19 replies to this topic

[davej]

I`ve been having a few issues with my brakes recently, I have changed all four caliper pistons as they were sticking and put new seals in. Bled the brakes this morning and the pedal is still not returning fully when driving but works fine when the engine is not running. This to me points to something with the vacuum to the servo from the inlet manifold. Can anyone shed any light on what the problem could be??

Thanks

Dave

[charie t]

If the pedal is not returning, the most likely cause is the pedal seizing on the shaft. They are never greased or inspected

Edited by charie t, 30 June 2012 - 01:58 PM.

[davej]

I thought that aswell but I've put wd40 on the linkages and pins and it seems to work when the engines not running.

[Ethel]

It could be the servo air valve sticking.

[davej]

Ah right ok, any ideas on how to sort it?

[Ethel]

The servo is pretty simple, just a diaphragm and and pushrod with some simple valves round it not far off a sink plug in function. When you press the pedal it pushes the pushrod which opens the first valve, which lets air into the rear of the case, it also closes another valve that stops the air being drawn through the centre of the diaphragm so you have vacuum on the master cylinder side and atmospheric pressure pushing on the pedal side. When you take your foot off the, the pushrod closes the first valve and reopens the one in the diaphragm so vacuum cam be returned to both sides. It sounds like that's not happening, either both valves are remaining slightly open (you should be able to hear air entering the foam filter around the pushrod), or the diaphragm valve is loose so the rod doesn't pull it open.

[davej]

Ok thanks Ethel, I did hear air entering the filter when the pedal wa s pressed. Is it time for a time a new servo?

[Ethel]

You can get a repair kit, no point in paying for a tin can when you have a perfectly good one.

[davej]

I`m going to have to drain the system again yeah? The missus will be pleased, I had her pressing the pedal yesterday while I bled them. I might have a go at getting the servo off later. How do you get it apart??

[RobWill116]

I dont think you'll have to drain the whole system. I've never worked with a servo because mine hasn't got one, but you can little threaded end caps for the pipe unions. I used them when I replaced my master cylinder. Didn't lose the fluid in the pipes, just had to empty the master. I'm sure I got them off fleabay for a couple of quid

[Ethel]

You should be able to detach the master from the servo without touching the hydraulics if you're careful. Seal the cap vent & arrange something to support the cylinder upright & so the pipes don't get too bent. I also wouldn't totally rule out a stiff pedal linkage as Charlie T suggested, it might do just enough to keep the valve closed. Start by removing the clevis pin & you can investigate that possibility.

The cylinder just unbolts from the front

http://www.british-c...18445015441.htm will help you.

[davej]

Great stuff cheers, I`ll take all the clevis pins out and do some investigating, hopefully its just them sticking.

[Ethel]

You only need to remove the one from the back of the servo.

[davej]

I was thinking of taking them all out and giving them a clean just to make sure.

[davej]

Right then I now have the servo off and a sore hand How do I take it apart? Does the front bit spin on the back piece until the notches line up if that makes sense?





Thanks

Dave