Brake master cylinder replacement

Post by: **potleyu18** » Thu Nov 12, 2015 5:01 pm

Having made the decision to replace both clutch and brake master cylinders and researched how to do this i decided to remove the whole pedal box ,carbs etc, not an easy task but i thought it worth the effort. so i ordered replacement cylinders from Paul Matty. Fitting went without too many issues but took a whole day. The remaining braking system was also replaced including pipes, calipers and pads.

Then booked the car in for its first MOT after an 8 year rebuild and 400m before getting to the garage the brakes seized solid. three weeks later after a servo replacement and trying all possibilities the garage concluded the shaft out of the cylinder connecting to the brake pedal must be too long.

A phone call to Roy at Paul Matty resulted in the information that indeed the new cylinders output shaft is too long and the old cylinders shaft should be transferred, and documentation should have been included in the packaging and on the invoice, unfortunately in my case this was not done and confirmed by Roy.

Now the car is back via a low loader and i now have the task of re doing all of the work to fit the correct shaft, needless to say i'm not impressed. So advice to anyone about to undertake this task is to check the output shafts of any new cylinders match the ones removed and save yourself a lot of frustration.

Steve

Post by: **Europatc** » Thu Nov 12, 2015 9:58 pm

Hello Steve you must be right cheesed off, It is quite a well known fact that you need to change the rod but it is easily missed. At least you know its now good to go, and stop.
all the best
Stuart

Post by: **mbell** » Fri Nov 13, 2015 12:15 am

Sorry to hear that, something that is easy to miss if not in the know.

Have you considered modding the pedal box so you can remove the masters in situ?

A common mod and one I diff when I pulled and stripped my pedal box.

Post by: **alan.barker** » Fri Nov 13, 2015 10:43 am

a quick mod to be able to drive the car home is to undo the nuts holding master cylinder to pedal box.
Put in place temporary spacers between master cylinder/ pedal box and nip up the nuts.
Alan

Post by: **Certified Lotus** » Fri Nov 13, 2015 11:20 am

I had the same problem when I replaced my brake master cylinder. The front brakes kept locking up. Until I realized I had the wrong length rod, my solution was to use a wrench to crack open the fitting on the master cylinder for the brake line, relieve some pressure and then drive away. The minute you use the brakes a couple of times the pressure builds back up and the brakes lock again.

The reason for this is there is a valve that is at the end of the master cylinder that releases the pressure after a stroke of the piston. The longer rod does not let the piston completely release and the pressure increases until the brake pads engage on their own. The shorter rod (3 1/2" for my S1) made all the difference in the world.

Post by: **potleyu18** » Sat Nov 14, 2015 9:23 am

Thanks for all of the responses and i will try the modification of the pedal box to gain access to release the cylinder assembly, and hope it works.

Cheers

Steve