Lotus Elan

Front disc to calliper clearance

PostPost by: Concrete-crusher » Sun Feb 19, 2017 3:34 pm

Hi having spent a Sunday morning reassembling my front brakes after replacing the vertical links I can see the clearance on the drivers side calliper to the disc is very small on the outside edge. About 005 thou. I reused the axial so maybe the new fitting into the vertical link is more than I previously had.

I'm wondering what will happen when everything warms up and expands , will the calliper wear away the disc or will the disc just create it own clearance being a harder metal.

Thanks as always for any advice.

Steve
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PostPost by: YellowS4DHC » Mon Feb 20, 2017 3:18 am

Had the same problem on my Europa when I replaced the front rotors with some aftermarket ones that were 20 or 30 thou thicker than the ones I took off. In my case, the inner edge of the caliper body actually dragged on the outboard side of the rotor when the end float was set.

I've always assumed that the caliper should be more or less centered relative to the rotor. So I had the caliper bracket bosses (where the caliper mounts) machined down about .040" to shift the caliper's position slightly outboard to better center the caliper. I don't know what the min/max clearance should be, but mine is now .020" to .025" on each side of the rotor and it appears to work fine. The left side is now about what the right side was without any modification.

Assuming that your reassembly is correct and what you're seeing now is simply a different tolerance stack up from what you had before, milling the bracket flange might work for you.

Rick
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PostPost by: rgh0 » Mon Feb 20, 2017 9:42 am

It sounds like the tolerances on your new uprights are poor or the assembly has not fully bedded the hub and bearings on the axle.

I would check the assembly and if possible run it on the road for a short time and then retighten the hut nut. You need to over tighten the hub nut to seat the bearings and then back it off for the correct end float. You also need to check the nut retaining the stub axle has been fully tightened and the axle has seated correctly in the upright taper it mounts in. I have recently been told that the GT6 uprights used on KO hub Elans have a different taper for the larger stub axle compared to the spitfire upright with its smaller stub axle used on bolt on hub Elans. I am not sure this true as I have never personally measured it but if their has been a mix up on the uprights supplied this could also cause the problem.

If the disc continues to be offset I would talk to whoever supplied the new uprights about the problem as the tolerances on the machining are not good enough which is not an uncommon problem with these components these days. The problem could be in the taper for the stub axle or in the machining of the caliper bracket mounting points

If your confident your hub, stub axle, disc caliper and caliper brackets are all good and they aligned previously I would be reluctant to machine them to correct for a problem in the upright as this will give you even more problems the next time work is done on this assembly.

cheers
Rohan
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PostPost by: Chancer » Mon Feb 20, 2017 1:03 pm

My suggestion is that you are not using the disc backplates (dustshields) which IIRC fit between the caliper mount and the caliper, please correct me if my memory is hazy as its been d?cades, I'm pretty sure on my Caterhams to run without them I needed to fit shim washers to the same thickness between the caliper and its mounting lugs.

Seem to recall posting this same advice not long ago, but hey my short term memory is even worse than the long term one!
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PostPost by: Concrete-crusher » Mon Feb 20, 2017 7:07 pm

Thanks for the advice , having looked at the assembled units and my before pictures I think maybe the stubb axial has not bedded as before. The other side seems fine and I have replaced both vertical links. So drive for a bit and re tighten seems appropriate.

Steve
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PostPost by: toomspj » Mon Feb 20, 2017 9:54 pm

I've recently had the same experience with new upright and new stub axle - just on the one side. I tried using the old axle as well with same result. As far as I can see it must be down to the machining of the taper in the uprights. I sorted it out by machining the bearing land for the inner bearing in the hub. Not ideal but it worked ok.

If you don't have any issues with calliper rubbing on disc rubbing with the system cold, I doubt that the situation will get worse when everything heats up.

Paul
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