Bracket Talk
4 wheel disc brake proportioning

This topic can be found at:
http://drr.infopop.cc/eve/forums/a/tpc/f/80760912/m/7037039296

March 23, 2020, 11:01 AM
HS professor
4 wheel disc brake proportioning
Wrapping up the brake lines on my new build and before I add fluid was just wondering what everyone was doing for proportioning front to back ?? On our Firebird we have nothing just a 1-1/16" master and 3/16" line front and rear and the brakes are excellent, but can lock the front's under overly aggressive braking. I was wondering if a proportioning valve in the front would help and if anyone uses any different set-ups ???



Thanks !!!
March 23, 2020, 05:21 PM
maliciousintent
Im in the same boat on my S10 build. Need answers.
March 24, 2020, 09:38 AM
HS professor
From Mark Williams site ………

Thanks Roy !!!!



Proportioning (Pressure Reducing) Valve

The front brake kits with the integral hub and adaptor are designed for Drag Race applications. The main advantage is the reduction of weight compared to the stock braking system they are designed to replace. Several considerations must be taken into account when installing these kits. When any four piston caliper is used with drum brakes on the rear, a pressure reducing valve must be installed for front pressure control. Because of the small front tire contact area compared to the rear large slick contact area, the rear brakes must absorb more of the stopping energy than the front (contrary to a normal street car). A starting point would be 70% of the rear line pressure to the front brakes. This is especially important when using drum brakes on the rear. With discs on both the front and rear the percentage could be higher depending on the weight distribution and tire size but should still use the pressure reducing valve. We have a pressure reducing valve, P/N 260-8419, and we recommend its installation with front brakes. The pressure bias should be adjusted with gauges, MW P/N 81105, in the front and rear to confirm the pressure differential and then do a stop test. When doing a stop test, for a drag race car, the front tires should skid equally or slightly after the rear tires. This test can be simulated at a very low speed (approximately 5 mph) by using a wet surface or gravel and observing the lock up sequence.
March 24, 2020, 02:33 PM
RacerVX54
Been running for years with out one on a 4 disk setup


"Just Shut Up and Race"

Brian Martin
Martin Racing
5.66 @121.55
March 24, 2020, 08:08 PM
DaleH
I respectfully disagree with the statement the rears should skid just before the front.

Any time the rear tires are skidding you are going to loose control almost instantly. If the fronts slide you most likely will recover if you react fairly quickly.

With the videos now available at most notable bracket races, look for any of the crashes at the finish line. The rear brakes are locked when they crash. Fronts typically only see smoke.

Ever throw on the e-brake when you were a kid? Quick way to spin out at any speed.

I know this was Mark Williams advice, I am just speaking from my own experiences.

Look forward to other opinions.


Dale
March 24, 2020, 09:24 PM
more cubes
quote:
Originally posted by DaleH:
I respectfully disagree with the statement the rears should skid just before the front.

Any time the rear tires are skidding you are going to loose control almost instantly. If the fronts slide you most likely will recover if you react fairly quickly.

With the videos now available at most notable bracket races, look for any of the crashes at the finish line. The rear brakes are locked when they crash. Fronts typically only see smoke.

Ever throw on the e-brake when you were a kid? Quick way to spin out at any speed.

I know this was Mark Williams advice, I am just speaking from my own experiences.

Look forward to other opinions.


Dale


I have the same take on this as well. You do not want the rears to lock first. IMO, if the fronts are trying to stop most of the weight of the car once the rear tires lock up, the rear end will try to push/pass the front end.
March 24, 2020, 09:27 PM
HS professor
I certainly don't want the rears locking up first Eek

I think the way it's worded on Mark Williams site requires a little common sense, wet surface or gravel lol
March 26, 2020, 10:33 AM
maliciousintent
Locking the rears first, if only for a split second prior to fronts, will lead to a disaster. Flipped a S/G Vega many years ago. Was not pretty or cheap.