94 GMC shuddering under load

[eleveniron]

My 94 GMC (extended cab, 4x4) has a problem where it shudders under load. You really notice it in overdrive and you start to climb a slight incline or accelerate slowly. Just before it kicks down from OD the whole truck shudders.

Lately it has gotten to the point where it does it in D too. I can be cruising along at 100 KMs/hour and if I try to slightly accelerate the whole truck will start to shudder. It almost seems as if it may be related to throttle position and/or vacuum pressure.

I'm pretty confident that it is not the transmission...it seems to be very solid in the shifts and have had no other problems. The fluid is up and clean and the tranny filter was done about 30K kms ago.

When I first started having this problem I had a whole tune up done (plugs, wires, cap, pcv, etc) and no fix. It is slowly getting worse and easier to duplicate when driving. It's gotten to the point where I don't use OD any more becasue it is so much worse in the higher gears.

Oh...and new fuel filter in there too.

Any suggestions appreciated.
Steve

[blabhern]

Steve

check out your u-joints on the drive shaft. Hopefully that's the problem (easiest to fix). If not then you need to start looking at the axle, tranny, transfer case, etc.

[planedude]

Sounds like your torque convertor, The nect time it does it just tap the brake. If it goes away then the tranny comes out and a new convertor goes in.....

[Kevcules]

Sounds like a tranny issue. A friend of mine just had his truck doing the same thing and he had it checked and they told him to try some "anti-shudder" additive . Sure enough , it went away, for now.
This is a definite wear sign, from many miles, or lack of TLC to the transmission.
It would happen to him under light load or low rpm's also.
Good luck

[eleveniron]

Thanks for the ideas...but you can almost feel the engine power drop off when it happens, which is why I'm thinking engine. It feels similar to an 8 cylinder running on 5 or 6 cylinders.

Ujoints, axles, brakes etc are all in good or recently new condition.

I've never heard of anti-shudder addative.

Steve

[Kevcules]

Originally Posted by eleveniron

Thanks for the ideas...but you can almost feel the engine power drop off when it happens, which is why I'm thinking engine. It feels similar to an 8 cylinder running on 5 or 6 cylinders.

Ujoints, axles, brakes etc are all in good or recently new condition.

I've never heard of anti-shudder addative.

Steve

The reason it feels like it's losing power is because the clutches in the tranny are slipping a little. What you describe as symptoms was EXACTLY what a friend described to me. This is why I answered this thread and thought I could help. Try dropping in at your local mechanic shop and see what he thinks. Loss of power in drive train is often related to tranny issues.
PS... While your there , see if HE has heard of Wynns " anti-shudder" tranny additive.

[Kevcules]

Heh Eleveniron

How did you make out with your "shuddering" problem?

Kevin

[eleveniron]

Hey Kevcules,

I haven't had a chance to get into it yet. In the winter I only drive this truck once a week or so and i'ts been too bloody cold to work on it outside.

I'll make sure I post my results though when I'm done.

I did drive it to work today and it sure sounds like a vaccum leak right when it starts to shudder.

Steve

[eleveniron]

I think I may have found my problem.

Gm service bulletin #37-71-10 deals with the torque coverter clutch shudder. It shudders when the torque converter clutch is locking or unlocking...sounds exactly like mine. They tell you to replace the converter assembly.

Sounds costly...arrgghh!

Steve

[Kevcules]

That makes sense.

Changing the torque converter is not that difficult though,just some time on the weekend.It's around $250 I believe for the converter and you might as well change your fluid and filter.( you will lose most of it anyway) I think the capacity of the tranny is something like 12 litres so have lots on hand. Alot will leak on the ground! I replaced mine about 3 years ago because something was broken inside and rattling around. It really helps if you have a tranny jack to lower the tranny and then raise it into position when done , it's fairly heavy. You should have a helper for this job. Good luck.

Kevin

[eleveniron]

Thanks kevin. This will be a job for the spring when things warm up a bit. When I first read the bulletin it looked like they wanted you to change the TCC solenoid which would be simple. But after reading it again it looks like its the whole converter assy.

Steve

[truk993]

I had same exact problem with my old '92 w/ 700r4. Tried everything and even new filters did not help. Have you tried flushing the tranny? I did this and instantly the shudder went away and got another 70K miles out of the tranny.

[eleveniron]

Haven't flushed the tranny yet but will take it in and have it done next time i take the truck to work. I'll post the results.

Steve