1970 GMC - Disc brake conversion recommendations?

[HD2000]

I'm considering knocking the dust (and other crap)_ off of my 1970 GMC project truck and getting back to wrenching on it (haven't turned the key in probably 8 years).
I've always wanted to swap out the front drum brakes so kicking around the thought of ordering a kit.
My criteria though... I'd like to be able to retain my 6 bolt 15" Rally wheels.
Any recommendations or reasons to go with (for example) CPP vs POL vs Brothers...
Most of the vendor web sites say "may not work with factory wheels" - any recommendations on how to determining (before ordering) if the kit will work with my wheels?
Also - currently running 4 wheel drums with vacuum assist - I assume my existing booster is fine - just need a new master cylinder and prop valve?

[SCOTI]

Originally Posted by HD2000

I'm considering knocking the dust (and other crap)_ off of my 1970 GMC project truck and getting back to wrenching on it (haven't turned the key in probably 8 years).
I've always wanted to swap out the front drum brakes so kicking around the thought of ordering a kit.
My criteria though... I'd like to be able to retain my 6 bolt 15" Rally wheels.
Any recommendations or reasons to go with (for example) CPP vs POL vs Brothers...
Most of the vendor web sites say "may not work with factory wheels" - any recommendations on how to determining (before ordering) if the kit will work with my wheels?
Also - currently running 4 wheel drums with vacuum assist - I assume my existing booster is fine - just need a new master cylinder and prop valve?

Factory drum brake wheels don't clear the calipers on a disc brake set-up.
6-lug truck Ralley wheels came after disc brakes were standard on trucks so they'll clear.

Post a pic of your wheels. Are they original GM wheels or aftermarket?

[HD2000]

A couple quick photos of my front rim:

[SCOTI]

Originally Posted by HD2000

A couple quick photos of my front rim:

Yup.... Those look like GM spec 6-lug (4x4 spec) truck Ralleys. Most are 15x8 but apparently some 7" wide versions were available as well.

[cwcarpenter98]

I used the same wheels when I went disc on my truck. No issues with fitment for me. A couple years after the initial wheel purchase, I bought another set of them for the caps and trim rings. After removing the tires, I discovered the set of wheels I thought were 15x8s turned out to be 4 15x7s. The outer lip was shallower than the 15x8s

[HD2000]

Cool - so I am ok with my wheels - great news.

Any reason not to go with a CPP upgrade kit?

[SCOTI]

Originally Posted by HD2000

Cool - so I am ok with my wheels - great news.

Any reason not to go with a CPP upgrade kit?

50/50 chance you get what you're supposed to & everything works as expected. Not sure any other options are any better though since ECE (Early Classic) went away.

[A1971Blazer]

I'm in the middle of swapping in disc brakes on my '68 with the CPP kit
so far everything fits well with the exception of the new hoses, I had to get an adapter to go from the 3/8 flare nut to 7/16 on the new hoses.
I'm adding a CPP 1-1/4" front sway bar as well....it fits nicely so far..

[67C10Step]

I rebuilt the entire front end in my 67 using Moog tie rod ends, cross shaft kits, and stock height springs. CPP 2-1/2" drop spindles, calipers, and rotors. I also replaced all the hard brake lines with a kit from Inline Tube. Everything went together fine and I ended up using flex lines from a 1969 Buick GS and they fit perfectly on the front.

[HD2000]

Well - CPP kit is on the way - another question...
Any low budget recommendations for master cylinder and prop valve?
Just hit the pick and pull for an 80s 1/2 ton and pull the prop valve and associated bracketry then order a new master for a disc/drum 80s truck?

[SCOTI]

Originally Posted by HD2000

Well - CPP kit is on the way - another question...
Any low budget recommendations for master cylinder and prop valve?
Just hit the pick and pull for an 80s 1/2 ton and pull the prop valve and associated bracketry then order a new master for a disc/drum 80s truck?

Local parts store for the master. Most carry their 'house' brand as well as other manufacturers. Whatever gives you the best warranty....

Using the 73-87 prop valve can work but the lines are routed differently vs pre-73. There might be some difference in the two so that's a decision you'll have to make. Lines were def routed differently on the 71-72's vs square-bodies.