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Old 11-23-2005, 08:37 PM
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Brakes that don't brake

I just bought a '39 Ford 2 Door Sedan streetrod. The car was built about 2 years ago and has a total of 39 miles on the chasis and drive train. The only serious defect with the car is a serious brake problem that has the builder (Tim's Two of Bakersfield, California) and the guys in the local cruise club stumped.

Here are the particulars:

The brakes basically do not work. With the pedal fully depressed, the car will not hold a roll on a 18 degree incline (and we have plenty of those here on the volcano island!).

The set-up is new Corvette discs all around with dual Corvette master cylinders (one for the front and one for the back). The masters are mounted on the frame under the front floor board at a level higher than the 'slave' cylinders.

I have tried all the conventional wisdoms with no improvement (bleed, check the calipers, check the pads, check for leaks). Nothing has helped.

I'm told the next thing I should try is pressure valves. Most agree I should add residual valves. I've had equal input pro and con on also installing proportioning valves. What do you think and if you agree with that being the next logical thing to try, where is the best location to install them (before or aft of the m/c? how far?

Any and all input is appreciated.

Mahalo en da kina tanks (pidgin for Thank You Very Much)!

Dok

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Old 11-23-2005, 09:12 PM
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What is the master cylinder set-up? Are you using two master cylinders? How are they plumbed? Problem sounds like insufficient fluid pressure in the calipers.
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Old 11-24-2005, 08:09 AM
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Brakes that don't brake

Aloha 'advanced design",

The system includes two new 1995 Corvette master cylinders. I think they are 7/8" pistons. They are frame mounted on each side of the chasis below the level of the calipers and under the front floorboard.

Yesterday I was told they may be too close to the exhaust pipe (about 2" clearance) and that heating of the brake fluid could contribute to loss of disk brake efficiency. However, the brakes seem equally ineffective when I first start the car as after it's run a while. To be on the prudent side, I plan to fabricate and install heat shields. Before doing that, I want to find out more about the proportioning/residual pressure valve I may need to add to the system. If that valve can or should be installed near the master cylinders, then my guess is that the heat shields should be made long enought to protect both.

Thanks for the quick response. It's 4 am here in Hawaii and I'm in the garage trying to figure out my dilema.
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Old 11-24-2005, 11:19 AM
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I agree with you the heating of the fluid is not causing the problem. You need residual pressure valves - 2 lb - for the disc brakes. There may be other factors regarding the two m/c's but the most likely issue is the lack of the residual valves.

Enjoy Thanksgiving in paradise. A buddy of mine lives there and sent me a note with pictures last night.

Doug
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Old 11-24-2005, 12:17 PM
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The first thing I would do is lose one of your master cylinders and replace the other with a single dual reservoir master cylinder. Then I would install a residual valve in each line between the master cylinder and calipers (somewhere near the master cylinder if possible). I would also add a proportioning valve as shown below. If you keep all brake lines at least 3-4 inches away from the exhaust you shouldn't have any more problems.

Your system should look like this for a setup using front and rear disks:

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Old 11-24-2005, 12:31 PM
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is teh pedal assembly fabricated or store bought ?

if its owner/ shop fabbed, the pedal throw might be off, and that would mean that the MC's dont build enough pressure
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Old 11-24-2005, 10:20 PM
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So, you didn't say, is the pedal low or high? Amount of pedal travel? Power brakes, manual? Pedal ratio?
I agree with 86ing the two 'vette masters. Use either one tandem master, or 2 single port masters. I would also be interested in the particulars of the current plumbing.
Tandem masters add to pedal travel because the front piston is a slave to the rear, so using all 4 ports of 2 tandem masters could easily cause a low pedal. If you blocked the front ports, and T'd the rear port lines to each respective axle, that would be better than nothng.

Also, late model Corvette masters I've seen have a proportioning valve integrated to the rear brakes at the front port. This valve reduces output pressure to that circuit.
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Old 11-24-2005, 11:25 PM
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no brakes

I have built my own street rod and had the same problem. Turned out the floorboard itself was stopping the brake peddle from going all the way down. Crawl under the care and watch the peddle action while someone else steps on the brake peddle, to see if you have enough floor board clearance. I used one dual master cylinder from a 69 corvette, installed a 2lb residual valve close to the master cylinder on each line and nothing else. That brake set up will throw you thru the windshield in a sudden stop if you don't have your seat belt on.
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Old 11-24-2005, 11:53 PM
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how about some pictures

loose the duel master

what happens if you bleed the system?

does it flow free
if you open the bleeder and push the pedal down are you getting fluid out?

are you getting enough VOLUME of fluid to make the system work??

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Old 11-25-2005, 07:45 AM
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Brakes that don't brake

Pedal is low with about 4", 90% travel. System includes a booster. I don't know anything about pedal ratio. The masters are not in tandem. They are mounted one on each side of the frame. One goes to the front disks the other to the back disks. I changed the masters to single chamber (GMs) yesterday with little or no change. I bled the system but did not have time to do much else (the turkey was waiting). It's 4 am here in Hawaii and I'm at it again, but I may not be able to do much until I find a residual/proportioning set up I can install without major mods (space is limited). Any ideas where to shop for valves?

Quote:
Originally Posted by yesgo
So, you didn't say, is the pedal low or high? Amount of pedal travel? Power brakes, manual? Pedal ratio?
I agree with 86ing the two 'vette masters. Use either one tandem master, or 2 single port masters. I would also be interested in the particulars of the current plumbing.
Tandem masters add to pedal travel because the front piston is a slave to the rear, so using all 4 ports of 2 tandem masters could easily cause a low pedal. If you blocked the front ports, and T'd the rear port lines to each respective axle, that would be better than nothng.

Also, late model Corvette masters I've seen have a proportioning valve integrated to the rear brakes at the front port. This valve reduces output pressure to that circuit.
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Old 11-25-2005, 04:40 PM
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There are a number of providers. I am sure Ralph at ECI would be able to steer you straight on this issue. http://www.ecihotrodbrakes.com/
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Old 11-26-2005, 09:04 PM
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Brakes That Don't Brake

Dudes, this brake thing is cutting into my tennis time and my beer money!

I spent most of the day today replacing the two masters cylinders with a new 95 Chevy dual chamber master. The folks at Napa said that cylinder has a built in proportioning valve. I left everything else as it was including the blue 2# residual valve that was already in line to the rear. Well, guess what? THE CHANGE WAS LITTLE OR NO IMPROVEMENT! Also, the new master cylinder is even closer to the exhaust than the two masters that were there before. (Makes me wonder if that's why they used the two smaller units when they built this baby?)

Ok, so for the next thing to try, her's my question. The disk/disk diagram in one of Centerline's replies shows residual pressure valves to both the front and the rear. Is not having that second residual valve on the line to the front disks part of my problem?
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Old 11-26-2005, 09:51 PM
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Quote:
Originally Posted by KONADOK
Ok, so for the next thing to try, her's my question. The disk/disk diagram in one of Centerline's replies shows residual pressure valves to both the front and the rear. Is not having that second residual valve on the line to the front disks part of my problem?
Yes, you need the residual pressure valve for the front also. Without it the fluid in the calipers is draining back into the master cylinder.
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Old 11-26-2005, 11:47 PM
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Wrong Master Cylinder

In your original post you stated that you had disk brakes on all 4 wheels. A proportioning valve is used on a disk, drum set up not on a disk, disk set up. A proportioning valve is used on the rear drums to decrease the rate of pressure to the drums to keep the rear brakes from locking up under hard brake conditions. You still have the wrong master cylinder on the car. If you get a new master cylinder (not rebuilt) for a 1969 Corvette, and put a 2 lb residual valve on both the front and rear lines close to the master cylinder, your brake pedal has enough floor clearance to go all the way down and all the way back up, you have bled the system of air, and your calipers are working properly with the bleeder valve in the up position, I guarantee you that will work. I have installed this set up on several street rods and every one has worked great with no problems. (Bench bleed the master cylinder before putting it in the car)

If it is going to be a lot of trouble to re-rout your exhaust away from the master cylinder you might have to install a heat shield between the master cylinder and the exhaust pipe.
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Old 11-27-2005, 07:58 AM
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Quote:
Originally Posted by HotRodMan
In your original post you stated that you had disk brakes on all 4 wheels. A proportioning valve is used on a disk, drum set up not on a disk, disk set up. .
Not true, mine came with 4 wheel Wilwood disk's and a proportioning valve. The valve is still needed to balance rear braking, even on rear disks.

Vince
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