84 disk brake axle on a 70 K10

[pwdcougar]

Found a nos military surplus disk brake front axle for my 70 Suburban. Originally the Suburban had non power drums. The previous owner changed it over to power drums which weren't much better than the non power brakes. I was told to look at 84 K5 Blazer parts for the axle and replaced the one caliper that was missing the brake line rubber plug during outside storage. My question is what brake booster and master cylinder to run. Someone told me that the drum brake mc wouldn't work for the disk brakes. Of course the Blazer mc I got won't bolt up to the booster. Has anyone done this swap to a square body disk brake axle in a 70?

Paul

[70 gmc c2500]

Just install a 70 disc/drum master cylinder or master cylinder/booster combo.

[pwdcougar]

Originally Posted by 70 gmc c2500

Just install a 70 disc/drum master cylinder or master cylinder/booster combo.

That's what's on the truck at present.

Any idea where to get a brake hose? The calipers use a banjo bolt setup and the drums used flare fittings going into the wheel cylinder. The 84 hoses are way to short.

[pwdcougar]

Ohhh just had the light bulb go off over my head. Maybe extended hoses for a lifted truck will be long enough!

[1970cstblazer]

Use the booster/MC and proportioning valve from a 1971/72 Blazer.

[HO455]

I would research the bore size of the master cylinder for the military vehicle the axle came out of. It's very possible that application used larger calipers (Like one ton or bigger) than would be found on a normal truck.

Match the bore diameter in the master cylinder you install and you should have good brake performance. In the later GM trucks there are various brake caliper versions not counting what the government may have specified.

[Mike C]

The military Blazer axle is virtually identical to the civilian axle. I find it strange that the master you bought wouldn’t bolt to the drum booster? When I did the disc swap on my C20 with power drums, a power disc master bolted right up. And I have seen no difference between 2x4 and 4x4 brake boosters.

You can buy a complete disc power booster kit, either full size or smaller diameter double diaphragm versions. Don’t see why you can’t use drum booster brackets on the disc booster, but…

The aftermarket booster brackets for a 67-72 are not near as nice and beefy as the OEM 71-72 brackets, they do work just fine however. Pick up a disc booster on eBay and a 71-72 1/2 ton 4x4 master from Rock Auto for the cheapest solution.

[Sheepdip]

I believe Earls makes braided brake lines in just about all configurations and lengths

[Richard]

Originally Posted by 70 gmc c2500

Just install a 70 disc/drum master cylinder or master cylinder/booster combo.

Disks were not available until 71 IIRC, an option in 71 and standard in 72. 1970cst blazer has a good path. Someone mentioned longer brake lines for a lift. Crown performance is a good option for extended brake lines. Had some lines made for my truck which required longer than availble brake hoses. If it is stock height 72 brake lines should work as long as they are mounted in the same postion.

[70 gmc c2500]

Originally Posted by Richard

Disks were not available until 71 IIRC, an option in 71 and standard in 72. 1970cst blazer has a good path. Someone mentioned longer brake lines for a lift. Crown performance is a good option for extended brake lines. Had some lines made for my truck which required longer than availble brake hoses. If it is stock height 72 brake lines should work as long as they are mounted in the same postion.

My son's 70 GMC 3/4 ton is factory disc/drum and I previously also owned a 70 Chevy 1/2 ton that was factory disc/drum.

[Darren Thorborg]

Yeah, swapping to disk brakes on a '70 with parts from an '84 K5 is a pretty common upgrade. You’re right that the drum brake master cylinder usually won’t work with disks because of the different hydraulic pressures needed. You’ll want a master cylinder designed for front discs and rear drums (if your rear is still drums). For the booster, many people use a later model square body booster that matches the master cylinder you pick.

[57taskforce]

Originally Posted by 70 gmc c2500

My son's 70 GMC 3/4 ton is factory disc/drum and I previously also owned a 70 Chevy 1/2 ton that was factory disc/drum.

Nope well documented that is not possible from the factory. Front disks were standard equipment in 71 and not available before that. End of story. Your trucks had to have been swapped.

[1970cstblazer]

Originally Posted by 57taskforce

Nope well documented that is not possible from the factory. Front disks were standard equipment in 71 and not available before that. End of story. Your trucks had to have been swapped.

X1000000000

[pwdcougar]

Braided lines for a lifted truck worked. Had to get some adapters and make a line for the driver side. The truck had non power drums and was converted to power drums by a po. IÂ’m going to see what happens with the master/booster setup for now.