DILLIGAS Dave...Residual valve ???

My chassis guy put a 2lb on the front, but not the back. M/C is 10-12" above ground. Do I need to add one in the back or try it and see how it does?

Thanks,
David

If the mc used doesn't have any built in valves & is mounted way below the calipers (say under the floor) then using the 2# valves is usually a good idea in a lot of cases. In the past I have seen some cars without the valves that did still stop OK. But it was common for some of these drivers to have to remember to pump-up the brake pedal at the front of the staging lanes before making a pass.

If the mc is mounted a little higher, like say just above the frame rails, (but still ends up being a little below the calipers) the need for the valves is reduced some. But they still might be needed.

I guess you could test the way it is now before changing anything. You could bleed the brakes, & test how fast the fluid might bleed back to the mc making it go from a good firm pedal to soft pedal. If it bleeds back quickly & the pedal goes soft fast, install the valves.

We run a 2 lb valve on our rear line but we have a dual caliper system and it made a huge difference and that is with the mc in the stock location.

whatbumper wrote:.........we have a dual caliper system.............

Does adding a second rear caliper each side feel somewhat like adding a second 'chute to a car?

Did using a second caliper each side ever work "too good" & cause the rear's to ever lock up unexpectedly?

I

DILLIGASDAVE wrote:

whatbumper wrote:.........we have a dual caliper system.............

Does adding a second rear caliper each side feel somewhat like adding a second 'chute to a car?

Did using a second caliper each side ever work "too good" & cause the rear's to ever lock up unexpectedly?

If you get too aggressive on the big end it will lock the brakes. We use the chute mostly and then just lean in to the brakes on the big end. Wish we could have a multiple setting proportioning valve that would switch after launch.

Great info! I will add one after I make sure the engine survives the dyno. Explain proportioning valve operation... I have one; where do I need to set it to start out with? Is it just a needle valve limiting the "flow" to the rear brakes or does it limit pressure? I thought it just prevented a lockup condition if the brake were applied hard abruptly?? Thanks, David

in factory form the valve is used to get the ~60-70% braking power to the front. we use it to get more pressure to the rear for staging the turbo car. it takes a lot of brake to keep the wheels from spinning at 1000 horsepower. while staging while getting up on the boost.

I'm sure Dave will chime in on proper operation on a regular ride.

David Willingham wrote:............Explain proportioning valve operation........

I haven't ever installed/used a proportioning valve on a big tire/full chassis car that also used the correctly plumbed aftermarket "Mopar" style mc (like say from Strange). In this situation/setup the front brakes usually lock before the backs anyway, so the proportioning valve isn't really needed to prevent the rears from locking first & spinning the car around.

But it might be a different story if a mc other than the aftermarket Mopar mc is used, I don't know for sure. I built a back half car years ago that the owner decided to use a Ford mc & a proportioning valve instead of the Mopar mc. The car seemed to stop OK, but I don't know if the car really needed the proportioning valve or not.

whatbumper wrote:

DILLIGASDAVE wrote:

whatbumper wrote:.........we have a dual caliper system.............

Does adding a second rear caliper each side feel somewhat like adding a second 'chute to a car?

Did using a second caliper each side ever work "too good" & cause the rear's to ever lock up unexpectedly?

If you get too aggressive on the big end it will lock the brakes. We use the chute mostly and then just lean in to the brakes on the big end. Wish we could have a multiple setting proportioning valve that would switch after launch.

Thanks for the info.

I knew from past pics that you guys were running the doubles, but I kept forgetting to ask what they were like on the big end.

I replaced my Strange MC a few weeks ago while hunting a soft pedal problem. In the process I called Strange and spoke with one of their brakes techs.

3 things I took away from that conversation that did not know:

In a drag car you want the rear brakes to do most of the braking. The fronts are skinny, so they will lock up easier.

If you do use a proportioning valve DO NOT put it in the line to the rear brakes, put it in the front for the above reason. Mine has the Prop valve in the rear line, but I opened it all the way up per Strange and braking is better. Any future issues and I will remove it.

A Strange MC is plumbed backwards as compared to a street car for the above reason. The MC's largest piston swept area is the port at the rear of the MC. On a street car you would plumb that port to the fronts so they can do most of the braking. Strange says plumb it to the rear brakes and take the rear fitting to the front. It does tell you to do that in the Strange MC instructions.

Only problem I have with Strange's suggestion of letting the rear's do most of the braking on a drag car is on a faster car with that setup you do run the greater risk of locking up the rear's first and sliding the big tires around & spinning the car. Locking the front's first is usually better in my opinion because the car isn't as likely to try to swap ends. Flat spotted front runners is better than backing the ass-end into a guardrail in my book.

I'm not sure if a 'chute deployed quickly would be enough to catch a rear locked car from spinning on around once the end swap has started. But that and blipping the throttle (at just the right point) are probably the best chances to try and stop/slow a locked rear from coming around once it's headed that way.