Dodgy Brake Servo??

[Brm Brm]

Every now and then when I hit the brakes the pedal feels very "hard" and I dont stop as quickly as I would like! The Master cylinder was replaced last year and there is no pull to one side so I dont think its a sticking caliper (somebody please tell me if I'm wrong!) so the only thing I can think of is a problem with the servo.

Anyone got any ideas and, if it is the servo, where does the V8 wedge servo come from so I can sub in a second hand one to suss out if it is the problem?? This is a tad disconcerting when it happens so any advice gratefully received.

[350matt]

There are a couple of things you could check, first is the vacuum hose to the manifold and connections at either end all airtight with no leaks etc? Best way to check is to lean the engine off a bit and spray lighter gas around the hose etc if the engine rev's up you've found your leak.
Also there's adjustment on the pushrod between the servo and master cylinder, whip off the cylinder and try unwinding the end on the rod a turn or so, being careful not to overdo it, binding brakes etc. Also there may be a one way valve underneath the vacuum hose inlet on the servo, which is held in place by an bayonet arrangement.

Matt

[Brm Brm]

Thanks Matt, the connections are OK and I cant see how the adjuster could account for what feels like a loss of servo assistance. If anything I have a little too much free play in the pedal but cant see how that would account for the problem. However, a sticking valve might just be of interest so will check at the weekend and let you know if I find anything. Any idea where the servo originates??

[350matt]

It may still be worth checking the free-play as I also sometimes suffer from inconsistent pedal feel and putting a little bit of pre-load into the system helped with mine. I don't know for sure but I'd guess the servo is Rover / Triumph origin as the brake master cylinder is TR7, however I think that this is one of those bits which were chopped and changed around a fair bit.

Matt

[shpub]

Either Triumph (unlikely as the TR7 bits were mainly on the 280i) or Ford Cortina (but be wary as that car had about five different varients as well. Currently seen seven different brake cylinder arrangements fitted to Wedges with no real rhyme or reason to when and why they changed.

Steve

[thegamekeeper]

To check if the servo is working follow this procedure.With the engine NOT running pump up the brake pedal and hold your foot on it. Start the engine and if the pedal moves down aout an inch the servo is working if not it isn't.First thing to check is that the servo hose is not delaminating, this means that externally it looks ok but under negative pressure the inner lining is being sucked in and blocking the vacuum. If in doubt treat it to a new hose anyway its not expensive and the one you have could be as old as the car.If that doesnt cure it then its the servo itself.
Couple of tips dont spray flammable liquids around trying to find leaks its like looking for a gas leak with a match. Dont buy used brake parts you already have them. Brakes are fairly important and if they are worn out they need NEW bits.

[Dave_H]

This may seem a daft question, but I've never had a Wedge (except at school ) but does a Wedge have duel circuit brakes with an in-line twin GP valve?

I had a simular problem as discribed where I'd get no "pull" on one side, and after testing everything else all I could put it down to was the GP valve.

The valves job is to distribute the fluid pressure between the rear and front so as to avoid rear lockup, mine when it developed it's fault caused one front caliper to go on strike.

Mabe this doent apply to a Wedge, but it's just a thought.

Cheers,

Dave.

[Brm Brm]

The problem is very intermittent so although I was getting the "inch" of assistance when starting up I couldnt rule out the servo; however, I hadn't thought of pipe delamination (thanks gamekeeper) and the pipe was old - have therefore replaced and will take her out for a test run - if it ever stops raining!

Quite agree about second hand bits - I just wanted one to sub-in to see if I could eliminate the problem and save myself buying a new servo if I didnt need one. Rest assured I'm not going to be relying on bits from a clapped out-Cortina for the slowing down bit!

Wedge brakes have separate front/rear circuits with a deceleration control valve to stop the rears locking under heavy braking. This is only on the rear circuit and as both rear calipers are supplied by a common fluid line downstream of the valve I dont think this is involved. I'm sure Steve will tell me if I'm wrong!

Thanks for your help guys!