Deceleration Brake Bias Valve

[Guest boggie]

Hi chaps,

 

Anyone have a picture of the Sierra deceleration valve in situ or know which way around it should be fitted? After fitting a 3.9LSD complete with rear discs I need to reduce the braking force to the rear as the car now has exactly the same front and rear. Not a good combination in the wet! I was going to fit a manually operated brake bias valve but the Sierra deceleration unit sounds a better plan. I have managed to get one but need to know which way to fit it.

 

Thanks.

[Guest superspec]

Nice Toys !!

[Les Welsher]

here's one

 

in at the fat end and out at the thin end

 

Les

[agent_zed]

just to add if you didnt know already the more you tip it forward the sooner it will work so you may need to adjust it a bit compared to the sierra. Its basically a large ballbearing that is thrown forward to block off the fluid.

 

The guy at the SVA test said he was glad to see mine in the correct orientation as he'd seen people put them in crazy positions including horizontally across the back axle!!! full breaking when turning hard one way and none the other?!

 

hth

[Guest boggie]

Thanks Guys,

 

I still can't make my mind up after trawling the forum and reading your replies. Currently I have no reducing valve. I have had no incidents but since the fitmant of the rear disc subframe I have exactly the same braking force on each wheel. It is only a matter of time before it goes ar$e about t1t.

 

In the garage I have a competition manual brake bias valve, a later type Sierra inertia valve and I managed to get hold of a brand new Fiesta master cylinder complete with the inline type valve. Which should I use? The Fiesta would be the simplest to fit but I have a flaring tool and some spare copper pipe so with a little time I can fit either of the other two. I suspect the Sierra will be difficult to set up and the manual valve will be a tinkering pain. Any thoughts?

 

Cheers.

[geoff shep]

I guess the separate deceleration valve would give the most flexibility but it would take a lot of trial and error. I am not familiar with the Fiesta setup but presumably the master cylinder has to be at a standard angle so the valve is set at the same fixed angle. The 'donor' cars have softer suspension and engines further forward so I assume that the setup would be different. There was a lot of talk about this back in the 90's - unfortunately one of the demo cars had the valve fitted transversely!

 

Have you done any hard braking tests to see which wheels lock up? I have removed the valve from mine as the fronts lock up first anyway (but I've still got drums at the back)

 

You presumably haven't got a Haynes Sierra manual?

 

Les: maybe being dull but I can't quite work out where we are looking - which way is you valve facing?

[Les Welsher]

Les: maybe being dull but I can't quite work out where we are looking - which way is you valve facing

 

the valve is near the passenger footwell with the small end facing towards the front of the car at about 20 degrees pointing up, a bit less of an angle than in the sierra as the front of the car doesn't nose dive when you jam on the brakes like the sierra does.

 

Les

[Dave R]

if you want one, i have an adjustable valve that i had got on mine, then decided i didnt need it (drums on the back)

[Guest Dan_Beeston]

I always used to have mine mounted through the cente of the bracket, so I could just loosen the bolt then rotate the valve a bit to adjust it...

 

It's not been fitted since I changed the pedal box for a bias adjustable setup, but I'm going to put it back on as I can still lock the rears first with either the standard Sierra fronts or Willwood 4pots.

 

The harder you stop the more weight is transferred to the front wheels (reducing the load on the back), if you've got decent front end grip you can get really goor weight transfer and eventually it becomes very easy to lock the rears. This has always been the problem with fixed bias brakes and why the deceleration sensitive valve was invented in the first place

[Guest boggie]

Thanks again guys. I am not sure how the Fiesta units work. I dont think they are inertia due to the orientation of mounting on the master cylinder, see HERE

 

My guess is that it is a pressure reactive valve. IE you step on the pedal lightly and not much happens but jump on the pedal and the rear feed is reduced. I am encouraged by Paul M and his conversation with the SVA inspector on THIS thread. As the Fiesta valve is the easiest way to go and would not involve any additional pipework (just fit it and bleed the rear system) I might try that option first. Once it is fitted I will pop back to the MOT station and get him to run it on the rollers and see the result.

 

If it works as Paul's SVA guy says then great! and I will be able to sell the rather overkill (and expensive) manual bias valve too. If not I might try the Sierra deceleration valve next.

 

Watch this space!

[geoff shep]

You may be right about the Fiesta setup. I was going to add above, that with the Sierra valve, or any inertia-based device, you will not see any effect on a standard MOT-type brake test or rolling road as the car has to be moving.