Disc run-out

Post your 'Wheel, Brake & Tyre' FAQs, comments & questions regarding Ducati motorcycles here.
Post Reply
User avatar
AndyCapp
Mariana
Posts: 29
Joined: Fri Jun 10, 2011 10:30 pm

Disc run-out

Post by AndyCapp » Sun Aug 10, 2014 8:21 am

My 1980 Darmah SSD rear disk isn't running true. Using a dial gauge I could see around 1.5mm of run-out when measured near the outer edge.
So first question - how much is too much ?
After inspection I found the disc itself is ok, but the problem is the disc carrier (long story, but this was machined 'true' many tears ago).
After some careful grinding down, the maximum run-out is now around 0.8mm. Does that sound a lot ?

User avatar
geodoc
750 GT
Posts: 169
Joined: Thu Jul 18, 2013 2:57 pm

Re: Disc run-out

Post by geodoc » Sun Aug 10, 2014 11:00 am

Heh,

In my experience, you will need to see about .1mm / .15mm max run-out to not end p with pulsation at the lever. When you say that the carrier is the problem, do you mean an aluminum carrier that the disc bolts up to and then that assembly bolts on to the wheel hub?

If that is the case, you might be in luck - the carrier can be affixed to a lathe (you'll probably have to make a fixture the secure it to the chuck with a live center in the tail stock holding that end centered). It can then be machined true and there you go. If the carrier turns out to be true, then you're looking at a poorly machined surface where the hub and carrier mate. That's easy to correct if the hub is un-spoked from the wheel. It might be possible to machine that surface to make it exactly perpendicular to the axle center line using an old-fashioned drum / disc cutting machine if you can find somebody that has one. Otherwise, you're in for de-lacing & re-lacing & will need at least six cups of coffee.

Here's hoping it just the carrier.

GD

User avatar
AndyCapp
Mariana
Posts: 29
Joined: Fri Jun 10, 2011 10:30 pm

Re: Disc run-out

Post by AndyCapp » Mon Aug 11, 2014 10:07 pm

It's the rear disk, so that nice big aluminium bracket allows a fair bit if lateral movement - so no pulsing on the brake pedal.
I noticed the problem after applying the brake and the pads had retracted, I could hear the pads were not clear during
half the wheel rotation. Due to disc wear/scoring over the years, it's not easy to measure less than 0.5mm

Post Reply

Return to “Wheel, Brake & Tyre Shop”