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Ralph Whitaker

Disc caliper shims

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Is it really necessary to use shims to centralise the disc brake calipers on a 3a. Surely as there are 2 pistons on opposite sides they will self centre after the first application of the brake. I have assembled mine without and there is plenty of clearance between the caliper and disc on both sides and the disc spins freely. Besides the shims are about a fiver each which makes it an expensive operation as I removed 4 rusty ones from each side of the car.

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I don't recall fitting shims when I replaced the pads on my TR3a and I haven't had any issues with uneven braking.

Rgds Ian

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I have this issue on my Grinnall TR8. I changed the pads when I first got it, to find the discs were offset about 0.5mm. However they both ran very true, and I took the view that the hydraulic interconnection meant the pistons were self balancing. It caused great controversy on the forum, but 5 years later I am quite clear this judgement is correct both thoretically (drawing on my Cambridge Uni & RR training) and in practice.

 

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I have spent some time as a motor mechanic, both as a job and as a hobby, and in 50 years of working on cars the TR3 was the first time I had seen shims used to centralise the caliper, and they are still available from Moss among others. I can only assume that as disc braking was in it`s infancy it was felt necessary to centralise the calipers. Perhaps the original pads were that bit thicker and could have caused binding on one side when new if the caliper wasn`t dead centre, or maybe the tolerances may have added up on certain cars causing the caliper itself to touch the disc. Anyway mine seem fine without, but if you ever change the pads and cannot quite get a new pad in at one side, maybe you need shims.

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When fitting new pads to a friends 3A we found that without the shims one pad was pressing on the disc, even with piston fully home.

Bob.

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My 1977 Scimitar GTE has shims on the caliper mountings, though only 10-12 thou. After removing and refitting the calipers, I always put the shims back as I found them, although I doubt it reall maatters much. There's been discussion about these shims on the Scimitar forum in the past, general consensus is they aren't necessary.

Nigel

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Disc positioning in the calipers goes to cock if you fit poorly dimensioned repro wheel bearings.

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I've never come across shims for the calipers but I do have uneven braking in the wet so could this be it? .

long distance A road/Motorway use in the rain I have to lightly apply brakes ever 5 miles or so, If I don't and have to brake it pulls alarmingly to the left.

I've changed (over the years) boat type calipers to pb's (tr6) stone guards on and off, now on. three different types of pads, now on Mintex and they are good.

Swirly drilled discs now fitted as thought this might break up surface tension?.....hasn't! 

I have always run the car on wires 60's, 72's, and now 70's centre laced....

any ideas on this one?

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It's a long shot, but if the wheel bearings on the right are a little loose, the pads will get knocked back as the disc moves around. This may mean they do not have the same bite as on the left. I find it hard to believe, but can't really think of anything else. Is there any disc runout, which might well have the same effect?

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well thought Acaie BUT a few years ago I did change over to the larger stub axle and equal bearing mod (as I had a trade contact who needed a mule to test on).

these have been checked a couple of times for test results and all "seems" even on end float/wear etc. I have to say the main reason for going over to this mod was I had pad knock-off when turning sharply into my garage, so very low speeds....that still seems to happen but perhaps  less so. 

The previous but one set of discs were standard/solid type, the last set were swirls and holes but warped quite quickly (well in my opinion they did but not the opinion of the supplier!) but then it does get used well B) so these latest discs were fitted just before we went on holiday ( you remember going on holiday???, just hold that thought....for some considerable time :( ) in the summer of last year so I'm guessing about 6-7000 miles ago but no judder at all from these (thus far)

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Another guess -  how about a piston that's a bit sticky but moves under higher pressure?

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yea, I did work the pistons back and fourth when I fitted the new brake pads about 5 months ago and it didnt seem to make any difference. I wondering if its aerodynamics mixed with water/spray?

Thought about making a small splitter to go on the front lower wing area to change airflow?

I have also been toying with the idea of making plastic discs to fit inside the wires just to see if this changes anything

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I don't believe the shims are fitted to equalise pads or anything of that nature. I have only come across them fitted where the caliper body itself is grazing the disc and the shim just centralises the caliper. Whether this is due to poor tolerance in the caliper, mounting bracket, disc or bearing I know not.

Jerry

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Caliper shims are more often needed with some of the thicker stub axle/ally hub kits as they dont seem to be that well thought out, FWIW Jaguar always ushed shims on their calipers though they were shim washers on each caliper bolt so very difficult to set up properly, I always use shims if required to centralise calipers as it does equalize the wear on both pads and discs.

Stuart.

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