Brake Help Requested - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**chevy71super** · 07-31-2005, 01:41 AM

The brakes on my 1971 K10 have been marginal scince I rebuilt the truck three years ago. The problem only got worse when I put on 35" tires. (More rolling weight.)

The brake system consists of all new component except for the hoses and the rear brake drums. (As least they were new 3 to 5 years ago.) I decided to try new hoses first, bought Superlift braided hoses. During the brake bleeding process after installing the hoses I noticed I had good "flow" to the rear brakes, i.e. when my wife held the brake peddle down and I loosened the bleeder value a steady stream of fluid came out once the air was gone. The fluid shot up in the air 3 to 4 inches. The front brakes (disk) were a different story. It took a good while to get the air out and once I did the fluid just trickled out. Not much of a stream out of either side, barely a trickle.

The brakes work better with the new lines but still are not up to their full potential. I can't get them to lock no matter how hard I stomp the peddle.

I getting to think I have a bad master cylinder. What do you guys think? I believe I should get better flow to the front brakes. What is your experience when bleeding the brakes? Should the fluid at least clear the caliper during the bleeding process. I can barely get it to trickle out. Thanks.

Americanrider · 07-31-2005, 02:07 AM

Most likely problem might be a plugged bleeder, but that would not explain the weak brakes. Remove, clean, replace bleeders and try again. If that don't cure it maybe you have a bad pro-valve? Crack the line running into to the front brakes below the valve and check the flow pressure by stepping on the brakes hard. It's going to be messy so have some rags handy to save your paint job. Also look for kinks or smashed hard lines.

JimKshortstep4x4 · 07-31-2005, 05:26 AM

You should be able to get a stream of fluid out of the front calipers. From your description I would suspect the master cylinder may be the problem. It may be the wrong master cylinder and not sending enough volume to the front. The prop valve seems to be letting fluid by so it is not shifted, (which shuts the flow off completely).

The way we check the prop valve for flow is to disconnect the front and rear fittings off of the valve, hook up two tubes to it and direct the flow into a container.

Good luck!

JIm

**chevy71super** · 07-31-2005, 06:30 PM

Thanks Jim/American! Good ideas. I was thinking about the proportioning valve and will test it as you have suggested. Doug

07-31-2005, 01:41 AM	#1
chevy71super Registered User Join Date: Jan 2002 Location: So Cal Posts: 658	Brake Help Requested The brakes on my 1971 K10 have been marginal scince I rebuilt the truck three years ago. The problem only got worse when I put on 35" tires. (More rolling weight.) The brake system consists of all new component except for the hoses and the rear brake drums. (As least they were new 3 to 5 years ago.) I decided to try new hoses first, bought Superlift braided hoses. During the brake bleeding process after installing the hoses I noticed I had good "flow" to the rear brakes, i.e. when my wife held the brake peddle down and I loosened the bleeder value a steady stream of fluid came out once the air was gone. The fluid shot up in the air 3 to 4 inches. The front brakes (disk) were a different story. It took a good while to get the air out and once I did the fluid just trickled out. Not much of a stream out of either side, barely a trickle. The brakes work better with the new lines but still are not up to their full potential. I can't get them to lock no matter how hard I stomp the peddle. I getting to think I have a bad master cylinder. What do you guys think? I believe I should get better flow to the front brakes. What is your experience when bleeding the brakes? Should the fluid at least clear the caliper during the bleeding process. I can barely get it to trickle out. Thanks.

07-31-2005, 02:07 AM	#2
Americanrider Registered User Join Date: Dec 2004 Location: NW, WA. Posts: 1,421	Most likely problem might be a plugged bleeder, but that would not explain the weak brakes. Remove, clean, replace bleeders and try again. If that don't cure it maybe you have a bad pro-valve? Crack the line running into to the front brakes below the valve and check the flow pressure by stepping on the brakes hard. It's going to be messy so have some rags handy to save your paint job. Also look for kinks or smashed hard lines.

07-31-2005, 05:26 AM	#3
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	You should be able to get a stream of fluid out of the front calipers. From your description I would suspect the master cylinder may be the problem. It may be the wrong master cylinder and not sending enough volume to the front. The prop valve seems to be letting fluid by so it is not shifted, (which shuts the flow off completely). The way we check the prop valve for flow is to disconnect the front and rear fittings off of the valve, hook up two tubes to it and direct the flow into a container. Good luck! JIm

07-31-2005, 06:30 PM	#4
chevy71super Registered User Join Date: Jan 2002 Location: So Cal Posts: 658	Thanks Jim/American! Good ideas. I was thinking about the proportioning valve and will test it as you have suggested. Doug



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