Rear brake compensator leaking

[Ben]

Hi all, 

I've got a leak from the rear compensator. Even 
before it was leaking I'm not sure it had been working correctly as my mot tester said there was little effort from the rears.
Looking at it with the car in the air the piston was in/closed, and looking at which way the trailing arm would push the spring and rod it looks to me as if it would try to close it further, which can't be right?

I'm considering getting a new one off eBay for £115, and trying to get it set up well. Also considering removing it along with the abs and replacing with a bias valve in the car. Or possibly two bias valves to retain the abs. It's a road legal track car, only driven on the road if it's dry or to get it to a track. 

Any advice welcome please and thankyou.

[carlukepeugeot]

It works a bit differently to what it would appear looking at it I think. As far as I remember, what actually happens is that when you put your foot on the brake, the hydraulic 'pressure' drives the piston outwards, increasing the volume of the chamber and decreasing the remaining pressure available to act on the brakes. The lever attached to the piston presses against a big spring. It's a bit like a 3rd wheel cylinder in the circuit.

When the trailing arm rotates upward due to extra load at the rear of the car, the spring is compressed making it harder for the piston to come out - so it comes out less - thus the volume increase is less than in the unloaded condition and more of the pressure is retained to act on the brakes. It will always be in the 'closed' position when the brakes aren't being applied. If I remember correctly there is a small return spring to bring the lever / piston back in too so when you lift the car all that happens is that the big preload spring goes slack as the trailing arm drops.

Mine started leaking and I nursed it for a while until it was leaving puddles on the pavement. Was a ballache to replace, mainly because I ended up having to renew most of the brake lines due to the unions being rusty and seized. In the end I just bought myself a decent brake pipe flaring tool plus a roll of cunifer pipe and the fittings, dropped the axle down at the drivers side and set about it.

[Ben]

Thanks for the reply, that makes sense now. When you say you nursed it through do you mean you were having to pump the brake pedal? I wasn't able to find the correct replacement compensator so I've ordered an adjustable bias valve to replace it with instead.

[carlukepeugeot]

Just meant that I was cleaning it up and topping up the brake fluid. I experienced a little bit of air ingress but nothing too noticeable.

[Ben]

Ok. I was having to pump the pedal up, hopefully the compensator is my only leak/air ingress.