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I am in desperate need of technical advice about how to prevent brake fluid leaking past the seals in the front brake cylinders and onto the brake shoes resulting in contaminated shoes and a pedal that goes almost to the floor.

I have just finished a complete ground up rebuild of my 1960 Mark 2 Zephyr. In order to avoid the usual brake issues common to our cars, such as seized wheel cylinders, I fitted all new piping, new wheel cylinders all round, and a new servo and dual circuit master cylinder designed for a Mazda RX7 and filled the system with DOT5 Silicone brake fluid.

I later found that the brake fluid was seeping past the rubber seals on the front brakes. The rubber seals in new cylinders are harder and may have some plastic in them. I drained the front wheel cylinders, cleaned everything and fitted a set of NOS Girling rubber seals to see if they would perform any better. After a very short time I find it has made no difference and the fluid still leaks onto the front shoes.

Any suggestions on how to fix this would be very much appreciated.

Thanks, Bernie.

Bernie,

I also own a '60 Zephyr.

I've done quite a few brake jobs on these and one reason you get leaky cylinders on both sides possibly seals are put on the pistons backwards, seal lip goes in the cyl first.

I would suggest relining the shoes as it's difficult to remove silicon from the linings.

Pete

Thank you for your reply, Pete.
I have two Zephyrs and a Zodiac so have done lots of brake jobs but this is the first time that I have used silicone brake fluid.
The seals are correctly fitted and have been changed once already after 2 weeks with no improvement. The cylinders are brand new so I am at a loss as to what is causing this so I am hoping that there is someone on the Forum who has experience of DOT 5 fluid.
Cheers, Bernie.

We use DOT 5 on my brothers Cortina MK2 and haven't encountered any problems. I believe the hydraulic system needs to be completely flushed of any old DOT3/4 before using silicon fluid but not sure if that would cause leakage with any remaining DOT3/4 still in the system.

My gut feeling is the new w/cyls maybe at fault.

Sure sounds like faulty cylinders. I have DOT5 in the VW for about 20 years now with no problems at all. So far I have stayed with LMA in the Prefect though because I was told years ago the British rubber doesn't do well with silicone. I since know several people who use it in theirs though with no issues. You said "new" wheel cylinders. Is that actually new or just different?

Thank you for your reply.
I have 2 Zephyrs and a Zodiac and have done lots of brake jobs on them over the years. The seals are correctly fitted and the wheel cylinders and, master cylinder, shoes, and all brake lines are brand new, not new old stock.

I have sent pictures to a major British supplier of new cylinders for all kinds of classic cars and they confirm that the ones I am using are the reputable brand distributed by most aftermarket suppliers.

I have ordered a service kit from them comprising the seals, springs and dust boots.

Fingers crossed,
Bernie.