[chiphead]

On the '67 LeMans with power drum brakes, does the brake block do anything but work the warning light? My brake block was shot so I pulled it. When replumbing the brake system, do I need a new one?

I want to run a T from the front of the M/C down to the front wheels, and then run a single line with a lineloc from the rear of the M/C down to the rear brakes. Is this OK? This would let me do a footbrake burnout and launch w/o dragging the rear brakes during the burnout.

I tried using the lineloc in the front brakes, but the car kept pushing through the brakes. When I stand on the brakes, the rears drag and screw up the burnout.

[Schurkey]

Your Chassis Service Manual would tell you for sure...but...I expect that block has no other function aside from distributing fluid and providing the switch for the brake light.

You could delete it if you are willing to disable the brake light.

[GTOGreg]

I'm with Schurkey...distribution meeting point for your lines to the fluid source and then for the warning light. That's it to my knowledge.

[deJudge]

Not to sure about the distribution block just being a meeting point for the lines. I lost all brake pressure just recently in my Judge, thought it was the master cylinder. I just so happen to know a guy who had one lying around that seemed to be new, put it on and go to bleed the lines and couldn't seem to get much out of the front ones.The back seemed to bleed OK but peddle still went to the floor. So I sprung for a brand new master cylinder, after many, many tries it and the lines, still no brake peddle. It would firm up a bit then we would go to another bleeder screw and loose all pressure again. I had 4 guys racking there brains trying to figure out what it could be. Even took the hold off valve apart, it was fine. They all thought it couldn't be the distribution valve. Anyways lucky for me my Dad was heading to the States for a holiday and picked one up from OPG and after putting it on my headache was solved. What a nightmare though!

[chiphead]

Judge- Whats your brake setup? You got disc brakes? Disc brake porp valves are different than drum brake units. Im just not sure how.

I've been running it without the brake block, but just curious if it hurts anything. I'm gonna redo the brakes and move the line lock to the back brakes. I footbrake during the burnout, so I need to hold off the rears.

Is there any difference between power drum and power disc brake boosters? I wanna replace the booster and M/C while I'm at it.

[Schurkey]

Originally Posted by deJudge

Even took the hold off valve apart, it was fine.

Why would a 4-drum car have a hold-off valve???

[Socrates]

The brake valve not only actuates the warning light, it seals off a leaky/dead half of the brake system as well. With your current setup without a block, if, say, one of your front brake hoses burst, all of the fluid in the master cylinder can run out through the ruptured half of the system. With the block in place, a faulty half of the MC is sealed off and the other half of the brake system can still stop the vehicle, with the brake warning light blaring to let you know you're soon to be in trouble and need of service, vs. pushing the brake pedal and getting nothing but a parking spot with a view, half way up a light-post or a tree...The valve is also critical for brake bias. In a hard stop the vast majority of the weight is transferred to the front of the vehicle, unloading the rear tires and making the rear wheels prone to locking up (always a bad thing for good stopping), and the valve will allow more brake force to the front wheels and less to the rear. In short, run the valve. There is every reason to do so, and no good reason not to run one...

http://www.studebaker-info.org/Brakes/bf50014.html
http://auto.howstuffworks.com/auto-p...ter-brake2.htm
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...

[Schurkey]

Originally Posted by Socrates

The brake valve not only actuates the warning light, it seals off a leaky/dead half of the brake system as well. With your current setup without a block, if, say, one of your front brake hoses burst, all of the fluid in the master cylinder can run out through the ruptured half of the system. With the block in place, a faulty half of the MC is sealed off and the other half of the brake system can still stop the vehicle, with the brake warning light blaring to let you know you're soon to be in trouble and need of service, vs. pushing the brake pedal and getting nothing but a parking spot with a view, half way up a light-post or a tree...

1. I'm not convinced that a safety valve will "seal off" the hydraulic system in case of a failure. Most GM safety valves are spring loaded to the center (light off) position when you release the brakes; and so fluid could just free-flow out the leak then. Many Ford safety valves are not spring-loaded; even so I don't think they seal the system. Perhaps. I haven't dealt with a Ford warning switch in thirty years.

Originally Posted by chiphead

I want to run a T from the front of the M/C down to the front wheels, and then run a single line with a lineloc from the rear of the M/C down to the rear brakes.

2. If the front reservoir and hydraulic system doesn't have any connection to the rear hydraulic system...how is a leak in one half of the system going to affect the fluid level in the other half?

Originally Posted by Socrates

The valve is also critical for brake bias. In a hard stop the vast majority of the weight is transferred to the front of the vehicle, unloading the rear tires and making the rear wheels prone to locking up (always a bad thing for good stopping), and the valve will allow more brake force to the front wheels and less to the rear. In short, run the valve. There is every reason to do so, and no good reason not to run one...

http://www.studebaker-info.org/Brakes/bf50014.html
http://auto.howstuffworks.com/auto-p...ter-brake2.htm
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...

Are you thinking this is a combination valve??? Many 4-wheel drum cars do not have a proportioning valve; in the same way that they don't have a hold-off (metering) valve. They have a brass block that includes a pressure-differential (dashboard warning light) switch, and no other valving. All four wheel cylinders see essentially identical pressure. Wheel cylinder diameter and brake shoe size difference are used to balance brake force front-to-rear. This is the cheapest possible way to do things...so it was popular for a long time.

[Socrates]

Schurkey, you may be right here. I may be overestimating the sophistication of the 1960's 4-wheel drum setup and confusing modern prop valves and modern MC's with how the old stuff works. If so, my apologies, but even being wrong I'd personally rather run a modern prop valve with functional warning light setup, which is a cake retrofit, vs. no valve and separate lines...

[chiphead]

When I tried to run the linelock with the stock brake block, I followed Hursts instructions but never could get any pedal. After I removed the block for header clearance, the system worked OK. I still cant prevent the car from pushing through the front brakes on the linelock, so I stopped using it.

Will blocking the rear brakes with the linelock (turned around backwards) work? I would energize the line lock before the burnout, footbrake with the fronts and then roll out of the burnout. Then I turn the linelock off to let the rear brakes work again.

Is there a larger booster/MC that works well with low engine vacuum?

[PontGuy]

I am pretty sure the block was the same for all cars through '69 whether or not they were power, drums or discs. While the bock didn't do any "proportioning" I think it does have an important function other than working the warning light. Here's how I have always thought they worked-

Since the front and rear systems are totally isolated, the spool in the block helps balance by keeping the pressure even in both front and rear systems. It will float back and forth as needed to do so. If there is a problem with one side of the system so that it doesn't build pressure then the spool will reach its limit, trip the light switch, and allow the good system to still build some pressure so that you still have some brakes. (I think a proportioning valve works the same way, but the diameter is different on the front and rear ends of the spool/bore so that the balance point is at different pressures.)

I don't think that the block will actually seal off a leaky system. And as someone already mentioned the GM blocks are spring loaded to center so the fluid would continue to run out of the leaky side as soon as you let go of the pedal anyway.

My understanding is that this was done as a safety feature, on the earlier cars a leak anywhere would result in no brakes at all. My experience is that it still didn't work very well- the pedal would go to the floor anyway with only limited braking from the good side of the system. But at least it was something. And as mentioned a block with a spool that leaks by or sticks could cause all sorts of crazy brake problems- been there before.

If all of this is correct, then eliminating the block and running independent lines would eliminate the balancing function so that the pressures would no longer be even, and either the fronts or rears would end up getting most of the load. I guess you might get lucky and the systems may be balanced good enough to work OK anyway.

[chiphead]

OK, I got the LL swapped to the rear brakes. It keeps the rear brakes from working when energized. The problem is the brakes totally suck under normal operation. The pedal goes almost all the way to the floor, and the brakes don't grab really well. Just a bit worse than it was when the LL was on the front brakes.

I bled the hell out of the system & all the fittings are tight. Shoes/springs/cylinders/drums are new. I used a parts-store T-block in the front brake lines from the MC. You know, the brass deal with the Inverted Flare fittings. The passages look kinda small... The rears are run from the MC through the LL to the rear of the car. Is the problem the T-block, the LL, air, or what?

How do I tell if the booster/MC is shot? The MC is 6 years old, the booster is stock '67.

[Schurkey]

Originally Posted by chiphead

the brakes totally suck under normal operation. The pedal goes almost all the way to the floor, and the brakes don't grab really well.

Low pedal is almost always one of three things---or a combination of the three:
1. Defective master cylinder

2. Air in the system

3. Grossly mis-adjusted drum brakes

[PontGuy]

The rod length between the booster and M/C is also critical. There should be just enough clearance to allow the spool in the master to return all the way. If you decide to replace the M/C be sure to check this before installing. I bought a "matched" Booster and M/C from A-zone, assembled in the box, and the rod was still the wrong length. It took me a couple of weeks to figure out what was wrong.

If the rod length is OK then I agree with Shurkey. The T-block or line lock won't cause a low pedal. And if the shoes are adjusted in snug then my bet is air.

Also with 4-wheel drum brakes make sure that the M/C has residual valves for both the front and back systems, or else you have to use good wheel cylinders with cup expanders in order to keep air from being drawn in when you release the pedal. I chased the wheel cylinder problem for months last year and it was really frustrating. The fluid that I got during bleeding was a little "milky" looking and no matter how much I bled the drums I always seemed to get a few air bubbles after testing the pedal. Where did you get your cylinders and what do they look like? The fix for me was replacing the junk "Chinese" cylinders that I had bought with new ones from Napa.

Walt

[chiphead]

Those are very good questions. I just ordered a new booster and M/C today. I should have it by noon. (from augusta, LOL)

I looked through my service manual and found that the rod should be adjusted to be 1.220" from M/C mounting surface to tip of rod. I'll check that for sure when installing the new booster/MC. They're separate so I'll be able to check that dimension.

I didn't think about air entering from the wheel cyls. Nice. I'm not sure where I got them, likely Autozone or Advance auto. How do you tell if the M/C has the residual valves?

Thanks!!

[Schurkey]

Originally Posted by PontGuy

Also with 4-wheel drum brakes make sure that the M/C has residual valves for both the front and back systems,

Good luck with that; my Delco service manual says that GM quit using residual pressure valves around '71 or '72. I bet the aftermarket followed suit soon afterward. Seems like short-sighted penny-pinching to me. Thirty years of stupidly carving out all the quality from a product could lead to consumer dissatisfaction and possible bankruptcy of the corporation. Good thing a huge corporation like GM is immune to that...

(Of course, aftermarket residual pressure valves are available.)

Originally Posted by PontGuy

or else you have to use good wheel cylinders with cup expanders in order to keep air from being drawn in when you release the pedal. I chased the wheel cylinder problem for months last year and it was really frustrating. The fluid that I got during bleeding was a little "milky" looking and no matter how much I bled the drums I always seemed to get a few air bubbles after testing the pedal. Where did you get your cylinders and what do they look like?

One reason I don't advocate vacuum-bleeding especially with drum brakes--you never know when you're done because of air leakage past the bleeder screw threads; and past the wheel cylinder cups.

Originally Posted by PontGuy

The fix for me was replacing the junk "Chinese" cylinders that I had bought with new ones from Napa.

Even NAPA is selling a lot of Chinese brake parts, packaged in boxes labeled "Premium" quality.

[PontGuy]

Shurkey,

I know that GM eliminated the residual valves on the M/C's meant for disc brakes back then, and relied on the cup expanders on the rear wheel cylinders. And I wouldn't be surprised to find out that most aftermarket masters even for 4-wheel drums no longer have them. It would be fine if the wheel cylinders out there were all designed/built with this in mind. But my experience is that this is not the case and it is making brake problem debugging a real challenge. If you read through all the brake threads there are some real horror stories.

Chiphead, I got my original wheel cylinders from Advance Auto on Hwy 1 in Aiken and I never even got out of the driveway with them. After installing the ones from Napa my brakes firmed up after the first bleeding and have worked perfectly ever since. Others on the board have had good success switching to the Napa parts too. I am sure there are other sources for good wheel cylinders, and I am not going to disagree that Napa probably has multiple suppliers, so its not a slam dunk. But its the best advice I can give.

I attached a pic of the two cylinder designs. The Napa cylinder on the left is working great for me, the one on the right went in the trash along with its partner in crime. By they way the Napa cylinders actually have "Made in the USA" cast on the back. Doesn't mean its so, but it made me feel better when I saw it.

Walt

[aldbeir]

when i switched my 66 to a dual master cylinder. i didn't use a distribution block. it works fine but there is no indicator for pressure differential. before the dual master cylinder the brake petal just went to the floor as an indicator.

[chiphead]

I did the MC/booster swap yesterday & bled the system out. The weird thing is there is no adjustment on the reman cardone booster. Brakes seem much better. Not perfect but much better. The LL seems to hold the rear brakes off and lock the fronts. More road & track testing need but looks good. Thanks for all the input guys!