It's about 7 years too late to be asking this, but with manual brakes, do you use the top or bottom hole in the brake pedal arm with a manual set up? When I did my disc brake conversion, I just put the clevis back in the hole it was in... the bottom. Bottom for manual? Could this by why my brakes suck? :clonk:

If it was in the top, there would be a much better mechanical advantage, but the pedal would probably hit the floor before full pressure in the system.

Top hole
Better leverage
If all the air is out of the system--and rears are adjusted correctly---not that much travel.

I bled and bled and bled this system. Did the master on the bench first, bled the ports when the lines were installed, bled the ports with plugs on the other side. Bought a power bleeder just to do this car, pumping always worked on everything else.

The bottom, huh? I haven't looked, what does that do the angle the rod hits the piston in the master?

Top hole manual brakes
Bottom hole power brakes because of the angle of the power booster

Top hole manual brakes
Bottom hole power brakes because of the angle of the power booster


yes! Brad's got it right!

I fully trust you guys' information, it only makes sense that you would need more leverage (upper hole) with a manual set up. That's what got my curiosity up to post. So what happened on my car? It was a manual 4-drum. The lines are all sized that they could have only matched up with a master cylinder mouted on the firewall. My original brake pedal (I did a TH400 to TKO conversion) only has wear on the bottom hole. ???

I am pretty close to the floor now. I will experiment with the upper hole and drive easy the first few times out....

MAKE SURE THE REAR BRAKES ARE ADJUSTED CORRECTLY

This can be a cause of low pedal.
If you have discs in the front-----pads/piston are always in contact with the rotor (very lightly)
The shoes, on the other hand, are pulled all the way back to the anchor at the top of the backing plate----and have to travel to get drum contact.

The closer the better.
If these are out of whack---even a little---you are going to have a lot of pedal travel.
Might want to double check the adjusters and make sure they are working correctly.

The shoes are out far enough that I have to "woggle" the drum to get it off.

OK, game plan...

1. Move clevis pin to top hole.

2. Get new disc/drum proportioning valve from CPP, SSBC didn't tell me I needed to ditch the drum/drum unit.

3. The new proportioning valve has dual outlets for the front brakes, one each wheel. The old one just had one line with a Tee. Get new hard lines to each from wheel from CPP.

4. Bleed the crap out of it and hope it works better. I really don't want to fork out for a Hydroboost.

Start with the upper hole before you spend any money - that will make a big difference. The clevis pin should have a little adjustment in it too. Try that second.

From what I understand, the distribution block makes a big difference, too. CPP definitely sells one of each type, disc/drum and drum/drum. I don't know what the internal differences are, but enough to be two different units.

As is, if I put my foot under the pedal, and push it in, the pedal stops before it starts to mash my foot. I am skeptical that I that the pedal won't hit the floor in the top hole, but am going to try to do what's needed to make it work.

Some of the distribution blocks have a fixed proportioning ratio to limit the pressure to the rear. That won't help your throw problem. That will just keep the rears from locking up prematurely. You will get more throw by moving to the manual hole, and then extending the clevis pin if necessary.

I pulled the boot off the master from the inside so I can see what's going on. I have .020" or so of clearance between the rod and the piston. I will snug that up when I re-do things. I will be relying on the rubber bumper on the dash frame work to stop it at it's upward position. That's kinda/sorta the set up now, just not really firm against it.

Looking at how a master works, the piston starts to move, and travels a bit before it passes by the holes in the bottom of the reservoir. I am guessing you don't want to try to get fancy with preloading the piston a bit with rod adjustment, huh? I guess preloading it a few thousandths isn't going to make a huge difference when I want the pedal to stop and inch further up from the floor.

If I recall, the manual system requires a pedal return spring (power boosters have an internal spring) to work properly. If the piston is not going all the way back , then the fluid ports could be covered, preventing proper fluid flow. The pedal should be back against the rubber bumper.

I took the boot off of the cylinder from the inside, and can see that the piston is against the circlip at the end of the housing. So it's getting all the way back...

definitely a return spring on the manual setups -
http://1964-77chevelleparts.com/catalogPDFs/A1%2005%20brakes.pdf

Jeez... I guess I am lucky I haven't crashed it yet??? It's the little things, like having the clevis in the right hole, and a return spring, huh? When I got this car converted to discs, I wondered what the big deal about discs was, except for less brake fade in case I was driving down a steep long canyon. Maybe I might be satisfied once I get it dialed.

I don't think the spring is that big a deal, the only thing that would happen there is they drag a little more than they should. Mechanical leverage (changed by the clevis hole) is very important to the equation - just as important as MC bore, piston diameter, etc....
I did a 4 way swap to C5 calipers and was initially underwhelmed with the improvement. I went through 3 MC's before I got it close, and at one point even tried the manual hole. Out of all the small changes I did, mechanical leverage had the most positive impact.

I don't know what I was thinking, maybe it was the laying upside down... my clevis pin is already in the top hole. And my master is a 1". I am running out of possible dumb installation errors I could fix to improve the function without the massive Hydroboost conversion.

What is a C5 master? I know, dumb question. I do know some niche stuff, ask me what a floating jockey is... (hint: it's on a bicycle)

C5 refers to corvettes from 97-04 - I didn't use a MC from that car, just the calipers. I think the C5 MC uses a 1" bore.....