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post #1 of (permalink) Old 08-20-2001, 04:35 PM
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transmission clunk, 2-3 shift (long)

I have a 1990 K1500, 350V8 with the 700R4 transmission.
The truck has about 126000 miles on it, but the motor runs
like a top.

Here's my problem:
My transmission/driveline clunks as the 2-3 shift occurs.
This occurs at no other shift.
I have done the following to troubleshoot and/or correct
the problem:

1) ATF fluid has been changed about 5 times this month.
The pan was dropped and filter was changed at the second
ATF change. For the first three changes, Lubegard additive
(black bottle) was added in order to get rid of previous
problem of torque converter clutch (TCC) shudder. TCC shudder
was gone after the first ATF change. After suspecting the
Lubegard may have altered shift quality to produce the shift
clunk, it was discontinued for the last two fluid changes.

2) All U- joints were inspected and seem to be in good shape.

3) Rear transmission mount was replaced. Old mount was not in
too bad of shape, but the new one was installed anyway.

4) Transfer case was drained, flushed twice, and refilled with
Dexron III as per recommended literature/manuals.

5) Slipyoke on driveshaft was lubed with CV joint grease with
no effect on clunk.

I suspect that there is something internal in the transmission
that is causing harsher than normal shifting to occur. My first
theory is that an accumulator piston is sticking or that the
accumulator piston spring is worn out or broken.

The condition of the original fluid that I removed from the
transmission was such that a slight haze of metallic particulate
matter was suspended in the fluid. It did not appear to be burnt nor
did it smell burnt.

The transmission had had several filter/fluid changes since
its known history with us after 80,000 miles.

Any ideas? Is there any way a simple solution could save the unit
so that a rebuild can be delayed? All other functions of the
transmission appear to be good.

Thanks for reading this long post!!

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