Most likely place Brake fluid would leak from?

[Jamesk]

There is a leak in the brake system but i just cant figure out where it is coming from, Does anyone have any experience where is the most likely place could be. What is most worrying is that its not dripping on the floor suggesting its laying on the car somewhere! The car has been standing still for around 10 years if that helps, perhaps a seal may have gone somewhere?

[Heuer]

Check the reservac - fluid leaks past the reaction valve and fills it up. If so you need to empty it and replace the valve on the end of the master cylinder. Only other place is the low pressure pipes from the fluid bottles - they become porous over time and 'weep' fluid onto the frames

[christopher storey]

If this is a 4.2 another likely spot is in the servo master cylinder. If the seals in this are defective, under vacuum conditions fluid is sucked backwards into the vacuum side of the servo unit and thence to the reservac . This is a nuisance job to do, but not all that difficult provided you make yourself a tool for dismantling the servo itself ( assuming your servo is the early type where you have to rotate the two halves relative to each other - the later ones have a circumferential band and are much easier to dismantle. A usual, but not invariable , telltale if this is the source of the leak is that the left hand fluid bottle empties first

[Jamesk]

Cheers for the replies! the car is indeed a 1969 series II 4.2 roadster. Having looked at the master cylinder it appears to be the earlier type with rotatation of the two halves needed to open it up. So would you recommend the first step would be to remove the reservac and check if it has liquid in it, if so then check the valve and then the seals of servo master cylinder. I must admit im abit apprehensive working with brake fluid, it is nasty stuff but il give it a go!

[PeterCrespin]

It's the vacuum servo you open up to empty fluid, not the master cylinder. The master is the one connected to the brake pedal. But yes, if the servo does have fuid in it then you will need to do the slave anyhow.

If you are nervous of brake fluid with regards to your paint, then fine - just cover everything up before you split any connections. If you are nervous of brake fluid because of unfamiliarity with brake work in general, you might be better off just buying an exchange servo/slave assembly complete. DIY refurbed brakes can still cause troube if the cores are worn or corroded or you buy craptastic seals.

[christopher storey]

James : yes, first thing to do is to examine the reservac to see if there is fluid in it . If there is , examine the pipe from it to the servo, and if this is contaminated with fluid then the most likely source is the servo master cylinder . You could also, as David has suggested, take the reaction valve apart - it's a 5 minute job - and see if there is any fluid there . Incidentally, the problem with terminology on 4.2 E types is that there are two master cylinders. I always refer to them as "pedal master cylinder" and " servo master cylinder" so that the position is clear

[Jamesk]

Well I removed the reservac to find about 3/4 of a glass of brake fluid. I then opened the reaction valve to find fluid in it. The hoses to the servo were luckily clear, I plan on changing the reaction valve tomorrow but it looks like this is where the fault lies! Cheers for all the help!

[Tony]

Well it is good to have the solution solved. I feel all to often problems are discussed with good debate and lots of ideas to resolve the issue. However the originator once the problems is solved forgets to post the final solution.

Maybe this should now moved to the "Final Solution Sticky"

[mgcjag]

Hi James.......You say that fluid was in the reaction valve & so you will change it........I dont think you will find it is a valve problem as there should be no fluid getting to the valve as this is only a device controling air vacume....read back on Christophers comments re the servo cylinder leaking fluid back into the vacume area....Steve

[christopher storey]

Well,Steve, there is actually a hydraulic seal on the pin which leads from the pedal master to the reaction valve , which I suppose can leak , but it is a very small one, about 1/8 inch / 3mm diameter . The virtue of changing this first is that it is so much easier to do than dismantling the servo master cylinder

[mgcjag]

Hi Christopher.......Think I may have made a fundamental error....is the Reaction valve the unit that fits to the top of the Vacume tank or the white attachment to the master cylinder....Thanks Steve

[PeterCrespin]

Steve, have you got a parts book or workshop manual? You need to get things straight with braking systems - be it your own or advising others on theirs. Too much at stake to wing it...

The reaction valve is the white platic mushroom on the end on the master cylinder which controls the vacuum circuit that activates the large servo. The small check valve is a little grey metal thing screwed onto a stub atop the reservoir tank or held to it by a short piece of hose and clips, depending on model. These do tend to break after many years but i haven't bothered replacing it. i just put a cheap generic n in-line one-way valve coming out of the back of the manifold, rather than the expensive and slightly suspect tank valve. I know of someone who had a new one fall apart.