving, but rather it would bog down. I’ve worked on engines for 30 years. I’ve rebuilt them. I’ve also changed clutches and rebuilt standard transmissions. I’ve literally rebuilt everything on a car BUT an automatic tranny. I’ve removed and replaced automatics, but never opened one up, nor do I feel I have the talent or tools to do so, especially now with the high tech stuff.
I am 99% SURE whatever is going on is in the transmission or transfer case. I’ve checked the u-joints, I’ve jacked it up and run it in gear to listen to the rear axle. It’s IN the tranny somewhere, but I don’t know what to look for. Was hoping to find someone here with transmission experience. I appreciate your suggestions but this question is specific to the tranny.


#9

“I’ve worked on engines for 30 years…”

Sounds like you’re competent to rule out the kinds of things that people guessing on an internet forum would come up with.

It’s time to find a good independent trans mechanic to lay hands on the patient.