Brake master Cylinder Leak. Options?

Technical advice Q&A

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eddiecross
Posts: 132
Joined: Thu Sep 15, 2016 9:36 pm
Location: Egham
Great Britain

#1 Brake master Cylinder Leak. Options?

Post by eddiecross » Thu Jan 14, 2021 7:43 pm

Hi there,
Just when I thought i was out of the woods with the cooling system refresh...

67 S1. Brake master cylinder leaking from the piston onto the floor.

These are the steps/options. Comments welcome.

Strip out the master cylinder and piston and inspect the bore. If pitted, replace with a new m/c (about £200).
If the bore is ok, I have the rebuild kit including the reaction assembly. I have a spare old m/c (had a S2 with the same problem) in case I need parts or anything goes awol

Next is whether I go on to replace the servo unit while I'm working. No obvious leaks (yet) but may be false economy to ignore. My preference is to replace as I tried rebuilding my S2 unit before and internal parts were broken and I don't want the hassle of replating the vacuum parts. Plus you seem to be able to get one for £180. Related question- are the cheaper replacements from David Manners and others ok for the price or should I step up to the £300-400 units. Not crazy about spending the extra if I don't need to.

Finally, if I replaced both, can I then replace the fluid with silicon with just a full bleed/purge of the rest of the system without any further stripping?
The car will be mainly in storage and I know the clock is ticking on mineral fluid life plus the mess it makes when it leaks.

All the best
Eddie
67 FHC

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Joes66
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Joined: Sun Apr 26, 2020 7:16 am
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#2 Re: Brake master Cylinder Leak. Options?

Post by Joes66 » Fri Jan 15, 2021 4:56 pm

May as well change both and it was me,and it recently was, I would replace with new units
If one is rusting then probably everything is rusting as moisture has got into the fluid
Does the car sit for long periods?
Do you have the history of the brake components and when they were last replaced?
Once I got into mine I found everything was either stuck,sticking or leaking in some way
2 of the rear pistons were also stuck and not working
I have heard of some people re sleeving the master cylinder
Not sure why but there may have been faulty or bad new units in circulation
I replaced every part of my breaking system and I fitted one of the £150.00 servoes and a master cylinder from David manners
I have had no problems with either and I fitted the DOT5 silicone fluid
Brakes are excellent
If you are going to change to the DOT5 then make sure you purge through all the old fluid thoroughly
It will mean throwing away the purged fluid you take out rather than re using it in a completely clean un filled system
Its expensive stuff and can't be mixed
Personally I can't understand anyone still using DOT4 on any car that's sits for long periods of time
Its a death sentence for brake parts
Joe
1969 series 2 2+2

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Topic author
eddiecross
Posts: 132
Joined: Thu Sep 15, 2016 9:36 pm
Location: Egham
Great Britain

#3 Re: Brake master Cylinder Leak. Options?

Post by eddiecross » Fri Jan 15, 2021 7:43 pm

Thanks Joe,
Useful information on the cheaper M/C and servo.
Yes it will sit for long periods.
No history on the car at all- came from a dealer in LA a couple of years ago. No evidence yet of any brake components swapped in.
Good advice too on the Silicon fluid. I replaced all the brakes on my 68 Camaro last year and was the 1st time I used silicon fluid. So glad I did as there were many leaks to fix and would have done serious damage. Other reason is that it could easily sit for a year or so in storage so want minimum deterioration.

I'll go ahead and strip the m/c. Soon as I can check the bore I'll know if its scrap or not. Good advice on calipers but I'll probably take a chance and draw the line at fitting the m/c plus possibly the servo.
The XKE is back at mine on a stop over for just the major jobs then back in storage as have another car that I just have to finish ('68 Camaro RS/SS 396 4 speed so it deserves seeing through to the bitter end).

Image

Any other comments welcome.
Thx
Eddie
67 FHC

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