Soft brake pedal problem - new 4-wheel manual discs

[dhardison]

I've purchased and installed the Touring-Classics front Hybrid kit and rear kit for my '70 Nova. This is a manual drum to manual disc conversion. Today I finally got around to installing/plumbing the master cylinder and bleeding the entire system (after bench bleeding the master cylinder).

I've bled the ENTIRE system 3 separate times (no air bubbles at all) but the pedal is still VERY soft. My bleeding order is RR, LR, RF then LF. On the first stroke the pedal travels at least half way before I feel ANY resistance. If I pump the pedal a couple times I get decent pedal, but not what I'd call 'firm'.

I've read that I should tap the calipers with wood blocks to release any trapped air, but after 3 complete bleedings I can't imagine there's any air left.



Any thoughts on firming up the pedal would be great. I can't drive it the way it currently is.

Thanks,
Dan

[MrQuick]

Hi Dan,
getting a decent or better pedal after a continuous pumping would tell me it has air in it...what master are you using and are you running a prop or combo valve?

[David Pozzi]

You might try bleeding at the master cyl fittings, it's messy though.
It sure sounds like there is air in the system somewhere, or you have air leaking in. You might go over all the line connections and loosen a half turn, then tighten again. Sometimes a brass seat is not fully seated on a new master cyl and a re-tighten can help. On your system, only a tiny amount of air can cause trouble.

Pump up the brakes and hold it for a while, a leak may show up. Make sure all bleeders are at the top most side of the calipers and the emergency brake cable is released.

[dhardison]

Vince: I'm running the m/c that came with the kit. It's a non-power 1" bore unit. Yes, the stock combo valve is still installed (per instructions) as well as a new prop valve. Maybe air stuck in/around the prop valve?

David: I'll try pumping the brakes and holding to find a suspect leak. All bleeders are at the top of the calipers and the e-brake is released. I'll try breaking the fitting and retightening as suggested as well.

Thanks guys!!
Dan

[dhardison]

I've bled the system at EVERY fitting including the m/c, prop valve and comb. valve fittings. I've re-bled the entire system an additional two times, once with a Mity-Vac, once via gravity. These are the 4th and 5th times respectively it's been bled. No air bubbles at all either time. I've held the pedal for 2-3 minutes and no fittings are leaking.

Any other suggesstions? Bad m/c maybe?

Thanks,
Dan

[Rick Dorion]

If you plug the line ports on the MC, you can determine if it's at the MC or outbound. If the pedal is firm and fine when the ports are blocked, you can do one port ( front or rear) at a time to identify which circuit. If your pedal is still soft with the ports plugged, it's the MC.

[dhardison]

EXCELLENT idea Rick! Let me throw this out as well. I have a line lock installed on my Nova (locks front circuit). If I set the line lock and pump the brakes once, the pedal is still spongy, but upon a second pump the pedal is rock hard. If I hold the brake and release the line lock the pedal stays hard until I release the pedal and press it again, which at that point it's soft again. I don't know what this means but I thought I'd toss it out there.....

I'm really leaning toward a defective m/c.....

Thanks,
Dan

[Van B]

Is there a bleeder on your line loc soleniod? It looks like it is higher than the MC, maybe an air bubble is stuck at the line loc and can't go anywhere.

Jeff

[dhardison]

Jeff, No bleeder but I did bleed the solenoid at both line connections. I may bypass the line lock alltogether to rule it out as the problem.

Thanks,
Dan

[1bad69+70]

Let me know the fix,having same prob on 69 camaro.All manual drums,new mc,hoses,shoes,wheel cylinders,and still soft pedal.Gravity bled,force bled with pump the works still no pedal.

[paul67]

Is the master cylinder new if you can get some one to push the pedal leave the top off the master, if you get a shot of fluid shoot up or bubbles sounds like the seals in the master are passing or the bore is worn or scored.How I found this also, is pump brake till pedal is solid then everso gently start to lift foot off the brake just as the car moves forward put foot on the brake if the pedal goes to the bottom or you have to pump brake its the master as the fuild is coming back into the cylinder under pressure. Also try using a kit that pushes the fuild throught the pipes a self bleeder.
paul67

[dhardison]

1bad: I'll update this thread with whatever I find.

Paul67: At one point I had the top off the m/c and had my wife push the pedal somewhat gently. Fluid squirted up from the front chamber (rear brakes). I've also noticed A LOT of excess fluid on and around the seal of the m/c cap, like it's definitely being squirted up and trying to get out. So, does this sound like a bad m/c?

Thanks,
Dan

[paul67]

Is the master designed for a front disc rear drum set as they are diff from drum/ drum,on disc/ disc as there is a valve washer in the rear drum brake master to keep the presure on the drum springs but has to be taken out on a disc disc set up as it does not allow the disc pads to come off the disc.
paul67

[dhardison]

The master is for a manual disc/disc set up. At least it's the one that came with the kit and it specificed as such.

Thanks,
Dan

[paul67]

That were the problem is wrong master
paul67

[Rick Dorion]

I have a C3 MC in a disc/drum application and did a normal brake bleed with fine results. It's cheap from any auto parts place but the choice of MC may not be the problem.

[dhardison]

Small update: I plugged both ports on my m/c and had real good pedal. For now I've removed the line lock from the equation and will re-plumb one circuit at a time to see what gives. I have speed-bleeders on the way to make it a one-man job.

Dan

[Rick Dorion]

Good progress, Dan. Keep us posted!

[MrQuick]

Hey Dan, after looking at you picture and beating my head against the wall for about an hour I think I figured out your problem.
The master is good,
routing from the master is good.(front port to rear disc,rear port if the front disc)
Its in your line lock routing. Your supposed to block off one side of the front and tee off of the other.What happening is when your pumping the brakes is going back into the master through the combo valve...if you look at the line lock instructions it should show a front port (at the combo valve) being blocked off. Also your master should be the highest point.
So to recap...front plumb from the master to the combo valve should be a solid line.
Then one front side line is capped and the other line goes into the line lock then tees out to both the left and right side. And mount the line lock lower on the firewall or frame.
The adjustible prop valve should be plumbed in after the combo valve not before.
If that isn't it remember I was banging my head against a wall for an hour. "gee it smells alot like flowers"

[dhardison]

Vince, Thanks for banging your head! I know it's hard to tell from the pic, but the line routing for the line lock is just as you described. I had this line lock installed with my manual drum/drum set up and it worked fine. I agree that the line lock itself is too high and should be placed lower that the m/c. I didn't even consider that the prop valve needed to be after the combo block, makes sense.

Thanks!!
Dan