1956 Master Cylinder to Power Booster

kerry a berg · Monday at 6:40 PM

Replaced front drum brakes with disc brakes nearly 20 years ago with by brake vendor. I just rebuilt brake power booster and observed that the power booster was connected to the rear drum brakes. This does not seem right as front brakes generally supply 70 to 80% of braking. I’m want to change that. Can I go from master cylinder (dual bowls), to brake power booster, to proportioning valve, with the two forward lines of porortioning valve (large bowl master) to front disc’s brakes and rear line of proportioning valve (small bowl master) to rear brake lines?

Tom Alpers · Tuesday at 2:26 AM

I agree with you, that doesn't seem right. Set up that way I would expect the rear wheels would be locking up all the time. Before I changed anything I would put the new booster on it just like it was set up before and see how the brakes feel and work. I presume you had the booster rebuilt because it wasn't working and you thought the pedal effort was too high. It may be that you don't need the booster at all if it was only connected to the rear brakes before since that means you have had manual brakes in the front for 20 years and presumably thought that worked fine.

kerry a berg · Tuesday at 10:21 AM

Tom Alpers said:
I agree with you, that doesn't seem right. Set up that way I would expect the rear wheels would be locking up all the time. Before I changed anything I would put the new booster on it just like it was set up before and see how the brakes feel and work. I presume you had the booster rebuilt because it wasn't working and you thought the pedal effort was too high. It may be that you don't need the booster at all if it was only connected to the rear brakes before since that means you have had manual brakes in the front for 20 years and presumably thought that worked fine.

Thank you for responding Tom. Before the front brakes were replaced with disc brakes the vehicle stopped with little pedal effort. After disc brake install on front I got the car back without booster. When I asked about booster they said it would not make any difference but I insisted that it be put back on. Ever since it has been like manual brakes with hard pedal. I just took that booster apart and rebuilt with new parts from Harmon Brakes. The old parts we all worn, pitted and in poor shape. The booster they put back on was not the same booster they took off.

cokefirst · Tuesday at 7:10 PM

Are you using the original Midland power brake unit? This power brake unit is mounted on the inner fender and has a line running from the master cylinder to the power brake unit. From there it has a hose that attaches to the unit that is then connected to a distribution block on the frame. If this is the unit you have, it can be configured to provide power brakes to either the front or rear brakes, but not both.

kerry a berg · Tuesday at 10:32 PM

cokefirst said:
Are you using the original Midland power brake unit? This power brake unit is mounted on the inner fender and has a line running from the master cylinder to the power brake unit. From there it has a hose that attaches to the unit that is then connected to a distribution block on the frame. If this is the unit you have, it can be configured to provide power brakes to either the front or rear brakes, but not both.

Thank you Cokefirst,
Yes, this is original Midland brake power booster which I recently rebuilt. I had a company put on front disc brakes but kept the rear drum brake. A dual brake fluid reservoir was also added with the large bowl plumbed directly to the front brakes with a simple splitter. The front reservoir small bowl is plumbed to the Midland brake power booster which is plumbed to the rear drum brakes which makes no sense to me. What I want to do is replumb the large bowl of the brake reservoir to the Midland brake booster to a porportioning valve which has two lines leading to the front brakes independently and one line from the small brake fluid reservoir, to the porportioning valve rear wheels the out to the rear wheels. Would greatly appreciate any input into my thinking and if anyone has done this. Thanking all in advance!!!

Tom Alpers · 2025-04-02T00:34:24-0400

kerry a berg said:
Thank you for responding Tom. Before the front brakes were replaced with disc brakes the vehicle stopped with little pedal effort. After disc brake install on front I got the car back without booster. When I asked about booster they said it would not make any difference but I insisted that it be put back on. Ever since it has been like manual brakes with hard pedal. I just took that booster apart and rebuilt with new parts from Harmon Brakes. The old parts we all worn, pitted and in poor shape. The booster they put back on was not the same booster they took off.

Sounds like the shop wasn't fully up to speed on how to do things. Since the fronts do 80% of the work and the booster was only on the back brakes you did have mainly manual brakes. I would try to get the booster in the line that feeds the front brakes. I suspect the shop didn't to it that way because all the plumbing off the master is so close to the proportioning valve they found it easier to just put it in the line to the rear. I have always thought the easiest way to do it with a dual master would be to not use that proportioning valve and just run the line from the master that's for the front brakes to the booster and the booster out to the distribution block that's already down on the frame that feeds the fronts and rears on the original setup. Remove the line to the rears and plug that hole. Then run a new line from the rear out on the master to the line that goes to the rears. That will make the boost on the front only. Would have to drive it to see how balanced it felt but seems like set up that way would work pretty well.