Converting a drum/drum to disc/drum, MASTER CYLINDER QUESTION!

[dropanddrag71]

Hello..
I just put a disc brake set up on in the front and i have heard of a way to convert my drum/drum master to disc/drum. Is it true all i have to do is screw a screw into the front port (2 port master) of the master and pop out the residual valve and thats it? Or is this just internet baloni!??

[brad_man_72]

New master cylinders are pretty cheap, and good insurance.
Be sure to swap out the distribution block for a porportioning valve.
I don't know the answer to your question, sorry.
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[geezer#99]

On a disc/drum setup the back port of the master is for the front brakes. If your master has a residual valve in the one for the front then remove it.

[jocko]

it was indeed internet baloney. Need to use the correct mc for a disk/drum setup and route the lines appropriately to/from the mc (for the size truck it is, i.e. C10, C20, etc - there is a difference from what I've learned on here recently thanks to some brake-smart folks).

[67chevemall]

Looking for one myself for the 1967 C10

I tryied what you said in your first post and it does work but not
that well. I get sticking a lot. But if you just need to move it around until you get more cash then it does release the front disc's.

I took the check valve out of the drum/drum master to get the disc brakes up front to "let go"

Now I a searching for a 1972 MANUAL master cylinder. That will bolt right up where the 67 master is. Not so easy so far.

Today I called around local, to see if there is two part numbers for a 1972 disc drum master cylinder. One for manual and one for booster set ups.
Can't seem to find the answer so I searched and am here now.

[elimontfort]

I got mine from performance online bolted right up. Call them and thy will get you straight. There tech department was real helpful also.


http://www.performanceonline.com/60-...ts-components/
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[67chevemall]

http://www.performanceonline.com/Dis...h-Performance/


Great call man!! This looks great

[Tx Firefighter]

I've always just used a master cylinder for a 71-72 truck. It's a bolt on to the firewall and pedal. You can even use a 73-87 type if you prefer. In the mid 80s they went to an aluminum body unit with clear plastic reservoirs that looks a little more trick and doesn't rust.
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[67chevemall]

Originally Posted by Tx Firefighter

I've always just used a master cylinder for a 71-72 truck. It's a bolt on to the firewall and pedal. You can even use a 73-87 type if you prefer. In the mid 80s they went to an aluminum body unit with clear plastic reservoirs that looks a little more trick and doesn't rust.
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I have a 72 on order but don't want to pick it up because they can't tell me if it will bolt up WITHOUT the booster (manual) and my brake rod.

Trying to find if there is two part numbers for a 1972 master cylinder.
One for Manual and one for Booster.

?

[67chevemall]

http://www.bendixcatalog.com/PartDet...ter%20Cylinder

Bore is 1"
pri 1/2 x20
sec 9/16 x 18

Also mentions a 9 1/4" push rod?


http://www.bendixcatalog.com/PartDet...ter%20Cylinder

Bore is 1 1/8 "

Prim and Secondary are flipped oposite??

????????????????????????????????????????????????????????

Which one to bolt on a 1967 with manual brakes?

I think it is the 11581 P# but I am not sure if a part for a 1974 will bolt up on a 1967???

[67chevemall]

http://www.summitracing.com/parts/ben-11581

Well I ordered this one. We will see.

[cleanfreak]

Originally Posted by 67chevemall

http://www.summitracing.com/parts/ben-11581

Well I ordered this one. We will see.

Just tripped on this thread , did the master I sold you not work out? - Bob

[HotRod C/10]

I used one from a corvette. larger reservoir. oreilleys stocks them.

[WIDESIDE72]

I bought a mc for my 71 gmc a while back from vautozone. I dont remember them asking if it was manual or power brakes. Pretty sure there is no difference as i recall adding pb booster to trucks in the past by unbolting mc from firewall and bolting booster/ brackets and reinstalling mc, never touched brake lines.

[Steeveedee]

Power brake master cylinders usually have a bigger bore than manual masters, because you have boost to make up for the loss of hydraulic advantage in manual brakes. This is why, with power brakes, the pedal is so hard to move if the engine stalls, after a few pumps. The wheel cylinders are different, too, for the same reason- power brake wheel cylinders are generally smaller than the manual cylinders. The power/manual master cylinder could be the same, but the wheel cylinders will be different.

Most vehicles have a higher front to rear weight distribution, like 60/40, so I'm not sure why someone would put on a Corvette master, when that master is pretty much a 50/50 distribution. Under normal circumstances, it would probably be OK, but when the brakes REALLY have to work properly, it could be dangerous. I really hope that anyone who hasn't done their homework on their brake "upgrade" isn't behind me when they have to make a panic stop. More rear braking with an incorrect master/proportioning valve is going to have them swapping ends.

I'll be putting disc brakes on my truck eventually. This will require replacement of the master cylinder, proportioning valve and the rear wheel cylinders (if they aren't the same- sometimes power/manual are the same). This appears to be the case for my truck, BTW, after a search on OReillys.

The truck stops well with factory 4-wheel drum, but I prefer the added safety margin provided by disc brakes in the rain, and the reduced fading.