I have had this bad shudder in the driveline when backing up for some time.

I asked Bill @ ZFDoc about it and he didn't think it was coming from the transmission, so that leaves the rear diff.

It's really the only part going "backwards."

This problem existed before I did the ujoints last year and it's been getting progressively worse.

It almost feels like the clutch is slipping, but again, it's been there since before the clutch was replaced a few years back (but only 20k miles).

I can't find anything about this in the Helm manual...

Thoughts?

That is strange. I don't think it would be a differential issue since it doesn't happen going forward. What if you put the rear end on jack stands and remove the load from the differential? That might be a good way to isolate things.

that's a good idea...

When in reverse the motor wants to torque counter clockwise when viewed from the cockpit. Suggest checking motor mounts for tightness, integrity etc. Hood open & brake torque in reverse should give a visual on motor movement.

Dog bone & bat wing bushings are also suspect.

C beam bolt torque OK?

good points.

I can't speak of the bat wing... that's a mystery.

The c-beam is tight, and has torque plates.

the motor mounts are new.

dog bones are not an issue, I have the full on Banski rear suspension kit. Everything is tight.

andy , you might want to ck the bottom motor mount bolt the vertical one . I found mine had worked loose . the other thought that came to mind was that maybe something is starting to go in the rear end like the pinion bearing .when you are backing up the pinion bearing would be trying to work its way out of the case . just what I thought it might be .could be way off base . only other thought would be the front yoke on the driveshaft might be worn .

Lots of good ideas I never thought about!

Well... lots of ideas, but lots of changed parts, too.

1. new ujoints showed no issues with the driveshaft.
2. the motor mounts are new, and the problem existed before that... but I will check for any loose bolts, just to be sure.

If anything it's either my technique - meaning I am over slipping the clutch - or the input shaft bearing is going south...

There is a guy over on CAC asking the same thing.....he has a ZR1 Super Natural.......what is a Super Natural...?


http://www.corvetteactioncenter.com/f ... dder-when-backing-up.html

I'd check all the mounts, including the batwing and the C-beam bolts

I was the one asking for andy ,just thought to try another site and see if we could find a answer to help out our friend

Batwing and input shaft seem to be the most likely culprits.

Quote:

Very possible! Suspension parts act a lot different when reverse torque is applied. Plus, there is more torque applied in reverse simply from the much lower gear ratio.
Think how much wheel hop there was in the movie Bullitt when McQueen had to back up during the chase scene!

Joel

OK I posted an idea over on CAC, but what about adding positraction additive to the rear end. It sounds like posi-clutches slipping.


????? Maybe? That's what my 64 did back in the day and that fixed it. Not so sure I didn't have to add it to my 94 too.

I would almost bet money the positration additive will fix it.

Nice thought, but the oil in there is about 20k miles old, and has 2 bottles of additive in it already!

that was one of the reasons I moved on the clutch when I did (summer 2009). I pull the engine, did all the oil seals and gaskets, did the clutch and such.

Last year, May /June, I did ujoints... and about a year ago, I did an entire engine swap... with new motor mounts.

If I am going to tear into the batwing, bet your ass I am going to get the diff rebuilt, too. No wasting all that labor.

andy , I emailed bill b and here is what he said , he believes either the bolts that hold the pressure plate aren't tightened down evenly or your motor mounts are loose .do you have a puck type clutch ? if you pm me your email I will email the message he sent me . I am in the hospital now but can still use my computer

Geez Brad mojo on getting out of the hospital, hope you are ok.....

Yea, Brad, get well soon!!!

I hope the flywheel is torqued... I used a torque wrench, in the proper sequence, set at the right ft lb...

If this was the flywheel, that means the last two flywheels I installed were lose, or, one came loose, but I use red threadlock on the bolts...

Also, the motor mounts are newer. I replaced the original 185k mile units with nice 61k mile units when the engine was swapped. And they were hammered home with an impact gun!!

You can email me at andy@corvetteguruforum.com

That's the public email for the site, so that's fine!!

THANKS!!!!

andy did you get the email sent to you ????/

yes! I just got home to read it.

THANKS!

To answer some of his points, the clutch, I don't think, is the problem. I replaced it due to wear/tear and such, plus, the shudder. Figured a new clutch would clear that up... no luck, unless I installed it exactly wrong like I would have had to the first time.

The motor mounts are 60k mile units, and are really tight.

The more this is developing, the more I think it's in the batwing and the differential.

The posi suggestion brought to mind a problem I solved on a customers car a long time ago that was posi related. Without going into a detailed explanation the problem turned out to be tires. Both rear tires had identical size markings however when both tire circumferences were measured there was a 1.5 inch size difference left/right.
Suggest measuring tire circumference @ the center of the rear tire thread.

Rear tires of identical circumference = a happy posi unit

Gee... I would hope BFG has better QC than THAT!

Besides... new tires, problem existed before...