Wah! Off the line shudder with new trans

[sleepertruck72]

Did The same posi unit exist prior to transmission swap ? A new transmission and new torque converter should not cause this shudder...since it occurs in 1st to 2nd gear under light throttle...the driveshaft should be ruled out. Likely a new transmission issue..

[davepl]

None of the (non-involved) trans shops locally thinks it can be the transmission; the back of the trans actually jumps up and down. They can replicate it on jackstands now with brake & throttle so its easier to observe. I'm told its not like trans shudder, and the TCC would have no business locking up yet.

It happens both held in First and held in Second, so its not a transition or attempted shift between gears, we know that much. Since it happens in two distinct gears, the thinking is it has to be outside the trans. But you never know.

The posi unit was installed at the rebuild/restoration but since I only had about 40 miles with the first trans, not a lot of experience. I don't think it happened with that trans. But the driveline angle theory would start with the new trans because that's when the new trans was longer which changed or created the unwanted pinion angle.

I guess we'll know tomorrow for better or worse!

[indymachinist]

Originally Posted by Shelby0099

One of the first items I would think of for shuddering under load, 1st and 2nd gear is the torque converter.

Agreed. First thing I thought of. Can you manually lock/unlock the converter with your transmission controller?

[davepl]

No, I cannot. I can make sure it doesn't attempt to engage, which I guess means we are manually "unlocking" it. At which point it still happens.

The road speed is under 10-15 mph so I can't imagine any reasonable controller would be trying to lock the TCC at that speed though (and I know the computer has a good speed reading because it controls the speedo, which is accurate).

I wish I knew what TCC shudder felt like - is there a separate "converter" shudder that is NOT related to the TCC? Or is all converter shudder the fault of the TCC?

[sleepertruck72]

Originally Posted by davepl

No, I cannot. I can make sure it doesn't attempt to engage, which I guess means we are manually "unlocking" it. At which point it still happens.

The road speed is under 10-15 mph so I can't imagine any reasonable controller would be trying to lock the TCC at that speed though (and I know the computer has a good speed reading because it controls the speedo, which is accurate).

I wish I knew what TCC shudder felt like - is there a separate "converter" shudder that is NOT related to the TCC? Or is all converter shudder the fault of the TCC?

IMO.. the easiest way to eliminate a faulty TCC is to swap it with a known good one..one that does not have a shudder issue..I am just as curious to see what the root cause will be.

[57taskforce]

Out of curiosity how much does the back of trans move around? Are we talking 1/2 inch or inch(es)? It seems to me that any substantial movement is not normal and likely to cause problems.

[indymachinist]

No, at low speed like that the torque converter should not be locked. I was just thinking if you had the ability I would get rolling at some low speed, force it to lock, and see if the shudder went away.

[davepl]

OK, I see. I don't think we could force the TCC to lock, so we can't get it to lock during the event (too low of speed).

I didn't see it moving myself, only felt it, he was under there not me! Apparently enough that he thought maybe the mount was bad, or too soft, that it let it move that much. But if his theory is right those would be some fairly strong forces.

[davepl]

None of us foresaw this coming, but: the repairs to the driveshaft fixed the issue! The trans, rear end, everything is fine.

If I wore a hat, I'd eat it. But they said the tube was out of round and that they replaced a worn stub shaft and slip yoke (I didn't think they were very worn, but there was a -little- play).

Problem solved. Unless the simple R&R of the driveshaft fixed it? Or replacement of the already-new carrier bearing on the stub shaft? At this point I'm just happy its done!

[kwmech]

See post number 10

[DBK81]

Glad you got it sorted, chasing gremlins is the worst feeling. If there was one piece of advice I would give people when doing any drive line length changes, is, GET IT BALANCED no matter what! Now you can just drive and enjoy.

[BugzC10]

Great to hear....any suspicious you may have had with your new tranny have now been put to rest.

[davepl]

It actually wasn't a balance issue (they said it wasn't out of balance much at all). It was the out of round, and more important, the wear on the splines.

Either way, glad it's not the transmission and glad it's fixed!

Now if I can ever find a tailshaft with a speedo housing that's not $625, I'll grab that and swap it. Otherwise, a windshield and my truck is done!