Deceleration Valve

[Guest Billfish]

Excuse my ignorance, but what does the deceleration valve do? I have the one that came of the sierra, will this do? does it need to be fitted in a certain way? I know it fits on the rear brake line, but location/orientation are a mystery.

 

Thanks

 

Bill

[Guest Paul Morgan]

Hi Bill,

 

The deceleration valve stops the back wheels locking up before the front under hard breaking. The one out of the Sierra has to be fitted at the correct angle for it to work properly. Some cars have passed SVA without a proportioning valve fitted but most don't.

 

I fitted one from a Ford Fiesta as it just screws between the master cylinder and the rear brake pipe and only cost me £1 from my local scrappy.

 

Paul

[Steve Walker]

Hi Bill,

 

The deceleration valve stops the back wheels locking up before the front under hard breaking. The one out of the Sierra has to be fitted at the correct angle for it to work properly. Some cars have passed SVA without a proportioning valve fitted but most don't.

 

I fitted one from a Ford Fiesta as it just screws between the master cylinder and the rear brake pipe and only cost me £1 from my local scrappy.

 

Paul

 

I can't see why the valve would have any effect on SVA/IVA. The valve limits the rear brake pressure, by the movement of a ball under the effects of deceleration (hence the angle of installation being important), but during SVA/IVA brake testing, the vehicle is static on rollers and the ball willl not move or does someone know something that I don't here?

 

SteveW

[Longboarder]

SVA has a provision to do a driven test of the deceleration valve when one is fitted in addition to the roller brake tests. Thus with the decel valve inactive on the rollers the figures may indicate premature rear lock-up and a fail but the tester can then progress to a driven test to check if the deceleration valve stops the rear lock-up and if so can give a pass.

I can't find any mention of this in the IVA regs but if it isn't there now it will probably be added.

 

Bill if you have rear drums there is a very good chance your brake balance will be fine without the valve. If you have discs all round then some sort of automatic/dynamic adjuster is needed but it must not be mechanically adjustable except for the initial setting up.

 

Nigel

[Guest mower man]

Hi re brake limiting valve ,23000 miles with out one but as previous comment only drums on rear but HI SPEC 4 pot+270 mm vent disc at the front ,normal road pads +std sierra est rear linings .It works for me ,others may differ HTH mowerman

[Guest robert elms]

Hi

 

Mine failed on the rear wheels locking up before the front, so looking at the posts i need this deceleration valve, could anyone post a pic of this as i dont know what they look like and am i right in thinking it just gets cut in to the rear brake line anywhere before it t's of????

 

Rob

[Guest combatsapph]

I have a spare valve in the garage - I'll get you a pic tonight.

 

Didn't need it on my Westy so it's surplus to requirements.

[ibrooks]

My 2B failed it's first test on "Too much rear braking effort". I pointed out that it had the Sierra deceleration valve fitted and that I thought he should have driven it as it would never do anything on the rollers but he said no. Since the failure list was so small I just took it on the chin and decided not to wind him up by beating him over the head with the rulebook. I ended up with the pressure limiting valve from a Rover Metro instead which did the trick. It had the donor brakes complete so 240mm vented discs up front and whatever drums '87 1.6 Sierras got at the rear.

 

The Sierra valve is mounted pointing "North-South" in the car and with the front end pointing slightly upwards. As people have mentioned the control is given by a ball moving forwards as the car decelerates. Obviously the degree to which the valve points upwards has an affect on the movement of the ball and therefore the characteristics of the valve. To an extent this means we can change it's performance by altering it's angle to the horizontal which allows us to account for the difference in weight in a lighter car (point it vertically upwards and it'll do nothing but point it horizontally and it'll work almost all the time). There is a spring in front of the ball so in theory the range of adjustment between "on all the time" and "off all the time" is from slightly downwards pointing to almost vertical with everything between giving a varying degree of effect to varying degrees of deceleration.

 

This is one of the worries I've got with the SPD200 as I can't fit the Sierra master cylinder in so I've got to go with twin masters and a balance bar of some sort on the pedal. I've modified the Sierra pedal box to do the job and work the masters but has anyone seen a clever way of setting brake balance within the IVA regs? Unfortunately it's a different wheelbase and weight to a Hood so I'm likely to need somewhat different requirements to most people here. I'm also interested in good ways of actually measuring the brake performance before the test as I'd like to be able to do my tweaking before the test as I'm less willing to go into a test costing as much as IVA with a view that it might fail but at least I'll get a list of what I still need to do.

 

Iain

[Guest robert elms]

There have been lots of people that did'nt need the deceleration valve put in and im wondering if mine failed due to the fact that i have the old sierra pads on the front and new drums on the rear.??? Would this make a differance to braking seeing as they've only had about 3 miles worth of bedding in???

[Guest Paul Morgan]

Tried to post a link to previous thread but it wouldn't work.

 

Click on the search at the top of your screen and type Deceleration.

 

11th thread down 'Brake Bias Valve Fitting', there is a picture of my Fiesta one in that thread.

 

Paul

[Guest woolly]

its a very long time since i used the roller brake tester. and i can't see how the tester can say that the rear brakes are too efficient compared to the fronts, when only using a single axle rollers.

unless he is measuring peddle effort ?.

i would expect in the rollers that the fronts give a poor reading and the rears a good due to the weight distribution at the time of testing.

 

do testing stations still have to keep the G floor meter that would be a fare way to try it out.

 

i don't have a valve fitted and if any thing its bias to the fronts (sierra vented discs & servo) also tried it with out the servo.

 

woolly

[ibrooks]

The brake test at SVA involved an aparatus where the tester wears a piston on his foot which is connected to a pressure gauge in his hand so they are looking at both braking effort and pedal effort. I assume IVA is going to be similar in this respect - reading the current manual it sounds like it.

 

I also appear to have a get-out clause as it states that they mustn't test it on the rolloer if more than one axle is permanently driven and since mine is using the Sierra four wheel drive system they are.

 

Anyone got a Tapley meter I can borrow when the time comes.

 

Iain

[Guest woolly]

thanks for the explanation and reminding me what the meter was called.

 

woolly