Mk2.5 MX5 brake problem: suggestions please

[911hillclimber]

Bog standard UK MX5, 63K miles.

After about 5 miles casual driving (no pancic stops etc) the brake pedal free-travel will slowly get less and less and the brakes will apply themselves tighter and tighter until the engine has difficulty over powering them and they end up smoking!(all 4 brakes are hot and locked on)

Car will not move.

Open the driver's side rear calliper nipple (and so releasing the system pressure and instantly the car is drivable.

Obviously, the brakes build a pressure that does not release in normal driving so could be the Master Cylinder, OR is it an ABS fault?

Does anyone on here please have real MX5 experience that can help me please?

Graham.

[MX-5 Lazza]

That's an interesting one. Sounds like a brake pipe might be blocked.
Try posting this on the Mazda-Menders forum for some good advice from those who know what they are talking about.

[sbird]

It won't solve the original problem, but if you haven't already, I'd recommend checking that all of the wheel nuts are still properly tight. I've had a set go loose after a brake disc got excessive heat into it.

[gdaybruce]

Asked my brother (who is a mechanical engineer) about this. His view is that the most likely cause will be swollen seals in the master cylinder which are failing to uncover the bleed hole when the brake pedal is fully released with the result that fluid cannot bleed back into the reservoir and the pressure in the braking system is not being reset.

The other alternative is that for some reason the piston in the master cylinder is not travelling fully home to seat against the retaining circlip when the pedal is released with exactly the same result.

[911hillclimber]

I'm with your brother.
That is the conclusion I have come to.

Getting a master off ebay tonight. You can also get a repair kit for the piston/seals etc.
While I'm at it I'll re-disc/re-pad the car.

[911hillclimber]

Just to finish this off:

Fitted the ebay master cylinder, gently bled the system twice getting so little out of the rears.
New discs/pads and clean/copper-slip the lot.
All cylinders pushed/adjusted back and all went together well.
Have driven the car 2 hours of urban driving and all is well!

Must have been the master cylinder.

Anyway it was great driving around with the roof down reminded me of my Spitfires and MGB's way back!

No wonder you all love these cars.

Thanks for all the help.
Graham.

[gdaybruce]

Good news! Have you bothered to strip the old master cylinder to see if you can spot the fault?