'98 Chevy Tahoe Shudder

jim_bo_in_ms

Not the TC, Tran or U joint Where do I go next?????

I have a 98 Tahoe that I lost reverse in so I ordered a rebuilt tranny and had installed. It immediately had a shudder between 50-60. I contacted the people who put in the transmission and the rebuilder they suggested putting in a slip additive. I did this twice and the problem remained. I toke the Tahoe to a transmission specialist who ran diagnostics on the transmission and told me there is some problem between the transmission and computer. That the transmission is fine and will shift correctly when instructed, no TC problem. They were unable to identify exactly where the problem was without just replacing one thing after another. So, what's a guy to do now?

Mr_Shiftright

It sounds internal to the transmission. A U-Joint wouldn't behave like that--the shudder would be more at low speeds and more constant. Sounds like this is happening as you shift into overdrive. Do you have an OD lockout button. See how it behaves with OD in the off position.

jim_bo_in_ms

I don't have an OD lockout button, but I can put it in 3rd not D which prevent the shift to OD. Did this and it still shudders. My first thoughts were that it was an internal issue with the new transmission so I took it to a specialist for diagnostics. Like I said earlier there seems to be no problem with the TC or transmission itself. The specialist pointed to some sensor that relays peddle position to the transmission???

jim_bo_in_ms

Oh yea one more thing I tried. I read that you could narrow this problem down by determining if the issue is a TC slip or not. To do this let the transmission get warm, then while in drive hold the break and apply a fair amount of torque to the transmission. If the problem with the transmission is internal or TC related the transmission will slip. If the transmission continues to deliver the torque to the rear end then the problem is not internal. I did this test a couple of times and never got any slip at all.

Mr_Shiftright

That's not really the best test. Try this:

A quick test

On many vehicles, one way to identify a torque converter shudder is lightly touching the brake pedal. While carefully maintaining vehicle speed with one foot, delicately apply the brakes with the other. If the shudder immediately stops, with brake application, the problem is likely the torque converter clutch.

ALSO--are you quite sure this isn't a misfire?

jim_bo_in_ms

I tried this break test several times and it had no affect on the shudder. And, no I'm not sure it isn't a misfire! It seems to run fine in park and when revved up it doesn't seem to misfire. How could I determine if it was due to a misfire? I would guess this could be caused by a cracked distributor, bad plug or plug wire? I could replace a bunch of stuff and still be no better off. What would be the best approach to eliminate this as a potential cause?
Thanks

Mr_Shiftright

Well a misfire will not necessarily throw a code---so a careful inspection of spark plug wires, coil packs, distributor cap and rotor----might indicate some arcing of the spark, or a crack somewhere ??

It's very difficult sometimes to discern between a TC shudder and an ignition misfire.