Having recently fitted lightweight calipers and disks to the front of the Indy, we found the need to shim the disk approx 1.5mm from the hub face to get the caliper/disk spacing correct. We used some suitably sized washers to do the job and are currently using these until we can find time to make something more substantial to do the job.

The question then…………….. could this method be a permanent solution? Your thoughts please………………..

FWIW, our opinion is that the disk requires face/face contact with the hub, rather than point contact.

I would also agree with you...would be better with face to face contact.

Easy enough to turn up some thin spacers though.

Hmm do the discs still have the locating grub screw?

You could machine up some shims and lock them in between the hub and disc with the grub screw and then tighten the wheels to compress fully.

Again - not ideal but slightly better

When I converted my rear drum brakes to disc I had to space the wheel hub from from the mounting face on the upright so the drive shafts weren't too compressed. I used washers to do this as a temporary fix but of course its been that way for a few months. I ask RAW about this and they do this on their cars including their race car with no problems. I will make some plates though as I feel its a bodge otherwise!

Thinking about the way that braking forces are applied, then ideally, face to face contact between the disk and the hub would be best, but BEC's generally only weigh half a tonne and the disk is sandwiched between the wheel and the hub, so whats to go wrong?

Machine the face of the disc down 1.5mm?

It removes weight and as the car is light I'll bet the disc will be just as happy regarding heat build up as it would on the saloon car they were designed for

I think machining the disc face is slightly dodgy as the disc's are already lightweight, please see picture attached
Rescued attachment IMG_0303.JPG

Should I mention the heat transfer aspect? Perhaps not. I'll get my goat.....

Hellfire,

My 2pworth: looking at the amount of metal which has been removed, it's hardly worth turning up "full faced" spacers, as most of the spacer would be butting up against thin air. Judging by your photo, the material you have left around the bolt holes is not much bigger than a washer anyway, so IMHO it would be a waste of effort making spacers.

If it was my car I would adjust the caliper position not the disc.

You have to consider that it is not just the disc that is mounted on 4 washers but the wheel as well. The disc would probably be Ok as all the forces are in one plane, but when cornering the wheel will put sideways forces into the disc and hub.

Also consider.....The disc is stopped from rotating by the clamping force and the friction between disc and hub, NOT the 4 studs. The studs / bolts are there to apply the bolting force not stop the disc rotating. Therefore with only 4 washers the surface area is reduced.

A comment on shims. These should really be hardened steel if they are quite thin (how thin I am unsure!) otherwise they can squash out and then you have a loose installation.

John

Frictional resistance depends on two factors only: clamping force and coefficient of friction, the area of contact is not a factor.

I would however also prefer to move the caliper if possible as moving the disc changes the scrub, track and arc of movement for the suspension.

Yes I am wrong now I think about it. If you clamp with say 100N over an area and compare it to an area twice the size then the force per area is halved.

The larger will be more stable though.

John

If you are spacing the disc I think a proper (laser cut perhaps?) shim would be much better than using washers.

Many washers are punched out of sheet material and due to distortion do not have consistent thickness which would lead to disc runout. Also as the wheel applies a clamping force over most of the hub of the disc, any irregularity in the wheel hub (from e.g. some corrosion or dirt) could cause the disc to distort when bolted up.

A kit i bought for 4 pots before came with 4 washers (ground finished i think) for spacing the caliper back from the brackets.