Brake fluid leak - between brake servo and master cylinder - 94 Favorit

[anewman]

Just noticed my brake fluid level has significantly dropped. I appear to have a brake fluid leak between my brake master cylinder and vacuum brake assist servo, the bottom of the vacuum servo is wet. It's possible that this was helped to happen by my bleeding of the brakes just over a month ago after replacing a brake pipe for my MOT.

Any ideas on what's likely to need doing to sort it out?

Thanks in advance

[TeflonTom]

i expect your bust the seals when you were pumping the brake pedal

[anewman]

Ah well, at least a new master cylinder is only £30 delivered from Jorily. Hopefully I can replace it without damaging something else

I guess the vacuum servo should be ok even though fluid has leaked all over it?

[Tech1e]

If fluid has leaked inside the servo which is probable by the sounds of it that will need replacing too.

[anewman]

Looks like i'll be round the scrap yards for a brake servo as my guess is they'll be expensive new.

Thanks guys - very helpful (although would rather I didn't need to sort this out :( )

[anewman]

Any tips on avoiding busting the new seals? Or is it just something that happens on old seals?

I tried to use a gunson eezibleed but couldn't get it air tight and it just sprayed brake fluid everywhere, even using lower tyre pressure :(

[rigsby]

It will have been age not you thet has bust the seal

[anewman]

Reviving my old thread as the brand new (well 10 month old) OE master cylinder is now also beginning to leak slightly where it meets the servo. Is slight leaking like this acceptable? Or do I have to renew the master cylinder again?

Cheers.

[rigsby]

If it is only 10 months old it should still be under warranty

[TeflonTom]

no a leak is not acceptable at all, it will allow moisture into the system, as a matter of interest did you adjust the length of the clevis pin on the servo when you fitted it to the master cylinder?? i'd have to look up the specs for it but there is a definite measurement you need to make

[anewman]

I adjusted it at a guess by lengthening it and then shortening it a bit each time until when I offered the mc up to the servo that no resistance was felt (then thread locking).

No matter what, even being very careful and using a digital micrometer, I came up with a different measurement each time when measuring following Haynes's directions (basically measuring a number of lengths and adding and subtracting).

I'll have to try dig out the receipt and see if the dealer will swap. (Edit: balls can't find it, oh well).

Edited 3 April, 2009 by anewman

[Richard Black]

Didn't see this thread when it was new, but here's a bit of advice re bleeding: if your master cylinder seals are getting old and knackered, they will usually fail when you bleed the brakes because the pedal travels down to the floor and the master cylinder piston also moves further than usual, bringing the seals into contact with rougher (probably slightly corroded) metal. If they're in good nick they'll survive it, but if they're getting old it'll probably be the last straw. In other words, they would have needed doing soon anyway.

If on the other hand you expect to get rid of the car soon and want the absolute minimum of work, simply make sure that whoever is pumping the pedal only moves it halfway down on each bleed stroke!

[Cepheuz]

you can remove the master cilinder and replace the seals and do a cleanup, refit and all is like new...

also, you dont necesaritly need to change the servo,,, i was lucky, the fluid did not damage anything it was a matter of disasembly, cleaning, re-asembly, and tuning, now i barely have to move the pedal to get braking

[robw]

The measurement from the Haynes is 50mm. Cause I've got exactly the same problem by the sounds of it.

Bugger....

[anewman]

Have done all the measurements diligently for the servo output rod on the Favorit.

From measures made of the master cylinder (as described by Haynes) I believe it should be set between 19.3mm and 19.6mm (with 0.6mm and 0.3mm clearance included respectively) - although there is probably some measurement error in there.

I measure the original servo to be set at 20mm.

I measure the setting on the new servo to be 20.7mm. Therefore a bit too long. So I guess it would be reasonable to believe that this caused the new cylinder to leak.