Brake Master Cylinder

[Wevster]

Hi Everyone

I have removed my brake master cylinder for inspection after complete brake lock up. There is slight score marks on the inside of the cylinder and wear on the piston. Is it the opinion that the m/c needs replacing? Doesn?t seem too bad to me, is it the spring when compressed that scores the cylinder or piston?

Any advice appreciated.

Kev.

[Panda]

Hi Kev, You are talking about brakes here. How much is your life worth? It could be resleeved and the piston replaced, but the cost would be approaching a new one. Go for it!
Alan P.

[Wevster]

Hi Alan

Thanks for comments, I will probably buy new as easy obtainable, however I was interested to know the thoughts on the wear with in the m/c and wondered if it was actually causing the problem?
This is on a 72 +2, with a Girling Mk2B Servo newly refurbished, new one way valve, Calipers all serviced with pistons and seals etc, new braided brake lines.
I've read many elan owners have experienced similar locking up of brakes and have spaced back the m/c using washers on the pedal box, which I might try next, any other thoughts?

Cheers

Kev.

[mbell]

Are you running the original push rod for the mc?

A very short one is needed and most replacement ones aren't short enough. If too long it can prevent the poison returning and pressure being released from the master.

[Wevster]

Hi Mbell

The push rod measures just over 82mm end to end and about 73mm to the centre of hole. Not sure if original or not.

Cheers

Kev.

[Wevster]

Just measured, are adjustable push rods available?

[vxah]

You should normally be able to "feel" for a push rod/master cylinder problem when installed on the car.. If you push the pedal gently by hand there should be a slight movement before the push rod contacts the back of the piston? This slight play would indicate that the piston is all the way back in the cylinder and not being held by a too long push rod or brake pedal issue such as stiff pivot bush etc?
Are you aware also that rebuilt Mk2b servo's can suffer from a problem that causes the brakes to hang on especially after rebuild! As far as I know it's caused by a wrong size seal in the kit that causes the reaction piston to be too tight in it's bore?

[Wevster]

Hi vxah

Thanks for the info, i didnt know that. I've ordered a new m/c from SJ Sports cars and they say locking on brakes is always a servo issue, I've also spoken to J&L spares in Rochdale who recon'd the servo and they say sounds like m/c!
Interestingly, a new pushrod does not come with a new master cylinder! Just use your old one, SJ said. Which doesn't help.
Anyway, what i'll do is fit the new m/c when it arrives, adjust accordingly, re-bleed system and see how it goes, if it locks up again, i'll bypass the servo with a small piece of brake pipe I've made up and see how that goes. If that works I know for sure it's the servo and send it back for 2nd repair.
Unless anyone else has any bright ideas?

Cheers

Kev.

[Wevster]

Servo, with bypass pipe.

[Orsom Weels]

Had this issue with my +2 after the servo was rebuilt. Went down the road for a test drive & on the first application of the brakes, they locked up completely & left me diagonally in the middle of a main A road . I stripped the servo down my self & rebuilt it again with a NOS seal kit I managed to find & it's been no trouble since.
I don't really see how a master cyl could cause the brakes to lock ? If it was sticky, it could stop them releasing if you hit the pedal hard & locked them up, but it will only transmit as much braking effort as you put in with your foot.

Regards, Tim

[Wevster]

Hi Tim, was your servo the same as mine a Girling mk2B?
I was told by J&L that a new kit is around ?100+ and its a one time fit job, so if you muck it up or take it apart again you will require a new kit! So I've left well alone, they do however, guarantee their work and will hopefully take another look. Just a pain sending it up to them again.

Cheers

Kev.

[Orsom Weels]

Hi Kev,
Yes, Girling mk2b. The only part that maybe one time fit only is the band that holds the two halves of the vacuum chamber together, they were originally crimped so you had to cut them off, but the replacement in the kit is designed with a clamp bolt through a couple of trunnions, so you can DIY it. This also has the advantage of allowing you to release it & re-use it. The rest is just seals & gaskets.

girling-mk2b-overhaul-kit.jpg (33.93 KiB) Viewed 1332 times

girling-mk2b-servo.jpg (39.65 KiB) Viewed 1332 times

Regards, Tim

[Wevster]

Thanks Tim,

That?s interesting as you can see from my photo the band on mine has a bolt through it, so can be easily removed + returned. Would it therefore be the seals within the slave cylinder that?s possibly at fault? If so does anyone know if they can be obtained separately?

Cheers

Kev.

[Orsom Weels]

Hi Kev,

The problem I had, & I suspect others as well, was the 'T' lever valve closed the vacuum vent, thus bringing the servo into operation, but then stuck & wouldn't open again to release the vacuum, so the servo just kept the brakes on. I'm not sure about finding the seals individually unless you could find someone with a good stock who was prepared to sort through & try to match them up.
Have a look at this,
http://www.northwestclassic.co.uk/GIRLI ... NDING..pdf
I think it will help you understand the above better & also give you an understanding in how it all works & what's involved in overhauling a Girling servo. It's really quite straight forward once you get into it

Regards, Tim

Edit, Just found this, http://www.head2head.free-online.co.uk/Rover/servo.htm
May explain some of it a bit better

[Wevster]

Thanks Tim I?ll print it off and have a good read.

Kev.