Stock Fairlane, drum brakes, want to add boost unit

[Tom S]

BTW, in the eBay ad from the link in your first post it says:
"2) a Ford correct drum drum master cylinder with built in residual valves"
But I think you ended up sending that one back.

[ROKuberski]

Okay, you got me on that one, but the first of the two links I posted says the opposite.

Although I did get a second master cylinder, it's exactly the same.  He did not what me to return the first one, so I have it on my bench.  I took it apart to see if I could determine why it was defective.  I could not.  All the rubber parts looked fine and this unit does not have a residual pressure check valve.  I've ordered a pair.

http://www.ebay.com/itm/161167720821?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

[RICH MUISE]

Good to see you back, Tom...was starting to wonder where you went.

[Tom S]

Okay, you got me on that one, but the first of the two links I posted says the opposite.

It doesn't really say the opposite.  It is right in the first paragraph. Not letting in air in case of a leak is just a secondary benefit of having the residual check valve, not the main purpose for them.  And there should never be any leaks in your brake system anyway.
Had to search for that post again. The link you posted is on page 3 in reply #31.
http://www.freeasestudyguides.com/residual-check-valve.html
Oh, ... I'm not trying to 'get you' but you definitely need those valves.  Sucks that you will have to bleed the brakes again.  I don't like bleedin' brakes.

[Tom S]

... Tom...was starting to wonder where you went.

Me too. Got a lot of catching up to do.

[BWhitmore]

Dave at Stop n Drop told me a few years back that most rebuilders of dual master cylinders do not install residual check valves in their master cylinders. 

[hiball3985]

Dave at Stop n Drop told me a few years back that most rebuilders of dual master cylinders do not install residual check valves in their master cylinders.

Thank you Bill, that's interesting and I didn't know that but I have never bought a rebuilt. I'm assuming that is because 99% of the cars don't need it or have external proportioning or combination valves?

[BWhitmore]

Dave explained to me that most rebuilders do not install residual check valves because of the mounting position of the master cylinder.  If I remember correctly he said that if the m/c is mounted above the centerline of the wheel cylinders a check valve is not needed.  A few years back I built a 32 Ford Roadster highboy with the m/c mounted on the frame, disc brakes on front, drums on rear.  In that case I needed a 10 psi check valve for the drum brakes. Jim you are also correct that most cars now have a combination valve.

[hiball3985]

That seems a little strange, considering most of my brake work has been on early Fords and all the fire wall mounted single MC have residual check valves. Maybe a dual MC is different?

Edit: Sorry, I'm thinking drum brakes and that info you provided is probably for a disc set up, apples and oranges..

Merry Xmas Bill

[KULTULZ]

This is a continual problem with conversion kits.

Usually, the MC type provided by the vendor is incorrect for the application (one fits all - maybe). You can test the MC for proper operation by plugging the ports and see if it retains pressure on application. If it does, the problem(s) are downstream.

The residual valves (10#) have to be used on drum brake circuits, period.

The GRANADA (70's) DRUM-DRUM MC is the most reliable retro-fit. But be aware it does not have included residual valves. You have to use free-standing valves.

[hiball3985]

For what it's worth I read an article about a guy having a similar situation on mid 60's Mustang. The brake tech Gurus told him that a 7" requires a minimum of 18 inches of vacuum a idle. I don't know if the difference between your 17 with the booster and 18 is that significant?

[ROKuberski]

I've been traveling recently and we've had snow covered roads.  I have the residual pressure valves installed and I will bleed the rear brakes tomorrow.  I've already done the front and did a bit of a test run before I had to leave town.  Even with air in the rear part of the system I could tell there was an improvement.  For some reason, I can't use my vacuum bleeder on the rear brakes.  When I open the bleed valve, the system goes to zero pressure right away.  Not so on the front.  The only thing that I can figure is that the rear slave cylinders leak air back around the threads when I open the valve.  The rear cylinders are replacements, not rebuilt originals like I have on the front.  So I will bleed the rear the old fashion way, with the help of my wife.  Also, the streets are now dry and I can test the brakes.

As to the vacuum that I have.  That's all you can get at this altitude even with the vacuum boost from the fuel pump.  However, I am using the larger diameter vacuum hose directly from the intake manifold.  I have considered using the higher vacuum that is produced by the unit on top of the fuel pump and installing a vacuum reservoir tank.  I am also sure that the new master cylinder (not rebuilt) did not have the residual pressure valves.  My gut feel is that this will make a difference, hopefully a big difference.

Kultulz, do you know what the bore and stroke is on the Granada master cylinder is?  The original for this car is 1" diameter and 1.28" stroke. 

Rich 

[hiball3985]

Rich,
At one time I saw bleeder valves for wheel cylinders that were made more like a one way check valve and only let fluid pass one way, similar to a zerk fitting, possibly they used those on your cylinders, maybe that would be worth investigating.

I don't ever recall other people having power brake problems at that altitude and they had to have lower vacuum also.

[RICH MUISE]

Cars definetly had to be tuned for high altitude if you were gonna spend any length of time there. I had a '85(?) plymouth voyager I had to have the engine rebuilt..had a cracked head...the head on mine was a high altitude version, the guy rebuilding the engine looked all over the country for one..finally found a used one in California. The newer cars with computers probably self adjust for altitude changes, but our old ones..definetly are affected, but I don't know how or if it affects vacumn. I wouldn't have thought it would have.

[ROKuberski]

Rich,

I am tuned and jetted for this altitude, 5,440'.  Higher altitude = lower atmospheric pressure.  That's just the way it is.  I've had cars to the top of Mt. Evans, that's 14,260', everything works at that altitude and there certainly ain't much air up there.

So, I've rebleed the brakes and have a very firm pedal.  I did a test drive and there is certainly an improvement is braking, but not quite as good as I think it should be.  If I give the brakes a quick double pump, then the brakes are very good. 

I'm going to pull all the wheels and make sure that everything is working properly.

Rich