MX-5 OC Forum

Hi all,

After replacing the brake discs and pads on my 5, I've noticed that the rear left wheel (and especially brake disc) is hotter than the one on the right.

Quick googling suggests this is a caliper seizing issue. However, the allens key adjustment seems to work fine (i.e. using it, I can retract and extand the piston).

Is this likely to be a caliper issue or could it be something else?

Secondly, I feel it may be because the pad is constantly touching the brake disc surface. As the pads are new, is this something that I should expect for the first 500-1000 miles?
And if so, is there any danger to using the car like this? There is no smoke, just that one brake disc gets hotter than the other.

Cheers.

Brakes are meant to get hot during use. So its possible there is something wrong with the other, cooler caliper. When seized calipers get hot, they are smokin', with the disc actually bluing.

Chock the front wheels, jack the car up, whip off the wheels, and get an assistant to test the foot brake while you put a bar across the studs (and try and turn them). Then check how easy they are to turn after you done a few hard pumps of the foot brake (handbrake off of course).

I had this last week when i had new pads on the back of my Merlot for the MOT. It did initially smoke after a couple of miles. But then seemed to be fine after about 10-20 miles and have had no trouble since .

How hot is the wheel (not the disc).  Hot enough to burn your fingers? Stupid of me to pitch in here, but is the hot one binding on.

Have you used a touch of copper grease so the pads slide back and forth?

Forgive me as I really knwo nothing - I haven't changed brake pads in many years.

AT:

Brakes are meant to get hot during use. So its possible there is something wrong with the other, cooler caliper. When seized calipers get hot, they are smokin', with the disc actually bluing.

The fronts give off roughly the same heat as the "good" rear brake which makes me think that the cooler rear brake isn't the problem. Another point is that the right rear brake disc is almost untouchably hot whereas the other side rear brake disc can be touched for a few seconds. Is this kind of heat normal for road use?

For reference, pads are EBC Yellowstuff - very, very, very dusty and not much better at braking than the ones they replaced!

Sorry to state the obvious...but did you grease the slider pins and adjust the caliper correctly after fitting the new pads?

If you use an infrared thermometer you will find there can be a differance of 15 to 20 C with no problem between sides.

In the last two years I have had two MX5 front calipers have that problem (100,000 miles), rebuilt one and replaced the other as the bleed nipple did not want to move. Great now but the new calipier is around 15 C warmer than the rebuilt one and both pistons slide in under hand pressure.

Offside front caliper on our Suzuki Jeep (34,000 miles) that I have rebuilt. Offside front on my Impreza (49,000 miles) which I rebuilt but the nearside is now getting a touch hotter (60,000 miles) so good that Subaru sell an axle kit of piston seals.

If you drive for say 5 miles at say 40 mph and get away without using the brakes, OK we live in a not very busy place you will find that the disks will be only around 30C.

greyphonic:

Secondly, I feel it may be because the pad is constantly touching the brake disc surface.

 Hi, The pads may just make a noise after adjustment but really they should not be rubbing. Did you adjust one side too tightly? There is no need, slacken til the pads do not rub, around 1/2 turn back from just touching. The handbrake is self adjusting and will notch up as soon as there is excess play.

 Hi I dont think no I am sure the handbrake is NOT self adjusting (hand brake in OFF position) you must first adjust the brakes at the wheel end first I used to adjust them with the wheels on so you can feel how the wheel rotates when adjusting Lock the wheel up then back off until you can freely move the wheel by hand pressure Then adjust the handbrake cable the adjuster is down under the handbrake gaiter pull this to one side and adjust the handbrake cable (think you will need a 10mm spanner or deep socket) until you have no more than 5 notches that is when you pull the handbrake on. Do a road test and check the brakes operate ok and that they do not over heat.

You must ensure that the car is correctly chocked and axle stands under the car to support it whilst you are under the car and its on level ground.   

Alan

alan yates:

 Hi I dont think no I am sure the handbrake is NOT self adjusting (hand brake in OFF position) you must first adjust the brakes at the wheel end first I used to adjust them with the wheels on so you can feel how the wheel rotates when adjusting Lock the wheel up then back off until you can freely move the wheel by hand pressure Then adjust the handbrake cable the adjuster is down under the handbrake gaiter pull this to one side and adjust the handbrake cable (think you will need a 10mm spanner or deep socket) until you have no more than 5 notches that is when you pull the handbrake on. Do a road test and check the brakes operate ok and that they do not over heat.

You must ensure that the car is correctly chocked and axle stands under the car to support it whilst you are under the car and its on level ground.   

Alan

Hi Alan,

You've said this before and I don't understand why you think the handbrake is not self adjusting.

Here is a stripdown of the caliper, http://www.miata.net/garage/ebrake/index.html

inc this pic of the adjuster which is inside the piston, courtesy of Lance Schall,

Figure M - This automatic adjuster. Its purpose is to compensate such that the travel of the parking brake handle does not increase as the brake pads wear. As the Enthusiast Manual points out, it has no serviceable parts. We took it apart anyway. It is held in the piston by a wire external c-ring (shown Figure Q). We used a puller to separate adjuster from the piston.

Thanks for the comments all. It's reassuring to know that a 15-20 degrees difference in heat is normal.

I readjusted the calipers on both sides (using the hex key and method of tightening until wheel/brake disc can not be moved by hand and then loosening off just until it can be turned - slightly over 1/2 turn for me).

The slider pins on both sides are also fine - it took me a good few hours of elbow grease and hammering to get the part of the caliper that sits on the slider pin off when I did the job the first time so I've made sure it's well lubricated now, for both sides.

I notice that the "sticking" caliper piston seal has a slight tear which might be causing this?

Another suggestion I had which sounds plausible is that even though the caliper piston can be seen to move with the adjustment key, it might not have full movement - which I think describes what is happening. This is also why I couldn't fit the anti-squal shim on one side (i.e. with new thick pads, the piston would not retract far enough for both pads and shims to go on) so I only put the shim on one side. Hence it's not fully seized just yet but might be on that road.

I was told by a mechanic at a chain garage that brakes can sometimes take up 3-400 miles to bed in properly and not to worry about it if there was no smoke visible when driving. I've covered 200 or so miles since the brake change so I'll see if it gets any better over the new few weeks.

greyphonic:

Thanks for the comments all. It's reassuring to know that a 15-20 degrees difference in heat is normal.

I readjusted the calipers on both sides (using the hex key and method of tightening until wheel/brake disc can not be moved by hand and then loosening off just until it can be turned - slightly over 1/2 turn for me).

The slider pins on both sides are also fine - it took me a good few hours of elbow grease and hammering to get the part of the caliper that sits on the slider pin off when I did the job the first time so I've made sure it's well lubricated now, for both sides.

I notice that the "sticking" caliper piston seal has a slight tear which might be causing this?

Another suggestion I had which sounds plausible is that even though the caliper piston can be seen to move with the adjustment key, it might not have full movement - which I think describes what is happening. This is also why I couldn't fit the anti-squal shim on one side (i.e. with new thick pads, the piston would not retract far enough for both pads and shims to go on) so I only put the shim on one side. Hence it's not fully seized just yet but might be on that road.

I was told by a mechanic at a chain garage that brakes can sometimes take up 3-400 miles to bed in properly and not to worry about it if there was no smoke visible when driving. I've covered 200 or so miles since the brake change so I'll see if it gets any better over the new few weeks.

Hi, yes that all makes sense. The piston with the split boot is probably corroded on it's outermost surfaces and is now sticking when returned. If bad they can sometimes leak as they are pushed back and the rusty part becomes aligned with the seal. As the pads wear the piston will come out and may work well again or it may corrode some more.

The long term answer is to change the piston, seal and boot before damage is done to the caliper body. At this stage it could probably be done on the car rather than need a full rebuild or exchange caliper.

The adjustment btw is,   

"3. Turn the manual adjustment gear clockwise until the brake pads just touch the disc plate."

that is, not so tight an initial setting that the disc is locked up. Then, when backed off the disc should be free to rotate by hand and the auto adjuster will take over from there.

The fact you couldn't wind the piston back enough to get the shims in that side though really points to corroded piston as the problem.

http://www.mellens.net/mazda/Mazda-Miata-2005/brakes.pdf

Thanks for this Rich.

The car is now pulling to the right under moderate/heavy braking (I didn't notice it happening before) so seized caliper seems likely.

How easy is it to fit the piston, seal and boot? The brakes were my first big job on the car and I had done a lot of reading and used several guides and forums to assist with the process. I'd like to try this on my own but is this a much harder task and would it be advisable to just take to a garage or is it worth trying myself?

If the latter, are there are good step by step guides on the topic? The PDF you've sent is great for understanding the anatomy and the parts involved, but some more detailed instructions would be helpful, even if it's only to boost my confidence!

 To recon, caliper seal kit arond £25 per side.

Chock other wheel, with the car in first gear.

Jack up and get axle stands in place.

Wheel off

Try to loosen the blead nipple if it is seized replace the caliper with  recon unless you feel you can drill the nipple out.

Remove two caliper bolts , tie caliper out of the way, remove disc pads

Put caliper back and lighty bolt up

Get someone to press the brake pedal to get the piston out.

Remove hose bango bolt from caliper and put a plastice bag over the end of the hose

Remove the caliper

Either replace with recon unit or

Remove the piston and clean piston and caliper

Loosen bleed nipple

Remove both outer and inner seals

Lightly grease piston and inner seal with special caliper rebuild grease not in the Mazda rebuild kit but Subaru include it.

Replace piston with new seals

Put on pads and caliper and attach hose.

Bleed brakes if the fluid is over two years old carry on and bleed all the wheels.

Wheels back on.

Lower car.

greyphonic:

Thanks for this Rich.

The car is now pulling to the right under moderate/heavy braking (I didn't notice it happening before) so seized caliper seems likely.

How easy is it to fit the piston, seal and boot? The brakes were my first big job on the car and I had done a lot of reading and used several guides and forums to assist with the process. I'd like to try this on my own but is this a much harder task and would it be advisable to just take to a garage or is it worth trying myself?

If the latter, are there are good step by step guides on the topic? The PDF you've sent is great for understanding the anatomy and the parts involved, but some more detailed instructions would be helpful, even if it's only to boost my confidence!

Yes if you want to do this after the work you've done so far it's a good next step and not hard. I've done similar on a variety of cars inc Girling, Lockheed, ATE, Nabco/Tokico etc but have not done this exact job on your exact brakes, even my Mk3 are different, so any corrections are welcome.

Pretty much as Eddie says but I'd do it on the car if poss as a new piston and seals should sort it rather than a complete caliper stripdown. This is quite common if the boot becomes torn or perished.

You need; piston, piston seal, piston boot. Check also the caliper pin boots. Sundries are brake hose clamp, brake fluid, red rubber grease and high temp brake grease such as Ceratec or Copaslip for the pad edges and backs.

Good point to make sure the bleed screw works before starting as this may change the course of things somewhat but otherwise,

Wind back piston and remove caliper. An upturned ordinary 2 gal plastic bucket is good for supporting it during what follows.

Clamp rubber brake hose

Slacken bleed screw and leave open

Wind piston out using adjuster allen key, fluid will spill from caliper then stop

Clean up carefully and remove outer boot then square section O ring seal inside caliper

Fit new square section piston seal into caliper - they had a tapered face on cars I've done so careful to replace correct way round if this applies

Lube outer piston boot with red rubber grease and piston with brake fluid and refit piston winding it back in again with adjuster screw. Getting piston started square in the bore is the tricky bit. The outer boot needs fitting to the piston then the other boot edge into the caliper, then the piston offered up and pressed in. Trial fit it a couple of times to be sure how it goes. It can be stiff as it meets the inner square seal and you may need careful use of a G clamp - but take you time, keep it square, and it will go in.  

Reassemble caliper and adjust pads as you've done before. Note caliper slide pins and boots are lubed with red rubber grease not mineral or brake grease which will rot them.

Remove hose clamp and bleed that caliper.

If you get into trouble at any stage the hose is already clamped so just undo the banjo and sort/replace the caliper on the bench.