brake upgrade question......

[Eagletucky]

Hello all,

I have recently performed the crossmember and rear end swap on my 61 with a 78 Chevy. The only master cylinder I had was from a early 90's s-10 (no booster). Its all finished and brakes properly bled, but I seem to be experiencing a "long" pedal. The truck stops, but not until the pedal is almost to the floor. Is an s-10 master too small of a bore? Btw, I am running the s-10 proportioning valve as well.

Any suggestions would be apprieciated.

Tim

[jgarverick]

i'm thinking the bore is probably too small. 78 master lists a bore of 1 1/8 in and 90 s-10 as 30 and 36 mm which i think is a dual bore size for front and rear division. anyone else have something?

[jgarverick]

actually 30 mm is 1.1811 in so maybe not... maybe theres a mechanical difference designed into the pedal assembly?

[Captainfab]

Are you running a power brake master without a power booster?

[overtimeracing]

http://www.summitracing.com/parts/WIL-260-1874/

Does it feel like you need to pump the brakes? Like a soft pedal? Im running these on my 68 Amc Javelin. I have manual disk brakes front and back. They help firm up the pedal. They make these for disk and drum brakes.

[Eagletucky]

Originally Posted by Captainfab

Are you running a power brake master without a power booster?

Yes, is that where I goofed up?

I was under the impression it didnt matter.

[62gmc910]

Originally Posted by Eagletucky

Yes, is that where I goofed up?

I was under the impression it didnt matter.

I run a 78 gmc c20 master with manual pedal and heavey 3/4 ton brakes , with the 78 proportioning valve with very little pedal travel ' just need lots of force,
The S trucks had small front calipers so it could be a volume issue.
Captainfab makes a real nice bracket to adapt a power booster if you dont need clutch master clearance Also check to see of your rear shoes are set up tight enough,IE that the self adjusters are working

[jgarverick]

sounds like the bore isn't the problem. maybe the mc just doesn't have enough bore length to pressurize the calipers sufficiently.

[Captainfab]

I was under the impression that it did matter. I've not tried it, so I can't say from experience. Although it seems that 62gmc910 has done this sucessfully, but with a C20 master on C20 brakes. So the master may be the difference. There were manual brakes available in the C10's up thru the mid 70's somewhere.

Originally Posted by Eagletucky

Yes, is that where I goofed up?

I was under the impression it didnt matter.

[Eagletucky]

I think I will try a manual C-10 master. I'll let you know how that goes!

Thanks guys!

[TimE]

I had a Camaro years ago that I removed the Power booster and retained the original MC. I had to change the length of the pushrod that goes from the pedal to the rear of the MC for it to function properly. It worked good for me once I had done this.

Someone correct me if I'm wrong, but on some of the disc installs I have read the pushrod was moved up on the brake pedal arm to change the pedal travel and pressure required to actuate the brakes on a disc conversion. IIRC, when I converted my '64 to discs, I shortened the pedal pushrod for it to work right...

Before you go buy another MC, check to make sure that the pushrod is long enough. This could be causing the "extended" pedal that you mention.

[68 TT]

Originally Posted by TimE

I had a Camaro years ago that I removed the Power booster and retained the original MC. I had to change the length of the pushrod that goes from the pedal to the rear of the MC for it to function properly. It worked good for me once I had done this.

Someone correct me if I'm wrong, but on some of the disc installs I have read the pushrod was moved up on the brake pedal arm to change the pedal travel and pressure required to actuate the brakes on a disc conversion. IIRC, when I converted my '64 to discs, I shortened the pedal pushrod for it to work right...

Before you go buy another MC, check to make sure that the pushrod is long enough. This could be causing the "extended" pedal that you mention.

On the vehicles where manual brakes were an option there are two sets of holes in the brake pedal lever. The power booster was angled slightly to use the lower hole for less leverage and the manual MC was level and hit a higher hole in the pedal which gave it more leverage with less effort.

[markeb01]

I also think the problem is in the compatibility of the m/c. I had a somewhat reverse problem years ago on a 67 Chevelle I switched to discs on the front. I don't remember the details but used the booster from either a non-disc setup, or the wrong application. There was no modulation in the pedal at all. The slightest touch of the pedal locked the brakes. My test run couldn't even get down the block, before I drove home using the emergency brake. The problem was a mismatch between the depth of the back of the master cylinder and the length of the push rod sticking out the front of the booster. I realize you aren't running a booster, just pointing out some of these dimensions are critical.

I ran manual discs on the front of my 1960 for several years using a 1975 C10 disc brake m/c and it worked fine other than requiring a lot of foot pressure. Back problems finally convinced me to install a booster.

[TimE]

Thanks for the clarification 68 TT!!