Stock Fairlane, drum brakes, want to add boost unit

[Ford Blue blood]

Why was the car wrecked to begin with..bad brakes? Are these like radiators, in that using them for years then sitting in storage is much worse than continued use?

Rich if I were a betting man my bet would be most cars in the yard are there because of a cranial/anal insertion problem, not a mechanical issue.......if the fluid in the hydro boost was clean and did not smell burned you should be good.  Power steering pumps run for years after sitting for years, my 62 Bird sat for 12 years, the fluid in it was perfect, no leaks, no loose seals, the radiator functioned perfectly but I had it checked out prior to putting the car back together just to be sure.

[ROKuberski]

Update on my project.

I received both a defective boost unit and master cylinder.  Both have been replaced and both are installed and working.  These parts arrived new in the box, but I had no problems getting the supplier to replace these parts.

HOWEVER, even though the brakes appear to be working, they are not stopping the car as well as they should.  I've bled the system twice, adjusted the brakes and done everything to make sure that they are working as well as they should.

Prior to starting this process, the original master cylinder did a good job of stopping the car.  Now with a new dual master cylinder and power boost unit, I still have to figure out why they are not working as well as the did before.

I spoke to a friend who is an automotive technology instructor at a local community college and he has suggested that I may need a device that holds some pressure in the system. 

Anyone have any experience with these units?  I understand that they come in different pressure, and he has suggested about 10 psi for this car.

Rich

[hiball3985]

I think your friend is suggesting a residual valve. The original master cylinder has one. I don't know if the type you have now has one or not. I may be wrong but I don't think that will not help your stopping, it only keeps a small amount of pressure on the line to keep the brake shoes expanded a little so there isn't as much brake peddle travel when you first apply the brakes. Once the brakes are applied the pressure going to the cylinders should be the same if you have one or not.

[BWhitmore]

Jim is correct..  A residual pressure check valve will not help stop the car better.  The residual pressure check valve is used for the rear drum brakes only and is used to maintain pressure on the rear drum brakes once the brake pedal is released.  This prevents the need to pump up the brake pedal every time the brakes are applied.  My Ranchero uses the stop n drop disc brake system with stock drum brakes on the rear with no power brake booster and stops great. 

[RICH MUISE]

Let me ask a general question here...is a booster that is too small worse than no booster at all, or is it a matter of not adding as much assist as it would if it were larger, but still better than no booster?

[ROKuberski]

First to answer Rich - The power boost unit is working as is the new dual chamber master cylinder.  The brakes are properly adjusted and the hydraulic system is bled.  I have a good hard peddle.  I believe I have sufficient assist from the boost unit and I don't believe that anyone is installing a larger boost unit because of the clearances issues with the exhaust manifold.  I don't believe my problem is with the boost unit.  As to the master cylinder, It was properly bled before any brake lines were installed.  I believe that I have good travel with the rod from the boost unit into the master cylinder.  However, this is something that I haven't done an accurate measurement on.  I can take the defective master cylinder and measure what would be full travel and I can also measure the amount the boost unit rod moves when the brake peddle is depressed.

Hiball3895 - I will check into the master cylinder that I have and see what the specs are on it.   Thanks for the reminder of the term "residual check valve."

BWhitmore - I believe my friend was suggesting this because we are currently unsure if the new master cylinder has a residual check valve. 

I'll see what additional information I can find out and let you guys know.

Thanks for the comments,

Rich

[hiball3985]

Forgive me if this seems elementary but did you check the vacuum at the manifold port?

[SkylinerRon]

What is the bore size on your new m/c? Could very well be a leverage problem.

BTW, The stock 57/58 Ford underdash P/B works great and is very rebuildable.

Goodluck,

Ron.

[ROKuberski]

Hiball3985 -Vacuum is 14 inches without going through the vacuum boost pump on top of the fuel pump, 17 inches if I go through the vacuum boost pump.  Right now, I'm not using the boost pump.  This is all the vacuum you can develop at my altitude of 5,440'.

SkylinerRon - The bore size is 1" and the stroke is 1".  That does not seem like much fluid.  The original master cylinder is 1.4 inch bore and 1.1 inch stroke.  I should have done this before.  Calculating the full 1" stroke for the new master cylinder, I am only getting 59% of the fluid out of the new master cylinder compared to the original.  This has to be the problem.

As to using a rebuilt original power brake master cylinder, frankly, I did not consider that.  I was not aware that they were available until recently.  Having the dual master cylinder does appeal to me, but only if I can get it to work properly. 

Thanks guys,

Rich

[SkylinerRon]

The stock 57 pb mc is 1.125", stock non power is 1.0".  I don't know the the stock strokes offhand.
My guess would be the power is shorter stroke as fluid is non compressable so you need the same quanity to activate the shoes and the power assist just applies more force.
Goodluck,
Ron.

[hiball3985]

The vacuum unit on the top portion of the dual diaphragm fuel pump is only for the windshield wipers to add additional vacuum when the engine is under load and manifold vacuum drops. The master cylinder booster should be connected directly to a vacuum source at the manifold. 

Have you tried disconnecting the vacuum line and comparing the pedal pressure required to stop as to when it is hooked up? It sounds like the vacuum unit isn't working properly.

[ROKuberski]

Jim,

I have the power brake boost unit connected directly to the intake manifold through the proper sized line.  It is working just fine.  Yes, I have tried the brakes with and without the boost unit connected.  I'm sure my problem is the volume of fluid displaced by the master cylinder.  A 41% reduction in volume means that the slave cylinders are not being pushed out far enough for the shoes to fully contact the drum.  I've sent an email to the supplier, but I don't expect to hear back from him until at least Monday.

Ron,

I measured the back end of the opening on the old master cylinder without removing the piston.  It was hard to get an accurate measurement.  It could well be 1".  In that case, my reduction in fluid displacement would be 40% not 59%, still a big reduction.

As best as I can tell, everything is working fine except for this one issue.

Rich

[hiball3985]

Sorting this out must be frustrating. I would think that a 1" piston in the new master and a 1" piston in the old one would produces the same volume?

Another off the wall suggestion: Have you jacked up the car and tested that both front and rear wheels are getting an application?

[ROKuberski]

The diameter of the piston means that they will produce the same pressure.  However, if the new master cylinder does not displace enough fluid for the shoes to come into full contact with the drums, it is like only pressing the brake down part way.  It is the stroke that makes the difference.  A shorter stroke will displace less volume.  If the shoes were in full contact, the pressure developed would be the same because the diameter of the piston is the same.  Also, I do know that all wheels cylinders are getting their share of the fluid.

Also, I've misstated the information on the reduction in volume.  I made measurements last night without disassembling the original master cylinder.  It is indeed a 1" bore and the stroke is 1.28", not the 1.4" previously stated.  So I have a 28% reduction, not a 41% reduction.  I still believe that this is the problem. 

I do not know if my replacement master cylinder has the residual pressure valve.  It could still be that having this would keep some fluid in the system under pressure meaning that I would have to displace a little less fluid for the full application of the brakes.  Just speculating here.

Rich

[hiball3985]

Maybe I'm wrong in my thinking but doesn't a dual master have two pistons and each is only supplying volume to two wheels? I'm just thinking I have a dual none power master and the actual stroke when the brakes are fully applied is only about 1/2 - 5/8 inch.

Edit: I think you may be correct about the residual check valve keeping more in the system and that would require less volume. I didn't think of that possibility previously