51 Buick brakes

[Dennis Hagen]

Hello all, I put a “rebuilt” Bendix Hydrovac unit in my 51 Super and am having a hard time keeping air (soft pedal) out of the system. When I first put it in I did everything new lines cylinders etc and it worked ok, seems that letting it set unused for 6 Months causes a problem.

I put a battlebornbrakes system in my 53 Buick and works great, maybe that is the way to go?

 

[NailheadBob]

Possibly you already did this, did  you do a major brake adjustment from the service manual, first adjusting the "anchor pin" and when bleeding the brake use the sequence L/F, R/F, L/R, R/R ?

 

Are battlebornbrakes similar to GM's version back in the day to the kit offered to add power brakes?

 

Just some thoughts

 

Bob

[Ben Bruce aka First Born]

May I ask what is driving the hydrovac?  Power steering?

 

  Ben

[Rusty_OToole]

When the system is completely dry it is possible to bleed it and after a day or 2, more air bubbles come out of the fluid and cause a soft pedal. The cure is to bleed them again being careful not to get any air bubbles in the fluid.

[Dennis Hagen]

I will try to answer the replies-questions: The battleborn unit is driven by vacuum and has a split master cylinder, front an rear lines are separate. The master, vacuum “can” and hanging pedal are mounted and replaces the access plate on firewall above steering column. I purchased this unit for my 53 that had a factory Kelsey-Hayes unit that was not working.

To Ben: The Bendix unit activated by intake manifold vacuum.

When I first did the brake system everything was fine, then after sitting over the summer (at winter home in Az) I had no pedal, replaced master cylinder and bled and was ok, now this fall I have a soft pedal. Car stops but pedal is close to floor, I will do a though bleeding again today and see what happens.

[Frank DuVal]

6 hours ago, Ben Bruce aka First Born said:

May I ask what is driving the hydrovac?  Power steering?

Hydrovac is vacuum boosted.

 

Hydro-Boost is the power steering boosted system used on low vacuum engines, like Ford 400s and GM diesels.

 

Dennis, look for a trickle of a leak everywhere along the system.

[Bloo]

The leak could be literally anywhere. Gravity wants to push the fluid back to those underfloor systems. Are there cup expanders in the wheel cylinders? The wheel cylinders are at the top and can let air in without a visible leak. There probably weren't cup expanders in 1951, but modern era repair kits almost always have them. Over the shorter term, the system's residual pressure valve takes care of this, but I don't think you could expect that to hold for 6 months. Almost nobody would have let the car sit that long as a normal thing back when it was new, and they probably would have never known the difference.

 

[Rusty_OToole]

I like Bloo's answer. In 1951 they would have used a residual pressure valve to hold the rubber cups tight against the cylinder walls, if the pressure oozed away they would leak or admit air. Around 1975 they started to put springs in the cups to hold them tight and did not use the pressure valve. I don't know if new replacement cylinders or kits have the springs or if you can add them.

[60ch]

I added a 10 pound residual pressure valve to my 29 Dodge. It it really made a difference in the pedal. Any leaks in the system will be amplified.  Where you thought there were no leaks, there may be  with 10 pounds of constant pressure in the system.