Proportion valve

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jam4ever

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Is a all drum proportion valve the same as a disc-drum set up? I got a set of small bolt disc that I'm going to switch this weekend and don't want to mess with the valve unless I have to.
 
Same?....No

A disc brake valve, is actually a combination valve

it has a proportioning valve for the drum brakes and a metering valve for the disc

master cylinders are also not the same from drum to disc...an all drum cylinder would have residual pressure valving on both ports
 
master cylinders are also not the same from drum to disc...an all drum cylinder would have residual pressure valving on both ports

Pleas expalin further if you could - and what might be the side affects if you retained the drum master cylinder when converting fronts to disk?
 
388dart said:
master cylinders are also not the same from drum to disc...an all drum cylinder would have residual pressure valving on both ports

Pleas expalin further if you could - and what might be the side affects if you retained the drum master cylinder when converting fronts to disk?
Click to expand...

Drum brakes have a residual valve so there is always about 2 - 5psi in the lines to keep the wheel cylinder pistons up against the brake shoes. There are some disc brakes that need residual pressure to keep the piston up against the pads (Corvette 4 piston brakes require this residual pressure) but most disc brakes do not need this residual pressure. Single piston/floating calipers do not and if you have a residual valve in the line the disc brakes will drag because of this pressure.

Now I have a question for the Kelsey Hayes guys. I just purchased a parts car with this setup and I am going to put them on my Duster. I have everything so I am just going to swap everything. Just so I know do the Kelsey Hayes calipers require a residual valve like the Corvettes being they are also 4 piston calipers? Or did Kelsey Hayes have a way for the pistons to stay out against the pads and Delco Moraine did not on the Corvette?

Chuck
 
Wanted to try and ask this here so I didn't have to start a new thread. Are the proportioning/combination valves the same on the 73 and up A-bods between power and non-power disc cars?
Thanks
 
Can you guys clarify for me. I am also converting a 73 duster drum car to 74 disc, in front. I was under the impression my manual brake 73 duster could use the manual master cyclinder and the original drum upper control arms since they had the big ball joints in 73. I have the proporioning valve from the disc donor car, but not the master cyclinder. What do I need, Walt :scratch:
 
you can use the same upper A arms,,, you willl need a disc/drum master,,weather you go manual or power,, i use a manual set up ,,stock 76 dart rotors/calipers and manual master,,i use to use just a store bought rebuilt master,,iron,,,worked great,,now i use the mopar performance master cyl,,15/16 bore manual,,,stock dart rotors and calipers,,still,,no porpotioning valve,,,,only an adjustable on the rear,,car stops on a dime,,,,BORE SIZE MATTERS,,,,,,,,,,,
 
yes, bore size is important. the smaller the bore, the more pressure and in turn more pedal travel but less pedal effort. the bigger the bore, the more volume and in turn less pedal travel but increased pedal effort. a 75 or 76 duster manual disc is what i think is the good one. i will have to check into it.

did i get it right or backwards? i am still amidst the first cup of joe.................
 
I believe the manual cars had the larger piston in the master. Seems odd Mopar would have done it that way. I would buy a NEW (not remanufactured) master cylinder anyhow. Go looking for the 15/16" bore. Also, if you replace your calipers, the 76 and later were larger bore. using these will shift your brake bias toward the front, as will smaller diameter rear wheel cylinders. You still need the combination valve from the disk car no matter what.
 
Dual master cylinders were introduced in 1967,as per federal requirments.With a dual master cylinder,the front reservoir and piston served the rear brakes,while the rear half of the master cylinder operated the front brakes.On drum brake
applications,both reservoirs were of comparable size,but disc brake master cylinders used a larger reservoir to feed the front brakes.Since brake calipers cannot be adjusted to compensate for brake lining wear as the brake pads wear,the caliper pistons must protrude further and further from their bores in order for the pads to maintain contact with the rotors.As the pistons move from their bores,the cavity behind them grows larger and larger.Additional brake fluid is needed to fill the voids left by the pistons.Without the extra capacity of the disc brake master cylinder reservoir,the possibility exists that a smaller reservoir could run out of brake fluid.Dont gamble with safety.When retrofitting to disc brakes,always install a disc brake master cylinder.Additionally both ports on drum brake master cylinders and the front port on a disc brake mc used in to the mid 70's were fitted with residual pressure check valves.Residual pressure check valves were used to maintain a small amount of hydraulic pressure in the wheel cylinders at all times so the air could not work its way past the piston cups and into the wheel cylinders.
By 75 or so,wheel cylinders were being fitted with small metal pie pan shapped expanders inside the cups.All wheel cylinders manufactured since that time and all rebuilding kits have included these expanders.If you use a mc intended for an application prior to the mid 70's,it should have a residual pressure check valve in its front port. If you use one intended for an application after roughly 1974, it probably will not have this check valve. If you think your car may still have the original wheel cylinders, it would be a good idea to change them or at lest rebuild them. Early disc brake quipped cars used an additional valve, as well. A valve in the brake line that fed the rear wheels was typically mounted to the inside of the left front frame rail a foot or two back from the firewall. Chrysler called it a proportioning valve. The proportioning valve limited the pressure applied to the rear brakes in a nattempt to reduce rear wheel lockup during hard braking. By 1970, some models were also fitted with a metering valve. it helf off pressure to the front brakes until the rear brake shoes began to cntact the drums. By 1973, everything was built into one valve, called a combination valve, but sill often referred to as a proportioning valve. If you wish to maintain a completely original apperance with your drum to disc brake conversion, you will need to install the valve(s) that the factory would have used on your particular car. If a totally original appearance is not of the utmost importance, a combination valve from a 1973 or later car of the same body style should result in acceptable brake proportioning, and often a simpler installaiton.

I hate typing !!!!!!!!!!

Anybody planning on doing modification's like this on there A-bodys,let me suggest a book for you.
Chrysler Performance Upgrades by Frank Adkins
This book has all the answers.Engine swaps,Transmissions,cooling systems,fuel,electrical,rear axles,driveshafts,suspension mods,brake systems,etc......
Hope this helps.
 
I plan to change to this one of these days on my son's Dart Sport.
You might want to consider this for your master cylinder question:

http://cgi.ebay.com/ebaymotors/ws/e...RK:MEWA:IT&viewitem=&item=280117877372&rd=1,1

For his '74 Dart Sport (drums on all corners) we swapped a disk/drum system over from a '76 Duster, including calipers and combination valve. We bought a replacement M/C from AutoZone. His car was not drivable when we bought it, so I can't tell you the difference in brake feel.

The only problem we have had is the brake dash light came on after just a few days of driving when it was put back together. The system was re-bled and the light came on again the next day. There are no leaks to be found.

Jerry
 
Here is the book.
A must have for these types of questions.

John

Picture 418.jpg
 
the light might be on due to the valving is not equalized inside it. you need to bleed it at the valve (fronts and rears) to center it for the light to go out.
 
I bought Conrads book a few years back and still refer to it all the time. Lots of good information in there on old Mopars.
 
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