Projects R p v valve

hello guys.
maybe you guys can shed some light. just changed over my 1941 ford to have disk brakes in the front. installed a dual master cyl under the floor. it has a 10 psi in the rear but none in the front. there is a brake metering/hold off valve there. do I need 2psi R P V valve in front?? also when I pump pressure and release it shoots up from the master cyl is there any starting point for the length of the rod to master cyl?

looks like speedway has rpv valves but some issues??

thank you!!!

 

You will get a lot of different opinions and experience. Here is what MBM Tech Support recommends.

 

Lots of questions.....
rod length: has to be 'loose", with some play with pedal up.
If you have a newer MC you should not need a RPV on the rear, but one will not hurt.
No, you should not need one in front.
I would not use a factory type metering block unless the front an rear brakes were off the same vehicle..

What is your specific problem??????

 

Well I have to pump the brakes to get a pedal. and after it sets the pedal goes to the floor. acts like air in lines but there is none... and fluid shoots out the top of master cyl with cover off

 

Well, here's more opinion, and experience.
Your '41 rear brakes need a residual, whether stock internally in the master rear outlet port, or an aftermarket 10 lb. inline external valve. (JFYI, I'm using Wilwood aluminum rpvs with no problems.)
The front discs may need a 2 lb. aftermarket residual because of the low master location. I would install one.
You don't really need metering/hold off, but an adjustable proportion valve would be a good addition.
With the pedal fully returned, and by it's own return spring, adjust the push rod for 1/16"-1/8" clearance with the primary master cylinder piston.

 

fluid coming out of the of the one port of the master while pumping up the brakes is normal its part of the equalization system ( not going into the complexitys of a master cylinder ) , just keep the lid on it , and 2 psi in the front and 10 psi in the rear as stated . the pedal to the floor means the fluid is returning out of the disc calipers since there is no rpv . and you have to fill them back up ( by pumping pedal ) and they take a large volume of fluid .

 

thank you for all your help. ordering valve now and will install as it comes. there is one in the rear...

THANK YOU!!!!!!!

 

any pointers on the 2psi valve install?? seems like everyone has leaks??

 

I have used Wilwood RPV with good success. Make sure you can bottom the master cyl. with out fluid or the dual safety system won't work correctly.




Ago

 

Ago. What do you mean see the bottom of the master??

 

4ford,

Just because you have a dual m/c is not the only safety factor.The dual master cyl. safety system to work properly if you develop a leak in one of the fluid circuits in an emergency. The m/c has to completely bottom out, or the second circuit won't displace enough fluid to bring the car to a safe stop. Too many non factory built cars don't have enough pedal travel. (pedal hits floor first) and the m/c doesn't function like it was designed to work on one circuit.

Ago

 

so what your saying is set the rod length so it goes all the way in and stops??

just installed the 2 psi valve and no luck with the peddle it goes right to the floor i bleed about a quart of fluid out so i cant be leave its air anymore.... think i got a bad master cyl??

HELP!!!

 

so what your saying is set the rod length so it goes all the way in and stops??

Yes, correct.


Did you bench bleed the M/C ?


Ago

 

yes i did. bench bleed. cant beleave its a new master cyl but anything is possible...

 

ok well i am a firm believer that the good come with the stupid!!! all the issues i had as you can see in the posts..
me dumb a** put the calipers on the wrong side so the bleeders were facing down!!
talked to the guys at ECI and they knew what was wrong right away.. thank all who have put their two cents worth in...

4ford

 

Good. That means it's a easy fix.

 

4 ford,

Make sure you have a small amount of free-play in your m/c push-rod, so the
piston can have a full amount of fluid for the next brake application.


Ago

 

don't feel bad , when I was a Teen I did the same thing on my Daily driver , after a week of trying to figure it out it cost me a hard earned 1985 50 bucks for the local shop to fix it for me . now when it comes to replacing calipers I mark them before they go on the car and also double check . Glad you found it was a easy fix .

 

Can i jump in here?
I have a disc drum set up simialr to the OP, and i have to pump my brakes once to get a good pedal, then once pumped it is good...rear drum are adjusted, and i have 2# in fron and 10# in back with no PRV, what would cause having to Pump once?

 

Bad master!

 

A previous owner of my Jeep installed a drivers side brake caliper on the pass side. Just about drove me nuts trying to figure out the mushy pedal as I couldn't bleed the air out. I finally had to get a buddy over to help me and he eventually figured it out.