Brake bias valve.
Discussion
Or is that brake pressure valve, proportioning valve, or control valve ?
Yes, I know it what it basically is & what it supposed to do..... but !
Being as I am doing an S3 total restoration....
What is the failure rate/are they a known problem part?
What/where was it sourced from, is there a readily available replacement ?
Is that seemingly silly angle its mounted at, a functional requirement for correct operation ?
IE. It carries some form of inertia control ?
TerryB.
Yes, I know it what it basically is & what it supposed to do..... but !
Being as I am doing an S3 total restoration....
What is the failure rate/are they a known problem part?
What/where was it sourced from, is there a readily available replacement ?
Is that seemingly silly angle its mounted at, a functional requirement for correct operation ?
IE. It carries some form of inertia control ?
TerryB.
Or brake bias valve 
It's basically a ball bearing that rolls up a ramp and progressively restricts the fluid pressure to the rear brakes as deceleration causes greater inertia. So yes, the angle it's mounted at is significant in its' operation. I'm not sure of the limits of tolerance as far as the angle goes.
I have no idea where the valve was sourced from, think it may be Ford.
As to failure, it is a fairly simple device, corrosion, contamination, mechanical damage and worn seals are the only likely causes I would suspect.
Of course, I may be talking a load of old codswollop.
It's basically a ball bearing that rolls up a ramp and progressively restricts the fluid pressure to the rear brakes as deceleration causes greater inertia. So yes, the angle it's mounted at is significant in its' operation. I'm not sure of the limits of tolerance as far as the angle goes.I have no idea where the valve was sourced from, think it may be Ford.
As to failure, it is a fairly simple device, corrosion, contamination, mechanical damage and worn seals are the only likely causes I would suspect.
Of course, I may be talking a load of old codswollop.
Edited by glenrobbo on Wednesday 10th February 22:26
glenrobbo said:
Of course, I may be talking a load of old codswollop.
Surprisingly not 
Ford refer to it as a deceleration valve
Not really a lot to go wrong in there.........
Then I guess it should be really called... A Gravity Activated Brake Proportioning Valve.
I haven't been able to locate the same one as 'ours' unless its the same as fitted on Escort Mk4 (x2 of them on that car apparently !).
I'll just give mine a external clean, & maybe flush it out too.
Although (in theory) to prove basic operation, if held in your hand vertically (outlet UP), fluid should flow. And if held 180o the other way (outlet DOWN) fluid should not flow.
But it may need a little pressure behind the fluid to prove this....
Read. Oily floor & hands.... Again !!
And for my second theory... If it did fail, then being as its 'normal' state is open to allow fluid flow, it could be more likely that the back brakes will continue to work if it goes faulty/inoperative (thus giving too good rear brakes under sudden braking).
I'm surprised you 'S racers' out there haven't played around with this, or swopped it out ?
TerryB.
I haven't been able to locate the same one as 'ours' unless its the same as fitted on Escort Mk4 (x2 of them on that car apparently !).
I'll just give mine a external clean, & maybe flush it out too.
Although (in theory) to prove basic operation, if held in your hand vertically (outlet UP), fluid should flow. And if held 180o the other way (outlet DOWN) fluid should not flow.
But it may need a little pressure behind the fluid to prove this....
Read. Oily floor & hands.... Again !!
And for my second theory... If it did fail, then being as its 'normal' state is open to allow fluid flow, it could be more likely that the back brakes will continue to work if it goes faulty/inoperative (thus giving too good rear brakes under sudden braking).
I'm surprised you 'S racers' out there haven't played around with this, or swopped it out ?
TerryB.
Edited by Blue 30 on Thursday 11th February 12:39
Edited by Blue 30 on Thursday 11th February 12:41
Edited by Blue 30 on Thursday 11th February 14:03
You can buy the smaller one fitted to Chimaeras and most Griffiths (no ball bearing in that) and hide it somewhere else underneath. That's what I did.
edited to add:
You can see it strapped to the chassis diagonal brace, just by where the handbrake crescent is dangling:
edited to add:
You can see it strapped to the chassis diagonal brace, just by where the handbrake crescent is dangling:
Edited by Kitchski on Thursday 11th February 14:27
Oldred_V8S said:
Makes you wonder what happens when travelling down a really steep hill.
Same as breaking hard I guess, all the weight is on the front, very little rear braking required ? Kitchski said:
You can buy the smaller one fitted to Chimaeras and most Griffiths
This onelooks like something similar was fitted to Mondeo's
That's the baby. I got mine here:
http://www.racetechdirect.co.uk/j0152-tvr-car-part...
And yes, early primitive form of brake balancing as fitted to mk1 Mondeos and mk3 RS Turbo Fiestas IIRC.
It's just a spring in a tube. Once your pedal effort overcomes it, it allows the fluid through at a lower rate than the front. Quite expensive for what it was, but they used to be about £40 + VAT when I was working at Ford. Not sure if they're still available directly.
Most Chimaeras have them fitted right at the back above the diff.
http://www.racetechdirect.co.uk/j0152-tvr-car-part...
And yes, early primitive form of brake balancing as fitted to mk1 Mondeos and mk3 RS Turbo Fiestas IIRC.
It's just a spring in a tube. Once your pedal effort overcomes it, it allows the fluid through at a lower rate than the front. Quite expensive for what it was, but they used to be about £40 + VAT when I was working at Ford. Not sure if they're still available directly.
Most Chimaeras have them fitted right at the back above the diff.
I would add though, there is more than one type fitted to the Fords. Three different ones at least, I'm guessing with different pressures. I couldn't decipher which one I needed when I rebuilt the S, so I played it safe and went for the Racetech one. The original Ford ones have part numbers stamped in, but are usually too corroded to make out.
Yep, otherwise it will be "fighting" what you're trying to do with the balance bar...
Alan's adjustable valve is a cheap 'n easy option to the dual master cylinder set up, both ideal for track use but maybe not so perfect for day to day road driving?
all imho
Alan's adjustable valve is a cheap 'n easy option to the dual master cylinder set up, both ideal for track use but maybe not so perfect for day to day road driving?
all imho
Edited by phillpot on Thursday 11th February 16:41
I went for the Mondeo type which is pressure actuated. Not surprising though since I upgraded the brakes to Griff 500 spec so assumed that as a similar weight and sized car the balance would be OK for my new set up.
I did, however, get a replacement inertia type from a place that Glen suggested to me - Sierras R Us or something similar I think. They had a shed load of them when I rang just a few months ago. Mine was corroded because the car had been standing for 9 years, but otherwise a second hand hand one from this place should be fine - IMHO.
I did, however, get a replacement inertia type from a place that Glen suggested to me - Sierras R Us or something similar I think. They had a shed load of them when I rang just a few months ago. Mine was corroded because the car had been standing for 9 years, but otherwise a second hand hand one from this place should be fine - IMHO.
My thoughts right now have turned to why, & what work TVR did in picking the inertia valve from Sierra, to fit onto the S.
Was it just 'well it was reqd on Sierra', so we'd better fit it to our car !!!!
And if so, what if any effort did they go to in creating their own mounting bracket, to get the angle right for the dynamic bias to kick in. Or again, is it just a standard Sierra bracket. (Anyone created & fitted a variable angle bracket ??)
Apparently on Sierra the valve was mounted at 25o. But on a shorter lighter stiffer car, is that too much of an angle ? And are they fitted in the same relative position on the car, based on front end 'dive' & rear end lift. Then there's all of those S cars that have had brakes, suspension, wheel & tyre changes, which will all have an effect. Maybe enough that in normal public road driving and braking, the valve rarely, if ever comes into play. But don't forget the master cylinder by design gives front/rear brake bias anyway. This is all leading me to wonder if a standard road only going S really needs it !!! As there are many 'like' sized & weight sports cars that don't have such a thing fitted.
And I don't think a preset or adjustable pressure limiter would be any better, or worse, not on the road anyway. Maybe fitting one of those in some respects would even diminish any advantage in fitting rear discs. Or is it needed more, being as the standing bias would have been changed.
Its all getting very subjective....
TerryB
Was it just 'well it was reqd on Sierra', so we'd better fit it to our car !!!!
And if so, what if any effort did they go to in creating their own mounting bracket, to get the angle right for the dynamic bias to kick in. Or again, is it just a standard Sierra bracket. (Anyone created & fitted a variable angle bracket ??)
Apparently on Sierra the valve was mounted at 25o. But on a shorter lighter stiffer car, is that too much of an angle ? And are they fitted in the same relative position on the car, based on front end 'dive' & rear end lift. Then there's all of those S cars that have had brakes, suspension, wheel & tyre changes, which will all have an effect. Maybe enough that in normal public road driving and braking, the valve rarely, if ever comes into play. But don't forget the master cylinder by design gives front/rear brake bias anyway. This is all leading me to wonder if a standard road only going S really needs it !!! As there are many 'like' sized & weight sports cars that don't have such a thing fitted.
And I don't think a preset or adjustable pressure limiter would be any better, or worse, not on the road anyway. Maybe fitting one of those in some respects would even diminish any advantage in fitting rear discs. Or is it needed more, being as the standing bias would have been changed.
Its all getting very subjective....
TerryB
Gassing Station | S Series | Top of Page | What's New | My Stuff