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-   -   Brake Booster (http://www.hotrodders.com/forum/brake-booster-217065.html)

LBL 03-21-2012 04:56 PM

Brake Booster
 
I recently installed a power booster on my 59 Ford and it has dual reservoirs. I bled all the air out of the system and still can't seem to get the brakes to stay up, the pedal goes to the floor . I ran one line from the back reservoir to the back brakes ( drums) and the other line from the front reservoir to the front brakes ( discs) . Do I need a proportioning valve in there somewhere and if so, would this be the reason the pedal is going to the floor istead of building up pressure? Is it possible that my rod from the pedal to the booster is too short ?Thanks

dtracy 03-21-2012 05:54 PM

How did you bleed the system, with a bleeder or manually?

You mention that the rod may be too short, does the brake mechanisim and the booster belong together?

Are you trying the brakes with or without vaccuum?

LBL 03-21-2012 06:44 PM

Manually
 
I'm using the 2 man system and bleeding the brakes manually. The booster and master cylinder are new this year but I put the discs on the front 2 years ago and used them without a booster for that period of time. I bled them without the booster hooked up ( actually just did it without the car motor running ) and they didn't pump up all the way and then when I started the car, the pedal had very little resistance and it went right to the floor. Maybe I can adjust the rod and see if it can go longer, I am using the original brake rod ...

dtracy 03-22-2012 09:02 AM

If I'm understanding you correctly you say that the brakes worked ok until you put the disks on the front, then no pedal. Sounds like the master cylinder displacement is too small for the size of the front caliper pistons. You could try using a master cylinder that matches the front rather than the back.

S10xGN 03-22-2012 09:09 AM

Quote:

Originally Posted by LBL
I recently installed a power booster on my 59 Ford and it has dual reservoirs. I bled all the air out of the system and still can't seem to get the brakes to stay up, the pedal goes to the floor . I ran one line from the back reservoir to the back brakes ( drums) and the other line from the front reservoir to the front brakes ( discs) . Do I need a proportioning valve in there somewhere and if so, would this be the reason the pedal is going to the floor istead of building up pressure? Is it possible that my rod from the pedal to the booster is too short ?Thanks

Are the reservoirs on the M/C the same size? Most aren't and the front discs need to be connected the larger reservoir which is usually the rear one. Sounds like you're piped up backwards...

Russ

LBL 03-22-2012 09:26 AM

What Changed
 
What changed was adding the booster and master cylinder. They worked fine when I first put the discs on the front but now with the booster, the pedal goes to the floor. The MS and booster came as a kit and the reservoirs are the same size. I have a meeting at noon , then I'm going to go back and see if I can lenghten the push rod from the pedal to the booster and see if that helps. If I have 2 separate lines from the ms, would a proportioning valve help matters?

dtracy 03-22-2012 10:05 AM

In this case I don't think the valve would matter as you don't seem to have any brakes at all. Be careful with the rod length, be sure you have some free travel or the fluid will not return from the wheels and as the brakes get hot and the fulid expands the brakes will be applied more until they go a fire. This has happened to me once so I speak from experience.

LBL 03-22-2012 10:10 AM

Thanks
 
I never thought about return flow. I think I have 2 adjustments, one from the pedal to the booster, and a second from the booster to the mc. I'll have a look at the setup right after lunch...

LBL 03-22-2012 01:44 PM

Damn
 
I went out and adjusted the slack in the rod from the pedal to the booster and thought maybe it was better until I started the car and then the results were the same , right to the floor. I took the top off the reservoirs and pressed the brake pedal and there didn't appear to be any return , I'm thinking there should have been a squirt into the reservoir when I pushed on the pedal, not sure if that tell much or not

dtracy 03-22-2012 04:49 PM

You might try unbolting the master cylinder from the booster and have a look. This is usually a job that takes two guys, one on the inside and one on the outside. Or, take the booster assembly off and clamp it in the vise.

Maybe someone else has a better idea.

LBL 03-22-2012 07:11 PM

i'm Thinking
 
of putting a different master cylinder on it to try. I shouldn't have to because the one on there is new but I can't think of anything else. I beleive that there should be some residual coming back into the reservoirs when I pump the brakes but i'm not seeing anything squirting up through the fluid like it should.

dtracy 03-23-2012 09:16 AM

Just because it's new doesn't mean it's ok. Everyone makes a mistake now and then. It sounds like a really good idea to try a different master cylinder just to isolate the problem.

Also, something to think about, the pedal leverage on a system with manual brakes is different than with power brakes. The idea being that manual brakes needed more leverage than power assisted and to keep you from being slammed into the steering wheel, the leverage was reduced. At this point the only thing this might apply to in your case is that the pedal is not pushing the rod far enough to apply the brakes. With the master cylinder off you could measure the full travel of the piston and also the full travel of the push rod from the booster. Might be worth a look.

Frisco 03-23-2012 09:36 AM

Quote:

Originally Posted by dtracy
Just because it's new doesn't mean it's ok. Everyone makes a mistake now and then. It sounds like a really good idea to try a different master cylinder just to isolate the problem.

Also, something to think about, the pedal leverage on a system with manual brakes is different than with power brakes. The idea being that manual brakes needed more leverage than power assisted and to keep you from being slammed into the steering wheel, the leverage was reduced. At this point the only thing this might apply to in your case is that the pedal is not pushing the rod far enough to apply the brakes. With the master cylinder off you could measure the full travel of the piston and also the full travel of the push rod from the booster. Might be worth a look.

I think your problem is what dtracy has mentioned above. The factory pedal ratio for non-power assisted front brakes is usually in the 6:1 or 7:1 ratio. Power assist brakes have a pedal ratio around 4:1 and less. Some manufacturers provide two different holes in the pedal to allow for changing the ratio.

The free play at the pedal should be about 1/2" max and is adjusted by changing the length of the pedal pushrod that goes to the booster or master cylinder. There is also an adjustment on the pushrod that goes from the booster to the master.

1971BB427 03-23-2012 09:45 AM

Since this is a new master/booster combo I'd be questioning that first. Did you bench bleed the master before installing the combo? Have you split the two apart to see if something is possibly missing when it was assembled? It's possible they didn't get something right when assembled; mistakes do happen.
When you bleed the brakes do you get good flow at each wheel? If not then you're most likely looking at an issue at the new master/booster assembly.
A prop. valve wont have any affect on the brake pedal pressure when bleeding. It will simply regulate pressure front/rear when stopping.

LBL 03-23-2012 10:52 PM

I Checked
 
I checked between the booster and the MS and everything looks okay. There is a small adjustable rod that is screwed out about 1/4" from the piston in the booster and everything seems to operate when the pedal is pressed. We didn't bench bleed the cylinder but we have bled the brakes until all we have is clean new fluid coming from each wheel . I'm just not sure why there isn't some residual fluid spraying up from the MS when I push the pedal down.


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