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Old 07-20-2010, 12:25 PM   #1
66_k10_manny
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Brake pedal travel

Just installed front disc brakes with mc and booster on my 66k10. The mc and booster come from a 97 blazer. Brakes are working great but my pedal drops down almost to the floor board. Thought i might have a bad booster so i swapped it out yesterday and no change. The brakes start grabbing with the pedal pushed about 1/3 of the way down and then full grab at about 2/3 down. With the engine off, if i pump the brake pedal, it firms up and stops at about half way down. If i then fire the engine up, the pedal drops down the rest of the way. May be this is the normal travel? Anyone have ideas or suggestions?
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Old 07-26-2010, 07:20 PM   #2
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Re: Brake pedal travel

Anyone?
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Old 07-26-2010, 08:38 PM   #3
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Re: Brake pedal travel

Long pedal travel can come from:
air in the system
wrong pedal ratio
too small bore master cylinder
booster push rod adjustment (booster to master cylinder)
pedal rod adjustment (brake pedal to booster)
misaligned caliper
brake shoe adjustment (within the drum)
wheel bearing adjustment (disc brake)
C-clip axle end play (disc brake)
parking brake adjustment (disc brake)
flexing firewall when brake is applied

The pedal drops more when the engine is running because the booster is working to boost the hydraulic pressure. As the pressure increases the pedal will usually go lower.

Danny Nix
CPP
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Old 07-28-2010, 01:23 AM   #4
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Angry Re: Brake pedal travel

I have the same issue. I have a late model booster in my 71 that was installed before I purchased it. I think I just need to make a pedal rod adjustment (brake pedal to booster). The problem I have is removing the rod from the brake pedal arm, the steering column is in the way to remove the bolt (large round head). Any suggestions?
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Old 07-28-2010, 04:36 PM   #5
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Re: Brake pedal travel

Good call danny. The list is a good one. Since the unit came out of a working truck, you can cross off most items.
1. check the adjustment of the rear drums, and fronts if they are drums. If you lift the tire, and spin it, you should be able to hear the shoes rub a bit.
2. then, bleed the brakes, again. to get all the air out, you will to push about 10 oz of fluid through EACH corner. 3 to 4 oz at a time, lf, rf, lr, rr, do this rotation 3x. - bench blead the master fisrt - you can do this on the truck with two hoses.
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Old 08-09-2010, 11:39 PM   #6
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Re: Brake pedal travel

The master cylinder is too small.You need to up the bore size.Willwood has the size math on its site.
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Old 08-10-2010, 08:36 PM   #7
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Re: Brake pedal travel

the cheap diagnosis would be my ball of clay. IMO, you need to check the clearance between the booster and the master. What I do is to take a small ball of clay 1/4" in diameter, and put it on the rod that comes from the booster. Tighten up the master cylinder to the booster with the clay installed. DO NOT APPLY THE BRAKES! Then remove the master again. see if the clay is crushed? If it is not, then the rod coming from the booster needs to be longer. I have removed this rod, and welded a bead on the end, and rechecked. You only need a 1/16 or less between them. Danny had a BUNCH of free checks that will probably help.
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Old 11-11-2010, 08:42 PM   #8
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Re: Brake pedal travel

Quote:
Originally Posted by 66_k10_manny View Post
Just installed front disc brakes with mc and booster on my 66k10. The mc and booster come from a 97 blazer. Brakes are working great but my pedal drops down almost to the floor board. Thought i might have a bad booster so i swapped it out yesterday and no change. The brakes start grabbing with the pedal pushed about 1/3 of the way down and then full grab at about 2/3 down. With the engine off, if i pump the brake pedal, it firms up and stops at about half way down. If i then fire the engine up, the pedal drops down the rest of the way. May be this is the normal travel? Anyone have ideas or suggestions?
I have this exact same problem in my truck that is almost back on the road. I am actually using the same master cylinder and booster as you too. I have already modified the pushrod so that there is no clearance between it and the master cylinder when everything is bolted together.

What solution did you come up with for this problem?

Thanks,

Derek
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Old 11-11-2010, 10:31 PM   #9
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Re: Brake pedal travel

Guys this is a SUPER common thing with the 88-98's. The best option is to put a master cylinder from a 99-04 [I think, I know 99-01 for sure] on and all will be good
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Old 11-11-2010, 11:28 PM   #10
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Re: Brake pedal travel

Quote:
Originally Posted by Tom View Post
Guys this is a SUPER common thing with the 88-98's. The best option is to put a master cylinder from a 99-04 [I think, I know 99-01 for sure] on and all will be good
What causes this common problem?
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Old 11-16-2010, 05:10 PM   #11
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Re: Brake pedal travel

Quote:
Originally Posted by DKN View Post
Long pedal travel can come from:
air in the system
wrong pedal ratio
too small bore master cylinder
booster push rod adjustment (booster to master cylinder)
pedal rod adjustment (brake pedal to booster)
misaligned caliper
brake shoe adjustment (within the drum)
wheel bearing adjustment (disc brake)
C-clip axle end play (disc brake)
parking brake adjustment (disc brake)
flexing firewall when brake is applied

The pedal drops more when the engine is running because the booster is working to boost the hydraulic pressure. As the pressure increases the pedal will usually go lower.

Danny Nix
CPP
What bore of Master cylinder (MCPV-1) would you recommend to run with your CPP 13" front / 12" rear disc kit?
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Old 11-16-2010, 08:07 PM   #12
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Re: Brake pedal travel

I ended up replacing the S10 master cylinder with a master cyclinder off of a C10 and it solved my problem. The S10 mc couldn't push enough fluid even though it had a 30/36mm bore.
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Old 11-16-2010, 10:49 PM   #13
DKN
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Re: Brake pedal travel

Quote:
Originally Posted by Hart_Rod View Post
What bore of Master cylinder (MCPV-1) would you recommend to run with your CPP 13" front / 12" rear disc kit?
With a booster use a 1-1/8" bore master cylinder. Use 1" bore if no booster.

Danny Nix
CPP
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Old 11-17-2010, 11:41 AM   #14
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Re: Brake pedal travel

Quote:
Originally Posted by DKN View Post
With a booster use a 1-1/8" bore master cylinder. Use 1" bore if no booster.

Danny Nix
CPP
Thanks, that's what I ended up using. I'm still trying to fine tune the proportioning valve and hope to have it dialed in the next week or so.
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1968 Farm truck: LS3/6L80/TVS1900: http://67-72chevytrucks.com/vboard/s...d.php?t=358692
1968 SWB - SHIFTED: PB Xtreme DM/LS1/Dakota Digital/AccuAir/Vintage Air/...http://67-72chevytrucks.com/vboard/s...d.php?t=551258
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Old 11-19-2010, 03:32 AM   #15
slepysal
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Re: Brake pedal travel

Manny did you change were the brake push rod mounts to the pedal? if not drill a new hole one inch below the original one that should do it.
http://www.classictrucks.com/tech/05...ter/index.html

Were in San Jose are you ?
Also by chance do you have any of your old parts from the swap? I am looking for the stock hubs let me know thanks
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Last edited by slepysal; 11-19-2010 at 03:35 AM.
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Old 01-17-2011, 08:53 PM   #16
66_k10_manny
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Re: Brake pedal travel

Sorry guys i havent been online in quite some time. Im still having the same issues with my pedal. I just bought that 1 1/8 inch bore MC and am going to install it. Hopefully it will solve my problem too. And im going to drill that other hole for the brake pedal to decrease my ratio. I ran 1/4 inch brake line front and back with my disc/drum set up. Will that new MC still push enough fluid to operat the brakes properly?
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