master cylinder question

[Rolling_Thunder]

alright guys - i am looking for a master cylinder to put on my satellite...      so here's the question - I have a spare brand new drum brake master cylinder for a 69 RR - could i use this on a disc equipped car ?  I know it'll mount up and i'll make brake lines and all that...     but i also know disc masters have larger reservoirs for the disc portions - would there be a problem running the drum master with discs ?

[Sixt8Chrgr]

Do you have a proportioning valve on your car now? This may be your issue more so than the reservoir.

[Rolling_Thunder]

I will be using a stock distribution block for the front brakes and will be using a adjustable aftermarket prop valve for rear brake adjustment.

So the fluid capacity is not as big of a deal ?  If not I'll just run the spare master I already have,

[tan top]

yes fluid  capacity ! when the disc pad wears the piston in the caliper moves out further i , using up more fluid   ! could run low & uncover the fluid ports in the bottom !  should never use a drum master cylinder on a disc set up

[Rolling_Thunder]

yep - i know the principal of that but honestly I do use the car rarely and I check all the fluids every month or so...     I honestly doubt it would be an issue - i mean the pads would have to go WAY down to uncover the ports...     

I just don't like the idea of using the old 1 pot master thats on the car already   haha

[tan top]

yeah get really low  thats true    also could come un covered under heavy braking  ! hard cornering  , bumps in the road ! if its really low  , just saying better to be safe ! 

but  like you say  check the fluid regular !!    suppose it would be ok !!  ,

[John_Kunkel]

The reservoir size is only one issue when using a drum brake MC with front discs, the drum brake MC has residual pressure valves (RPV) in both the front and rear ports while a disc brake MC has one only in the rear system. To use a drum brake MC with discs the RVP must be removed from the rear port (which is for the front system). An RPV in a disc system will cause the front brakes to drag.