mx5cartalk.com

before i go spending money i should ask here,

I have been unable to drive the mx5 lately because of a brake issue, the brakes are locking on, it started with the fronts, i had the slider pins lubed and brake fluid flushed, the rear started playing up too, had the rear slider pins lubed. it is now fine when i first start driving it but very quickly all 4 start to seize on, like within a short drive time of about 5 -10 minutes they seize to the point of slowing the car to a stop and being unable to drive. i have had suggestions that it may be the booster retaining pressure so each time i brake its not letting them off. this somewhat fits as last time i had an issue i turned it off then restarted it after about 10 minutes and it was ok again.

i have also been told it could be the wrong fluid and the master cylinder is shot.

any ideas from the experts here? and has anyone had experience with having a booster replaced or rebuilt what sort of cost am i looking at? i want to get this sorted before the track events next month

It's not the first time this has come up on he forum. First thing to do is to make sure that there's a little bit of free play in the brake pedal. The hydraulic pressure won't release until the master cylider pistons can return fully. If they don't then the pads drag on the rotors,the fluids heat up at the calipers and pressure builds in the whole system, eventually locking the brakes.

If that doesn't fix it then it's usually problems with the master cylinder - typically in the vacuum booster unit. Just replacing the hydraulic master cylinder component doesn't fix it, you have to replace the whole unit. Suggest you borrow one and swap it in to see if it fixes it.

Here's one earlier discussion. viewtopic.php?f=30&t=46321&p=582397&hilit=master#p582397

Booster rebuild is about $240 plus fitment. The job is pretty easy to do, particularly if you have an extra set of hand when removing / lining things up.

You will need to do a full fluid flush afterwards on all brake lines.

Or you could just delete the brake booster!

Have you tried removing the hose to the booster? Is the issue the same with it connected or disconnected? Are the hoses to the brake booster in good condition?

Try this suggestion
http://www.roadkillcustoms.com/hot-rods-rat-rods/hot-rod-power-brake-booster-test.asp#axzz2qdKgc3xt

This could be good timing for you.
viewtopic.php?f=44&t=61742

Check simple things first. As Magpie said, disconnect the vacuum hose to the booster and plug the hose. Go for a drive. The brakes will work, just be a heavier pedal than boosted. If you don't get the same problem then replace the booster.

If you get the same symptoms then it's time to look at the other suggestions.