Disc brake proportioning valve

[Paul 500]

My friend has a 70 RR thats had a front disc brake conversion,
The problem is when he brakes the back wheels lock up, the car also pulls to the left & brake fluid leaks out of the master cylinder. Its an older conversion with a new disc brake master cylinder, when it was converted they never added the disc brake proportioning valve.
Could this be the problem ?

[71charger_fan]

Sounds like the source of the problem. He should  be able to take the proportioning valve from another Chrysler product of about the same size that was factory disk/drum and plumb that in. The one in my Charger is out of a Volare four-door and it works great.

[phat69charger]

Check out these pages they should help some

http://www.mpbrakes.com/mpfaqvalving.htm
http://www.mpbrakes.com/mpfaq.htm
http://www.mpbrakes.com/troubleshooting.htm

The main page  http://www.mpbrakes.com/

[Ghoste]

If the car isn't being driven much (or sometimes even if it is) it could also be that the right side caliper has seized.  That can make it pull to the left pretty hard.

[Paul 500]

Thanks for those answers.
Should be getting a proportioning valve this week & fitting it next weekend.

[BlueSS454]

Also check the brake hose.  If the hose is bad, it will not release the pressure back into the system.

[Chryco Psycho]

You can fit an adjustable propotioning valve like the Wilwood one into the rear system & this will allow you to tune the drop in pressure to the rear brakes perfectly   

[Nacho-RT74]

Why aftermarket distribuition blocks  and GMs doesn't have proportioning valve on front disc assemblies cars ?

[Ghoste]

I'm not familiar with the GM system but there has to be something in there someplace to alter the pressure requirements in a disc/drum setup.
Don't confuse proportioning and distribution blocks in these questions.  The distribution block does just that, it distributes the brake fluid from the master cylinder to the four corners.  A proportioning valve is changing the fluid flow going to the drums because the requirements to operate a drum brake wheel cylinder are different than that required for a disc brake caliper.  I think most of the distribution blocks for our cars are still available, it's the proportioning valve which is nearly impossible to find (if you want a factory one).

[Nacho-RT74]

GMs distribuition blocks fits and match perfectly with Mopars, only difference is the built in proportioning valve on Mopars. Even warning switch fits perfectly.

Maybe GMs have the proportioning valve separated from distribution block ?

[Ghoste]

Maybe it was changed by the 3rd gens Nacho but for the 1st and 2nd's, the proportioning valve is a seaparate stand alone unit.

[Nacho-RT74]

Maybe that is because front disc brakes was available on any3rd gen model like part of equipment so didn't need a different setup on that and earliers the front disc were to R/Ts and some other models... standart was drum brakes, so with that optional front setup, only difference would it be add the proportioning valve ?

[Ghoste]

Makes sense to me.

[Nacho-RT74]

Oh well I think that more that 3rd gens, it's on that way since 73, because I remember 71 and I think also 72, stil front drum brakes were available.

[Ghoste]

Yeah, Mopar was kind of late to the disc brake parade.  In our defense though, I believe we did have bigger drum setups than many other car lines.

[phat69charger]

You can get the same type of combination valves cheaper for Disc/ Drum cars on ebay that they sell on the inline tube site,   http://cgi.ebay.com/ebaymotors/GM-STYLE-DISC-DRUM-PROPORTIONING-COMBINATION-VALVE_W0QQcmdZViewItemQQcategoryZ33565QQitemZ8036955465QQrdZ1QQsspagenameZWDVW

[BlueSS454]

I'll add in on the GM systems.  On 67-70 GM disc brake systems, there is a valve mounted under the master cylinder that goes inline with the front brakes.  It delays the fluid to the front discs so the car does not nose dive on hard braking.  From 1971 and on, GM disc brake cars used a combo valve, identical to the later style Mopar ones, so it should work theoretically.  Here is a picture of how my 70 Chevelle is set up:

[phat69charger]

The valve on ebay is a combination valve, the hot rod shops that sell them probably try to avoid multiple pieces when a single piece can be used.

[Paul 500]

We got the valve today, its not a proportioning valve its a metering valve . Will this be ok and sort out the problem or is it E-bay time.

[Ghoste]

You have both there.  The valve which is in the foreground of your photo is a proportioning valve.

[Paul 500]

Thanks Ghoste

[Shakey]

Attached is a photo of the metering valve and the proportioning valve from a '69.

[BlueSS454]

Is that valve a 69 specific item or can it be found on other years?  I've had no luck finding one in a junkyard yet.  I do, however, have a combo valve I was thinking of using instead, guess I would just need to fab up the hard lines.

[Ghoste]

They are on other years but the disc brake cars are so rare in late 60's Mopars that they are hard to find.  The location changes around a little too.  Mine is on the inside of the frame rail on the drivers side and back as far as about where the front edge of the drivers door starts (sort of under the door hinges).  But I have seen them on the inner fender and any point between those two.

[Shakey]

I have a spare proportioning vale from a '67.  I found it at a yard in NM last year.  It was mounted on the frame rail, just where you said it was Ghoste.  It doesn't look exactly the same as the one I got off of the '69 in CA last week.  That one is mounted at the base of the firewall, about a foot behind the metering valve.