What duel master cylinder to use?

Scott De Shields

Scott De Shields

Senior Member
Doing disc/drum brake conversion on my 40 and wonder if I can successfully use a drum/drum duel master cylinder for clearance under the floor or is it necessary to use the taller disc/drum master. Want to use my Motive Product power bleeder but the under floor clearance for the cover plate is restrictive. Is another style of MC available for this application?
 
1968-70 Mustang, what I've heard... The residual pressure requirements are different for drum and disc...
Karl
 
Thanks Karl. Already have lines run with 10lb rear valve and 2lb front valve along with porportional valve for rear brakes (later model rear end and brakes) and metering valve for front disc brakes. Hopefully there is master cylinder to fit under the floor that is not so tall with the correct bowl size.
 
If clearance is a problem go to a remote master like this from ECI ( have one on mine )
 

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Scott De Shields said:
Doing disc/drum brake conversion on my 40 and wonder if I can successfully use a drum/drum duel master cylinder for clearance under the floor or is it necessary to use the taller disc/drum master. Want to use my Motive Product power bleeder but the under floor clearance for the cover plate is restrictive. Is another style of MC available for this application?
Click to expand...

A drum/drum master cylinder can be used in a some disc/drum systems, depending on what vehicle or truck the master is designed for, but it's much better (safer) to use a disc/drum or disc/disc master, to be sure of enough fluid volume for the calipers.
Master cylinders come in many different sizes and profiles, as well as with large metal or small plastic caps, so you should find one that meets your requirements. The '68-'71 Mustang power disc/drum and the popular Corvette-style masters are very good choices.
I would not, however, base your choice solely on that bleeder you intend to use, because it's nothing more than an over-priced garden sprayer, and is really not the best way to bleed a brake system, but that's my opinion. :)
 
Thanks V8 Bob for the input. Since I am running a Dana 44 rear end with non 40 rear cylinders and POL front disc conversion what size piston in the master do you recommend?
 
Scott De Shields said:
Thanks V8 Bob for the input. Since I am running a Dana 44 rear end with non 40 rear cylinders and POL front disc conversion what size piston in the master do you recommend?
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Using the stock '40 pedals, I would not go smaller than 1" in a non-powered system to be sure the master can be bottomed out before the pedal, but this has to be checked reguardless. (The '40 master had an 1 1/16" bore)
 
Scott De Shields said:
Doing disc/drum brake conversion on my 40 and wonder if I can successfully use a drum/drum duel master cylinder for clearance under the floor or is it necessary to use the taller disc/drum master. Want to use my Motive Product power bleeder but the under floor clearance for the cover plate is restrictive. Is another style of MC available for this application?
Click to expand...

Shouldn't all this Chinese be in the street rod section????
 
The residual valves should not be used if the master has them built in. Need to check that because you will never get a good pedel with both.
 
I have the Mustang 68/70 aluminum MC on my 37 utilizing the stock pedal assembly. It works Great!
 
Do not use a drum/drum master if you have discs in the front.
They have the required 10 pd residual pressure valve in them which will not work properly with discs. If you remove the residual pressure valve you should be ok, assuming there is enough fluid for the discs in the reservoir.

I would check with ECI on sizing.

Scott De Shields said:
Doing disc/drum brake conversion on my 40 and wonder if I can successfully use a drum/drum duel master cylinder for clearance under the floor or is it necessary to use the taller disc/drum master. Want to use my Motive Product power bleeder but the under floor clearance for the cover plate is restrictive. Is another style of MC available for this application?
Click to expand...
 
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