Hellfire
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 posted on 12/5/06 at 01:05 PM |
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Friday's Debate?
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.
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flak monkey
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| posted on 12/5/06 at 01:08 PM |
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I would also agree with you...would be better with face to face contact.
Easy enough to turn up some thin spacers though. 
Sera
http://www.motosera.com
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muzchap
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| posted on 12/5/06 at 01:14 PM |
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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
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If you believe you're not crazy, whilst everybody is telling you, you are - then they are definitely wrong!
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bimbleuk
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| posted on 12/5/06 at 01:34 PM |
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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!
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Hellfire
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| posted on 12/5/06 at 01:42 PM |
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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?
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Nick Skidmore
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| posted on 12/5/06 at 01:47 PM |
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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
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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Hellfire
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| posted on 12/5/06 at 03:42 PM |
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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
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owelly
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| posted on 12/5/06 at 03:49 PM |
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Should I mention the heat transfer aspect? Perhaps not. I'll get my goat.....
http://www.ppcmag.co.uk
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TL
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| posted on 13/5/06 at 12:48 AM |
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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.
Cheers,
Terry
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JB
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| posted on 13/5/06 at 05:23 AM |
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Disc caliper Mounting
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
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Lippoman
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| posted on 13/5/06 at 06:06 AM |
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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.
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JB
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| posted on 13/5/06 at 06:50 AM |
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Friction / Clamping Area
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
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MikeRJ
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| posted on 13/5/06 at 09:33 AM |
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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.
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jono_misfit
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| posted on 13/5/06 at 10:07 AM |
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A kit i bought for 4 pots before came with 4 washers (ground finished i think) for spacing the caliper back from the brackets.
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