65 Chevy C10 rear drum brake woes. please help.

[Gumby83]

Originally Posted by grubsster

I agree with geezer99. It is such a simple hydraulic system. I was thinking about the master cylinder. Did your rear brakes work before you changed it? If so, are you sure that the push rod is sitting correctly in the cylinder? I know that some look alike but that there are different types where the pushrod goes. One takes a short rod and the other one takes either a spacer or longer push rod. I had accidentally bought the wrong one once and had a similar problem. Doesn't move far enough to produce pressure. Otherwise I can't think of what would cause the issue. In my opinion, the only thing to do is start troubleshooting at the front and go to the back.

I am trying to remember... i think i did have the drums working before with that master cylinder. I think after i rebuilt the brakes they didnt work.... i got a 1960-1972 drum brake rebuild kit. i thought all the drums were the same.... but it might be that blue screw thing i need to really bleed those rears... the master has two pots, one for the rear, ans one for the front. i have two lines that come for the front two calipers. and one line that goes to the rear. (edit: Just remembered. i did pull a wheel cylinder off, and taped up the brake line so it wouldnt leak when i went to get a new one, came back and the tape had let go, it drained the entire rear brake pot in the master. maybe that triggered the safety valve or whatever to lock out the rear brakes? i ordered one of those blue screws again to try to bleed the system)

[MikeN]

If you have gone from manual brakes to power-assisted brakes, you MUST move your master cylinder pushrod down to the lower hole on your brake pedal arm. If your brake pedal arm only has one hole, you need to drill a new hole one inch lower on the arm. If not, you are not getting enough travel on the pushrod.

[MikeN]

This was just discussed back in June - moving the pushrod to the lower hole corrected the issue.

https://67-72chevytrucks.com/vboard/...d.php?t=852953

[Gumby83]

Originally Posted by MikeN

This was just discussed back in June - moving the pushrod to the lower hole corrected the issue.

https://67-72chevytrucks.com/vboard/...d.php?t=852953

Hot damn... i just went over the instructions... i don't know how i missed this....

[Gumby83]

Originally Posted by MikeN

If you have gone from manual brakes to power-assisted brakes, you MUST move your master cylinder pushrod down to the lower hole on your brake pedal arm. If your brake pedal arm only has one hole, you need to drill a new hole one inch lower on the arm. If not, you are not getting enough travel on the pushrod.

So, i looked at my pedal. it looks like i only have one hole (was a manual brake truck) but my centerline with the booster is already off. my linkage is a bit low/left of the booster, according to the instructions with the booster it has to be inline with the booster. however, if i put a hole higher on the pedal its going to lose even more plunger travel. the pedal goes hard as is when i press the brake pedal down about 4-5 inches. about half of the available travel of the pedal. I have to assume i somehow locked the rears out by bleeding without that blue screw.. I will contact CPP and see if they have any thoughts.