Brake Proportioning Valve with OEM ABS (issue)

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01-04-24, 03:26 PM

#26

SETaylor

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Quote:

Originally Posted by TwinCharged RX7

This might not be exactly the same, but I believe it's the same in concept. I've been doing a lot of research on the MK60 system. For several actual racers (including some really nice C5 vette race cars by privateers), they use the a proportioning valve if a race car. Less relevant on a street car. They use it because for things like trail braking, dialing in the bias is helpful, because the ABS is not engaging. But when standing on the brakes hard in a braking zone, the ABS does its own pressure adjustment to obtain the fastest possible deceleration and essentially makes it seem like the proportioning valve doesn't exist.

TwinCharged (and others), you may find some value in this recorded presentation regarding braking systems, specifically the topic of ABS strategies (preemptive, which you would see on a road car v. reactive, which is what you are likely to encounter in a race vehicle), among other facets that should be taken into consideration. Start at around the 19:45 mark for the section on ABS braking events. While modern ABS systems are far more complex than what we are familiar with in our cars, the fundamentals are similar. The Brake handbook by Fred Puhn also has a section on the function(s) of proportioning valves that you may find useful. It can be found in PDF format through various resources on the web.

Last edited by SETaylor; 01-04-24 at 03:28 PM.

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01-14-24, 11:54 PM

#27

chrismore

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Update! It's fixed

The system is working and bias is adjusting fine. It was a bad bias valve. I had everything connected correctly to start.

Replaced the valve, bed the system, and pedal feels great. Haltech data confims the front to rear brake pressure ratio changes as I turn the ****. Once Texas thaws out, I'll be getting real data from threshold braking.

I spent 30 minutes on the phone with Chase Bays and went over all possible scenarios. All we could come up with is a bad bias valve. They sent me a new one and we're good now.

Once I get data, I'll update again.

Thanks all.

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02-06-24, 10:17 PM

#28

Billj747

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Quote:

Originally Posted by TeamRX8

first, I would also never recommend flex hoses between the MC and ABS module for braking, especially for autox. That’s guaranteed to kill feel and response. Even though they’re new; hard, yet easy to plumb, cunifer lines are preferred.

edit: this was before I realized it’s suppose to be a manual non-ABS system. Flex hoses may be ok for manual brakes. My comment above applies to a pulsing ABS system.

Braided lines between the master cylinders and ABS module is perfectly acceptable, does not affect pedal feel, and is used on almost every modern GT4 and GT3, race car.

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02-06-24, 10:23 PM

#29

chrismore

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Data

I data logged with Haltech the front and rear brake pressure. Data looks great and I pedal feel is amazing. As a test, I can also lock up the rears before the front of I'm running 50/50 bias.

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