I've just replaced all four discs and pads on SWMBOs Mazda MX5 as it failed its MOT on these items.
I have been unable to get the brake shims back in despite making sure that the pistons in the calipers are fully home. I have been doing jobs like this for years and usually manage to get them back in with a bit of juggling!
So option one is to use the car for a few miles and see if the initial wear allows sufficient room for the shims which of course they eventually will (the new pads had some abrasive compound on them to clean an old disc. I would imagine that this will wear off in the first few miles), but my concern is, if I take it back to the testing station on Monday, could they fail it again if they notice that these shims are missing?
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It must be a very close call, the shims are only a few thou thick.
Have you cleaned the general accumulation of rust/debris from both sides of the shims? Did they clip onto the pads closely and fit snugly?
Did the pistons in the rear go fully back with the alan key and stop dead?
The shims are thin enough not to have any real impact on the braking. I would try a gentle drive of a few miles to see if they bed/settle in a bit.
I made the mistake of using anti-sieze grease on the sliding pins when I did my son's and was rewarded with sticking pins caused by the rubber boots swelling. Had to fit new rubbers and use rubber grease to cure it.(Not linked to your problem, just operational experience :))
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>>could they fail it again if they notice that these shims are missing?
No, providing that the brakes perform adequaely when tested on the rollers.
Number_Cruncher
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It might be that the old shims are a bit corroded. In my experience the whole lot goes togther with a little bit of clearance (say 0.5mm). Maybe the pads or discs are a little thicker than spec?
Anyway, it should pass the MoT and I would then treat it to a brand new set of shims from the dealer - they are only a couple of quid. Put a little copper grease each side to help them work better (they are there basically as an anti-squeal measure).
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Hi,
These shims are anti- rattle shims. Leaving them out won't do any harm as the pads are locked in place. Probably the reason you can't get the shims in at the moment is because you have a rust lip around the outside of the discs thus preventing full contact. If you use it for a week you will probably be able to fit them after that as they've bedded in. Don't worry though - you can't do any harm running it without them.
--
These are the views of Robin the Technician with 35 years in the trade. I fix, therefore I am...
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I've been running without the shims for six years now. They (the the clips) only come in the hugely expensive Mazda pad kit.
Agreed also about not using copper grease the slider pins or the rubber bits that slide on them swell and stick.
Edited by martint123 on 17/11/2007 at 22:33
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I've been running without the shims for six years now. They (the the clips) only come in the hugely expensive Mazda pad kit.
I bought some shims in January. Come as a 'axle set' for under £5 from local dealer.
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I don't think that I would have paid for new discs with a built in rust lip.
:)
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I've left them out before, but if you've replaced rear discs handbrake adjustment is critical on these, done via the recessed allen screw in the caliper. MX% rear calipers are the achilles heel of the car, they tend to seize/malfunction.
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Thanks for all of the advice everybody.
The old shims are slightly corroded, and were getting dragged out of place when I was putting the caliper back into place, and on the front, with them in place, with the caliper being tapped down gently with a rubber mallet, locked the wheel, before it was fully in place.
I suppose my main concern was the fact that the tester appeared less than pleased that I was going to do the job myself, and I was concerned that if he checked my work with a fine tooth comb as it were, if he could get retribution by failing me on these missing items.
With the testers attitude being such, I did think that he may have been trying to drum up some unnecessary work. The front discs were not perfect but were probably serviceable for another year, but the rear discs were quite bad and did need changing.
I have already managed to damage very slightly one of the handbrake adjusters. When I was winding the piston out on one side, I think that I carried on trying to turn the adjuster when the piston was right back, and the edge of a few of the splines got slightly damaged. So i took about 10 thou off the damaged face with the grinding wheel. It seems OK now.
Thanks again
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Please let us know how you get on with the MOT, and if you get any squealing problems.
PS We have a set of MX5 alloys in the garage, if you are interested. ----
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The car has passed its MOT without the shims.
Thanks for the advice . I will get some new Mazda shims in the next few days and see if they will go in!
mjm, thanks for the offer of the alloys, but SWMBOs car already has alloy wheels.
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