Master Cylinder Upgrade

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mrzods13

mrzods13

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I just purchased a 1974 Plymouth Duster with a 360 HP Magnum Block. It has Wilwood 10 inch discs on the front, manual brakes. The master is leaking from the lid, time for an upgrade. I read some people using the late model truck master cylinders with the dr diff adapter. Some are saying bigger bore is the way to go and some are saying smaller bore. I want to be able to stop better, I never had a car with manual brakes so I am new to all of this. This is the master with the 1 1/8" bore I was looking at with the adapter plate. Any help is appreciated thanks

12.JPG
 
my master cylinder is doing the same thing anyone have any ideas on how to seal it?
I replaced the cover and the don't know the name of the wire.
Still leaks from the front area.
Thanks
Dan
 
a lot of guys here like the 15/16 bore if you are going to run manual disc brakes, the reason being with the smaller bore size the more line pressure it generates and you get a firmer feeling pedal. i am changing over to front disc now and i am going with the 15/16 bore
 
I tried one like that - required way, way too much leg effort for my taste. Panic stop? Forget it.

I run a 1-1/32" Aluminum (Doctor Diff) now which is much better but could stand to be a little smaller yet. We put a 15/16" Aluminum (also from Doctor Diff) on my son's BB D100 truck with manual brakes. It works really well.

I think you be happier with something under 1".
 
Thank you I will see if I can get the 15/16 from drdiff.
 
15/16" is the way to go. I even converted my Challenger from power disks to manual disks with the 15/16" master. Better line pressure, better brake modulation and feel. The pedal stroke is slightly longer, but it's barely noticeable. Pedal effort isn't bad at all.

The larger bore m/c will result in a high pedal with a short stroke. The pedal feels harder because of the short stroke, and the brakes are a little harder to modulate for threshold braking because the shorter stroke makes things touchier. I definitely wouldn't go bigger than the factory 1-1/32", and personally I like the 15/16" much better than even the 1-1/32".
 
I wouldn't trust the reservoir cap in post 1 to seal any better than a 1970's Dart MC (looks similar), plus I find cast-iron heavy and rust-prone. With a $30 2 to 4 bolt adapter plate (ebay), you can use many modern aluminum MC's w/ tight-sealing reservoir. They also have a low-level sensor you can wire in parallel w/ your e-brake dash lamp. I used one for 95-99 Breeze/Stratus ($25 new). Dr Diff sells the plate & MC for ~$95. Get the smaller bore option for manual. Linked at least once a month, but I'll show again since that apparently isn't enough.

Dr Diff MC & plate.jpg
 
BillGrissom said:
I wouldn't trust the reservoir cap in post 1 to seal any better than a 1970's Dart MC (looks similar), plus I find cast-iron heavy and rust-prone. With a $30 2 to 4 bolt adapter plate (ebay), you can use many modern aluminum MC's w/ tight-sealing reservoir. They also have a low-level sensor you can wire in parallel w/ your e-brake dash lamp. I used one for 95-99 Breeze/Stratus ($25 new). Dr Diff sells the plate & MC for ~$95. Get the smaller bore option for manual. Linked at least once a month, but I'll show again since that apparently isn't enough.

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Yea I am going to get the drdiff combo. It is 125 for the 15/16 one but it seems to be well worth it.
 
Bigger bore = Harder push
Smaller bore = Softer push

Genrally 1+ inches is power brakes. Anything under an inch is manual brakes. The bigger the bore, the harder the pedal.

As for leaking master. Mine did that forever. They just leak. Welcome to a-body brakes. No. You can't buy just the gasket. Period. I looked for two years. You can try and bend the wire to make it snap the top harder. Might help. In the end on my setup (power, disc front) I just bought a new master and replaced it. Probably didn't need to. But it wasn't crazy expensive. And was worth it to solve the constant problem of atmo getting in my brakes. And all the leaking going on.
 
after having the old bailing wire hold down style MC constantly leak and destroy the paint on my firewall. I went with the plastic screw on cap type as shown above from Dr. Diff and so happy I did so. No more worries of leaks !
 
mrzods13 said:
Yea I am going to get the drdiff combo. It is 125 for the 15/16 one but it seems to be well worth it.
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That is the easy way, but was too rich for me. I paid $30 for the adapter plate and $25 for a new Breeze MC (both on ebay). Also gives a low-reservoir warning switch (wire to gnd in parallel w/ e-brake switch).

Re "a leak removes paint", I use silicone fluid in 6 of my 7 vehicles. Two have ABS, which DOT 5 bottles say "not for", but I decided to test that. So far no problems, so must be the lawyer's input (ABS wasn't qualified w/ that fluid, ...).
 
BillGrissom said:
That is the easy way, but was too rich for me. I paid $30 for the adapter plate and $25 for a new Breeze MC (both on ebay). Also gives a low-reservoir warning switch (wire to gnd in parallel w/ e-brake switch).

Re "a leak removes paint", I use silicone fluid in 6 of my 7 vehicles. Two have ABS, which DOT 5 bottles say "not for", but I decided to test that. So far no problems, so must be the lawyer's input (ABS wasn't qualified w/ that fluid, ...). Some here fuss, "if you drip water in your reservoir", but never explain why they don't similarly worry about water in their p.s. fluid.
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