Transmission shuttering at super slow speed

Driveline shudder, caused by a worn U-joint.

Isn't it common fo the lock-up unit on these to be a failure point? Wouldn't that shudder at very low speeds as it tries to lock up prematurely?

Richard -- I think I've got your answer. I chased the exact same symptom for a year in my '97 318 @ 103K because of its variability: some days it was there, some days it wasn't. Eventually I was led to discover the fragile nature of the magnum cylinder head -- cracked valve seats. Not enough to see in a vacuum flutter or compression test, and not big enough to push coolant out or suck it in, but enough to get CO in the antifreeze. The ever-so-soft cylinder just fires with a little less gusto under high vacuum conditions -- your no-throttle take-off. As soon as you crack the throttle open, the higher load completely masks the symptom.

Run a test for CO in your antifreeze, and/or a leakdown test if these conditions make sense to you and your truck, and let us know.

FYI: think about where you put your money....I was in a bind on a Sunday afternoon, and we magnafluxed a dozen "core" units -- all cracked on the valve seat. I settled with an awful pair of new Asian castings for cheap money to get the truck running, but one failed before I was "ready" to sell it and move on...so personally I rolled the dice with an ebay reman'd OEM unit. For my money, however, the bare pair from Hughes plus a local valve refacing would be the way to go...it's priced right.

Jon

Richard Howard wrote:

Richard - I'd be interested in hearing what you find out. I have a

If you can't post it here, please let me know at

" john.redcord AT gmail.com "

Thanks,

Robert

If you've had it all the time, and you have a vehicle with a two-piece driveshaft, sometimes shimming the center carrier bearing mount (adds a bit of angle on the front U-joint, lessens the angle on the rear) can cure this. I didn't mention this to the OP, because he said it had only recently developed.

Also, some have reported (Roy here being one of them, IIRC) that a procedure to "align the drivetrain" has cured this shudder. This involves loosening the engine and transmission mounts, driving forward about 100ft., driving backward the same distance, then re-tighten the mounts WITHOUT moving the vehicle. It seems some drivetrains were installed in a slight bind, and this has been shown to cure some shudder-on-takeoff problems.