Lash In Driveline

[Kiwi Ed]

My 04.5 LLY Allison 4x4 has a nasty amount of lash (slop) in driveline from overun to drive. Worst at low speed and in low gears but is noticable in all gears. From a standing start is quite smooth as everything is loaded in one direction (against the brakes).
The Alison changes quite smoothly.
Slight surge just above idle - only when cold.
Throttle is a bit touchy.
Any ideas on lash?????
Have seen others describe similar thing.
LB7 models I have driven didn't seem to be a problem.

[More Power]

Are you saying you see the driveline lash when manually shifting from overdrive to drive?

If so, at what speeds?

MP

[CJC]

I have this too. It seems to be gone when the converter locks up, but when the converter is unlocked, it is very noticeable and annoying. Because of this, I am assuming that it is not lash in the rear end, but in the tranny or transfer case. I've tried it in low range also, but the truck is so balky in low that it's real hard to tell if the lash goes away. I had the dealer look at it twice, and as expected, they said it was normal. Of course that's always the diagnosis for the first three trips until they realize that you're not going to give up. You could drive your truck in there with it on fire and they would pull up some GM document that said it was normal.

The first week in January I'll be driving an 05 that they have on the lot as a basis of comparison, and depending on how that one feels, I'll have them look at mine again. I'm convinced that this is not normal because it makes it so annoying to drive, and I would have seen a hundred posts on it if everyone had it.

Let me know if yours seems to be gone with the converter locked up.

[Kiwi Ed]

MP - I'm trying to describe lash during on/off throttle driving at low speeds - say just moving to 20 mph - not drive to overdrive.
At what speed does the converter lock up - have seen posted approx 53 mph not in tow haul.
Was trying to describe lash can still be felt at say 50-60 mph when going on/off throttle, but of course is not uncomfortable at those speeds.


CJC - I believe it is in the tranny or transfer case. Also will be trying another 04.5 truck but a Chev crew cab to compare. Owner of it reckons it is alright. Very uncomfortable and annoying driving at intersections when nearly stopped and need to go.

[More Power]

With the transmission in park - engine off, rock the truck back and forth by hand. You'll then be able to see the total amount of free play in the driveline. Looking closer, you should be able to see where the most play is - such as differential, u-joints, txer case, trans, etc. You'll also see the rear leaf springs deflect.

Some of what you are describing could be due to the rear axle rotating back and forth as the engine loads and unloads the axle while moving. Some amount of axle rotation is (to varying degrees) normal due to the rear leaf springs winding and unwinding under torque. This is less noticeable with a load in the bed, because the leaf springs are more heavily loaded, and aren't as affected by engine torque.

The latest Product review (http://www.thedieselpage.com/reviews/caltracs.htm) could help explain the axle-wrap and leaf spring deflection a bit better. If that is contributing to your situation....

MP

[Kiwi Ed]

Had done most of above.
Had a 2,600lb odd load in bed the other morning - no difference.
But will keep spring wind/unwind in mind.
When rocking, diff looks okay, some play in trans/transfer case but could be some movement in park pawl.
Would LLY reflash help as some say it gives you a less sensitive throttle? As is, it is very hard to drive smoothly over bumps. Idles smooth, only slight surge just above idle when cold.

[ 12-29-2004, 11:11 PM: Message edited by: Kiwi Ed ]