69_340_GTS
Well-Known Member
Can I use a master cylinder off a car with disc/drum on a disc/disc conversion? Will that old master cylinder work on a car with 4 wheel disks? ('69 Dart)
Can I use a master cylinder off a car with disc/drum on a disc/disc conversion?
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LIME TWIST DART
Well-Known Member
Work? Possibly. Get you the pedal travel and feel you want, probably not. After quite a bit of reading and experimentation, I believe it comes down to having an apples to apples comparison to determine. If not, a bit of experimentation is on the horizon .
salinasjoel
Learning Daily
Just pull the residual pressure valve out of the drum side
69_340_GTS
Well-Known Member
I assume that is inside the M/C itself? Is there a diagram somewhere showing this? Thanks!
67Dart273
Well-Known Member
This is well documented, and is in all the service manuals. Download one from MyMopar
you can use small sheet metal screws forced into the seats to pull them out with a claw hammer. I used my original 67 master with 4x disk brakes. I didn't even remove them!!! I just took a nail and punctured 'em from the outside LOL
If I'm not mistaken, most new manufactured masters don't have residual check valves in them anymore. The reason for the check valves was to keep pressure against the cups in the wheel cylinders so they didn't suck air. Most all wheel cylinders have cup expanders in them now so the check valves are redundant.
69_340_GTS
Well-Known Member
Thanks, that looks pretty simple.
69_340_GTS
Well-Known Member
tohnloke
Well-Known Member
When I talked to a wilwood guy at the power tour a couple years ago, he told me that if I ever went to 4 wheel discs I'd just have to pull out the proportioning valve. This was assuming I used their master cylinder.
That's almost bad advice. Really, if you're going to upgrade to four wheel disc brakes, wouldn't you want to optimize them? Yes, remove the prop valve and metering block or combination valve. Replace them with an adjustable proportioning valve in the rear line. Tune your brakes to work best for you and your car.
BillGrissom
Well-Known Member
I 2nd post #6.
I also 2nd post #10. True that factory disk-disk cars don't need a prop valve, but that is because they carefully selected and tested caliper sizes to give optimal braking, and that only works if you stick w/ OE spec tires. I doubt your system will be so optimized and you might have wider tires in the rear or such. A rear adj prop valve lets you fine-tune the braking. Keep increasing the rears in a wet parking lot until they lock-up before the fronts, then back off. BTW, rear disks are not needed and mainly for bling, even in new cars.
I also 2nd post #10. True that factory disk-disk cars don't need a prop valve, but that is because they carefully selected and tested caliper sizes to give optimal braking, and that only works if you stick w/ OE spec tires. I doubt your system will be so optimized and you might have wider tires in the rear or such. A rear adj prop valve lets you fine-tune the braking. Keep increasing the rears in a wet parking lot until they lock-up before the fronts, then back off. BTW, rear disks are not needed and mainly for bling, even in new cars.
tohnloke
Well-Known Member
^Yeah that all makes sense. I had never given much thought to it really. Rear discs are way way (years) down the line for me so I hadn't thought much about tuning them 
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I have 4 wheel disks (Cherokee rears) and no problems with the stock master, I just am using a adj prop valve and removed the distro block. One thing you have to keep up with checking the brake fluid since the reservoir is very small.
67Dart273
Well-Known Member
The thing is "it is" a crap shoot. Front and rear tires, (when you change sizes or compound), front to rear car loading (passengers, other weight, trailer?) which is why an adjustable valve is nice.
The only real reason disk systems use larger "tanks" on the master is to accomodate large amounts of PAD WEAR. Day to day operation requires very little fluid, as the calipers don't move very far.
Bore size of the master has nothing to do with front / rear brake proportioning.
The only real reason disk systems use larger "tanks" on the master is to accomodate large amounts of PAD WEAR. Day to day operation requires very little fluid, as the calipers don't move very far.
Bore size of the master has nothing to do with front / rear brake proportioning.
Well said!
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