Master Cylinder Size

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dICKj

dICKj

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What size piston do I need to convert a 1974 Duster Power Disc Brakes to manual disc brake?
 
I went with 15/16's. I had a MC that was a bit smaller and it took a massive amount of pedal pressure to stop the car. This MC I have know doesn't have too much travel but I found it's a bit of a trade off with pedal travel and stopping without using both feet! I'm running SSBC disc up front with 10" drums out back. on a 72 Demon. I'm sure everyone has there own opinion but it's really what you personally like. But I think the 15/16's MC is a good starting point.
 
Not sure, never thought of converting from power to manual disc's.
 
Check rock auto. Might be that it uses the same MC

67 uses the same MC manual vs power
 
I 3rd a 15/16".

When I replaced the original 1-pot on my 66 Barracuda I went with a 1- 1/8". Yup, it was hard as a rock. Swapped to a 15/16" and bam, just the ticket. I did buy an adjustable pushrod for the first one, but I might be able to go back with the original.
 
I went with a 15/16ths when I upgraded to front discs.
No power booster before or after.
 
15/16” is a good size. I’ve converted a couple of my cars from power disks to manual disks. Much better feel with the manual disks, and the pedal effort with the 15/16” master cylinder isn’t bad at all. I really dislike the soft, squishy, vague feeling you get with the stock power booster.
 
Keith Mopar said:
I went with 15/16's. I had a MC that was a bit smaller and it took a massive amount of pedal pressure to stop the car. This MC I have know doesn't have too much travel but I found it's a bit of a trade off with pedal travel and stopping without using both feet! I'm running SSBC disc up front with 10" drums out back. on a 72 Demon. I'm sure everyone has there own opinion but it's really what you personally like. But I think the 15/16's MC is a good starting point.
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if you had a smaller master cylinder the pedal pressure would be much lighter.
 
I like a hard pedal. — like to feel the road and the car. Do you think a 1” would be a good compromise?
 
dICKj said:
I like a hard pedal. — like to feel the road and the car. Do you think a 1” would be a good compromise?
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Honestly I don’t think so. 15/16” provides plenty of feel for the car and the road. It’s not like it’s a soft pedal. The problem with larger diameters is that the pedal stroke gets shorter, which is why the pedal feels harder. That gives you less “touch” when controlling the brakes, they go from completely off to locked up in a shorter pedal stroke distance. So it actually makes it harder to control the braking application in my opinion.

Obviously this is a “feel” thing, you may like that better and the only way to know will be to try. But having used 15/16” up to 1-1/32” I much prefer 15/16”, and believe it gives the best braking control and modulation of all the ones I’ve tried.

You’re trading effort for travel. The other thing is, the smaller diameter master cylinder actually gives a higher brake line pressure. So, more clamp force. It just takes a longer throw to do it. You don’t want to go too small, as you need to have enough travel available to fully engage the brakes. And the longer travel will mean it will take longer to fully apply the brakes too. I think in the general range from say 7/8” to 1-1/32” that time difference will be pretty darn small, but it is something that will change. It’s all a balancing act.
 
ir3333 said:
if you had a smaller master cylinder the pedal pressure would be much lighter.
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Yea, I meant I went to a smaller MC. The Master I had was 1 1/16 from a fwd Chrysler. The 15/16's Master made a decent difference.
 
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abodyjoe said:
i always get confused by this.. i call dr.diff and buy what he tells me to buy...lol
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Yep. I told Cass at Dr. Diff that I wanted a firm pedal and he said to go with the 1 1/32" master. It was just what I was wanting, but I'm sure some would think it's too firm.
 
dustertogo said:
Yep. I told Cass at Dr. Diff that I wanted a firm pedal and he said to go with the 1 1/32" master. It was just what I was wanting, but I'm sure some would think it's too firm.
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When I went and visited him a couple of years ago, I bought the 15/16'' aluminum master with adapter from him and installed it in my Dart Sport.
It was right on for my tastes and installation was easy like he said.
Another vote for the Dr. Diff 15/16'' aluminum master with the 4 bolt to 2 bolt adapter.
I didn't even have to change my push rod from the factory cast iron manual one that I had.....
 
SGBARRACUDA said:
Your ignoring what has been said here by many. So like I said. It’s your money waste it if you want.
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I wasn't ignoring anything. You seem to have me confused with the OP. I have already purchased the 1 1/32" mc and installed it on my car and I'm totally satisfied with it. My post was like many others responding to the OP with my opinion. I was just telling him what I had done and let him go from there. The fact that you and others had recommended the 15/16" mc was immaterial to me.
 
That's where the problem lies.
A person tries one product and says it's great, couldn't ask for better, - how do you know ?
Unless you have tried misc "widgets" and tried them on the same vehicle, numerous times, how do you know which is best, when you have tried only one.
At that point, you're opinion is worthless. No offense, lotta folks do it.
Lotta folks, including myself, build custom brake systems for race cars, rally cars, dragsters, all having different requirements.
When you've studied, experimented, and practiced enuff, -. Then your opinion can be considered .

dustertogo said:
I wasn't ignoring anything. You seem to have me confused with the OP. I have already purchased the 1 1/32" mc and installed it on my car and I'm totally satisfied with it. My post was like many others responding to the OP with my opinion. I was just telling him what I had done and let him go from there. The fact that you and others had recommended the 15/16" mc was immaterial to me.
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jmo
 
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