- My model of MX-5 is: __ MK3 NC 2.0 PRHT 2008
- I’m based near: __ Hull
- I’m looking for technical help or recommendations on: __
Hello all, recently removed the wheels to paint calipers, since then had an issue with osf brakes binding and getting that hot that they are smoking after only driving a couple of miles and making the disc look blue, i park up for 20 mins while they cool/free off then limp home, I’ve had the caliper off, given everything a good blast with brake cleaner, re greased the sliders with moly grease, greased the pads and shims with copper grease but to no avail, the caliper itself has been a little sticky in the past but never this bad and never picked up at mot, the caliper is probably the original one from new, the car isn’t a daily does 2k a year max does this sound like a straightforward caliper change or could it be something else.
Cheers
How easy can the piston be pushed back in to the caliper ?
Does it also come out fairly easy after intalling it on the car ?
To be honest when i removed the caliper the piston was fully retracted into the caliper, it didn’t pop out and i didn’t have to push it back in at all to get it back over the pads.
If you have an assistant - I would take the caliper off the carrier.
Ask the assistant to push slowly on the brake pedal until the piston has moved out around 10mm.
Then see how hard it is to push back in.
Not long after I got mine - I had the same - one rear and one front was getting very hot.
I ended up doing a full rebuild of all 4 calipers - they are excellent now.
Ok thanks for the info, I’ll have to try it back end of next week now as having to go away with work tomorrow, I’ll get back with what happens.
Thanks again.
My money is on siezed caliper piston.
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Are your hoses in good condition, sometimes they can fail internally and act as a one way valve.
Try releasing the bleed nipple till a little fluid comes out and see if that releases the grip.
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I would definitely try a brake bleed before anything else. You say you removed the caliper since the problem started and the piston was retracted all the way? It could be a sticky piston but since you removed the caliper with no trouble, that seems unlikely, unless it has only just stuck.
Why would a sticky piston suddenly return when given a chance to cool down? Either it’s stuck or it’s not. What stands out to me is that you let it “cool down” and it releases. Also that the piston was retracted ALL THE WAY, which I’ve never known even with brand new brake pads. This says to me 2 things seem most likely:
- There is air trapped somewhere in the brake line of that caliper. Once it warms up through pressure and friction, the air expands and applies the brake. It doesn’t need much to start heating the disc, and generally you will feel it vibrating in the steering wheel at faster road speeds if your piston is stuck. Once it cools down, the air contracts and pulls the piston back with it. If not air then your brake fluid is shot, has absorbed water (brake fluid is hygroscopic) and is therefore boiling, creating the same effect.
- Have you checked that your brake pedal returns ALL THE WAY nice and promptly? There is a spring inside the brake booster that is responsible for returning the pedal. The pedal’s pivot point could be a bit gummy or corroded? But then again that would affect all of your brakes, not just one.
Lastly, have you tried driving without traction control if you have it? The car might be thinking that wheel is turning faster for some reason and is trying to slow it down?
Sorry Malc, didn’t mean that to be a reply to you
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Morning all
Thanks for the advice, the brake/clutch fluid was changed a couple of years ago so i think we can rule that one out, all hoses appear to be ok, I’ll try driving without the DSC on when i get home later next week and see if that makes a difference, if not I’ll try bleeding the caliper, I’m no expert mechanic by any means so it’s interesting to read what Ron has posted, i did get the caliper off relatively easily however it did need a little gentle, and i mean gentle, persuasion with a few taps of a hammer so i may have been mistaken in thinking that the piston was all the way back so i guess it’s either air or a stuck piston, if bleeding doesn’t do the trick I’ll change the caliper.
PS
Would it be wise to change both calipers to avoid a brake imbalance ?.
Thanks again all your advice is much appreciated.
Yes - I would always do brake components across an axle for balance.
I wouldn’t rule it out just because it was changed a couple of years ago, unless you changed it yourself and know for a fact that it was a complete change using brand new fluid that hasn’t been sat on a shelf with the seal broken for ages. Plus sometimes sh*t happens and you get some water in your fluid, even if it is reasonably new!
The simplest way to bleed if you don’t have a vacuum bleeder (about 10 pounds from ebay for a basic little one) is to get an assistant to sit in the car, top up the brake fluid a little over maximum, loosen the bleed nipple (use a bit of pipe and a jar for a cleaner job if you have some little plastic pipe), then have the assistant push the pedal gently smoothly down, obviously you will get fluid out of the nipple at this point so be careful it doesn’t spray everywhere. Really important that the assistant does not let the pedal travel back up at any point, tighten the nipple (not too tight, common mistake people make and get them stuck) again once the pedal is depressed and then they can let the pedal back up. Top up the brake fluid if needed or repeat the whole thing if you’re not satisfied/want to make sure. Don’t let the reservoir go below minimum or you’ll have air in the master cylinder!
You don’t need to change both calipers if the other side is working correctly.
A very quick way to test your piston and also push it back so you don’t need to do any hammering is to use a flat screwdriver: push it into a convenient gap somewhere (usually between the disc and pad somewhere, obviously being mindful not to damage the pads) and gently use that as a lever or wedge to get the piston back. Don’t force it, and if you have to force it then your piston’s a bit sticky.
If your piston is sticky, sometimes allowing it to get some travel simply by pushing it in or letting it travel out a bit (careful not to pop it out!) and then back in can sort it. If you’re careful, before pushing it back in whether or not you let it travel out, you can pull the dust boot out of the way carefully with a little pick and get some lubricant in there. Somewhat of a bodge but it can save having to replace/rebuild the caliper.
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Dodgy brake calipers can become even more problematic once they get hot. A piston that has already become tight can become stuck solid with heat in it.
I’ve said before, it’s the piston sticking in the caliper. I’ve hd these exact symptoms and stripped the caliper. They rust under the dust seal. New caliper from mx5parts at about £72 is a small price to pay to get it right. I used these exact ones and they are 100%
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I’m sorry but I have to disagree, a stuck caliper is a stuck caliper and it doesn’t matter if it is hot or cold. It has a flexible seal that accounts for any changes in dimensions due to heat and deforms when the piston is driven outwards, so there is actually pretty much no travel between the seal and the piston. If that seal was bad (rust breaking/gripping the seal) you’d be leaking brake fluid when the pedal is depressed. How can a stuck caliper become unstuck when it cools down and move back under its own volition? The only way it could do that is if there is air/vapour in there pulling it back as the master cylinder has already returned and you can’t have the vacuum effect without air taking the place of the brake fluid. Again, you need to see if your brake pedal is fully returning before you assume the caliper is stuck.
Stripping the caliper involves a lot of different factors, such as a bleed, so I wouldn’t be so quick to assume it is stuck and that solves it when you could be solving a different issue, although yes that can be an issue and maybe it was yours, and of course it’s never wasted time to refurb the brakes. I have cars with older calipers, way older than OP’s that still move freely, in fact a 1990 NA I have with its original calipers has been absolutely fine after I “unstuck” them with a g-clamp.
And again, you would feel a stuck piston in the steering wheel, you’d know it was stuck when you were driving, at least I can. I could be wrong but this doesn’t sound like a stuck piston to me.
Oval slider pin bores in the caliper is what I had after over heating brakes.
Calipers, sliders and hoses replaced on both fronts and never a problem since.
If the slide pin bore has gone oval (HOW?) then you need to make sure you give the pins a good sand before you regrease them to remove the old solidified grease that might be binding. Give them a bloody good polish. OR rebore the slide pin bores with a smooth round file or appropriate tool if they truly have gone oval, no need to replace caliper for the sake of the slide pins.
To check the slide pins is easy: take the pads out and wiggle the caliper in the pins. If your slide pin boots are working properly, they should be airtight. Moving the caliper as though the piston was pushing them should cause the boot to compress but keep some air in, so when you let go of the caliper you can see this air cushion push it back towards the piston, this will confirm if your slide pins are at fault.
Cheaper to rebuild the calipers rather than replace them anyway, just takes a bit more time.
Hello all
I gave the sliders a good clean the other day with brake cleaner, gave them a good coating of moly grease, admittedly i did forget to clean the bores and i did have to wiggle the lower one a bit to stop the rubber bush sliding up the pin, as mentioned I’m no expert mechanic but I’m not sure this is the cause, i leave the house in the car, all is good, within a couple of miles and with limited use of the brakes you can feel the car slowing down quickly between gear changes and you can smell the burning, i pull over and with the handbrake off try to push the car which is impossible, i sit for 20 mins while the smoking stops, i can then push the car easily with the handbrake off so i then limp home using the brakes as little as possible however by the time i get home the wheel has become scorching hot again but not smoking, when i get back home later next week I’ll check the brake pedal, and try bleeding the caliper to see if that solves the problem.
Once again thanks all for the input.
I will say again, when this occurs you need to crack each bleed nipple and see if the pressure is released, if only to rule out a cheap repair option.
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I would not be using moly grease on the sliders in case it reacts with the rubber sleeve.
Try red rubber grease or proper ceramic brake grease.
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I”m with @richardn on this, it’ll be a failed caliper.