Thread: On car brake disc machining query

I bought an on car disc machine at auction some years ago. I used it on a few vehicles and on sold it. worked very well. Make sure your wheel bearings are to spec. Loose bearings give an untrue result. Main problem with them is that motor mechanics are not machinists and seem unwilling to take a decent depth of cut to get under the hardened skin that develops on cast iron from repeated heating and cooling. You need to be cutting in the soft metal under the hard layer or the insert might be skidding over the hardened skin. This also uses up the inserts early.

Hello Lionel,

Oh no not another one!

Kind regards
Lionel

Just fit the new pads.......if the lip is big I’d be surprise if they would clean up to the minimum thickness

No credit for this repair technique, but it did work a treat!

Ensure wheel is spinning, apply angle grinder to lip, inside and outside....

Lip gone.

Originally Posted by weeds

Just fit the new pads.......if the lip is big I’d be surprise if they would clean up to the minimum thickness

I’m with Weeds. I don’t think its worth machining discs, rather just let the new pads bed into the grooves. As Weeds said, if the discs are so bad they need machining its unlikely they’ll clean up to the minimum thickness.

Cheers,
Jon

If you leave the lip this gives you a good indication when your pads are worn out without destroying the rotor.
Pads these days do not come with the wear indicator.
Mark

I only had the on-car machine for a short time. It worked OK but I had bought it for resale and did so. Normally I machined discs and drums in the centre lathe. I was never too fussed about manufacturers specified minimum thickness if the grooves were not bad and cleaned up without taking a big cut. I suspect the makers were a bit conservative about thickness to cover their arse. Badly damaged discs where they had been run metal to metal for instance, I would dump in the bin.

With the cost of discs these days is it cost effective to machine discs. Usually the first pad change doesn't need machining unless overworn or rock damaged.

Oh and min thickness is specified to stop the pistons popping out when both pads and discs are worn . (I've seen some interesting mechanics overseas)

Thoughts?