Video - Rear Axle Wobble

[CobraFan460]

Folks,

There is a wobble in the driver side of the rear axle that has me a bit concerned. From the video links that Eddie posted in other threads, I know the axle ends will flex under cornering loads but mine is different. It appears to be a constant wobble as if a bearing were not seated or the axle shaft is bent.

Facts:
1. I purchased the rear (8.8, c-clip, 31 spline, torsen, 3:08 gear) a number of years ago but I am still building the car so it is not licensed and has only been driven around my subdivision for a total of about 10 miles.
2. I noticed the wobble on the driver side when I stopped driving in the subdivision (illegal since not licensed) and started idling in the driveway with the rear on jack stands and trans in gear. This has put approximately another 15 to 20 miles on it. (In other words, the rear has about 30 miles on it)
3. Getting as close as I can safely, I don’t hear any unusual noises from the rear over the sound of the exhaust.
4. Except for a very minor amount of run-out, there does not appear to be any wobble in the passenger side.
5. I swapped the rotors in case the driver side rotor was warped, with no change to the wobble.
6. The wobble causes the caliper, caliper mount and brake hose to flex back and forth in sync with the wobble.

Questions:
1. Is the wobble bad enough that it must be fixed or is it really not an issue? (I plan to run the car on the dragstrip a few times and along with highway cruising, I can’t see how the rear will last very long with that much wobble – my biggest concern is safety)
2. As indicated above, I have not yet driven it on the highway – will the wobble be noticeable at highway speeds?
3. Any ideas on what might be causing the wobble?
4. If this were YOUR rear axle, what would you do or would you be concerned about it?

If I got the links right, there are 3 videos below of the wobble. I apologize in advance that I did not use a tripod for the camera but I think you can see the issue. Again, the rotors were swapped before any of the vids were taken and one vid is w/o the tire installed, the other 2 are with the tire installed.

Let me know your thoughts.

Thanks,
Todd

P.S. I don’t seem to have access to edit my profile on this forum so, in case it matters; the rest of the drivetrain is 460 BB and C4 trans.

[OVCobra]

It does appear that you have a bent axle...you mention c-clip; is it a c-clip rearend or does it have a c-clip eliminator? To check for the bent axle, pull the caliper and rotor off and use a dial gauge to measure radial and face runout directly on axle flange. Another fairly simple way to double check would be to switch axles from side to side to see if the wobble follows the axle.

If the axle is indeed bent, I would replace it as it will generate vibration which apart from being annoying will likely affect the axle seal and/or bearings before too long...tire won't like it either. Lots of replacement options at your favorite mail order racing supply or one of the forum suppliers like Forte's.

Dave

[CobraFan460]

Hey guys, thanks for your thoughts. I will attempt to get a measurement tomorrow and post it up here.

Todd

[dforthof]

Todd,
Answers to your questions:
1). Yes, this is too much run-out.
2). Yes, You'll feel this for sure.
3). Make sure the end of your axle (where the rotor mounts) is CLEAN. Clean it with a wire wheel, if you have the means, remove the studs before you clean it to make sure you have a perfectly flat surface to mount the rotor on. Also, make sure your lug nuts are always torqued to spec (~100-120 ft. lbs) when you do the run-out check. Check for cracks in the housing mounts (where they are welded to the housing and where the tubes are welded to the pig, this is usually a sure sign that something got tweaked. If none of this helps, pop off the diff cover and c-clips and swap the axle shafts side-to-side to see which one is bent. If the runout follows the shaft, then obviously it's the shaft, if not, then you get to go housing shopping. I've also (once) seen someone install the outer axle bearing without fully seating it and this happened so there's one last-ditch thing you can check if it's looking like the housing.
4). Obvously, if this was mine, I would be concerned.

[CobraFan460]

Ok, I have a really bad camera so the pics are not good but at least you'll get an idea of what I was doing.

Measuring on the edge of the axle flange (vertical motion), I saw .006 in.



Measuring on the face of the axle flange (horizontal motion), I saw .010 in.



Things you can't tell from the pics:
-I verified the rotor has plenty of clearance for the axle center hub; no binding there.
-I verified the axle flange surface was clean and free of debris; nothing to cause the rotor to sit high in any particular spot.
-I verified there is no binding as the rotor slides over the axle studs; the rotor sits tight and flush to the axle flange.
-The rear brakes use the drum brake set up for the e-brake which is the other stuff you see in the pics but the main brake is the disc rotor.
-I inspected the axle tube end and did not see any cracking or issues with the weld.

So does anyone have any info on whether or not those numbers are too much? And what are my next steps?

Thanks,
Todd

[OVCobra]

Todd
Try the same thing on the other side for comparison. Also check the rotor the same way. The wobble on the rotors seemed to be a lot more than the numbers you measured on the axle flange...maybe just a bad rotor?

Dave

[Arrowhead]

Todd
The wobble on the rotors seemed to be a lot more than the numbers you measured on the axle flange

But the rotors are twice as large as the hubs so the wobble is multiplied.

Personally I think you are going though more grief by trouble shooting and analyzing than just putting in a new axle. It's not worth the headache, just do it and be done with it.

[CobraFan460]

Thanks guys. Due to work, I won't be able to get back to this problem until next week. I'll chime back in then.

Thanks,
Todd

[CobraFan460]

I was able to get some time on the cobra and have a few more measurements and another question. Bottom line concerning the new measurements – the data shows a problem with the driver side axle.

I measured the run-out of both wheels and both rotors mounted to the passenger side axle since that side is ok.

Pass tire = .004” H(orizontal motion) – measured at bead face
Pass tire = .028” V(ertical motion) – measured on inside wheel wall
Driver tire = .007” H – measured at bead face
Driver tire = .009” V – measured on inside wheel wall
Pass rotor = .003” H – measured at un-used pad surface
Pass rotor = .012” V – measured at pad rotor edge
Driver rotor = .002” H – measured at un-used pad surface
Driver rotor = .007” V – measured at pad rotor edge
Pass axle flange = .002” H – measured on flange face
Pass axle flange = .003” V – measured on flange edge

If I took my measurements at acceptable locations, the data indicates I had the good wheel and rotor mounted on the bad axle which probably helped to minimize the wobble. Next, I was going to swap the axles to see if the problem followed the driver side axle but was unable – which brings me to the question:

Isn’t the block inside the diff (held in by one small bolt) supposed to easily pull out or slip back into the diff? And is it’s only purpose is to take up the space between the axle ends?
I snapped off the end of a screwdriver trying to pry the block out and it absolutely will not budge. Any ideas or tips to try to help remove it?

Thanks,
Todd

[dforthof]

Ahhh yes, the good ol' torsen! - I envy you for you're purchase - True to form, hot-rodding is NOT dead!
Anyways, the block on the torsen doesn't just "fall" out, it gets pressed on by about 20-30 ft. lbs of force on each side from the stacks (think of it as getting pushed on by each axle shaft). It would require significant force to just "yank" it out without relieveing the side pressure first due to ridges on the block. I've seen it removed many ways, but here are my personal favorites:
1). Use 2 screwdrivers gently pounded between the block and each stack end to relieve the pressure, then grab the block with a large pair of channel locks and pull it STRAIGHT out with a wiggle move, watch out to make sure the screwdrivers don't get you in the eye on the way out, because they will pop once it clears the ridges.
2). Use a brake caliper clamp in reverse (through one of the holes in the end of the shaft) on the the passenger side axle shaft to "pull" the shaft away from the axle housing, thus relieveing the pressure on the block and making it easy to pull out. Your essentially trying to compress one of the stacks enough to relieve all the pressure from both of them (it doens't damage anything and will bottom out).
I wish I had some pictures for you, but I don't... hopefully I'm helping it's hard to describe in words, easy once you've done it - no special tools required.

[CobraFan460]

Hmmm, I'm not sure what you mean about the "stacks" but I'll get in there this weekend and take a closer look. The first time I pulled the block it just pulled out with little force. Never got it back in or out again after that. But you have given me more to puzzle over - thanks!

Todd

[CobraFan460]

4/30 update: I pulled the axle assembly out of the chassis and dropped it off with Gordon Levy today for the repairs.

[dforthof]

The whole Axle? Diff and all? or just one of the shafts?

[CobraFan460]

The entire assembly - I can't get the block out of the Torsen diff to allow removal of the axles, it won't budge, so I had no choice but to take the whole thing to Gordon.

[dforthof]

I'm interested in how it turns out CobraFan. Best of luck!