Author Topic: Mk3 Wheel Cylinders (Front)  (Read 2069 times)

Offline 4X419

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Mk3 Wheel Cylinders (Front)
« on: February 23, 2015, 08:17:11 PM »
Howdy Folks,

I am chasing some divine wisdom please!!

I am in the process of doing up the front wheel cylinders on my Mk3.  The piston was stuck in the passenger side one, but with a week of soaking and working the piston I got it out.  What I found was that the piston itseff was quite heavily rusted all the way around its circumference.

For those of you who have done work on theirs, do you think the water (from the road) gets up between the inside of the backing plate and the wheel cylinder face that bolts up to it??  I suspect that is what has caused the rust in mine.  I am considering putting a gasket on this face just in case - thoughts or advice is welcome??     

Kind regards,

Tom

P.S.  I do a lot of reading on this forum, but don't do much posting so please adivise of any protocol I might have breached in doing so. 

Offline Ravvin

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Re: Mk3 Wheel Cylinders (Front)
« Reply #1 on: February 23, 2015, 08:39:57 PM »
Tom, something I read or heard a while back was that the older styles of brake fluid absorb moisture out of the air over time. This would make its way to the lowest point in the system, being the wheel cylinders.
While the reservoir has what appears to be a rubber seal under the metal top, there is a tiny hole to allow air in and out. The idea is that when the brake is pressed and the master cylinder piston moves, the fluid level drops. The air has to get in and out as the fluid levels change. Any air coming in carries tiny amounts of moisture and over time they would build up.
If you are looking for a long-term solution, do what Restless Rover (ex Red Rocket) did, and have the cylinders sleeved with stainless and get someone with a lathe to turn up a couple of stainless pistons. Its a simple and quick job and shouldn't cost much. I intend doing it to mine shortly.
Restless Rover used 3 of his MK3's for years as part of his business and said that once he sleeved his cylinders, he never had another issue with them.

Offline 4X419

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Re: Mk3 Wheel Cylinders (Front)
« Reply #2 on: February 23, 2015, 08:51:59 PM »
Good advice Ravvin!!

Thanks!!

Tom

Offline john.k

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Re: Mk3 Wheel Cylinders (Front)
« Reply #3 on: February 23, 2015, 11:29:42 PM »
A tip from a longtime time machinist-dont put stainless on stainless.You may may have a monumental seizure.Make the pistons from brass.I have stripped stainless relined cylinders from a number of front axles in my paddock,and sold them to Action Brake.I think the Girling pistons were hardchromed ,but the army also made some rough looking ones themselves from steel.Regards John.

Offline Ravvin

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Re: Mk3 Wheel Cylinders (Front)
« Reply #4 on: February 23, 2015, 11:59:17 PM »
Thanks again John.
I had issues of stainless on stainless binding when rebuilding some industrial gearboxes a while ago so I should have remembered that.
Brass would also be a lot easier to machine.

Greg.

Offline bush man

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Re: Mk3 Wheel Cylinders (Front)
« Reply #5 on: February 24, 2015, 09:55:46 PM »
    one should remember to change the brake fluid every few years to illuminate this problem we change our oils snd other fluids but don't think about the brake fluid in fact the older brake fluid gets the less effective it becomes.
     regards john

Offline 4X419

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Re: Mk3 Wheel Cylinders (Front)
« Reply #6 on: February 25, 2015, 07:47:14 AM »
John,

Yes, that's been a key observation for me.  The amount of gunk I have flushed out of the brake lines has amazed me!!  I am going to flush the whole brake system annually, and keep the fluid fresh.

Tom

Offline Chazza

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Re: Mk3 Wheel Cylinders (Front)
« Reply #7 on: February 25, 2015, 08:47:17 AM »
I now flush the fluid on all of my cars once per year - the Disco is 19 years old and the brake hydraulics are still fine,

An alternative is to use silicone fluid, which does not absorb water but when I rebuilt my Alpine 2 years ago, I couldn't buy any anywhere; even the brake specialist did not have it,

Cheers Charlie
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