70 4x4 sub brake questions - The 1947 - Present Chevrolet & GMC Truck Message Board Network

madnad15 · 11-13-2013, 03:05 PM

Hi all , im a new member to the forum , but have been lurking for a year or so, you all have some great info and knowledge. I have a few brake questions that im hoping someone can help me with, Ive got a 1970 4x suburban, with drum brakes all around, im gathering parts to do 1 ton axle swap, this is currently my daily driver so would like to have it buttoned up in a weekend.

1st question , can i use a 1/2 ton master cylinder and prop valve? (eventually going to go to hydra boost, so just looking for something that will work)

2: Front brake lines, currently stock, set up for drums, i believe to be 1/4 line, i have received conflicting information, do i need to swap out to 3/16 line or will the original lines work ?

3: If stock brake lines are usable, what Brake hoses, what size fitting is the original drum brake fitting where the outboard brake hoses attach to the frame brake lines? I need to build or buy extended lines , and would like to have them before i start the project, I know alot of people have have done these swaps, and i cant get any of the brake hose manufacturers to clearly answer my question.

Any info or advice is greatly appreciated, thanks Chad

swamp rat · 11-15-2013, 12:42 AM

You would be better off with a 3/4T-1T booster and master.

Per the lines i think they would be all 7/16, 5/16 was used later on with earlier models

The banjo bolt for front calipers on a 72 are 7/16-20 tpi, about 1.250 long, i have no idea what a 1T axle would have or what the original drum fitting would be

madnad15 · 11-30-2013, 01:03 AM

Okay so a little update , I've picked up a hydro boost unit and MC off of a 81 K30 truck(same style truck the axles came out of) . The front brake lines on the sub are 1/4" lines , My new question is , is there a downside to running 1/4" line to disc brakes with a hydro boost system? Should I be concerned about to much volume with the disc and 1/4" line , I'm sure someone out there has done this before does it work well or does it just work or is new brake lines (3/16) a must? thanks

11-13-2013, 03:05 PM	#1
madnad15 Registered User Join Date: Oct 2013 Location: santa maria,ca Posts: 2	70 4x4 sub brake questions Hi all , im a new member to the forum , but have been lurking for a year or so, you all have some great info and knowledge. I have a few brake questions that im hoping someone can help me with, Ive got a 1970 4x suburban, with drum brakes all around, im gathering parts to do 1 ton axle swap, this is currently my daily driver so would like to have it buttoned up in a weekend. 1st question , can i use a 1/2 ton master cylinder and prop valve? (eventually going to go to hydra boost, so just looking for something that will work) 2: Front brake lines, currently stock, set up for drums, i believe to be 1/4 line, i have received conflicting information, do i need to swap out to 3/16 line or will the original lines work ? 3: If stock brake lines are usable, what Brake hoses, what size fitting is the original drum brake fitting where the outboard brake hoses attach to the frame brake lines? I need to build or buy extended lines , and would like to have them before i start the project, I know alot of people have have done these swaps, and i cant get any of the brake hose manufacturers to clearly answer my question. Any info or advice is greatly appreciated, thanks Chad

11-15-2013, 12:42 AM	#2
swamp rat Registered User Join Date: Oct 2007 Location: Spanaway Posts: 8,451	Re: 70 4x4 sub brake questions You would be better off with a 3/4T-1T booster and master. Per the lines i think they would be all 7/16, 5/16 was used later on with earlier models The banjo bolt for front calipers on a 72 are 7/16-20 tpi, about 1.250 long, i have no idea what a 1T axle would have or what the original drum fitting would be __________________ Mike. Swamp Rat build thread : http://67-72chevytrucks.com/vboard/s...d.php?t=595019 72 3/4T 4X4 4" BDS Lift 33" BFG's

11-30-2013, 01:03 AM	#3
madnad15 Registered User Join Date: Oct 2013 Location: santa maria,ca Posts: 2	Re: 70 4x4 sub brake questions Okay so a little update , I've picked up a hydro boost unit and MC off of a 81 K30 truck(same style truck the axles came out of) . The front brake lines on the sub are 1/4" lines , My new question is , is there a downside to running 1/4" line to disc brakes with a hydro boost system? Should I be concerned about to much volume with the disc and 1/4" line , I'm sure someone out there has done this before does it work well or does it just work or is new brake lines (3/16) a must? thanks



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