‘69 c10 Brake master reservoir layout
 

Recently finished swapping to a dual pot master cylinder from a ‘69 c10 on my ‘63 now with discs up front and still drums in the rear..

Had a bit of an interesting time bleeding the brakes last night and I’m wondering if I got the layout of the reservoirs wrong. I piped it front to rear and rear to front.

Is that correct?

Re: ‘69 c10 Brake master reservoir layout
 

It is my understanding that the "backwards" lines were used on the 3/4T trucks. Their 1/2T little brothers used the standard front reservoir to the front brakes. You didn't mention which reservoir you purchased.
Need some more information. But generally I would say it's backwards. You seem to be missing the proportioning valve that also indicates if you lost fluid on half the brakes. (Never mind, I see it attached at the firewall now I looked closer).

Should be a great upgrade.

Re: ‘69 c10 Brake master reservoir layout
 

I believe it’s a 69 half ton brake master.

Re: ‘69 c10 Brake master reservoir layout
 

A couple notes, some have already been highlighted. While it likely has nothing to do with bleeding problems, there are a few issues with your setup:
- a 69 C10 MC is not a disk brake MC. 71+ were disk MCs.
- on a 1/2 ton truck MC, the front reservoir feeds the front disk (or front drum) brakes. If disk, front lines should be 3/16"; if drum, front lines should be 1/4". The rear reservoir feeds the rear drum brakes and should use 1/4" lines.

If I'm interpreting your first post and picture (flipped below) correctly - you currently have the front res going to the rear drums with 3/16" lines - and the rear res going to the front disks with 1/4" lines - is that correct? While that may (kinda) work once you get the bleeding issue sorted out, it won't work as it was designed. Can you confirm this is actually the case?

If it is, recommend:
1) replace MC with a disk brake MC (recommend doing this regardless)
2) run 1/4" lines to rear drums (from the rear MC res)
3) run 3/16" lines to front disks (from the front MC res)

Sorry, not what you want to hear I know. Again, pls confirm I'm reading your post correctly - quite possible I'm mininterpreting.

Also, is that a residual or proportioning valve? If the latter, both front and rear brake lines from the MC normally go into a prop valve as it is designed to balance front/rear bias. Not sure what I'm seeing there though, so just asking.

Re: ‘69 c10 Brake master reservoir layout
 

Incorrect master for disc brakes. The valve that’s plumed in is an adjustable prop valve, which only gets plumbed into the rear circuit.

Re: ‘69 c10 Brake master reservoir layout
 

Nice job on the lines, at least.

Re: ‘69 c10 Brake master reservoir layout
 

To reinforce what was recommended above:

1. Get a M/C for a 71-72 C10. It will have a larger front reservoir which feeds the front disc calipers via 3/16" line. It will also have a 1-1/8" bore, whereas the 69 M/C has a 1" bore.

2. The proportioning valve should be in series with the rear brake line, which is 1/4". Crack it wide open to start, and don't adjust it unless the rears lock up before the fronts during a panic stop.

3. If you already have a 3/16" rear line, I'd probably go with it. Square body trucks had 3/16" front and rear, at least that was true for my 82 C10.