Deceleration valve?!?

[ed_crouch]

From reading Steve Heath's book, it seems that my car (as are all wedges??) is fitted with something called a deceleration valve, which prevents the rear wheels locking up before the fronts to stop spins under heavy braking.

Thing is, I have brought the car to a quick halt a couple of times, and I felt a mild kick through the brake pedal, not dissimilar to a single ABS chirp.

Does anyone else get this, or perhaps my decel valve is seizing up?!?

Also, does anyone know the donor car for this valve? I guess maybe its SD1 or TR7 or Granada...

Ta.

Ed.
P.S. Also, is the valve anything special (like does it sense how hard the car is decelerating with a spring-and-mass araangement controlling the valve or this like?), or is it just a boggo standard proportioning valve??

Edited by ed_crouch on Saturday 15th September 19:16

[combine]

Ed, what does this valve look like , any pics ?

[ed_crouch]

Found out about it! It IS an inertial sensing deceleration valve.

Afraid I dont have any pics at moment, but it is a grubby little block of metal that sits under and slightly in front of the master cylinder, with 1 union in and 1 union out.

I had a look in Hillier's, and found out about it, plus theres loads of patents on freepatentsonline. Basically it has a ball inside that rolls uphill inside a bore when the car is slowing down quickly.

The ball rolls until it seals off a port to the rear brakes (which is actually a drilling through the stepped bore piston Im about to mention). When this happens, it causes pressure to the rear brakes to be reduced by actuating the rear brakes through a stepped-bore piston arrangement, thus reducing rear braking pressure to prevent a lockup at the rear. Its last trick is to have a hefty preload spring on the piston, so the pedal pressure has to be rasied by a significant amount to unseat the piston in the first place.

When braking lightly, the ball sits at the bottom of the bore (out of the way), and the drilling through the piston allows brake fuild to flow to the rear brakes as normal.

Damn clever stuff.

Also, I think my clonk might be something to do with the fact that my battery has no strap and shifts forwards under heavy braking...

Oops!

Still, learned something new...

Ed.

[TVRleigh(BBWR)]

wow never knew the wedge had somthing so complicated

[combine]

So its a sort of early ABS system , sounds rather useful for a wedge , how come you have one and we all don't ! Or some of us don't know ? How do we get one and how much is it ?

[jmorgan]

I got one of them, that's where it sits. No idea if it works though.

[Wedg1e]

combine said:

So its a sort of early ABS system , sounds rather useful for a wedge , how come you have one and we all don't ! Or some of us don't know ? How do we get one and how much is it ?

Hmm, not exactly, it just serves to shut off fluid to the rear brakes so you don't lock the back wheels all the time. I had a '72 Simca with something similar except it was linked to the back axle so that as the bodyshell nose-dived and lifted on the rear springs, the axle pulled a lever that turned off the fluid. I suspect most cars have something similar these days...

[GreenV8S]

Every modern car will have one. What they do is compensate for the weight transfer under braking. If you didn't have one then your car would either understeer like mad under braking in the rain, or oversteer under heavy braking in the dry.

[jmorgan]

GreenV8S said:

Every modern car will have one. What they do is compensate for the weight transfer under braking. If you didn't have one then your car would either understeer like mad under braking in the rain, or oversteer under heavy braking in the dry.

Mine works then.