Brake bias valve?

[bigtalljim]

When I first got my S the brakes were past their best so fitted new discs and pads. The brakes were better but not as good as expected.
My mate MOT it recently and the brake figures were more than enough to pass but he noticed that the rear brakes were producing more 'power' so to speak.
I noticed that a valve of some sort sits in the pipe work splitting the front and rear brake pipes. Is this a bias valve, and if so what is it off to replace it?

Also brakes feel a bit wooden, how easy to fit new booster, what car is it from and is it a weekend job to replace?

nearly summer for top roof off fun

[GreenV8S]

Fit the right brand of pads bedded in correctly flushed through with fresh fluid and clean calipers. You can tell if the servo is working by holding the pedal down while you start the engine. The servo will pull the pedal down half an inch or so if it is working properly. If you need a new servo you can get one from TVR Car Parts.

[s3swiss]

The bias valve is there to make sure the lightly weighted rear-end brakes don't lock-up when you apply heavy braking pressure. This would not be nice, especially in a bend! The valves are in my experience usually pretty reliable and I'd suggest the problem is more likely with the front brakes not giving sufficient effect for the pressure applied. Have you got braided brake hoses? If not, and the original (17 year old?) brake hoses are still in use, they'd be my first job to replace. Are the pistons in the front calipers fully free? If you've had to replace pads, it is not unknown for a ridge to have formed on the pistons affecting their performance when new pads are fitted. If you do end up replacing the bias valve, I don't know where the S ones are from but you can buy adjustable valves from most of the motorsport suppliers (demon tweeks etc etc). You'd then need to set the valve so that the front brakes always lock-up first when slamming on the anchors. Best done by trail and error on a stretch of non-public road! (Gravel roads reduce the speed necessary to check this proportioning due to being able to lock the brakes easier on a loose surface). Whatever you end up spending - money spent on brakes is always worth it in my opinion

[MWBS3]

I assume its the 'brake pressure reducer' you refer to.

Mine was v rusty and the bracket fell apart ( I made another) . I cleaned it up and the unit is a ford part - if you remove it and clean it up the part no is on the rear ( larger face ) probably from a sierra.
I also replaced my servo which was saab 9000 others can be sierra the servo with a separate fluid res' is saab ( but check ).
I recall seing another posting from a person who found a source on 2nd hand servo units inc master cylinder.
I paid about £180 from a motor factor company for a basic servo which was not too hard to fit.

Hope it helps

Mark

[whitty]

I had a similar problem, the rears locking up before the fronts, then the pedal stopped coming back as quickly as it should, scarry when you go for the breaks going into a 90 left, turnned out to be the servo, mine was saab 9000, got one off a scrappy for a tenner, doddle to fit if your a bit agile (upside down in the footwell to remove), I was quoted £180+ for just a new servo so figuered the £10 was worth the risk.