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Brake Bias


Tony J

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Hi, a brake bias question!

I have recently bought a 1990 SEi wide with rear discs.  My first (deliberate!) attempt at an emergency stop in the damp resulted in the rear end locking up before the front :0 .  The car had been standing for quite a while before I got it so the front calipers may be a bit sticky although it does stop in a straight line.   The master cylinder is twin outlet, do I need a bias valve to reduce the pressure to the rear end?  I have heard talk of reducing the rear braking efficiency by using harder pads.

any suggestions?

Cheers

Tony Jeffery

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They all do that sir.......

Harder pads at the rear, or grippier pads at the front (or both). Improving the fronts worked for me with no other mods, although I have 4 pot calipers on the front of my car.

There has been much talk on other BB's that the extra heat generated in the rear brakes can contribute significantly to their eagerness to lock up. The rears are poorly cooled compared to the front, so it is reasonable to assume that heat build up is slower to dissipate, leading to them running at a more optimal temperature. It sounds plausible, but I am yet to see any empirical data.

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I have an 1800 zetec beastie and also get lock ups on the rear under severe braking of the brown trouser variety.

I spoke to Westfield about this and they suggested what Blatman mentioned. Also suggested I buy their four pot calipers and disc set for the front (funny that !)

They had another reason for the lock-up which was that the front running gear is basically from a Ford Cortina and the rear from a Sierra. The age gap in technology results in better rear brake action thus the lock ups and random sideways action.

However, this may be a load of old tosh, just passing it on

Stu

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Thanks Dave, that looks quite simple to do. Did you use a valve off an old mini or did you buy a new one? For something as important as braking, I am tempted to get a new one.

Stu  :)

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My car actually failed SVA on this.  Since it was a modular kit I insisted that Westfield sort it out and their solution was a mini compensator mounted where the t-piece to the rear brakes was.  They told me that they would probably make this standard fitment at the time but they haven't done so (AFAIK).

Not adjustable but, as far as I can tell, all 4 wheels lock up at the same time.  Only one track day so far but the brakes seemed to behave themselves.  Do have a problem with the pressure switch not bringing on my brake lights under light pressure though  :(  (but I don't think that this is linked to the compensator)

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Having too much rear brake is potentially very dangerous, as you and other contributors to this thread are testifying. Rears locking before fronts can cause your car to try to swap ends. Because it was damp when you tested them, your brake balance wasn't actually at it's most dangerous although I guess it would be "more interesting" trying to stop the car from rotating in these conditions. A damp or wet surface will actually lead to the fronts locking earlier and the rears locking later as there is less weight transfer to the front in lower grip conditions, so the fronts contribute less and the rears contribute more. So if the rears lock when it's wet they are going to lock even earlier when it's dry. You want, as I am sure you know, the fronts to lock just before the rears on a top grippy surface. Get a friend to watch you brake to assist adjustment.

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After reading all this, I am really tempted to put some four pot calipers on the front wheels. Apart from the Westfield type, what others will do for a 1800 zetec westie with ford runnign gear? Also, how do I put a wife-friendly spin on this? Should I go for "...because the car will be safer in an emergency" or "......because it will outbrake other westies on track days"

Stu

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I run Princess 4 pots, which, whilst cheap, are VERY heavy compared to "modern" 4 pots. Have a look at the Willwood Dynalites at Rally Design's web site.

I had to fit a larger bore master cylinder to get the pedal to feel the way I wanted it to. You may find that 4 pots on the standard Westfield master cylinder lead to too much travel at the pedal. I have a c******m AP Racing master cylinder, which is a direct swap, and is absolutely perfect for the job. I believe a similar master cylinder is used on the factory Megabusa racers.

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Stuey,

I used one from a Mini in the breakers, the latest valves are a different design and cant be used in the same way.

FWIW I use the Wilwood Dynalites and they are excellent, but be aware that they have no dust shields around the pistons which can lead to premature corrosion of the pistons.

Dave

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[pedantic]"......because it will outbrake other westies on track days"

[/pedantic]

I think you'll find that track day organisers might frown on the idea of people outbreaking each other into corners.... ;)

And as far as wives are concerned always go for the safety aspect !!

I'm going to be upgrading my brakes to the Wilwood Dynalites and, as Blatman has pointed out, Rally Design do a number of kits specifically to fit Westfields.

However, for ease of fitment, the Bremsport calipers sold by Westfield are a simple bolt on job.  BUT Cat Motorsport do the same calipers for significantly less money so check out their site at :

Cat Motorsport

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:devil:

Hi.  i have a sppedsport which had similar stoopping problems.  I followed dave Andrews solution.  Brought a mini bias valve, drilled & tapped it, mounted in place of the T-piece at the rear.  It was fun setting it up on a round-about.  

It works. I've had no problems since - roads or track days

|Pete

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For 4 pot brakes try

www.hispecbigbrakes.co.uk

Currently, I'm using Princess 4 pots with green stuff pads and their braking is superb BUT they weigh 14 lbs each.(6.5 kg) without pads.

I've therefore just taken delivery of some of Hi Specs billet 4 calipers c/w EBC green stuff pads, fitting brackets and brake unions for £325 INCLUDING VAT and carriage. These weigh 2.3 kg each INCLUDING pads and brackets. They look good and fit under 13" wheels

I believe Cat motorsport do some Bremsports as do TAS (Trans Auto Sport) in Leyland which do not require brackets ie fit straight on. These are probably the ones that the factory sell with a different name on.

John

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TAS make / market Bremsport and Cat Motorsport and Westfield sell them - they are all the same caliper and are basically a direct replacement for the Ford M16 Caliper.

Cat Motorsport are, I believe, the only ones who include pads in their quoted prices.  

They are also in the process of developing their own calipers which include dust seals, thereby making them a bit more road resiliant.  Might be an idea to hold off your purchase for a little while and see what comes of that particular project.

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Bremsport from Cat with pads = £395

Bremsport from TAS without pads = £264

Expensive pads !!

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