mk1-forum.net

Hello chaps,

My S is running ! BUT ( ) I can not make it stop braking !
Master cylinder (old S renewed one), linings, cylinders, pads, shoes, almost everything is new,
except the mastervac.

When driving, it seems the fluid pressure builts up, up to the point that the brake tail lights switch on.

I suspect a faulty valve on the mastervac, but what you experts think ?
Trouble is how to find a rebuilding kit for my Vac ?

Sorry for my poor english,
hope you still understand me,

Regards
Etienne

Assuming the system is bled correctly & it is a case of the pedal changing pressure as you use it then it is almost certainly something to do with the vac servo.

Some people still have repair kits, it may be worth you contacting "The Mini Works" he managed to find me a couple of kits that I was after for a member on here a while ago. Althernatively the repro servo units that are available from Minispares are fairly good value & although not identical to the originals are a pretty good match . . . . . & they do work

Thank you Mark,
is "The Mini Works" you are suggesting Simon at http://www.theminiworks.co.uk/ ?
If so, I will contact him.
Bendix vac servos are available in France at a better price (€ to £ conversion !),
a close match I must say, but still quite different aren't they ?

That is the correct MiniWorks, I meant to put the link up,but forgot.

Yes, there are differences, but it's a better option to have one that looks different to one that doesn't work.

but it's a better option to have one that looks different to one that doesn't work.

Right !

You can also ask Giovanni Percossi, "Italian Job" on the bay. I think he still have some kits.

Is your pedal smooth or hard when you push it ?

Hello Alex,
hard pedal, very different from my last ride to Le Mans Classic,
goes worst while running, but braking is very efficient and ... easy !

I cannot find Italian Job on bay.com, is Percossi italian ?

Yep, Italian, from Trieste. --> http://myworld.ebay.co.uk/italian-job

If the pedal is hard, I also think it's the mastervac. Mastervac is for coward and faint hearted !

Is it 18G8189 you need ?

Also worth checking the right master cylinder pushrod is fitted. I cames across this a year or so ago, the pushrod was too long & sat on the inside of the bulkhead stopping the fluid returning to the reservoir when releasing the brakes. Un-doing the two nuts that hold the cylinder down should be enough to proove if the brakes release & the lights go off.

Mike.

Hi boys!

Mastervac is a french term (Peugeot) for servo... Why don't use servo?

Buy a new one, Etienne... very close look and NO problem !
Here were fed up with repaired servo, not great results!

COOPERCO wrote:Also worth checking the right master cylinder pushrod is fitted. I cames across this a year or so ago, the pushrod was too long & sat on the inside of the bulkhead stopping the fluid returning to the reservoir when releasing the brakes. Un-doing the two nuts that hold the cylinder down should be enough to proove if the brakes release & the lights go off.Mike.

As soon as I read the first post I thought of the master cylinder pushrod free travel. Had this same problem an a race Mini years ago, 1/2 a lap and the brakes came on. It seems the vibration and natural movement was enough to pump the pedal hard so gave the peadl a little more free travel and fixed it.

Al

Mike, Al,
Thanks, you might well be right !
The trouble came after fitting a renewed S master cylinder in place of the standard one that was in the car.
This would suggest I hadn't the right kit ...
Any chance of a part number for the kit, and an exploded view of both master cylinder and servo ?
Would be great, thanks.

Also, Al, how did you give more travel to your pedal : I am sorry not to be sure to understand exactly what you mean, it is pretty much a matter of language.

Simon Drew seems to have a kit for the servo, but without the diaphragm.

Enguerrand, you know I like difficult paths ...

Mike, Al,

I am slightly confused because - until now - I only found one reference for all 0,70" bore master cylinders pushrod.

Any idea ?

Hi,

If you still have your old cylinder you could swap the bottom pushrod over. Under the rubber boot is a circlip, remove it but keep the end of one finger over the hole in the end of the cylinder. The spring inside will push all the internals out otherwise If the internals do come out just be carefull when you push the seals back in so the lip does not get damaged. Swap the pushrod over & refit the circlip. Practice on the old one first.

Mike.

To prove if the fault is in the servo, why not just disconnect it by fitting a new brake pipe to by pass it temporarly.

Etienne B. wrote:Also, Al, how did you give more travel to your pedal : I am sorry not to be sure to understand exactly what you mean, it is pretty much a matter of language.

Hi Etienne,
There should be a rubber gasket between the master cylinder base plate and the bulkhead, also between the master cylinders and base plate. It is important to have a gasket thick enough to give you adequate free-play. In your case, you could add another or thicker gasket.

Regards
Al

Stupid perhaps but better safe than sorry;

Ensure that the ventilation in the master cylinder cap is fully open - otherwise you could end up with a vacume/ sticky brakes.

Thanks guys for your help,

66S wrote: It is important to have a gasket thick enough to give you adequate free-play. In your case, you could add another or thicker gasket.
Regards Al

Right, that is what I thought, even thinking of having a special plate made to the right thickness in a thin sheet of metal.

IAIN wrote:To prove if the fault is in the servo, why not just disconnect it by fitting a new brake pipe to by pass it temporarly.

Yes Ian, I wanted to try this too,

COOPERCO wrote: Hi, If you still have your old cylinder you could swap the bottom pushrod over. Mike.

Right Mike, the previous master cylinder was a non S model, with the plastic extension that was mandatory in france after 1964. I do not know the exact type of cylinder it is though, and at first, I do not believe the two pushrods can be interchangeable ...

Another good company for servo parts is J&L Spares.

http://www.jlspares.com/sealkits1.htm

They can supply all the seals & parts for the Lockheed Type 5 1/2 and also offer a reconditioning service.

Two other possible causes that I have seen on other peoples cars resulting in the same sympton:

Is the non-return valve operating correctly / fitted in the right way?
Are the hoses to the calipers not twisted?