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Old 08-15-2011, 02:54 PM
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Brakes

Hi everyone I have a brake problem on my 31 ford coupe i have disc brakes,
i had to bend my brake pedal in a Z shape to clear my ex haul and steering. i have a new 7" booster and 1" bore master cylinder, i bled the cylinder and brake lines still no pedal and when i start my rod the pedal goes to the floor.
I need help from you experience hot rodders.
Thanks
Chiecoq

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Old 08-15-2011, 05:50 PM
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That sounds like a bad booster. How are you bleeding the brakes?

Vince
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Old 08-16-2011, 12:35 AM
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More information

1. Where is the master cylinder located? Firewall or under the floorboard?

2. If its under the floorboard, do you have 2lb residual valves installed?

3. When you made this Z shaped brake pedal did you have someone check it while you pushed the brake pedal down to make sure it is pushing the rod in the master cylinder all the way forward and then coming all the way back?

4. How did you bleed the brakes?

5. Did you ever have a firm pedal even for a short time?
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Old 08-16-2011, 06:57 AM
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We do need more info as to what kind of calipers you have and was it a new or rebuilt MC.

As far as bending the pedal arm, it should have little or nothing to do with changing the ratio so rule that out. I had to bend mine as well.



If you are using Wilwood or other specialty calipers, you have to open the upper bleeder screw to remove the air. If they are GM or other OEM caliper modified for use, that bleeder has to be on top. Air will always be at the top and no amount of bleeding will remove it - ever.

Did you bench bleed the MC? If it's the Corvette type, they hold a lot of air and even bench bleeding it seems to take a while.

If that MC is a rebuilt, gotta say, some are junk.

You do need residual valves in the lines. If it's 4 wheel discs, 2 pounds front and rear. If you have rear drums, a 10 pounder in that line.

Is the MC plumbed correctly? The large chamber is for the front and since the MC is usually turned around, occasionally they get done incorrectly. There are some that say it doesn't matter, but I disagree with that.

Do you have a correct length MC operating rod? Is it adjusted to just minimal clearance in a free state?

Dave W
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Old 08-16-2011, 10:07 AM
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Quote:
Originally Posted by chiecoq
Hi everyone I have a brake problem on my 31 ford coupe i have disc brakes,
i had to bend my brake pedal in a Z shape to clear my ex haul and steering. i have a new 7" booster and 1" bore master cylinder, i bled the cylinder and brake lines still no pedal and when i start my rod the pedal goes to the floor.
I need help from you experience hot rodders.
Thanks
Chiecoq

If the 7" booster is a single diaphragm, it isn't worth using. You will need a dual diaphragm at a minimum.

The bore size of the master when using a booster should be 1 1/8" to work and yield some pedal for 4 wheel disc brakes.

Most important when running disc brakes all around with a booster is to have the pedal ratio close to 4:1. Most aftermarket pedals come configured for a non boosted setup and have a pedal ratio of 6:1. This is why you are not getting any pedal or at best a very low pedal.

Basic rule of thumb.

Non power assisted brakes...6:1 or even 7:1 pedal ratio. 7/8" -1" bore master cylinder. Yields higher line pressure and requires less pressure applied by your foot to the brake pedal. The reservoir must be able to hold enough capacity to fully move the wheel cylinders.

Power assisted brakes...3:1 or 4:1 pedal ratio. 1 1/8" bore master cylinder. A minimum of a 7" dual diaphram booster.

For under the floor mounted master cylinder...If disc brakes on installed on the front, have a 2 p.s.i. residual valve installed in the front line close to the master cylinder. If drum brakes or GM disc brake calipers with the built in parking brake are installed on the rear, run a 10 p.s.i. residual valve installed in the rear line close to the master cylinder. Most other disc brake calipers installed on the rear will only require a 2 p.s.i. residual valve.

For either firewall mounted or under the floor mounted master cylinder, install an adjustable proportioning valve in the rear line to enable you to 'balance' the braking bias from front to rear. Normally, you do not want the rear brakes to lock up before the front brakes.
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Old 08-17-2011, 01:41 PM
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Quote:
Originally Posted by 302 Z28
That sounds like a bad booster. How are you bleeding the brakes?

Vince
This is a new 7" booster and Master cylinder. I bench bled the Master cylinder and bled my lines starting at the RR, LR, RF AND LF ABOUT 4 TIMES.
STILL VERY LITTLE PEDAL?
Thanks
chiecoq
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Old 08-17-2011, 01:54 PM
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Quote:
Originally Posted by HotRodMan
1. Where is the master cylinder located? Firewall or under the floorboard?

2. If its under the floorboard, do you have 2lb residual valves installed?

3. When you made this Z shaped brake pedal did you have someone check it while you pushed the brake pedal down to make sure it is pushing the rod in the master cylinder all the way forward and then coming all the way back?

4. How did you bleed the brakes?

5. Did you ever have a firm pedal even for a short time?
Reply to your questions
1. MY MC is under the floor board
2.Ido have a 2lb residual valve for the front brakes
3. My pedal goes all the way to the floor
4. Ibench bled the MC and bled my brakes starting at the RR, LR, RF AND LF ABOUT 5 TIMES.
5. Verry little pedal
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Old 08-17-2011, 02:11 PM
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Quote:
Originally Posted by Irelands child
We do need more info as to what kind of calipers you have and was it a new or rebuilt MC.

As far as bending the pedal arm, it should have little or nothing to do with changing the ratio so rule that out. I had to bend mine as well.



If you are using Wilwood or other specialty calipers, you have to open the upper bleeder screw to remove the air. If they are GM or other OEM caliper modified for use, that bleeder has to be on top. Air will always be at the top and no amount of bleeding will remove it - ever.

Did you bench bleed the MC? If it's the Corvette type, they hold a lot of air and even bench bleeding it seems to take a while.

MC is a rebuilt, gotta say, some are junk.

You do need residual valves in the lines. If it's 4 wheel discs, 2 pounds front and rear. If you have rear drums, a 10 pounder in that line.

Is the MC plumbed correctly? The large chamber is for the front and since the MC is usually turned around, occasionally they get done incorrectly. There are some that say it doesn't matter, but I disagree with that.

Do you have a correct length MC operating rod? Is it adjusted to just minimal clearance in a free state?

Dave W
Dave
I bench bled the MC twice and bled my lines 5 times starting at RR, LR, RF and LF. MY Booster, and my MC are new i have a residual valve for the front brakes and a proportional valve for the rear. I don't know who made the calibers, but the bleed valves are on the top.
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Old 08-17-2011, 03:19 PM
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Quote:
Originally Posted by chiecoq
Dave
I bench bled the MC twice and bled my lines 5 times starting at RR, LR, RF and LF. MY Booster, and my MC are new i have a residual valve for the front brakes and a proportional valve for the rear. I don't know who made the calibers, but the bleed valves are on the top.
Read my post above again.

With disc brakes at all four corners you will need residual valves on both the front and the rear brake lines. If you are using GM calipers in the rear with the built in parking brake, then the residual valve in the rear line must be a 10 p.s.i. unit. The proportioning valve in the rear brake line is to balance out the brake bias between the front and rear.

The pedal ratio is very important when using power brake boosters. The pedal ratio should be no more than 4:1 with power brakes or you will get either a very low pedal or no pedal at all.
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Old 08-17-2011, 03:56 PM
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Quote:
Originally Posted by Frisco
Read my post above again.

With disc brakes at all four corners you will need residual valves on both the front and the rear brake lines. If you are using GM calipers in the rear with the built in parking brake, then the residual valve in the rear line must be a 10 p.s.i. unit. The proportioning valve in the rear brake line is to balance out the brake bias between the front and rear.

The pedal ratio is very important when using power brake boosters. The pedal ratio should be no more than 4:1 with power brakes or you will get either a very low pedal or no pedal at all.
Frisco
Then i need a residual valve for the rear brakes 10psi. I found out that my calibers in the rear are GM with the built in parking brake
Thanks Frisco
Chiecoq
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