Disc Runout

tetlow · Post by **tetlow** » Fri Jun 22, 2007 12:13 pm

I have been having a pulsing hissing sound coming from the passenger front wheel.
I have stripped the unit down and found a lot of disc run out. They are pretty new slotted and dimpled discs.

After repositioning the disc 90deg I have reduced the runout to about 6 thou or 0.15mm. It this good enough?
If not is it possible to get the discs ground?
Regards
Dave

sidecar · Post by **sidecar** » Fri Jun 22, 2007 2:19 pm

tetlow wrote:I have been having a pulsing hissing sound coming from the passenger front wheel.
I have stripped the unit down and found a lot of disc run out. They are pretty new slotted and dimpled discs.
After repositioning the disc 90deg I have reduced the runout to about 6 thou or 0.15mm. It this good enough?
If not is it possible to get the discs ground?
Regards
Dave

6 thou sounds pretty good to me. I guess the "proof is in the pudding"...go for a spin

tetlow · Post by **tetlow** » Fri Jun 22, 2007 3:01 pm

Can't. No front or rear suspension, and no motor.
Can't even pressurise the brakes as not connected.

kiwicar · Post by **kiwicar** » Fri Jun 22, 2007 3:43 pm

sounds about right for now then!

Mike

tetlow · Post by **tetlow** » Fri Jun 22, 2007 4:01 pm

I am in the process of rebuilding the front and rear suspension, removing all the Koni shocks and replacing with standard ones, and replacing the gear box with a 5 speed jobbie.
I do not want to rebuild the front hub units only to have to strip them again!!

sidecar · Post by **sidecar** » Fri Jun 22, 2007 4:32 pm

tetlow wrote:I am in the process of rebuilding the front and rear suspension, removing all the Koni shocks and replacing with standard ones, and replacing the gear box with a 5 speed jobbie.
I do not want to rebuild the front hub units only to have to strip them again!!

I guess the only way to be sure if you can't drive the car is to check out the runout limit in the manual.

I used to race an F1 sidecar and spent hours moving disks round on splined shafts to get the lowest run out figure. I would have been happy with 6 thou.

Regards,

Pete

ian.stewart · Post by **ian.stewart** » Fri Jun 22, 2007 4:58 pm

Somewhere in my distant memory, 0.002" is the max runout for a disc.
may be wrong, I have been before,
Ian

tetlow · Post by **tetlow** » Fri Jun 22, 2007 8:01 pm

Iv'e dug out an old B manual and found the lowest runout is 0.003", so it looks like a regrind.
Thanks y'all.

Dave

Post by **katanaman** » Sat Jun 23, 2007 12:12 am

An often overlooked part is the hubs themselves. There are quite a few cars out there that can and do warp the hubs so give them a good check over as well.

davemgb · Post by **davemgb** » Mon Jun 25, 2007 1:04 pm

Before dashing off to get the discs ground check the bearing end float.

Are you getting some of that 6 thou from the bearing movement?

I suggest removing the shims from the bearing pack and tighten the hub nut to about 10 lbft then check the run out on the disc.

Dave

tetlow · Post by **tetlow** » Mon Jun 25, 2007 8:15 pm

Thanks Dave.
I had adjusted the endfloat to about zero with the shims.
I have checked all mating surfaces for burs etc but all seems OK. The hubs are nearly new.
I bit the bullet this morning and the discs are in for grinding at £12 each, which thought was not too bad.

I will update when I refit them.
Cheers
Dave.

Sondar · Post by **Sondar** » Thu Jun 28, 2007 1:21 am

Guess the other thing is to make sure that they're seated flush against the hub / disk bell.

tetlow · Post by **tetlow** » Thu Jun 28, 2007 8:14 am

Guess what.

Just got discs back. Look great. Same problem as before.

I checked hubs and as per katanaman said

they seem to be distorted.
The hubs rotate true but the lip that the discs bolt to goes up and down.
I have checked the surface and it seems OK, i.e. no lumps etc.
I will try this morning to see if my local engineers can true the hubs.
At least I know the discs are good now.
Dave

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Disc Runout

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