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Calipers Drag after drum to power disc brake conversion

7K views 22 replies 8 participants last post by  tom991 
#1 ·
I had my front manual drum brakes converted to power disc brakes on my wife's 65 I6 200 convertible with a 4 lug kit from Summit Racing. The problem encountered was in order not to have the brakes drag the rotors the installer put 1/8" inch shims between the Master Cylinder and brake booster. The problem there was the brake peddle goes 1 3/4" from the floor before the brakes stop the car with the shims between the MC and Power Booster. I removed the shims it raies the peddle to a normal 4" from the floor to stop the car. However after stopping a couple of times the brake pads continue to grip the rotors and don't release when stepping off the brake peddle.

Has anyone had this issue and figured a way to fix the problem? Could the problem be in the new booster? How can I test the booster to make sure the new booster isn't the problem?

I would appreciate any advice and/or solutions to try to give me a normal brake peddle height and no over drag of the pads on the rotors when the brake peddle is released.
 
#2 ·
A friend had a similar problem and it was that there was not enough room between the brake pedal rod and the master cylinder. The piston inside the master cylinder must come back all the way to open up the feed/relief port and release the hydraulic pressure. If not it will apply some pressure onto the calipers and onto the brake pads. Also as the rotors and calipers heat up the fluid will expand and apply some pressure if not relieved. You should has some freeplay between your rod and the master cylinder at rest (about 1/8"). By taking out the washers you might have removed this freeplay. You might try a washer (or shim stock) that is thinner than the original washers that were installed to provide some freeplay and moves the pedal away from the floorboard. If you are running drum brakes in the rear make sure they have been adjusted so you don't have excess play as this will add pedal travel before they make contact.
 
#3 ·
Make sure that you have a master cylinder appropriate for disc brakes.

MC's for drums have a residual valve that maintains some pressure on the shoes for better stopping. When a drum MC is used on a disc car the brakes will lock up after being used and not release unless the car sits for a while.
 
#5 · (Edited)
The pushrod going from the booster to the master cylinder
should be adjustable. I'm guessing that it's not. The installer
discovered this, hence the 1/8" shims......

Yup, it would be nice to be able to ID this booster.....


ex-Global West GM
1991-1995
 
#13 ·
The push-rod from the MC to the booster isn't adjustable. Someone, I don't know who, told my installer to either cut the push rod or use shims between the MC and the booster. He elected to use 1/8" shims which increased the brake peddle free play until the brake peddle was within 2" from the floor. I removed the shims and expoerienced the calipers locking up. I'm leaning toward the problem being in the MC not releasing pressure to the calipers as 67t5ponycoupe and PetesPonies suggested.

Is there a specific MC that is recommended?

Thanks,
 
#12 ·
I believe the MC is a power brake MC is a DORMAN M36445 a power brake MC that covers 73 Mustangs and 74-77 Mavericks. Can someone recommend a different MC is this isn't correct.

It must be a combination valve then proportional and distribution block. It has an adjustment knob on top to regulate the percentage of pressure to front and rear brakes. One line from the rear, larger bowl on the MC goes in for the front brakes and two come out for the left and right front brakes. Another from the smaller bowl on the MC goes in for the rear brakes and and the rear brake attaches to the valve that feeds the rear brake line.
 
#10 ·
Some master cylinders have a residual valve behind the seat in the port for the front brakes. You either have to pull the seat out or get a small wire that will go through the hole and see if you feel something rubbery behind the seat. If you do that will mean you have a drum/drum master.
 
G
#15 ·
That was designed as a truck MC and is a disc/drum MC. I don't know the piston size and how that works best for your braking. The size of the piston will effect the effort needed and the distance that the pedal will have to travel to accomplish the task.
 
#16 ·
Thanks. With that I found that the part is for a 83 Ford Ranger with manual disc/drum brakes. It's got a 15/16" cylinder bore. That could be part of the problem since it is for a manual not power.

The body is aluminum compared to cask iron on the MC for a 74 Maverick that someone locally recommended but the mounting holes don't line up with the booster bolts unless I drill them out and I don't want to do that.
 
#17 · (Edited)
As originally supplied to Ford, that's an aluminum Ranger master cylinder, disc/drum,
non-power applications, 15/16"....... from what I see.
Check to see if you can make the adjustable rod shorter.

I see you already got that info....
Where is Summit during this whole ordeal? They should be teching
the stuff they sell.

ex-Global West GM
1991-1995
 
#19 ·
If you have the master cylinder out, check the snap ring that holds the piston in place (it's where the pushrod enters the master cylinder). I had a snap ring twist on me once and that prevented the piston from fully releasing. Experienced the same symptoms you have.

Once I fixed the snap ring, everything worked fine.

I think when I was installing the master cylinder, the pushrod hit the edge of the snap ring and popped it sideways...so be careful when putting your new parts back in the car.
 
#20 ·
Received the new MC from Summit for my SSBC drum to Disc conversion kit. Good thing I have my own bench bleed kit. The kit SSBC supplied has two 1/4" bleed stems one to go intothe rear brake supply which is 1/2x20 and the one for front supply which is 3/16" fine thread. Makes me wonder why SSBC didn't include adapters, OR, two different size brake line connectors with the disc brake kit instead of two brake lines with 3/16" connectors. I think I'll have my own 1/2x20 line made so not to have failure points on my brake system.
 
#23 ·
Update. Installed the new SSBC replacement master cylinder I received from Summit. I used the 1/2x20 to 3/8" fine thread adapter. I'll get around to making a 1/2x20 brake line eventually. The brakes disc brakes work well, much better then the drums did. The car stops with about 3 1/2" of brake pedal left above the floor board.

Would adjusting the connecting rod under the dash doing anything as far pedal height? The pedal is up to the top and there is about 2" of free play before it starts braking.
 
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