I have a quick question about the master cylinder that is in the car I currently have. 1965 Plymouth Valiant. I acquired this car 2 years ago and it came with drum brakes all around, but it has an equal sized dual port/bowl, MC not a single port/bowl MC. I am converting it to disc brakes which leads me to my question... Do I need to upgrade/ replace this MC for one that had a larger port/bowl for the front brakes? Or can I get away with what I have? Thanks in advance!!
Master Cylinder Question
- Thread starter 85glht
- Start date
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Locomotion
Well-Known Member
It's my understanding that you do need the larger master cylinder reservoir to work with the larger fluid capacity of disc brake pistons.
Don't forget the standard or adjustable proportioning valve. Adapter probably needed if using a newer aluminum M/C.
Don't forget the standard or adjustable proportioning valve. Adapter probably needed if using a newer aluminum M/C.
Luckily for me, the previous owner installed an adjustable proportioning valve... I'm assuming due to it having 10" drums in the back and 9" in the front
Thanks for the input!!
Professor Fate
Push the button, Max...
Drum/drum master cylinders also have residual valves in both ports, they are not used for disc brakes; so the rear one (circuit for the new front discs) would need to be removed.
I would just get the proper master, then you can match the bore to your new application- you didn't mention what size your current MC is.
I would just get the proper master, then you can match the bore to your new application- you didn't mention what size your current MC is.
We have the equal sized bowls on our MC in our 67 cuda with factory disc. The MC may have been swapped out, but we haven't had any issues with brakes. But I've never had to lock it up either.
No idea on size... You do mean bore size, yes? If so, how do I determine what I have??
I couldn't tell you what this mc is from... Not sure if it is factory or not
This is easy. I used the stock "equal" drum brake master on my 67, with FOUR wheel disc. I simply punched a nail through the residual valves. I could have tried to take the seats out the way the book shows, but may have damaged them. Equal master is fine YOU SIMPLY NEED to check the brake fluid once in awhile. the larger section is not for "daily operation," it is rather for pad wear, as the disc side "uses" fluid more than the shoe side.
"Punching a nail through the Residual valves". I'd end up screwing that up. Hell, I don't even know where they are...
I'll look into it... Thank you!!
You can determin the current mastercyl bore but you hjave to remove the master to measure it. You MIGHT be able to measure it from under the dash if you pull back the dust boot. You will need a caliper as the typical sizes are:
15/16" = 0.9375
1"
1-1/32" = 1.03125
15/16" = 0.9375
1"
1-1/32" = 1.03125
And how tight this car is, that isn't happening... If I end up removing the MC, I'll just replace it with a correct one.
4 nuts and the front seat is out and then there is plenty of room
No, that would not be the factory MC. Factory disc MC had one rounded end, one square end, unequal-sized reservoirs and a wire bale closure. The OEM A-body ones were somewhat smaller than on the B-bodies, but that part number was superseded, and all the rebuilds running around now are the slightly larger ones. To clarify, I mean larger as in external dimensions — I am not talking about the bore size. That varied by application, as discussed previously.
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