Stock Fairlane, drum brakes, want to add boost unit

[BWhitmore]

An easy check for a residual check valve in the master cylinder is to insert a wire (paper clip) into the outlet for the drum brakes.  If you feel resistance there is a residual check valve present.  If no resistance there is no check valve. 

[ROKuberski]

BWhitmore,

I have confirmed that there is no residual check valve.

hiball3985,

In my volume calculation, I am assuming that since the total travel of the brake rod into the dual master cylinder is 1", then the displaced volume of fluid is pi*radius squared * length.  Same calculation on the stock master cylinder. 

I don't have a clue what the difference would be with the residual check valve, but from what I have heard, there is one on the stock unit.  Using the test mentioned, I can push a wire straight through the outlet hole on the dual master cylinder, but not through the same small hole inside of the stock master cylinder.

http://www.freeasestudyguides.com/residual-check-valve.html

http://www.thebrakeman.com/valvetechi

From reading, the residual check valve is to prevent air from being drawn into the brake system through the wheel cylinder seals.  I also saw where it takes about 75 psi to overcome the resistance of the brake return springs.  So, my assumption is that I likely need these valves, but they may not help with my problem.  I found a pair of 10 psi valves on eBay for $24, not a big deal.

Rich

[BWhitmore]

If you install a residual check valve do so for the rear drum brakes only.  Installing a residual check valve for the front disc brakes will not allow the brake pads to fully release and the front brakes will drag  and probably overheat even when the brake pedal is released. 

I don't think a check valve is going to help your issue - it also won't hurt.  If you install the valve you need the red -10psi valve.  From what you have described it sounds like an issue with brake pedal push rod travel.  Jim is also correct that your vacuum source for the power brake booster should be manifold vacuum and not from the fuel pump.  Bill

[hiball3985]

If you install a residual check valve do so for the rear drum brakes only.  Installing a residual check valve for the front disc brakes will not allow the brake pads to fully release and the front brakes will drag  and probably overheat even when the brake pedal is released. 

I don't think a check valve is going to help your issue - it also won't hurt.  If you install the valve you need the red -10psi valve.  From what you have described it sounds like an issue with brake pedal push rod travel.  Jim is also correct that your vacuum source for the power brake booster should be manifold vacuum and not from the fuel pump.  Bill

Bill, JFYI he is using the power unit for OEM drum brakes all around, no discs

[BWhitmore]

Jim - I guess I should read more carefully.  Thanks.

[ROKuberski]

BWhitmore,

I would agree that the residual check valve won't hurt, but won't help the issue of not stopping properly.  As to pedal push rod travel, I checked the full travel with the master cylinder attached to the boost unit and then checked the travel with the master cylinder removed from the boost unit.  I get more travel without the master cylinder attached.  That tells me that I have bottomed out on the master cylinder.  I am getting all the travel that the master cylinder allows.  That also means that I am getting all the fluid out of the dual master cylinder possible.  Quite frankly, at this point, I can't imagine that the problem is anything except that the new master cylinder is not providing enough fluid to push out the brake shoes into firm contact with the drum so that the car will stop.  If the supplier has any other bright ideas to try, I will let you guys know what they are.  Otherwise, I see another master cylinder in my future.

Rich 

[SkylinerRon]

Are your brakes adjusted tight?  If they are loose it will take more fluid to activate them.
Just taking a stab, sometimes the simplist things get overlooked.
Goodluck,
Ron.

[ROKuberski]

I know this is getting to be a long thread, but I previously noted that I did adjust the brakes.  However, prior to starting this process, the brakes were working well.  so the new system should have been working better.

I just got an email from the supplier.  I can either return everything for a refund or he has offered to send me a new master cylinder with a 1-1/8" diameter bore.  If this unit has the same 1" stroke, then the volume of fluid would be 1.1% less, essentially a match.  However, there would be an increase pedal effort of 26.5% because of the larger diameter.  This will wipe out some of the gain with the power boost unit.

I can't be the only person on the planet that is doing this.  I've tried to look for specifications on master cylinders.  Basic information like bore and stroke, but I have yet to find this.  Does anyone know of a place to find this?  I would rather have a master cylinder that has a 1" bore and about 1-1/4" stroke.  That would be perfect.

Rich

[hiball3985]

I wish all of us could be more help but doing it over the internet rather then hands on is more guessing then anything else. Just my opinion but I don't think the stroke length is the issue. I just went out and looked at my 60 F100, same basic 4 drum brake design as a 57. I had adjusted the brakes recently and it has a good high pedal. The push rod going into the master moves less then a 1/2" with the brakes fully applied. Almost makes me think you still have air in the system. I'm not familiar with the type of master cylinder you are using but I know there are some that can only be power bled. You didn't say how you bled them. I might be worth taking it to a brake shop that can power bleed it if you don't have the equipment.. 

[ROKuberski]

I was provided with the stuff to bench bleed the system.  I am quite sure that there is no air in the system.  While I think that there is no air in the system, I now believe that I have a hard pedal because I am bottoming out on the master cylinder.  I will bleed the system once more and check the adjustment on the brakes once more.

I certainly understand that no one is going to give me an absolute solution to this issue via the internet, but it is good to have extra brain power working on a problem.

Rich

[hiball3985]

Rich, can explain how you bled the wheel cylinders. I'm sorry, I'm just a stubborn old man but I still think if your master is bottoming out you are compressing air rather them moving fluid

[ROKuberski]

The kit came with a pair of plastic tubes and a special clamp that held one end the tubes under the fluid level.  The other end was a tapered plastic point that went into each of the outlet ports of the master cylinder.  I've seen these before, I thought every master cylinder came with them.  You pump fluid until there is no longer any air bubbling up in the chamber in the master cylinder.  It came with instructions and I followed them.

It is possible that there is air in the system, anything is possible.  I bought a vacuum pump device so I could bleed the brakes myself.  It works fine on the front slave cylinders, but on the rear, it appears that air is leaking into the slave cylinder around the threads when I loosen the bleed valve screw.  So, I started over and bled the system the old fashioned way with an assistant.

It's going to have to warm up a little before I do it again.  Next weekend looks like a good opportunity.

Rich   

[BWhitmore]

Rich - did your assistant help you bleed the brakes from each wheel cylinder starting at the right rear and moving forward?  Your first description describes bench bleeding the master cylinder only. 

When you described the car not stopping as well as you thought it should does that mean that you had to pump the pedal or that the car simply dud not stop as quick as you thought it should with the addition of the power brake booster?  Power brake boosters really will not help the car stop quicker, they simply provide a vacuum assisted advantage to applying the brakes.

I mis-read your first post and thought you had disc brakes on the front and drums on the rear.  If you have drums all around then a residual check valve is needed in both the front and rear brake lines (10 psi - Red).

[ROKuberski]

I have the hydraulic system split.  I do the longest line first in each half.  There is no agreement as far as I can tell on this method.

I am sure that I am hitting the bottom on the master cylinder.  Prior to starting this project, the car stopped well.  I wanted to reduce pedal effort and have a split system.  I know that the addition of the boost unit will not decrease stopping distance. Pumping the brakes does not improve stopping. 

I am 99% sure that there are no residual check valves on the new master cylinder.  I will order a pair of 10 psi valves.  However, from what I have read, the purpose of these valves is to keep a little pressure on the rubber parts in the slave cylinders so that no air can get back into the system.  I also read that it takes about 75 psi to overcome the brake return springs, so these valves can't do much to change the way the car stops.  Perhaps without the residual pressure valve, I am getting air back into the system.  I may not get anything done until after Christmas now.  If I find air in the system again, I will know how it got there.

I appreciate all the comments.  I think we have narrowed the problem to just two issues.  Air in the system or not enough fluid displacement from the master cylinder.

Rich

[Tom S]

.... Perhaps without the residual pressure valve, I am getting air back into the system.

Residual pressure valves are not made to prevent air from being drawn into the brake system through the wheel cylinder seals.  Air shouldn't be getting in there anyway.  If it is then something else is wrong.
All drum brake systems that I know of have residual pressure valves.  I don't think you are going to see any improvement until you get the residual pressure valves installed.
Without the residual pressure valves the slave cylinders are pushing their fluid back into the master & you have to fill them back up again each time you press the pedal so it is a good chance that you are bottoming out the master cylinder before you can get sufficient pressure on the drums from the shoes.

It's even in the link you posted.
http://www.thebrakeman.com/valvetechi

We may as well start with the residual valve, because it is the first one that should be determined whether or not it is needed. This valve does exactly as its name suggests. It keeps a pre-determined amount of residual pressure in the line after you remove your foot from the brake pedal. This aids in preventing excessive pedal travel as well as insuring consistent height to the pedal.