Completely new brake system, no pedal

[CantPutTheSmokeBack]

I have a 1969 C30. I've been working on it for a couple months and my goal has been making it mechanically brand new. I've replaced the entirety of the top end of the engine, steering, suspension, and brakes. Brakes is where I'm having trouble.

I absolutely cannot get a good pedal. It does stop, but it feels like I've only got about 1/2 to 3/4 of the brakes I should, or at least of the brakes I'm used to on everything else I have driven. Not enough to be comfortable driving it. The pedal is soft and I don't feel like there is a lot of travel in it, but I haven't measured it for reference. It doesn't hit the floor, stops solid a couple inches short and again haven't measured anything but I certainly can. I don't believe it's air because I don't get any pedal back if I pump them.

I have replaced everything from the booster out. The booster is for a 1969. I have converted the front to disc brakes so the master (1.315 bore), front calipers, pads, and rotors are all for a 1985 C30 truck. I also had a smaller bore master on it just to see what happened (1.125) and it didn't act any different.

A previous owner replaced the factory rear end with a DRW 14 bolt corporate rear end. I replaced the drums, shoes, wheel cylinders and all hardware. Again, all ordered for a 1985 C30.

I ran all new lines for the truck. 3/16 front and 1/4 rear. I have a CPP PV-2 proportioning valve, and I did get the little plastic bleeder tool to hold the valve center when bleeding.

I gravity bled the whole thing and had assistance bleeding the whole truck 4 times over. I bought one of those air powered vacuum bleeders and had it on the whole truck several times as well. I took the master back off and attempted to bench bleed it again and got no bubbles, then did the lines again. I've probably got 6-8 hours into bleeding this thing.

Maybe I should post in the 73+ section since the brake system is for all intents and purposes a 1985.

[Steeveedee]

Have you adjusted the rear brakes so that the shoes just clear the drums? That would be about the only thing left to check.

[geezer#99]

Was the truck originally power or non power brakes?

And how much vacuum does your motor produce?

[CantPutTheSmokeBack]

Originally Posted by Steeveedee

Have you adjusted the rear brakes so that the shoes just clear the drums? That would be about the only thing left to check.

I have adjusted the rear brakes. I adjusted until they just touched and could hear/feel them on the drum. I took it out and did the reverse panic stop deal. I over adjusted and made them touch too much. Got no change at any time.

[CantPutTheSmokeBack]

Originally Posted by geezer#99

Was the truck originally power or non power brakes?

And how much vacuum does your motor produce?

I have no idea if the truck was originally power or not. It was power when I got it. When I got it there was no glove box interior so whatever sticker is usually in there is gone.

I have 14-15" of vacuum.

[geezer#99]

You’re borderline on vacuum.

Sometimes pedal ratio can cause your issues.
Non power is 6 to 1.
Power is 4.5 to 1.

https://techtalk.mpbrakes.com/how-to...ng-pedal-ratio

[CantPutTheSmokeBack]

Originally Posted by geezer#99

You’re borderline on vacuum.

Sometimes pedal ratio can cause your issues.
Non power is 6 to 1.
Power is 4.5 to 1.

https://techtalk.mpbrakes.com/how-to...ng-pedal-ratio

Wouldn't lack of vacuum cause the opposite issue and give a hard pedal? That's what I've experienced before.

Are the pedals on these trucks adjustable for power/non power? I haven't looked. I would need to make sure it's on the bottom hole if I'm looking at that link correctly.

[geezer#99]

You’d need to measure the ratio.
Some pedals aren’t dual drilled.

If you brake twice do you get a hard pedal.
Can you lock the brakes up?

[CantPutTheSmokeBack]

Originally Posted by geezer#99

You’d need to measure the ratio.
Some pedals aren’t dual drilled.

If you brake twice do you get a hard pedal.
Can you lock the brakes up?

Pumping the brakes doesn't give me a harder pedal. I cannot lock up the brakes.

[geezer#99]

Stupid question but it’s happened before!

Are the bleeders on the calipers on top?

[CantPutTheSmokeBack]

Originally Posted by geezer#99

Stupid question but it’s happened before!

Are the bleeders on the calipers on top?

Yes they are. I did a rear disc conversion on my other truck and made that mistake then. Learned from that one. That's the kind of stuff I'm looking for though. I've obviously got something wrong, hoping someone else will see it.

[geezer#99]

How about the pin from the booster to the master.
Is it set right?

[CantPutTheSmokeBack]

Originally Posted by geezer#99

How about the pin from the booster to the master.
Is it set right?

I have it set where its just barely making contact with the master. There is almost no play at all, maybe 1/16" if that.

[geezer#99]

I guess that leaves checking your pedal ratio.

[CantPutTheSmokeBack]

Originally Posted by geezer#99

I guess that leaves checking your pedal ratio.

I'll check that tomorrow. I did just go look and mine isn't dual drilled so I'll have to measure.

[geezer#99]

I found some info on bore size and pedal ratios.


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

[Nh4clo4]

I just had this problem, double check the master to booster rod. If it has any preloading at all, pedal doesn’t work, or there may be a loose joint, or a loose plug on the distribution block

[CantPutTheSmokeBack]

Originally Posted by Nh4clo4

I just had this problem, double check the master to booster rod. If it has any preloading at all, pedal doesn’t work, or there may be a loose joint, or a loose plug on the distribution block

I can double check that tomorrow. I can clay it and see if its actually making contact. I have gone all through the distribution block and taken care of any leaks. It's possible theres some preload on the master, it's very tight.

[CantPutTheSmokeBack]

Originally Posted by geezer#99

I found some info on bore size and pedal ratios.


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

Just read this and made a quick excel sheet so I can plug and play numbers easy. Thanks!

[Nh4clo4]

Originally Posted by CantPutTheSmokeBack

Just read this and made a quick excel sheet so I can plug and play numbers easy. Thanks!

I verified it by loosening the master from the booster, then trying the pedal again.
Same as you all new, it took me a couple days to straighten out.

Also one of the rear drum cylinders, popped out of track and wasn’t pushing on the shoe. So there were a few issues.
Good luck it is frustrating

[pjmoreland]

Maybe the brake pads didn't get bedded in properly when they were first installed, and now they're glazed. Wouldn't explain the soft pedal feel though.

https://help.summitracing.com/app/an...-and-rotors%3F

https://www.treadmagazine.com/vehicl...ds-are-glazed/

[CantPutTheSmokeBack]

Originally Posted by pjmoreland

Maybe the brake pads didn't get bedded in properly when they were first installed, and now they're glazed. Wouldn't explain the soft pedal feel though.

https://help.summitracing.com/app/an...-and-rotors%3F

https://www.treadmagazine.com/vehicl...ds-are-glazed/

I haven't even gotten to that part yet. All I've driven it is down the driveway backward to try to adjust the rear brakes, then back up. It's been up and down the driveway just a couple times but I haven't had it on the road yet. When I'm coming back up to park it is when I notice having to give it more brakes than it should need. It's not leaving until I get a good pedal.

[A1971Blazer]

always check the booster push rod to piston clearance FIRST
that can cause major issues with the brakes....with everything you've done...it should stand on it's nose
I have a tool I made but you might be able to borrow or rent one to set the clearance to 1/32"-1/16"
looks like this

[geezer#99]

And here’s another read for you.


https://www.onallcylinders.com/2014/...der-bore-size/

[CantPutTheSmokeBack]

Originally Posted by Nh4clo4

I verified it by loosening the master from the booster, then trying the pedal again.
Same as you all new, it took me a couple days to straighten out.

Also one of the rear drum cylinders, popped out of track and wasn’t pushing on the shoe. So there were a few issues.
Good luck it is frustrating

I verified I do not have any preload in the pushrod, and even added a washer to each stud between the master and the booster to make more clearance but no change, still soft until it stops. I can feel the dead slack in the pedal now as well as feel when the rod makes contact.