MAster cylinder & prop valve help

[355_79bu]

Here is a copy of the e-mails I sent to both MP Brakes and Wilwood Engineering:

My question:
I have a 1979 Chevy Malibu that I am installing rear disc brakes on. Currently the car has the stock disc/drum combo valve (prop. valve) in place. I know I need different bias front to rear with the rear discs. I plan to remove the stock combo valve and install one of your adj. prop. valves in the rear brake circuit to achieve the proper bias front to rear. Then I will run the front brakes straight off the front port of the master, to a T fitting, and off the T fitting to the front calipers.



Now, removing the stock combo valve is raising some concern for me safety wise. I know the stock combo valve has a metering valve and a warning light switch built in along with residual valve for the rear drums. I know I don't need the residual valve for the rear discs, but do I need the metering valve? Also, if a leak was to develop in one circuit of the brake system (front or rear), would I still have the safety feature of fluid being transferred to the circuit without the leak still allowing me to stop safely? I assume this feature is controlled by the master cylinder and not the combo valve correct? Are there any other concerns with doing away with the stock combo valve?

MP Brakes Response:
An adjustable prop valve for your rear disc brakes is adequate. If there is a failure in your system, you will still have half of your brake system (because of the dual master cylinder). This will enable you to get home and/or get your car to a repair shop without total system failure. The warning light exists because the average driver has no clue (not their fault) that there’s a problem with their brake system. Based on your questions, you have a clue


Thanks for contacting Master Power Brakes.

Randy

Tech Support

888.351.8781 x206

http://www.mpbrakes.com

Wilwood Engineering's response:
Thank you for using Wilwood products.

Stock combination valves serve many purposes, but transferring fluid from one set to another during a fluid loss condition is not one of it's duties. There is no safety concern about removing the stock valve. A tandem outlet master cylinder will provide the safety feature of being able to stop if one of the hydraulic systems is compromised.

035

 

[LS6 Tommy]

Here is a copy of the e-mails I sent to both MP Brakes and Wilwood Engineering:

My question:
I have a 1979 Chevy Malibu that I am installing rear disc brakes on. Currently the car has the stock disc/drum combo valve (prop. valve) in place. I know I need different bias front to rear with the rear discs. I plan to remove the stock combo valve and install one of your adj. prop. valves in the rear brake circuit to achieve the proper bias front to rear. Then I will run the front brakes straight off the front port of the master, to a T fitting, and off the T fitting to the front calipers.



Now, removing the stock combo valve is raising some concern for me safety wise. I know the stock combo valve has a metering valve and a warning light switch built in along with residual valve for the rear drums. I know I don't need the residual valve for the rear discs, but do I need the metering valve? Also, if a leak was to develop in one circuit of the brake system (front or rear), would I still have the safety feature of fluid being transferred to the circuit without the leak still allowing me to stop safely? I assume this feature is controlled by the master cylinder and not the combo valve correct? Are there any other concerns with doing away with the stock combo valve?

MP Brakes Response:
An adjustable prop valve for your rear disc brakes is adequate. If there is a failure in your system, you will still have half of your brake system (because of the dual master cylinder). This will enable you to get home and/or get your car to a repair shop without total system failure. The warning light exists because the average driver has no clue (not their fault) that there’s a problem with their brake system. Based on your questions, you have a clue


Thanks for contacting Master Power Brakes.

Randy

Tech Support

888.351.8781 x206

http://www.mpbrakes.com

Wilwood Engineering's response:
Thank you for using Wilwood products.

Stock combination valves serve many purposes, but transferring fluid from one set to another during a fluid loss condition is not one of it's duties. There is no safety concern about removing the stock valve. A tandem outlet master cylinder will provide the safety feature of being able to stop if one of the hydraulic systems is compromised.

035

That's very interesting. Randy set me up with my system, and told me NOT to use an adjustable prop valve instead of a disc/disc combo valve. I guess it'll work either way. i learned something new. Again.

As for having 50 front/50 rear bias, be prepared to have your rear end swinging all over the road every time you get on the brakes. :lol: Seriously, I know what you're saying. Just an FYI- The proper rate is approximately closer to 70/30. I don't know if you can tune that much rear out with their adjustable valve. Generally, with the car up in the air, you should just barely be able to turn the rear wheels by hand at the earliest point of not being able to turn the fronts by hand. That's a good starting point for tuning bias.

I've also developed a bias towards Wilwood after seeing 3 or 4 "custom" systems they designed for people that either didn't stop right/safely or just plain failed. Hopefully you'll not experience anything of the sort.

Tommy

 

[Doober]

I was thinking the same as Tommy on the bias, once you hit the brakes the weight starts to transfer towards the front of the car, unloading the rear tires. One of the best ways to tune the brake bias would be to actually use a gauge to check line pressure to each of the brakes. If I had the tools that's probably what I would do, and calculate it somewhat close to what the factory was if you stick with a small block setup, maybe add another 5% to the front if going witha BB or other heavy motor, 5% less with a v6.

 

[355_79bu]

The Wilwood valve I installed is adjustable from 100 psi to 1,000 psi. line pressure so I think I'll have plenty of adjustment there. Tommy, thanks for the tip on setting the bias in the air. I was not to thrilled about the idea of flat spotting my tires in a parking lot somewhere. It sounds like fun but, my tires were not cheap! :lol: That method will get me a lot closer to start with.