mx5cartalk.com

This follows a post by jeo describing caliper flex on his car - viewtopic.php?f=30&t=53169

I'm looking for a solution using OEM calipers for an NA8 running comp pads.

I've had the same problem for a while. I get radial pad taper, where the surface of the outer front pads nearer the rim wears faster than the surface nearer the hub and I get excessive heat build-up on that part of the rotor. This has nothing to do with brake alignment or sliders - it's all about the caliper flexing (i.e. spreading) under high load.

These might explain it a bit:
http://www.trackhq.com/forums/f297/afte ... ndex2.html
http://www.youtube.com/watch?v=coja8O871Po

It's basically a track car. I compete in MX5 Vic Modified, MX5 NSW Modified and CAMS Supersprint 2B. The regs for all these classes that require me to retain OEM calipers. Flex has a significant impact on pad wear, rotor problems and braking consistency.

I'm wondering:
1. Is there any known difference in caliper quality/performance between the various models using that size caliper?
2. Do new calipers outperform old calipers in terms of flex?
3. What else can be done?

Buy some solid calipers and move away from floating calipers.

Outwise rotate you pads left to right side after each track day.

project.r.racing wrote:Buy some solid calipers and move away from floating calipers.

I'd love to but not permitted in the CAMS regs.

I think this is the video you meant to attach:

I too would be interested to know.

Thinking about it though, the only way to fix it would be to attach some kind of brace to it, but I have no idea how one would do that.

You wouldnt be able to as the flex is within the sliders mostly, i would imagine. one could have a machine shop make super high tensile sliders. You could sell those.

Dann

NitroDann wrote:You wouldnt be able to as the flex is within the sliders mostly, i would imagine.

I don't know , Dann. I thought the back of the caliper itself is flexing when you get radial taper.

As I think about it, this car has done 200,000kms and around 2,000 laps. I figure the 2,000 laps makes it about 8,000 times I've really stood on the pedal. With that many heat cycles on the castings maybe it's just plain metal fatigue. If no one else has any experience about better quality calipers or metallurgy in MX5 brakes then maybe it's just a matter of buying younger, fresher ones?

I have not heard of this problem here, but apparently our US cousins have experienced it. The links seem to indicate their problem stems from some after-market calipers.

First up, have you replaced the calipers? with after-market ones? If you have, I would do the test shown in the vid, but with two dial guages - one on the inside as far out radially as possible, the other outside as close to the stub axle as possible. That will quantify the problem, but interpreting it is another matter as I suspect that there will always be some twist there. You could run that same test on Guran's car for comparison, he has the best kept stock brakes that I know of (see his garage thread). You need to run it on someone's car that is doing what you are doing, but not experiencing the same problem - I will volunteer the GM, as I never had that problem when I was supersprinting and I think we have the same brakes?

I would do a full overhaul of the calipers, including new sliders (unless yours are nearly new and in perfect condition) and new seals in the piston, making sure that the pistons and bores are in top shape, and that all the right greases are being used. Then if the problem persists, I would look at new factory calipers perhaps.

Of course, you could just cut to the chase and throw some new (Mazda) calipers (and sliders) at it without doing any of that ...

I am assuming that there has been no front end damage that might have bent that part of the front upright?

Dann, the sliders will need more than strength, they also need to allow the caliper to slide - part of that is the lube, but I believe it is also part of the properties of the steel used in the pins.



Afterthoughts: If (a big if in my opinion) the arms are flexing, the dial guages will probably not show much: it is really about the pressure on the pad face, and unless the pad material is compressing under pressure, a static test will not reveal whether one part of the face is under more pressure than another. On the other hand, if there is differential movement (ie not a clean even sliding movement), that suggests to me there is a more fundamental problem - bent sliders, bent upright, sticking piston, sticking slider(s), worn sliders, worn slider housing ...

Well, my front calipers have new pins (4 of them), and I rebuilt them all with new rubbers and all that, and yet I still had that wear. I have no idea how old the calipers are, however, but I do know that they are OEM mazda items.

Phil

If your convinced that the calipers are flexing then fit latter model units re: NB or later.

Back in the olden days caliper flex was a very common problem for high performance vehicles especially alloy calipers.Holdens with Bendix units were notorious for not being able to stop chasers from high speed pursuits, and cleverer people than me found that the alloy would flex up to 5mm on hard applications, multiply that by 4 calipers and arse pucker time!!

With time and updates this concern was overcome and the fix was basically more gussets and then better alloys.

Scooter is fitted with NB calipers and I don't think I could get a much better or consistant feel or performance.My pads wear reasonably flat as well.

I don't know about Sprints but 2B and 2F car are free on calipers, rotors etc.

Terry he's sorta of back atm

The calipers themselves are the same from the first NA6 to the last NB8A?? I assume you are referring to NB8B brakes?

tbro wrote:arse pucker time!!

Terry, I knew you would appreciate the gravity of the situation,

What happens with these now is they start to pull up OK when you first squeeze them but as you increase the pressure they can go feral. The car might dart left or right a meter or two, usually in the middle of the braking zone. I normally like to put an outside wheel over the fog line as I run up to the turn in point. I can't do that now because I need margin for error. If they start to dive then I'll steer it towards track centre before turn in. As well as that I'm starting to brake abut 10m before the newbies. All up it's costing me 1 - 1.5 secs per lap. After a few sessions the outer rim of the rotors is glazed and the pads are tapered.

This has been getting worse for a year and it was doing my head in trying to find it. A whole lot of detail suspension set up changes mitigated the behaviour a bit.

I just checked the parts catalogues. NA8C, NB8A and NB8B all use the same calipers/same part numbers. So if you found an improvement with later units it could be either better metallurgy that they didn't bother to flag or simply age.

GM, these are OEM units, undamaged. You're dead right. I should do a full check and re-build or else just bite the bullet and see what new/newish ones do, along with new pins.

Thanks to all for the advice.

Hey Phil,

Funny how on the track you kinda like the brakes to work real good, getting soft in our old age

From what your saying it sounds like it could be a few small things combining to make life suck.

Sliders very slightly bent, when the heat is increased during braking your getting binding ???

Do you have an adjustable Bias control, see where I'm coming from ?? Too much front bias maybe.

Darting under brakes can also be from suspension concerns, binding bushes???? Front and/or rear.

And finally, due to the calipers being supplied by an outside company, Mazda will only change caliper part nos IF they want mods done, so updates are usually at the discretion of the manufacture, so different alloys or slightly different moulds etc used.
JFYI, Mazda change part numbers by changing the last letter to the next one for each update a to b to c etc, in the case of the old E2000 style transmissions they were up to "h" with the mainshaft in the gearbox. and it was still no better.

Probably giving you more headaches than help, but its somewhere to start from.

Now I'm off to Lakeside to freeze my arse orf!!!!

Terry

tbro wrote:Terry he's sorta of back atm

Great to see you back, Terry!

I recall this problem back in the dark ages in the real Cooper S.

It was cured by better cooling.
Explanation was that the outer part of the disc heats more than the inner section.
More heat = More pad wear.

Has this been looked at in the MX5?