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Which Master Cylinder to Use #1000519
05/26/11 10:28 PM
05/26/11 10:28 PM
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Louisiana
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duckblind Offline OP
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I have a 68 charger with power brakes. Both front and rear brakes are disc. The front calipers are from a 73 b body (rotors came from an unknown source) and the rear brakes are Ford Cobra (purchased a dana set-up with disc brakes for Doctor Diff). Anyhow, I am wondering if it would matter if I used a all drum brake or front-disc/rear drum master cylinder? The reason why I am asking is because I have both type master cylinders and am not having good luck with either one so I am wondering which one I should concentrate on.

Re: Which Master Cylinder to Use [Re: duckblind] #1000520
05/26/11 10:54 PM
05/26/11 10:54 PM
Joined: Jan 2003
Posts: 8,016
Polson, MT
DoctorDiff Offline
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Polson, MT
What problem are you having?

What is the bore size of your master cylinder?

Power or manual brakes?

What size wheels?

Are you running a proportioning valve?

Re: Which Master Cylinder to Use [Re: DoctorDiff] #1000521
05/27/11 07:34 AM
05/27/11 07:34 AM
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Louisiana
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duckblind Offline OP
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You name a problem and I probably have it in regards to the brakes. Because of the cam in the engine I needed to get a vacuum pump for the brake booster. I bought a vacuum pump from summit and hooked it up to the booster and still no power brakes. I ordered a reman booster from summit (a Cardone). For the first hour or so the vacuum pump would cycle on and off when I would apply the brakes (this is as I am trying to bleed, not while I was driving since it is not really driveable without brakes). After around an hour the pump just kept running. I disconnected the check valve from the booster and put my finger over the check valve hole and the pump stopped so the leak must be coming from the brake booster. I have a manual brake pushrod and manual brake firewall bracket in my attic. I am about ready to pitch the entire power brake idea and go with manual.

Anyhow, the car sat up in my garage for about 1.5 years as I was doing some body work on the car and also did a swapover from auto to 4 speed. One of the front calipers froze up so I decided to change both front calipers. I ordered reman calipers from summit and changed them. I also ordered a reman master cylinder. I don't know the bore size as it doesn't say on summits website like it does for most other master cylinders. The one I ordered was http://www.summitracing.com/parts/AAZ-10-1323/. Somehow I ordered the drum brake mc instead of the disc brake one. Now, I pump and pump the brake pedal and it never seems to get hard.

I am not running a proportioning valve. I am only running through the little stock 5 port brass metering block or whatever the block is called.

The tires are 265R15something or another. Nothing too large but a little bit wider than stock.

These brakes are about to drive me crazy. I thought brakes were supposed to be simple. That is why I am about to pitch the booster and vacuum pump. Maybe I got too much clap trap. Maybe if I simplify it will get better or maybe the problem is that since I have brakes that are non-stock, I need to do something different with the master cylinder.

Re: Which Master Cylinder to Use [Re: duckblind] #1000522
05/27/11 08:06 AM
05/27/11 08:06 AM
Joined: Jan 2003
Posts: 8,016
Polson, MT
DoctorDiff Offline
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Polson, MT
Big cams and power brakes don't work well together.

I would run manual brakes with a NEW 15/16" bore master cylinder and a drum brake distribution valve. I will have 15/16" bore aluminum masters back in stock soon. Otherwise, you can buy an 15/16" iron master for a '73-'75 A-body POWER disc brake application.

Make sure all calipers are mounted with the bleeder valves facing upward.

Re: Which Master Cylinder to Use [Re: DoctorDiff] #1000523
05/27/11 08:15 AM
05/27/11 08:15 AM
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Posts: 474
Louisiana
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duckblind Offline OP
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Thanks doctor diff. I learned my lesson a few years ago about not having the bleeder valves facing upward.

Where do I get a drum brake distribution valve? Is it a stock part that is non-adjustable or is it something that can be adjusted?

Re: Which Master Cylinder to Use [Re: duckblind] #1000524
05/27/11 08:32 AM
05/27/11 08:32 AM
Joined: Jan 2003
Posts: 8,016
Polson, MT
DoctorDiff Offline
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That would be a stock, brass distribution block from a DRUM brake car. Sounds like you may have one installed already.

You do not need an adjustable prop valve because the Mustang rear calipers are small. You will not be rear biased.

Re: Which Master Cylinder to Use [Re: DoctorDiff] #1000525
05/27/11 07:12 PM
05/27/11 07:12 PM
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Tampa FL
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hemibeep Offline
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Tampa FL
a follow up question??

if I am running wilwood 12" front and rear, what is the correct size MC? currently, it takes a LOT of leg, and car acts like there are no brakes? doesn't really want to stop...

Re: Which Master Cylinder to Use [Re: hemibeep] #1000526
05/27/11 07:12 PM
05/27/11 07:12 PM
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Tampa FL
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hemibeep Offline
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Oh, manual brakes using stock brass valve.

Re: Which Master Cylinder to Use [Re: hemibeep] #1000527
05/27/11 09:08 PM
05/27/11 09:08 PM
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Posts: 8,016
Polson, MT
DoctorDiff Offline
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I normally recommend a 1 1/32" bore master cylinder and adjustable prop valve in the rear line for Wilwood brakes.

You must disgard the stock prop valve.

Re: Which Master Cylinder to Use [Re: DoctorDiff] #1000528
05/27/11 10:30 PM
05/27/11 10:30 PM
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Louisiana
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duckblind Offline OP
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A few months ago I bought the manual brake fire wall bracket and a manual brake pushrod. Is there anything else I need once I order the 15/16" master cylinder? Unless I bought the wrong thing or don't know how to install it, it appears as though the two bolts built into the bracket will bolt through the firewall. Will I have to secure all four bolts for the the master cylinder through the firewall too?

Re: Which Master Cylinder to Use [Re: duckblind] #1000529
05/28/11 01:37 AM
05/28/11 01:37 AM
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Posts: 8,016
Polson, MT
DoctorDiff Offline
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Polson, MT
Depends on if you have a 4-hole or 4-stud style master cylinder/brake pedal mount.

Some cars use nuts to secure the master cylinder under the hood. Other cars use nuts to secure the master cylinder under the dash.

Re: Which Master Cylinder to Use [Re: DoctorDiff] #1000530
05/28/11 07:39 AM
05/28/11 07:39 AM
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Louisiana
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duckblind Offline OP
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I don't have any studs on the firewall as the brake booster had studs that went into the firewall for securing to the brake pedal mount under the dash. So I will bolt the plate to the firewall and see where I need to drill holes into the firewall for the master cylinder.

Re: Which Master Cylinder to Use [Re: duckblind] #1000531
05/28/11 01:23 PM
05/28/11 01:23 PM
Joined: Jan 2003
Posts: 8,016
Polson, MT
DoctorDiff Offline
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If you have a firewall stiffening plate from a manual brake car, you shouldn't have to drill any holes for the master cylinder.

Re: Which Master Cylinder to Use [Re: DoctorDiff] #1000532
05/29/11 07:19 AM
05/29/11 07:19 AM
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duckblind Offline OP
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I have the stiffening plate. It as two bolts built into it that hold it to the firewall.

Re: Which Master Cylinder to Use [Re: duckblind] #1000533
05/29/11 03:48 PM
05/29/11 03:48 PM
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Polson, MT
DoctorDiff Offline
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The stiffening plate should also have 4 additional bolt holes that retain the master cylinder to the firewall/brake pedal frame.

Re: Which Master Cylinder to Use [Re: DoctorDiff] #1000534
06/01/11 09:21 AM
06/01/11 09:21 AM
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Louisiana
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duckblind Offline OP
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the plate does. Hopefully the holes are pre-drilled in the brake bracket so that all I have to do is drill through the fire wall.

Re: Which Master Cylinder to Use [Re: duckblind] #1000535
06/01/11 06:32 PM
06/01/11 06:32 PM
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sweden
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cuda-sweden Offline
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hm.do you haVE a conversion plate that uses a 2 bolt mc? but you want to use a 4 bolt mc?should there really be any drilling nessescery?maybe you should use a oem stiffening plate?.

Re: Which Master Cylinder to Use [Re: cuda-sweden] #1000536
06/02/11 10:28 PM
06/02/11 10:28 PM
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Posts: 474
Louisiana
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duckblind Offline OP
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This is the plate that I have. I am thinking the two bolts go through the firewall and brake pedal bracket and the master cylinder bolts on to the bracket but may also need to go through the firewall. I am thinking right?

Re: Which Master Cylinder to Use [Re: duckblind] #1000537
06/03/11 02:53 AM
06/03/11 02:53 AM
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Posts: 8,016
Polson, MT
DoctorDiff Offline
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DoctorDiff  Offline
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The master cylinder studs pass through 4 holes in the firewall stiffening plate, then bolt to the brake pedal frame under the dash.







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