Brake Disc Run-out

[Mike Molloy]

Having had problems with what I thought were binding brakes at Silverstone, I removed the hub, re-packed the bearings and stuck it all back together. Hub nut tightened until there was just no play in the bearings. Measured against the wing-stay, there was still about 0.1mm of variation measured near the edge of the brake disc.

 

I guess this could be one of two things:

1) Warped brake disc (but holding a steel rule across the surface reveals no obvious oscillations - maybe more accurate measurement required)

2) Hub not true, somehow. Bearings are new. Races fitted correctly (as far as I can tell).

 

I don't know what to do next. Tempted to buy the Caterham uprated hubs and see where I get to.

The other side also has some perceptible run-out, but doesn't seem to be binding on the brake pads as badly.

 

Any advice on how to check the disc and/or hub concentricity?

 

I have basic measurement tools but nothing fancy.

[oldbutnotslow]

I take it that we are talking about the fronts. The only accurate way is with a DTI - Not that expensive to buy - with a mag mount, should be between £30 to £40

There are interesting threads on this that will be worth looking up. The perceived wisdom is that warped discs are unusual. I fitted new bearings and discs earlier in the year and found that I was getting pad slap from the movement in the fronts- a bit disconcerting when you hear this coming from the brakes!

I found the problem to be the centre hole. In the new discs this was not chamfered as much as the old discs and that it was fouling on the bearing carrier in the centre of the hub. I also found that the mating faces on the alloy hub were out of true. Not by much but enough to exacerbate the situation. I trued the mating faces up with an oilstone and very very carefully increased the chamfer and kept checking with ‘engineers blue’ untill it waf flat.

You have to be careful about balance on the discs if you go mad.

It’s also worth checking the bearing cups again. When you belt the old ones out it is possible to damage the seats. Make sure that they are fully home in the carrier. They make a different sound when you tap them when they are fully home.

If you are anywhere near Norwich I will happily lend you my DTI & Mag mount

 

 

Grant

[Rob Walker]

Mike,

 

I had what I thought was disc runnout and returned my uprated front discs to CC for replacement under warranty. I fitted the new discs and the problem remained. I traced the fault to the hubs and ended up removing highspots of the hub disc mounting flange until the disc runout was minimised. You will need a dial test indicator to determine where the high spot is. It should be possible to get runout to less than .010".

 

On my latest car I have the new uprated hubs which are machined from billet Ali and run bigger bearings and massively strong stub axles. These are great but have one massive flaw in their design ie CC had a very course thread machined on the end of the stub axle and this makes adjusting any bearing endfloat very difficult . Why CC did not spec a metric fine or UNF thread I do not know?

 

 

Rob

 

[Luke Beaumont]

Hmm, are you sure about a tenth of a mm? That's 4 thou, which isn't too bad. It would be nice to get better than that but in the real world you invariably have to accept a few thou runout.

[JAG]

Hi Mike,

 

I understand that current mainstream production cars have values between 0.040 and 0.060mm (40-60 Microns). Anything around 0.100mm on an old hub design like the Caterham is pretty good.

 

 

Justin

 

A closed mouth gathers no foot.