Disc Brake Adjustment

[MochetVelo]

My 1909 Buick has a disc brake replacing the original drum brake on the driveshaft. This seems to work well, but the pads drag on the disc. I don't know what model the brake unit is. Can the calipers be adjusted on these?

To the left in the photo are the planetary transmission drums.

 

Phil

 

 

Edited October 4, 2020 by MochetVelo (see edit history)

[edinmass]

Go to the hot rod supply places, and get a proportioning valve that has the bleed off built into it. It allows the caliper to release more than normal. Often used on dragsters and other track cars.

[MochetVelo]

Thanks. I see several of these at Summit, but I don't see any bleeds on them. Would one like this work?

 

Phil

 

 

[joe_padavano]

The purpose of a proportioning valve is to reduce the pressure to the rear DRUM brakes in a disk/drum system to prevent premature rear wheel lockup. There is zero reason to use one in a single emergency brake application. It will not do what the OP wants. Most disc brake calipers are self adjusting. The square cut elastomer seal rings will distort slightly as the pistons move outward when the brakes are applied. When pressure is released, the seal rings relax and retract the piston slightly. All disk brakes drag somewhat for this reason (excepting modern low-friction calipers). This is why drag racers would replace front discs with drums to allow the drum brakes to be adjusted loosely for less drag.

 

[edinmass]

Joe......I understand your comments, but there are valves with bleed offs for drag racing......we had them on our top fuel machine....disk brakes all around..........although it was ten or fifteen years ago, they were off the shelf........I’m certain they would have been expensive.......the machine was running in the 6’s and 225MPH  on a 1/4 mile....... So it was no Sunday afternoon toy, and it was set up correctly. I wasn’t suggesting the standard off the shelf proportioning valve.....and not a street valve. I have zero clue where we got it, but I remember the conversation clearly with the brake guy setting up the system.

 

I was just a crew member and not one of the engineers or builders of the machine, so I don’t have all the details locked into memory.

 

Edited October 4, 2020 by edinmass (see edit history)

[joe_padavano]

1 hour ago, edinmass said:

Joe......I understand your comments, but there are valves with bleed offs for drag racing......we had them on our top fuel machine....disk brakes all around.

 

OK, but they aren't called proportioning valves. The device that the OP posted a picture of is what is commonly called a proportioning valve in the street rod world and will not bleed off pressure the way you describe.

 

In any case, there should be no residual pressure in the brake hydraulics with the pedal released, unless there's a residual pressure valve or unless the pedal is improperly adjusted and doesn't allow the M/C piston to return to the fully unapplied position. Some master cylinders incorporate a residual pressure valve in the outlet port - this can be removed if so equipped.

[MochetVelo]

So, can I adjust the calipers so they don't drag as much?

[DFeeney]

It has been my experience that disc bake calipers that are not used much stick out and do not release completely. The cheapest thing to do would be track down the caliper part # and replace it to see if it makes a difference.

[joe_padavano]

10 hours ago, MochetVelo said:

So, can I adjust the calipers so they don't drag as much?

 

Go back and re-read my post about how calipers work. There is no adjustment to make. DFeeney is correct - the only repair is to replace or rebuild.