65 Chevy C10 rear drum brake woes. please help.

[Gumby83]

Hey fellas, i rebuilt my 65 c10 and put disc brakes up front. i planned to keep the drum brakes in the rear so i ordered a rebuild kit. I couldnt get the rear brakes to work after the rebuild.

Since i put in all new brake lines, hydrobooster and master cylinder i decided it must just have air trapped in them. so i bled them by pumping the brake.
still nothing....

bought a vaccume hand pump, and tried bleeding them like that.
still nothing.

Thought "Maybe the drums are really glazed?" so i used a die grinder with a flapper wheel to sand the inside of the drum.
still nothing.

bought an AC 110v vaccume pump and pulled a monster vaccume on the master cylinder...
still nothing.

I figured "maybe i collapsed the original 65 rubber hose from the frame to the rear axle" so i bought a new one.
still nothing.

So i bought a pressure bleeder. and forced 40psi of brake fluid through the system, bleeding over a litre through the rears.

Still.... Nothing.

I adjusted the adjuster through the slot in the drum each time. expanding it till it dragged hard and i cant get so much as a change in resistance with the brake. i swapped the wheel cylinders to another set...

Still Nothing...

What is going on here? did i rebuild the brakes with the wrong kit? is there a oddball drum or something? I looked for new drums, but couldnt find any with the slot in the front for getting to the tensioner/adjuster. i don't have a hole in the backing plate... i am really close to just buying a CPP rear disc brake kit, but i couldnt run 15 inch wheels then. If anyone has an idea, throught or suggestion please let me know. i am at my ends wit here...

[Braunschweiger]

I had the same problem with my '62, the previous owner had installed a master brake cylinder from the Corvette, which is for 4 disc brakes,
the residual pressure valve for the drums was missing, so the drums are not preloaded,
I solved my problem with a new master brake cylinder for disc/drums,
the residual pressure valves are available separately, so that it can be used in the rear circuit.
Was the bench bleeding carried out properly?
If the rear circuit does not work at all, even after repeated pumping,
although it has been properly bled,
then your new master brake cylinder is already broken.

[grubsster]

Did you "lock out" the proportioning valve when bleeding the brakes? Others on here can explain this better but, I used a cheap special made tool to bleed mine. It goes where the brake warning light would connect to the valve. Otherwise, I think the shuttle closes off the perceived failed half of the system. It looks like the one in the picture.

Good luck.

[Gumby83]

Originally Posted by grubsster

Did you "lock out" the proportioning valve when bleeding the brakes? Others on here can explain this better but, I used a cheap special made tool to bleed mine. It goes where the brake warning light would connect to the valve. Otherwise, I think the shuttle closes off the perceived failed half of the system. It looks like the one in the picture.

Good luck.

I don't know if i have a spot for that on my proportioning valve. i have one but it seemed way too big for mine. maybe i need a smaller one? i have an adjuster knob for bias. i've tried it every way i can. its almost like my wheel cylinders are too small and dont push the shoes out far enough or something.

[grubsster]

I read everything you did again. If you are getting fluid coming out the wheel cylinders when you bleed them then, I'm unsure what could be happening. When I replaced the wheel cylinders on my 66 I bought the Delco replacement. I do have disk/drum. If you have a helper available, maybe remove one of the drums and have your helper push the brake pedal a small amount to see if you have movement. Not enough to pop the cylinders apart but just to see them move. If they don't move then check your master and proportioning valve. I can see why you are stumped.

[Gumby83]

appreciate the help, i am going to order new drums and see if that fixes the issue.

[geezer#99]

New drums won’t help.
Do the front brakes work?
Can you lock up the wheels?
From your description you have plenty of liquid. You don’t have enough pressure though.
What’s the size of your master cylinders bore?

[Gumby83]

Originally Posted by geezer#99

New drums won’t help.
Do the front brakes work?
Can you lock up the wheels?
From your description you have plenty of liquid. You don’t have enough pressure though.
What’s the size of your master cylinders bore?

front brakes work great, brand new 13 inch discs up front. (it does have a slight pull to one side, going to disassemble and lube up the pins etc to see if that solves it) master is 1.125 IIRC. I just googled it to look it up. it seems like it has a brake switch port, which means that blue proportioning valve screw thing should work..... Gotta find it now :/ https://www.summitracing.com/parts/c...vwvC8s4Q47EpaO

[geezer#99]

Possibly the pull to one side could also be from not enough pressure.

[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.

[geezer#99]

https://www.speedwaymotors.com/the-t...e-system/30895

[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

[BigElittleg64]

Gumby83 I had this same problem. Here is my setup- 1964 C10, LWB Stepside, 350, 700r4, 1987 front cross member swap along with rear diff. Even used the PS and brake booster/master cylinder from the 87. Replaced all components like OP and then got lucky to see a thread started on the on the subject. Its was the thread that MikeN calls out in his post. I drilled my brake pedal and moved the rod like MikeN said. Rock hard pedal, and all brakes work properly now.

[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 BigElittleg64

Gumby83 I had this same problem. Here is my setup- 1964 C10, LWB Stepside, 350, 700r4, 1987 front cross member swap along with rear diff. Even used the PS and brake booster/master cylinder from the 87. Replaced all components like OP and then got lucky to see a thread started on the on the subject. Its was the thread that MikeN calls out in his post. I drilled my brake pedal and moved the rod like MikeN said. Rock hard pedal, and all brakes work properly now.

Beautiful, thank you man.. i am so stoked to go try this. appreciate it!

[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.

[Gumby83]

Heres a few pics

[grubsster]

Hole should be one inch lower from the original position... not higher.

[Gumby83]

Originally Posted by grubsster

Hole should be one inch lower from the original position... not higher.

This is where i hit the conundrum, do i drill a hole 1 inch lower and ignore the install instructions for the streetbeast hydrobooster or do i go higher to follow the install instructions? the pedal is hard only 3-4 inches into its travel. So its unlike the issues with other fellas boosters that almost go to the floor. Going to try bleeding with this blue screw first and see if a combination of that and the new drums do the trick. That will be tomorrows adventure.

[Agv63]

Bleeding the brakes with engine shut off should still bleed correct at the rear with pushrod in original location. It works like manual brakes, Its when the booster is active when the pedal feel changes, then the location must change. If it bleeds thru but no brakes it could be that someting is limiting slave cyl travel, like those 2 ears on the backing plate to stop piston popping out. It could be those small pushrods that connects piston to shoe is on short side, Piston depth can vary from different suppliers. Orthe original drums is worn to such a point that normal thickness shoes is running out of travel to make contact, coming back to piston hitting those stoppers, to verify a long bolt can be used to make new pins but longer, cut head off ,and a slot cut in , lenght can be choosen where needed and another cut and a rounding be made on other side.

Cheers.
Adriaan.

[MikeN]

If you have a stock pedal that came with a non-power brake system, drilling a new hole one inch lower will get you where you need to be.

[Gumby83]

Talked with a CPP tech today. Apparently the master cylinder will apply pressure to the rears before the front which means its not a travel distance issue. I did rebuild the rear drum brakes and have never got them to work, so its the kit i got off speedway motors that is suspect now. i ordered new wheel cylinders (ACDelco Cylinders, and Doorman 1 inch bore) and new wheel cylinder links/pushrods. If anyone has a complete list of all the items i need for a complete, from scratch rebuild i would appreciate it since the drums were missing parts from the PO i don't know if i am missing something or not. The best info i got is from this quick diagram video, but its missing the parking brake strut.... https://www.youtube.com/watch?v=h_YSiNFlwe8


LMC also, shows there are different rear brakes for these trucks... meaning i probably got a mis-match of parts. https://www.lmctruck.com/mechanical/...ake-components

[grubsster]

You may need the parts you ordered. I don't know. However, there are many threads on this forum and in the Faq's that talk about converting to disc brakes, which include, relocating the pushrod hole at the pedal. Maybe the CPP guy is right...

All I can say is that many people on this forum have tried to help and, the simplest piece of advice from MikeN, BigElittleg64, and your own illustration in post #16, all point to push rod location modification. I would try that first before changing everything in the brake system.

Hope you get it figured out soon.