Rear brakes won’t bleed - no fluid

[Andy69]

C5 front brakes, Camaro rear disks, eBay chrome vacuum reservoir with a replacement 69 disc brake Mc. I originally had a chrome MC for disc/disc cars but had to replace it. Currently there is no fluid to the rears. Cracked the line at the distribution block and fluid comes out. Pedal is weird - about halfway down it feels like it hits a mechanical limit, but I’m not sure if it’s not just the front pressure. It’s been a while since I installed them and the front brakes work.

im thinking maybe there isn’t enough travel in the system to get the part of the MC piston that supplies fluid to the rear brakes to the correct location. I trie adjusting the push rod but it’s coming out as far as it can. Do I need to just swap in a replacement stock vacuum reservoir?

 

[Shovelrick]

C5 front brakes, Camaro rear disks, eBay chrome vacuum reservoir with a replacement 69 disc brake Mc. I originally had a chrome MC for disc/disc cars but had to replace it. Currently there is no fluid to the rears. Cracked the line at the distribution block and fluid comes out. Pedal is weird - about halfway down it feels like it hits a mechanical limit, but I’m not sure if it’s not just the front pressure. It’s been a while since I installed them and the front brakes work.

im thinking maybe there isn’t enough travel in the system to get the part of the MC piston that supplies fluid to the rear brakes to the correct location. I trie adjusting the push rod but it’s coming out as far as it can. Do I need to just swap in a replacement stock vacuum reservoir?

We’re they working before you changed a component? I’m using a 1968 Vette MC for 4 whl disc

 

[Chevelle_Nut]

Use a hand pump and keep pumping. Do you have a proportioning valve? Make sure it is not tripped. It took me forever to bleed my gold car's brakes, finally they started bleeding.

 

[Andy69]

Ive tried the hand pump. Couldn’t get it to pull a vacuum. It works, I tested it. It doesn’t feel like the pedal is pushing any fluid and the reservoir doesn’t need refilling. I’m thinking something is off with the MC. I bench bled the MC first so that’s not it. The pedal doesn’t go all the way to the floor but also isnt soft like you’d expect brakes with air to feel like. It’s soft then hits a very stiff limit about halfway down, which feels like the MC is reaching the end of its travel rather than hitting fluid pressure. Does that make sense?

I’m using DOT 5 silicone fluid, which I know takes longer to bleed.

 

[kmakar]

I know there are different length push rods. Maybe a combination of the MC and rod length?

 

[Shovelrick]

I had to make a PR for inside the MC but can’t remember if and I think it was a little longer out of 1/2” rnd stock IIRC it was about 1/4” longer and I had to grind sides down to roughly .480

 

[cheveslakr]

I had a very similar problem with a vega, used too small of a master. It needed a bigger bore and a bigger reservoir.

 

[Shovelrick]

I’m thinking the replacement 69 Mc could be your problem since those are either Drum/Drum or Disc/Drum, I’d try a disc/disc MC, seems like you’d get some juice back there but maybe not enough to push the brakes together

 

[Chevelle_Nut]

Is your proportioning valve tripped?

 

[Nashville Cat]

I’m thinking the replacement 69 Mc could be your problem since those are either Drum/Drum or Disc/Drum, I’d try a disc/disc MC, seems like you’d get some juice back there but maybe not enough to push the brakes together

Yes, a Corvette MC and correct proportioning valve.
With your C5 brakes up front and Camaro rears, you probably don't need a proportioning valve at all.
I was told that about my setup which is 2002 Camaro 4 wheel discs. The rears will never lock before the fronts because the fronts are so much bigger.

 

[Shovelrick]

Yes, a Corvette MC and correct proportioning valve.
With your C5 brakes up front and Camaro rears, you probably don't need a proportioning valve at all.
I was told that about my setup which is 2002 Camaro 4 wheel discs. The rears will never lock before the fronts because the fronts are so much bigger.

I'm using a Wilwood adjustable P valve

 

[Andy69]

I’m thinking the replacement 69 Mc could be your problem since those are either Drum/Drum or Disc/Drum, I’d try a disc/disc MC, seems like you’d get some juice back there but maybe not enough to push the brakes together

I had to go back and find the info on it but it’s a 1” bore disc/disc replacement MC. It’s stock looking for 68-72.

 

[Andy69]

Ok, took the MC off the booster and this fell out. I don’t have the instructions that came with it but I seem to remember thinking I needed that to be in there for some reason. Seems to go all the way to the floor now so I’ll try bleeding the tears again and see what happens.

 

[Shovelrick]

Ok, took the MC off the booster and this fell out. I don’t have the instructions that came with it but I seem to remember thinking I needed that to be in there for some reason. Seems to go all the way to the floor now so I’ll try bleeding the tears again and see what happens.

It goes inside the MC between it and the booster, dish facing booster, I made one out of round stock

 

[Andy69]

This is all together just weird. I’ve been pumping now for a half an hour and the MC fluid level has barely changed. I may have to just bite the bullet and get something I know is going to work

 

[Shovelrick]

When I bought the 68 Vette MC (3rd MC) that was replacing another MC that I don’t remember what it was for, I originally bought a 4 whl disc kit from Pirate Jack 10ish yrs ago that was nothing but Pure Garbage, replaced the MC with ?? then bought the 68 new not rebuilt Vette MC but had to make a longer PR like I showed in the pic, black rod came with the MC but about .250 too short, they sell diff length rods but I didn’t know how long I needed so I experimented till I thought it was good

 

[Raoul Ross]

Did you bench bleed the MC first? I've always used a pressure bleeder, don't know anything about vacuum bleeding.

I've always had good luck bench bleeding the MC first (DO NOT go full stroke!) In fact very small stokes have worked best for me. Watch the reservoir for tiny bubbles... when gone, you're done.

Just as an FYI, I quit high school my senior year to go work on cars at a brand new shiny Sunoco station in 1972... was a mechanic for 25 years including a stint as a Chevy dealer Certified Chevy mechanic from '77-'79, been there done that!

 

[Andy69]

I was finally able to get some fluid to the rear wheels. I bench bled the mc before I installed it but I used the bleeders again to see and a bunch of air came out. After that gravity took over and while it’s still full of air and I can’t get a pedal at least there is some fluid back therr

 

[Chevelle_Nut]

I was finally able to get some fluid to the rear wheels. I bench bled the mc before I installed it but I used the bleeders again to see and a bunch of air came out. After that gravity took over and while it’s still full of air and I can’t get a pedal at least there is some fluid back therr

Keep going, it will all come out eventually. There is no reason they need to be such a PITA to bleed.

 

[Shovelrick]

I was finally able to get some fluid to the rear wheels. I bench bled the mc before I installed it but I used the bleeders again to see and a bunch of air came out. After that gravity took over and while it’s still full of air and I can’t get a pedal at least there is some fluid back therr

I like using a Mighty Vac or similar brand to hand pump or suck the fluid through