Dennis Hagen

[Dennis Hagen]

I have a 51 Buick with  Bendix power brake booster. Drum brakes with relined shoes. After about a ten mile drive today and quite a few stop lights the brakes seem to drag. Weather is about 70 degrees. Should I try to back off on shoe adjustment or could it be a vacuum issue? I notice when the car sits awhile I have pump the pedal a few times to make it more firm, once driving I can lock them up easily.

Anyone have any ideas?

[Littlestown Mike]

Is this the first drive after doing brake work, or is this the first time this problem has shown up on brakes that worked fine previously?

 

[Dennis Hagen]

I have 1000+ miles since the brakes were done. This happened once before and I backed off the shoes some and bled the system again, I was hoping to get some ideas, thanks for looking.

[hook]

I had a 54 Olds with a tredlevac power brake system that would do that. The Tredlevac system was mounted under the peddle below the floor and was too close to the new exhaust system and it would heat up causing the problem.

[Dennis Hagen]

Thanks for the reply. Mine is mounted under the hood on firewall where a modern booster would be so I don’t think heat is the issue but I will check it with a temp gun. Just thinking the lines run down to original master cylinder

 on the frame and they go by exhaust pipe, I’ll look into that.

[Dennis Hagen]

Thanks for the reply. Mine is mounted under the hood on firewall where a modern booster would be so I don’t think heat is the issue but I will check it with a temp gun. Just thinking the lines run down to original master cylinder

 on the frame and they go by exhaust pipe, I’ll look into that.

[DFeeney]

This is not a unusual problem.  I would check all your free play adjustments.  Perhaps one is to tight not allowing the brake rod to return, thus holding the brakes slightly on.

[Dennis Hagen]

Another thing to check. Thanks

[Jolly_John]

It's also possible one or more of the flexible brake hoses has deteriorated on the inside, failing to remain "open" under vacuum. In essence, this keeps the brakes partially or fully on. These hoses can look 100% fine on the outside, but they still aren't good.

 

If the three(?) flexible lines weren't replaced as part of your recent brake job, I would do so now. Good preventative maintenance, even if they aren't the cause of your problem. John

 

P.S. You also might garner more replies to you post if you changed the title to something like "1951 BUICK Brake Problem". Good luck!

Edited March 30 by Jolly_John (see edit history)

[Ltc4748]

If all the brakes are dragging/getting hot I would be looking at the Master cylinder. In a master cylinder there are 2 holes, 1 is much larger than the second one. The smaller one is about .020" in diameter. If the smaller hole gets plugged by a piece of dirt or the DOT 3 has moisture in it and it corrodes shut, the fluid in the lines cannot return back into the master cylinder as it expands from warming up due to heat from braking, underhood engine temperature, and ambient temperature. A quick way to check if this is happening is to carry a wrench with you and use it to crack one line ( 2 lines for a dual reservoir system)  loose for a second and relieve the pressure. If the brakes work fine after relieving the pressure I would disassemble the master and probe the smaller hole with a number bit that measures no greater than .020". 

 

Another possibility is if the residual valve would hold too much fluid pressure in the brake line. If the residual valve is doing it you would relieve the pressure and after driving some more the brakes will begin to drag again. relieving the pressure again would relieve the pressure and the brakes would be free again.

 

Some master cylinders are open enough that you can probe the small hole on the vehicle to see if it is open. I have seen this several times over the years, it is unusual.