brake problems

[super1ton]

i did a axle swap on my 72 gmc 1/2, put dana 60 in the front and dana 70 in the rear. went to 3/4 ton booster and master cylinder. i can't get the rear brakes to work, tries putting 1/4 lines to each wheel cylinder and readjusting them, still nothing. they are drum brakes and everything is brand new. anyone have any idea's, i was told i might have to go with an adjustable prop. valve? any help would be much appreciated, i am on the verge of getting some dynamite to fix the problem.

[dznucks]

Are you getting any fluid out of the rears when you bleed them? do your front brakes work? Did you bench bleed the master cylinder?

You should have a flexible brake line in the back. That will collapse internally and look perfectly fine from the outside.

Also, has your propotioning valve popped one way or the other? Is the brake light on? if so that will cause that problem too.

[super1ton]

I am getting fluid to the rear and my front brakes work great and i did bench bleed the master cylinder. i have a braided stainless soft line on the rear that is brand new so i don't think that is collapsed. i have no brake light on and the prop. valve looks to be ok. i have noticed that some of the prop. valves are plummed differently as far as what resevoir goes to where on the prop. valve. mine front of mc to rear of prop. valve, could that be the problem?

[dznucks]

That could be a problem. Most of the ones i have seen had the front of the master cylinder going to the front of the proportioning valve. Where do the lines go from the proportioing valve? the back of the proportioning valve should go to the rear brakes, it should also be a bigger line.

are you running disks in the front and drums in the rear? Or Drums front and back? Do you know what proportioning valve you have? ie. drum-drum or disk-drum. that could also be a problem if you have the wrong valve.

Are you adjsuting the rear brakes out until they just barely drag on the drums? can you confirm that the wheel cylinder is moving by having a buddy pump the brakes?

i installed one of these valves, mine was disk-drum though, for the same price.

http://cgi.ebay.com/ebaymotors/Chevy...Q5fAccessories

[budman k20]

I have one of each and I know that the 3/4 ton master cylinders are opposite the 1/2 tons or at least plumbed opposite. Sitting at work (SB working not surfing!) I can't verify the exact difference right now. I would also suggest you get the matching 3/4 ton prop valve (not 100% certain this is necessary)

Hope that info helps in some way!

[super1ton]

i have the front of the m/c going to the rear of the prop. valve, that is the way it was before i did my axle swap and went to 3/4 ton m/c and booster. they are disc/drum. i am using the same prop. valve from my 1/2 ton brakes, i have not seen one specifically for 3/4 unless i am not looking in the right places, lmc, brothers, jegs. i have adjusted the brakes to wear they barely drag. i will check my wheel cylinders to see if they are moving.

another question though, if i do have these plummed wrong, which line goes to where, i have 1/4" line and a 3/16" line? the way i have them now is the front bowl on the m/c goes to the rear on the prop. valve and is 1/4", the back bowl goes to the front of the prop. valve and is 3/16"? thanks again for your help!

[budman k20]

Send (PM) me your email address and I will email you a photo of my functioning 3/4 ton 4x4 MC and Prop valve tonight when I get home.