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Binding R/F Caliper

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#21
Bench Racer

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Different Strokes For Different Folks


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#22
Eric Orton

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This issue has existed as far back as one cares to search. Can one truly say no real harm/non-issue without at minimum doing a heat test of RF and LF? I had the same issue on my 85 RX7 Spec7 race car.


I think I posted about it on here, and Saul pointed out that road-vibration -> pad knock-back would overcome the difference in pull-back in any real-world scenario. I did a road test, since I have reasonably rough roads around my house. I only used the e-brake to slow the car coming home. I put the car up on stands and tested the "drag". All gone---LF/RF tires both spun the 10ish revs.


Eric Orton


#23
callumhay

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certainly do not want to hijack the thread as the OP had a pretty simple question...which looks like it could be the proportioning valve from what he is saying (and either it's normal or maybe he should consider replacing it? is there a consensus?)

 

In looking at the design of it, there are wear items such as the seals and spring..I'm assuming there is no re build kit? Anyone tried that?. At $145 or so it seems like a reasonable item to buy when you consider the cost of a racing Miata. And given the fact that the brakes are used a lot, it is not without possibility that this thing could cause issues, albeit still work but not function 100% as intended. Clearly it is not designed to fail in a way that is catastrophic..but it could fail by redistribution of fluid which for highway driving might never be really an issue.  Interesting that the line to the LF comes off the MC while the other to the RF has to go through the valve...this is presumably due to the distance of the RF brake line being longer? Anyone know if that is the real answer? 

 

I've always looked at that valve as just something that sat there and did it's job and not really looked at it the same way as replacing or servicing the brake calipers, lines etc. Was aware of the graphs on the brake pressures from the FM site which gives a pretty interesting evolution of what Mazda was trying to do as they developed the cars.

 

Cal


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#24
Steve Scheifler

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Yes they can fail or operate sub-optimally and I would not dissuade anyone from replacing it if there is any hint of a problem, or just an otherwise unexplained issue. One of our 1.6s had an inconsistent pedal and braking seemed less stable than another car. After various other changes I did the prop valve and since then it has been the best stopping car of any I’ve driven. So I replaced it on my own car just for good measure.

The specs changed over the years and a popular “unauthorized modification”, particularly around the Chicago & Wisconsin area, was to swap in a particular later version. I’d wager a lot are still that way even if not recognized by the current owner.

But, in this case I would not expect replacing it to change the perceived issue of the OP.
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#25
Brandon

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Judging from that Flying Miata graph, irrespective of the platform (NA8/NB) going with an ABS-sourced proportioning valve would seem to shift the bias (rearward or forward?).

Knowing you are permitted to remove ABS, I wonder how many ABS-equipped cars maintained the stock (ABS) valve and didn't shift to the non-ABS one?

 

Is it performance advantage to have the bias weighted to different levels? Plausibly based upon driving style, IMO.


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#26
Icedawg

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By the end of the race season now, were you able to resolve the issue?

 

I bought an SM this past Spring, and found both front calipers did not release well after coming in from a race.  I could turn the wheels by hand, but with the wheels off the car I had extreme trouble turning the hubs using the studs for leverage.  The left was the worst, but both were poor.

The previous owner had found he was replacing a front wheel bearing after every weekend, and I had to also.

 

I had this problem with sticking calipers once on a 1983 RX7, and was only able to resolve it by changing the master cylinder, after individually changing everything else in the system.  The Miata calipers are a very similar design, single piston, the same arrangement for how they float, and for how the brackets mount.

 

On the SM I replaced both front calipers, brackets, and the master cylinder, all at once, and that resolved the problem.  However, the right wheel is still a little bit harder to spin after coming in off the track than the left is.  The wheel bearings have lasted for 3 weekends now, so reducing the brake drag was helpful. Sadly, my lap times did not seem to improve.

 

So the problem you describe could also be in the master cylinder, along with the possibility of the bias unit.



#27
Bul Winkle

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Having the problem at more than one corner suggests the proportioning valve may be an issue, but if it still isn't resolved, have a look at the brake booster. These are also old enough units, and if degraded, can contribute to brakes be held on after time driving. They will release, but very slowly. It'll also give an artificially hard pedal. Check the rod from the pedal before and after driving.







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