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Brake bias question


thewheelerZ
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Does a brake bias valve work when you have two hard lines going to rear brakes?

 

i can't seem to get my abs working and want to find a more consistent way to get front to rear bias other than pad selection. If there are two hard lines would I need two valves? i cant imagine as that would be a disaster trying to calibrate it all up. 

 

Any help would be appreciated. 

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3 minutes ago, thewheelerZ said:

Does a brake bias valve work when you have two hard lines going to rear brakes?

 

i can't seem to get my abs working and want to find a more consistent way to get front to rear bias other than pad selection. If there are two hard lines would I need two valves? i cant imagine as that would be a disaster trying to calibrate it all up. 

 

Any help would be appreciated. 

Use a "T" to merge the rear lines, put in your prop valve, then use another "T" to split them off to each wheel.

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9 hours ago, enginerd said:

Use a "T" to merge the rear lines, put in your prop valve, then use another "T" to split them off to each wheel.

 

What wpuld happen with abs if I did this? Would front still work? Would rear work but with limited effect because both lines are sharing one modulation from the abs module?

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1 hour ago, thewheelerZ said:

 

What wpuld happen with abs if I did this? Would front still work? Would rear work but with limited effect because both lines are sharing one modulation from the abs module?

I think you are correct. Front should be unchanged, the rear may behave goofy because a locking rear would cause one of the rear channels to pulse, but both rears  would feel it, and both rears would also feel the pressure from the unpulsed channel. 
 

It may resemble e30 brakes. The e30 ABS has a single line going rear and speed sensors on each axle. If one rear locks, both rears get the ABS modulation. 

Edited by enginerd
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1 hour ago, thewheelerZ said:

 

What wpuld happen with abs if I did this? Would front still work? Would rear work but with limited effect because both lines are sharing one modulation from the abs module?

If you bypass the rear altogether, the front should still work with no abs on the rear but you can adjust the overall brake bias.

 

You can add then mechanical load valves from an R12 to both rears that you can fine-tune for a crude rear ABS if you like. Just a thought.

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Be careful. I covered some of this in the tech videos Champcar released. 

 

Is your car front\rear split or a diagonal braking car? Lots of FWD cars are diagonal circuit (one master port does LF, RR). 

 

If you tie both rears together on a diagonal car you have created a single circuit brake system (from a dual). Any leak will result in a total loss of system pressure, vs a split system where at least one circuit can make some pressure. 

 

This is assuming one circuit could even slow the car enough to soften the wreck. I have finished a race on one circuit, but had it been somewhere else on track the car would have been much shorter. 

 

You will find bias adjusters have a fixed bias adjustment, and you are just changing the point at which the lower bias is activated. If you are really out to lunch you will need to resize brake caliper bore on one end or the other (also covered in the braking videos).

 

 

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Looking through alldata there is a difference between abs and abs with tcs, but no matter, they do not specifically say diagonal split or not but I suspect it may be as the bleeding order is : RR-LF-LR-RF

 

For reasons explained above, please do not connect the rears together ESPECIALLY if ABS is still a option, it gets scary quick when the ABS attenuates the wrong wheel.

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  • 3 weeks later...

Without seeing the hydraulic system layout I can't know for sure, but your best bet is likely splicing the adjustable biasing valve before the ABS module, but then again, many abs module have an internal automatic brake balancing systems. I would be sure to do my homework on this.

 

Another option for you might just be ap racing's twin-bore proportioning valve. I think this valve allows for two independant systems to be metered simultaniously.

https://apracing.com/race-car/actuation-products/proportioning-valves/lever-type-prop-valves/twin-bore-cp4550-1

 

Aside from being incredibly unsafe, tying the two rears together would eliminate the benefits of having a 4-channel abs system.

Edited by EngEtan
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  • 3 weeks later...
On 2/3/2020 at 5:17 PM, EngEtan said:

Another option for you might just be ap racing's twin-bore proportioning valve. I think this valve allows for two independant systems to be metered simultaniously.

https://apracing.com/race-car/actuation-products/proportioning-valves/lever-type-prop-valves/twin-bore-cp4550-1

 

I looked at the latest BCCR and can't tell if the above would be points, no points, or not allowed.  Does anyone have any insight to share?

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20 hours ago, Racer28173 said:

I looked at the latest BCCR and can't tell if the above would be points, no points, or not allowed.  Does anyone have any insight to share?

 

13 hours ago, TimS said:

I don't know exact line in the rulebook or maybe in new tech knowledge base, but brake master cylinders, pedal assemblies, and bias valves are allowed and no additional points.

I asked this in the knowledge base since, like flywheels it's one of those thing that everyone is doing already with out an official ruling.
Yes, prop valves and aftermarket master cylinders are allowed for 0pts.
https://champcar.org/tech/knowledgebase.php?article=30
https://champcar.org/tech/knowledgebase.php?article=29

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