brake bias question

[modular93fox]

I just did a rear disc brake conversion on the ol 87 silverado as seen on this thread:
https://www.pro-touring.com/forum/showthread.php?t=66403
and was wondering if I should gut the prop vale, modify it somehow, or gut and install a adjustable prop valve for the rear.

A quick search shows GM D-52 pistons are 2.80"
An alldata chart shows the Dodge Ram piston to be 2.12"
total of 4.92"
front 2.80/4.92= 56%
rear 2.12/4.92= 44%

Not quite a natural 70/30 split. Currently with stock fronts will start to screatch before they lock up (when at a real low speed) before the rears when the pedal is mashed and held. The fronts have got to be glazed becuase I did a very hard stop... could smell the pads once I pulled back into the shop. Right now I have no complaints about stopping becuase it feels great having 4 wheel brakes.


So what are your recommendations to the brake bias?
Leave it -or- Change it


Thanks,
clint

[David Pozzi]

Don't compare bore diameters, compare bore area in square inches. Compare a single piston to multi-piston caliper by only using one side of the multi-piston caliper area in sq inches.
Rotor diameter matters too as well as tire height.
David

[6'9"Witha69]

For me, once you leave the factory settings/setup, an adjustable prop is mandatory. A lot of R&D went into setting the factory prop valve/bias properly. Simply gutting the factoert valve doesn't ensure good results. Get an adjustabple prop, and then go test to ensure it works properly. I start with a lot of rear pressure. Get up to ~40 and jam the brakes. If the rears lock up, back out pressure and try it again. Continue @ 40 (making very small adjustments) until the rear lockup goes away. Once gone, repeatedly. Perform the test @ 50, then 60, then 70. If consistent, you should be dialed in well.

[modular93fox]

does anyone perfer any brand of prop valve over another. Im sure they are just about the same just different brand.
thanks for the replys,
clint

[6'9"Witha69]

Wilwood has a slick new distribution block/adj. prop valve. I use Wilwood everything already.
http://wilwood.com/MasterCylinders/MasterCylinderValves.aspx

[wmhjr]

That's a nice valve. I like that it splits your front right at the valve as well as allowing bias adjustment. Too late for me, but it's cool.

[Bryce]

I have my proportioning valve adjustable from the drivers seat. I use the wilwood, I have no issues.

[cheapthrillz]

I have my proportioning valve adjustable from the drivers seat. I use the wilwood, I have no issues.

Bryce, got pics of this? I'd be interested to see your control ergonomics....

[Bryce]

let me look through my pics and see what I can find. I am here at work right now.

[Bryce]

https://static1.pt-content.com/images/pt/2010/04/tn_full_pics_002jpg_Thumbnail1-1.jpg (http://www.motortopia.com/photos/455829)

it sits through the floor right next to the front left seat mount. kinda hard to see in this picture. best I have right now.

[68Formula]

Make sure the wife doesn't mistake it for the lumbar adjustment! :)

[cheapthrillz]

In the floor beside the rocker? Thats cool. I was trying to think of a good place to mount one. I was thinking near the trans tunnel would be easier/quicker access, but packaging may be a little difficult....

I really like your door panels too.... Did you do them? They look really simple and clean.

[Bryce]

HAHA, lumbar. support!!! actually I have that built into the seat its on the passenger side of the driver seat. you can see the grommet in the side of the seat.

Per NHRA rules, the brake lines can not be run down the drive shaft tunnel. the must be on the outside of the frame rails. That is the reason for the proportioner in that location.

Yep i made the door panels. My next set will be all aluminum with tweed inserts. For more questions about my car not "brake bias" subject please ask in my thread, see my signature. i dont want to hijack the OP thread.

[John Wright]

I have mine mounted just ahead of the driver's seat. I might re-do mine because I like the way Bryce's is set up.....I have brake lines under my driver's seat and it could rub a hole in the line where they go through the floor(even though I have rubber grommets)

[Bryce]

My brake lines remain under the car. Just the handle of the PV pokes through the floor. And I can still reach if I had a 5 point harness on.

[cheapthrillz]

Per NHRA rules, the brake lines can not be run down the drive shaft tunnel. the must be on the outside of the frame rails. That is the reason for the proportioner in that location.

Interesting..... do these same rules apply to NASA (or equivalent)?

Ever run across a remotely mounted prop valve controller?

I'm just thinking out loud....

[Bryce]

yes, wilwood makes a cable drive handle for their proportioner. Im not sure if NASA has that rule. but it makes sense. If you have a u-joint failure or break a driveshaft you dont want it taking out your brakelines.

[John Wright]

The M/C is on the driver's side...so it makes sense that the rear brake line travels down that side of the car anyway....my camaro rear brake line runs along the driver's rocker so it was a piece of cake to plumb in the prop valve right there.