"Deceleration Control Valve"
Discussion
The rear wheels on my 350i (which has a standard brake setup) lock up before the front wheels (don't ask me how I know).
It looks like the Deceleration Control Valve (as the SH Bible describes it) can be set at diferent angles to alter the pressure distribution under heavy/emergency braking, but there's no mention of servicing or adjusting it in the bible. Has anyone ever had a go at their own?
My feeling is that it has siezed inside (my guess its a ball bearing and spring arranegemt) and all the available pressure can be fed to the rear, causing them to lock.
I haven't changed any of the pads or discs since I got the car this Spring as they were all new when I got it. Could it be that there are different compounds front and rear that is causing the problem?
It looks like the Deceleration Control Valve (as the SH Bible describes it) can be set at diferent angles to alter the pressure distribution under heavy/emergency braking, but there's no mention of servicing or adjusting it in the bible. Has anyone ever had a go at their own?
My feeling is that it has siezed inside (my guess its a ball bearing and spring arranegemt) and all the available pressure can be fed to the rear, causing them to lock.
I haven't changed any of the pads or discs since I got the car this Spring as they were all new when I got it. Could it be that there are different compounds front and rear that is causing the problem?
Maybe the front pads/discs are extremely worn, or the front pistons are stuck. It shouldn't be a brakepad compound difference causing it, but i've had old brakepads / discs in the front and new ones in the rear and the same problem with a previous car.
Would make it easy to fix! If you want to be thorough when you replace stuff like that, also get a overhaul kit for the calipers. That way you'll be braking well for ages to come!
Would make it easy to fix! If you want to be thorough when you replace stuff like that, also get a overhaul kit for the calipers. That way you'll be braking well for ages to come!
Sagger Maker, I think this sounds like a more fundamental problem than the control valve after all it’s a ball bearing rolling round in brake fluid so unless its been stood dry for a while I cant see how it would stick, One of my Wedges ( I wont say which one ) had the valve mounted the wrong way round as in east west rather than north south, so it was in fact doing nothing! This never caused locking up and made no difference when I re-mounted it the correct way round. I would agree with Vampire, you may have a front caliper problem, easy to overhaul and that would be my first job.
Just how much rubber did you lay down when you first discovered this problem? And did you leave marks anywhere else?
Just how much rubber did you lay down when you first discovered this problem? And did you leave marks anywhere else?
had the valve mounted the wrong way round as in east west rather than north south,
I wonder if mine has that arrangement, the rear left wheel locks up before the others. It is great for slowing down and pulling in towards the curb at the same time when you belt round the corner and see a tractor coming towards you in the middle of the road (apparently).
I wonder if it will pull to the right if I over brake to avoid someone stepping off a curb? do TVRs have auto obstacle detection brakes...
I wonder if mine has that arrangement, the rear left wheel locks up before the others. It is great for slowing down and pulling in towards the curb at the same time when you belt round the corner and see a tractor coming towards you in the middle of the road (apparently).
I wonder if it will pull to the right if I over brake to avoid someone stepping off a curb? do TVRs have auto obstacle detection brakes...
I thought mine was adjustable because it has elongated holes for the fingers that engage in the plate. When I looked closely the fingers were actually positioned in opposite corners of the rectangular holes so there was no room for adjustment. Curious!
It's easy enough to make a new plate if you want to adjust it's position; but I'd start by reconditioning all the calipers and replacing the pads/discs if necessary.
It's easy enough to make a new plate if you want to adjust it's position; but I'd start by reconditioning all the calipers and replacing the pads/discs if necessary.
Also had this issue, I fitted an adjustable brake bias valve in place of the original 'G' valve to allow balance to be restored. http://www.ebay.co.uk/itm/BRAKE-BIAS-VALVE-NOVA-CO... . You'll also need these; http://www.ebay.co.uk/itm/320672050503?ssPageName=...
Thanks very much for the help and comments...
Yes, it was a hairy moment when I discovered the rears were locking up first...spun it into an island in the damp and nearly got hit head on by a following Merc who didn't expect to encounter a TVR braking while going backwards. Lucky it was a big island with room to come to a stop before I hit anything hard. Phew...
The brake limiting valve on mine runs 'north-south', which is a start I suppose. However, it is pointing up at the maximum angle possible on the bracket. I will try is adjusting it down as far as it will go first to see what happens. At least the slots have been cut correctly to allow adjustment.
Thanks for the eBay links Simon. I'll save them in case if I end up needing them.
I'm not using the car until the weather gets better and the salt has gone, so it'll be a while before I can have a mess.
A few other jobs to do first, including fixing (or replacing) a leaking rad and sorting out a screeeeeching cooling fan. It's like fingernails down a blackboard!
Yes, it was a hairy moment when I discovered the rears were locking up first...spun it into an island in the damp and nearly got hit head on by a following Merc who didn't expect to encounter a TVR braking while going backwards. Lucky it was a big island with room to come to a stop before I hit anything hard. Phew...
The brake limiting valve on mine runs 'north-south', which is a start I suppose. However, it is pointing up at the maximum angle possible on the bracket. I will try is adjusting it down as far as it will go first to see what happens. At least the slots have been cut correctly to allow adjustment.
Thanks for the eBay links Simon. I'll save them in case if I end up needing them.
I'm not using the car until the weather gets better and the salt has gone, so it'll be a while before I can have a mess.
A few other jobs to do first, including fixing (or replacing) a leaking rad and sorting out a screeeeeching cooling fan. It's like fingernails down a blackboard!
My 280 rear brakes locked up at 70mph on a damp motorway a while back and the back skipped out quite a bit and i really struggled getting it straight again..Very scary..This has happened since i had a front brake upgrade..(Princess calipers)..Now im wondering would i need something like the balancing valve mentioned?..Cheers..Ziga
mrzigazaga said:
My 280 rear brakes locked up at 70mph on a damp motorway a while back and the back skipped out quite a bit and i really struggled getting it straight again..Very scary..This has happened since i had a front brake upgrade..(Princess calipers)..Now im wondering would i need something like the balancing valve mentioned?..Cheers..Ziga
Brake balance valve should have been fitted as standard Zig. Usually mounted just in front of the clutch master cyl., trace the rear brake feed down from the brake master and you should find a lump of iron mounted on a bracket 
Wedg1e said:
Brake balance valve should have been fitted as standard Zig. Usually mounted just in front of the clutch master cyl., trace the rear brake feed down from the brake master and you should find a lump of iron mounted on a bracket
That's true but my view is that the brake balance as standard isn't right and the existing valve isn't properly adjustable so there's nothing you can do about it without changing to an adjustable one.
or even knew where it was 
maybe its under a tree in Essex 
Wedg1e said:
Brake balance valve should have been fitted as standard Zig. Usually mounted just in front of the clutch master cyl., trace the rear brake feed down from the brake master and you should find a lump of iron mounted on a bracket
Thanks mate..I will have to have a look as i have a cable clutch so no clutch master im affraid..I think i recollect something like a lump of iron near the servo..Although thats probably the engine..
Zig, don't listen to these V8 nuts.... 
On my series 1 280, its mounted on a bracket above the chassis rail on the drivers side, a little in front of the master cylinder. It's pretty obvious, you can see the brake pipes in and out.
Unlike the V8s, it's NOT covered by anything...
I think it's actually from a Ford Granada mk2 ?
On my series 1 280, its mounted on a bracket above the chassis rail on the drivers side, a little in front of the master cylinder. It's pretty obvious, you can see the brake pipes in and out.
Unlike the V8s, it's NOT covered by anything...
I think it's actually from a Ford Granada mk2 ?
Edited by RCK974X on Friday 23 December 19:15
RCK974X said:
Zig, don't listen to these V8 nuts....
On my series 1 280, its mounted on a bracket above the chassis rail on the drivers side, a little in front of the master cylinder. It's pretty obvious, you can see the brake pipes in and out.
Unlike the V8s, it's NOT covered by anything...
I think it's actually from a Ford Granada mk2 ?
Cheers mate..I will have a look..ZigaOn my series 1 280, its mounted on a bracket above the chassis rail on the drivers side, a little in front of the master cylinder. It's pretty obvious, you can see the brake pipes in and out.
Unlike the V8s, it's NOT covered by anything...
I think it's actually from a Ford Granada mk2 ?
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