Brake Master Cylinder

[Hedgehog]

Okay folks I need a hard core, no wishy washy answers.

Some follow these threads some don't, not trying to bore those that have seen me write about this before.

'75, CJ5 with drum brakes all around, Dana 30 front axle. For more than one reason I'm getting closer to switching over to a '77, Dana 30 with disk brakes. It will be a neat and clean switch with rebuilt calipers, rusty but new rotors, all 6 bearings new or in great shape, new seals, new universal joints, new dust shields and new dirt slingers, my new Warn hubs will cap it all off.

Question: I know I'll need a new proportioning valve or is that assembly for a rotor/drum application. Do I also need a new master cylinder? My Jeep guy kinda wavers on the subject. He knows I just bought a '75 from him and I'm short on money. Wasting another $100 on a new master cylinder would hurt some, but if it is necessary it's necessary.

 

[mtnwhlr]

I would yes you need a master Cylinder for a Disc/drum because they are differant. Everyone I've knowen to do this swap has also changed the Master Cylinder because the disc brakes take more pressure to work right. Have you ever noticed with a Master Cylinder for Disc/drum that one bowl is bigger than the other?

 

[Hedgehog]

Yes I have. I always figured I needed to make the swap. Then a Jeeper said that he knew guys that did not make the switch. It seemed confusing to me, it probably sounded like a stupid question, but I asked it anyways.

 

[IOPort51]

Master cylinder won't set you back near that much and yes you need a master and prop valve.


No stupid questions about brakes.

 

[gutthans]

Hedge...drum/drum MC's are pressured differently than Disc/drum Mc's. In disc/drum the rear MC port(s) controls the front discs while the front MC port(s) controls the rear. Also, the rear port holds extra residual pressure against the caliper pistons so that the front brakes activate BEFORE the rear...(which is why rear shoes last longer than front pads, and why the front pads sit against the rotors).

You DO NOT HAVE to run a proportioning valve...but the low pressure warning system (brake light) operates off of that. You can mix/match any year configuration...it only depends upon the brake line fittings and the type of brake you have on each axle. I run a '72 Corvette MC for disc/drum with the ports reversed and a 2 lb. residual pressure valve from Wildwood inline for the rear pads. This combo activates my rear at the same time as the front for 4 wheel squat braking...I have a Wildwood font/rear proportioning valve in the rear line to adjust for terrain (rain/sand/concrete). I initially ran w/o the prop valve but didn't like the brake bias as it came out of the master...

I would suggest you do get a disc/drum MC at least...mine was a $49 rebuilt at AutoZone.

 

[Hedgehog]

Yeah I've been doing some hard looking. The replacement I have in the Jeep was expensive (+$135), but it appears that the one I now need can be had for not a lot of money. It sort hurts to throw away a brand new master cylinder, but this is a decision I made and the direction I chose.

I have access to quality used proportioning valves and they are a known quantity. Does anybody have experience with after market valves? Are some better than others?