proportioning valve question

[Nima]

Hi guys;
I have drums all around with power booster. I plan to go with front disk. When I do that, can I just change the proportioning valve or I have to change the whole master/booster and propotioning valve? Thannks

[ac102nv]

Nima,
The prop valve and master cyclinder will be need to be switched. But I believe the booster should be OK.....I think.

[Longhorn Man]

There are plenty here who never chainged any of that, and say it works fine.
However, from a mechanical point of view, you do need to replace all the items you mentioned with parts made for a disc/drum set up.

[Nima]

Thanks for info. I guess it is better to change them since I don't know how old are these current parts although money is always an issue. Thanks again.

[Bowtie67]

Drum brakes weigh less than disk brakes unless you spend some serious money on lightweight rotors & calipers, If there is no real serious reason for doing frequent high speed stops drum brakes work just fine. Most all of your current parts, wheel cylinders, brake boosters, master cylinders, shoes, and drums can pretty much be gotten at any parts store. I put new drums on the rear last year and got them from NAPA for about $26 each.

[RainFade]

IF your stock parts are all working as designed I'm pretty sure there should be residual pressure being held on the drum circuits, I'd also wonder if the bias is a wee bit different on drum/drum vs disc/drum ?

Residual pressure on calipers = dragging brakes.

In disc/drum the front disc circuit is normally held off (delayed) a bit to allow the drums to energize as well.
I'm thinking you best do master cylinder AND combo valve if you swap to disc's on the front IMHO

Disc brakes do better with water/mud etc., don't have balky alledged self adjusters seizing up and in the case of my ho52 finding rear drums can be a real PITA.
So I would argue that there are compelling reasons for such a swap.

[355]

Get a master cylinder for a '72 to '86 with the factory proportioning valve. Bolts right up. The disc need the disc/drum master for two reasons, 1) the volume needed for the disc is more 2) the disc portion of the master does not have a residual valve in it. If you use the drum/drum master you must drill out the residual valve and if you have a fluid problem with the front you may not see it in time before it becomes a safety factor. My 2 cents

[72MARIO]

You can get a adjustable prop valve. Run the front line right out of the master and T it off to the disks. Run the adjustable porp valve in the rear line. That's what I have done. I dont have the exhaust hooked up yet so I cant tell you how welll it works. Should be perfect though. Use a master for the correct application they are diffierent for a good reason. You cant use a Drum/ Drum master for a Disk/ Drum setup like Rain Fade mentioned. The boster can stay.

Later,