Run-out tolerance at bolt flange ~ vibration

oldbuickguy
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Run-out tolerance at bolt flange ~ vibration

Postby oldbuickguy » Mon Jan 30, 2017 11:10 pm

First, I want to say Thanks for maintaining this forum, and the great deal of information you've put here to help demystify the differential.

A 'core' 10 bolt BOP 8.2 posi 3.55 ratio was rebuilt by 'THE' differential shop in Dallas. Changed the bearings and checked the posi, but didn't invest in parts otherwise.

I had them chuck the axles in the lathe and spin them. There was some visible wobble through the middle section of both axles. Did not measure with dial indicator. They said it wouldn't make a difference. This was back in 2014.

Have just now gotten the vehicle to the point where it can be driven at more that 50mph and have eliminated the driveshaft as a suspected source of vibration (new driveshaft).

Dial indicator at the face of the bolt flanges shows ~.005" deflection, both axles.

Left: https://youtu.be/dE3TecyDOOQ Right: https://youtu.be/ZZ3oaGgkZ3M

All the wheels have some lateral run-out .020" (most) to .040" (one). I'll swap them front to rear and look for a difference.

Thoughts?

Jeff Schadt
Plano, Tx

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monzaz
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Re: Run-out tolerance at bolt flange ~ vibration

Postby monzaz » Wed Feb 01, 2017 10:32 pm

Jeff, It is really tough not having the parts here in front of us. So where we need to start is where the vibration comes in and goes out (if it does go out/ away) mph rpm etc.

Shocks new?
rubber on the tires how old?
Have you changed the axle bearing to new?
When they chucked the axles how did they do it? (if you can some what describe where it was clamped etc. )

Was the rear ever run in a car before this rebuild was done ? how was it feeling then?

Just trying to widdle this down some. :)
J D Race

oldbuickguy
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Re: Run-out tolerance at bolt flange ~ vibration

Postby oldbuickguy » Sat Feb 18, 2017 5:12 pm

HI Jim,

Thanks for giving some thought to my search for a vibration source. The vehicle has been a 15-year project addressing the suspension (polyurethane bushings) & brakes, motor, driveline (rear-end with 3.55 gears and 2004R transmission). Used 70-72 Buick Rally wheels and 225-60 tires.

There was a driveshaft vibration that I attributed all of the highway speed vibration to, which has been corrected. At the time I didn't suspect the wheels to be contributing, and the rear-end (2.78) was original to the vehicle, so I had no reason to suspect it as a vibration source.

The seller of the 3.55 rear end said it came out of a car that had been totaled, but nothing specific to say if the damage may have affected the rear-end.
I had it rebuilt, limited to bearings and seals, and I asked the shop to chuck the axles in their lathe. Looked to me like they just chucked the spline end and turned them. The irregularity that I saw was through the middle of both axles, a small amount of deflection, maybe .10" hard to say without a dial guage. I wasn't concerned because the builder said they all wobbled a little, and it wasn't noticeable at the axle flanges. You can see a small amount of deflection in the axle flanges in the videos.

Since my January 30 post, I replaced 2 wheels with the most noticeable wobbles. The replacement wheels are not perfectly true either (.020" to .030" deflection at the bead), but they have no visible deformations at the bead, that were obvious in one place of each of the 2 take-offs. I reused the tires, but the difficulty we had in balancing the better wheels and original tires told me that the tires are part of the problem. The tires have about 15K on them, and I suspect that 15K of life on wonky wheels has given them a 'custom' profile even if to the naked eye they look pretty good.

I haven't been able to go out for a long drive to evaluate the feel of the car, but for the short drives, the main concern, a high-frequency vibration coming through the rear of the vehicle is diminished the point of not being noticeable at 50-60mph. And at lower speed there's less 'busy-ness' in the way the car feels.

More seat-time is needed to better evaluate the new vibration pattern, but from where it was to where it is now is a big improvement. My interest in contacting you was to get your thoughts on what the small about of axle flange deflection may produce in the way of vibration.


Regards,
Jeff

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monzaz
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Re: Run-out tolerance at bolt flange ~ vibration

Postby monzaz » Sun Feb 19, 2017 10:31 am

AXLES - Well on the Chevy axles especially the 12 bolt Chevy early ones from 65-67 Nova and 64-67 chevelle were never true in the center of the rolled steel used in making them. the were only concerned that the spline and the bearing surface were true to each other never the center of the axle... That is just the way the OLD stuff was. If I had some examples you would certainly laugh a lot that that was aloud to even be produced that way...

Again some run out is ok.... The worst part is when the run out is from the bearing surface to the flange where the wheel mounts that will be most noticeable and that is the area needed to keep as true as possible.
WE get BRAND new Moser / strange customs axles and they still have run out too.

Keep trying and the more info thrown out there the betterwe all can solve the vibration problems alot of old cars suffer from years and years or tinkering and hard driving does to them.

:)

Jim Mitschke
J D RAce
J D Race


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