So, I'm building a '48 Ford Tudor Sedan. Thought I was going in the right direction by going with 4 wheel disk brakes. I found a disk-brake-equipped 8.8" rear axle from a '94 Mustang GT and got it mounted with a Posies kit. I ordered custom backspaced Gennie wheels from Wheel Vintiques so the P235/65R16 tires would tuck inside the wheelwells. I have a disk brake kit that will go on the dropped solid axle when I get to the front end. Today I called ECI to ask about their kit to adapt a dual master cylinder to the original frame that would also allow me to use the original clutch with the S-10 T-5 trans. Ralph there told me that combination will not work without a booster. I have not seen a way to add power brakes to the original x-frame while keeping the original clutch, so now I'm panicked. Ralph recommended I go with a drum brake in the rear. Does anyone make a bolt-on drum brake kit for an 8.8" Ford? Does anyone have another cost-effective recommendation that would hopefully allow me to utilize the stuff I've already bought? Thank you in advance. Dave
I think Ralph is wrong. I've built 2 cars with 4 wheel disc brakes (using the 8.8 rear axle). Neither car had a booster. One car used Wilwood master cylinders and the other used a master from CPP. Anyways, here's a bump for you... Edit - I've built 3 cars with 4 wheel disc brakes. Oops, forgot.
A booster is not a requirement for disc brakes, front, rear, or both. The only things critical are pedal ratio and master cylinder bore size. What calipers does the front kit use? That will help us make sure that the remainder of your components are correctly selected.
Consider a hydroboost from some vans. My Road-Racer Corvette never had a booster [poor mans ABS] at It would haul up at 170mph. Just use a smaller diameter master if a booster is out of the question
If you use a Wilwood master cylinder you will not need a booster. I have a disc/drum system in similar car with no booster and I stop fine. Sure, you need to push the pedal a little harder but not that much. Stops fine.
If you really want a booster, how about mounting it further back with a supported pushrod between the original pedal and the booster?? I have this setup on my Nash, and works great..
The "native" master cylinder bore for those calipers, with manual brakes, is 1", with the boosted system using a 1-1/8" bore. The "native" master cylinder bore for those rear brakes is 1-1/6", but that was with a booster. Manual brakes usually have you round-down to the next smaller master cylinder bore, which, for the Ford stuff, would be 15/16". Given that 1" and 15/16" are pretty close, I would just run a 1" bore master cylinder, just like the setup that @Chucky showed above, and call that good.
Yep, sometimes there's just no room to mount them without moving them back and using an extension rod. Works well. And a '95 geo metro is the smallest booster I've found, they work great.
Thanks for the reply. ECI said my issue would be with the Mustang GT rear disk brakes not having enough pressure without a booster. So, your advice is that I should be fine with a 1" bore manual master cylinder. I would probably need an adjustable proportioning valve though, correct? 3/16" brake lines OK?
Boosters are a "comfort item", so grandma Millie can drive the car. They boost YOU, so you don't have to push as hard, and they give you short pedal travel. The way around this, or what they did "back in the day" was a smaller bore master cylinder, higher pedal ratio, or both. The rear calipers will have no idea where or how the volume and pressure got there, booster, or not. 3/16" brake lines are fine. Size is not an issue in a hydraulic system, unless you went too small, per se. The proportioning valve show in the previous picture should be fine. Adjustable ones are more suited to extremely mismatch components. You should also have 2lb residual valves, one each, in the front and rear circuits.
I have Wilwood discs on one Willys and GM discs on the other. I use the Corvette MC with one and an eighth bore with no proportioning valve and have great stopping power with both cars. What most people call a proportioning valve is actually a combination valve. That is what you see mounted by the MC on OEM setups.
The thing about brakes is that it is both a volume and a pressure issue. If we p**** out just those front brakes, say from a 1980 Camaro, where they were a factory item, power brakes were an option. You could get discs with, or without the booster. The biggest difference in the system was the size of the master cylinder. With manual brakes, it was 1". With power brakes, it was 1-1/8". Why the difference? Ease-of-use for the operator. In all likelihood, the measured pressure in each setup was exactly the same. The difference would have been felt by the driver. Smaller bore master cylinders deliver more pressure, but you have to push the pedal farther, to get a particular volume. Larger bore master cylinders deliver less pressure, but a higher volume, so they deliver that particular desired volume with less stroke, but you have to push them harder. The solution there is to put a booster between the pedal and the master cylinder. Then you have the "best" of both worlds, high volume, high pressure, and short pedal travel. I cannot remember if the aforementioned Camaro had a different pedal pivot or pushrod hole, to alter the pedal ratio. The overall difference would have been that you would have had to push the pedal a litter farther in the manual brake car to get the same result. The thing that you do need to make sure of is, does the master cylinder you are choosing have the capability to deliver enough volume to drive a rear disc brake setup. Clearly, those made for drum brakes do not. Most of those that are made for disc/drum setups do not either. What you saw in the last picture is a "Corvette style" master cylinder. That is a disc/disc master cylinder, but has been used in disc/drum, and even drum/drum setups, with success. Mixing and matching would require a proportioning valve, likely of the adjustable variety.
You can use a remote booster if there is no room for a regular booster. But, there are some pretty small boosters, like 8" diameter. They barely stick up above the master cylinder.
I have a Geo Metro booster pushing a Corvette master cylinder in my Falcon. Go ahead and tell me that it doesn't fit. Everyone else does.
In fluid dynamics, there is always a formula. Methinks there is data for the diameter of the Mustang rear caliper bores, the Camaro pedal ratio (std. vs power, considering the 1" or 1.125" M/C bore) Good info here by Gimpys, but I can't find the bore of the rear Mustang calipers! (rebuild kits are 'available', but no specs.) Ratio of proportion is paramount in an application such as this...
Great info. Thank you. I see that ECI (and others) offer new 67-76 Corvette master cylinders w/1" bore for 4 wheel disks. The CPP version above is also an option. ECI and others also offer an adapter for mating that MC to the original pedals. The adapter comes with a new pushrod that is adjustable. That may make the ratio adjustable? I'm feeling a bit more optimistic about using what I've already got, thanks to you guys.
I figured that. The ratio would need to be adjusted by moving the pushrod attachment point on the pedal, correct?
Yep. Here's a underfloor booster I had to move back and use a long push rod. It's under the seat beyond the transmission tail.
Another option, Ch***is Eng makes an adapter that attaches a booster to the stock pedal ***embly, which does not interfere with the original clutch pedal. Part # AS-2058
Thanks Rich, I hadn't seen that. Now, my next question would be will my flathead produce the 18 lbs. of vacuum required for a booster or will I need to add a 12V electric vacuum pump?
You can get a vacuum gauge, cheap, at most auto parts stores. Many stores rent them, too. I have not lived in M***achusetts in over 20-years, so I am not sure what stores are out there now. Checking the vacuum would be best.
I'm afraid I'm a long way from firing the engine to test vacuum. I was advised by the machine shop I'm using to get the ch***is done first so the completed motor won't have to sit long before being fired once it's complete. So, that's why I'm trying to get these brake components put together and installed. Thanks again for all of the information you've provided.
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