Brake dilemma, need advice

[lolife99]

Originally Posted by 69chevyshort

They were worse. The rears would lock up really easy.

That doesn't make sense going thru a factory porportioning valve. Your's looks just like the one ECE sells in their kits.
(like a 73-87 version, with one front port closed off)

Also how deep is the pushrod hole in the back of the M/C?
Seems like I remember the "manual brakes" having a deep hole and the "power brakes" have just a shallow button to just center the pushrod.
(like an inch difference in the two lengths).

[Painter D]

Originally Posted by lolife99

That doesn't make sense going thru a factory porportioning valve. Your's looks kjust like the one ECE sells in their kits.
(like a 73-87 version, with one front port closed off)

Also how deep is the pushrod hole in the back of the M/C?
Seems like I remember the "manual brakes" havining a deep hole and the "power brakes" have just a shallow button to just center the pushrod.
(like an inch difference in the two lengths).

This whole thing doesn't make sense. Your info is getting my hopes up.


The depth of the hole is approx. 1 3/8" deep. If you look in one of the pics you can see the rod poking out of the booster. "It appears".............to be the propper length for this MC ,(I guess). Appearences and measurements are two totally different things though ,I'm probably wrong.

[lolife99]

Here's a couple pics from my '71 Big Block parts truck.
This thing is rusty, but mostly unmolested.

It has the exact same M/C and booster.
Same line sizes and placement also.
(3/16" line on the front reservoir and 1/4" line on the rear)

If you want,... I can run out and pull the M/C away from the booster while it's still daylight here.

I really think it's the M/C and porportioning valve combo,... but I hate throwing money at problems.

I'm running out of ideas.

[lolife99]

Your porportioning valve is a little different.

[lolife99]

I think what you have is correct.
I took mine apart, (because I just had to know), and it looks like the booster rod length is about the same.
4.031" total when I pulled it out of the booster, and approximately 1" past the rubber boot of booster.
I assume the small o-ring is still on this rod?

The plunger depth of the master cylinder is approximately 1.625", so that blows my theory.
Yours pedal linkage does have the same pivot assembly prior to connecting to the booster.

I know my M/C (that I got for my '69 from PerformanceOnLine.com), said to make sure that the depth of the plunger was the same.
I can't find my paperwork, so I must have thrown it away.

Sorry,... I'm not much help.

[lolife99]

These are right out of the POL (Performance OnLine) catelog.

My booster had Delco/Moraine stamped on the front.
Look at the different applications of the Moraine booster. (up to '78)
Also notice in the picture of the booster,... they show two different length M/C pushrods.

Hope this helps and doesn't add to the confusion.
(notice the C20 M/C has a 1-1/4" bore)

[Painter D]

THANKS for the info lolife, it helps.


The more I keep digging and the more people I talk to the more the MC and prop. valve keep coming up. I agree it's gotta be something with those two things. I ordered some stainless steel lines and I think I'm gonna just get a new MC and prop valve when they come in. If the problem still persists after that I have no idea what I'll do.


Like I said before the brakes work they just don't work as good as they should and they just won't lock up no matter how hard I push the pedal.

[tires2burn]

I have been watching this problem and am thinking that the pedal arm has 2 holes in it. 1 for power and another for manual. That could make quite a differance as far as the leverage goes.

[Longhorn321]

Originally Posted by 69chevyshort

A mechanic at work (#@$% dealership) suggested I try swapping the front and rear lines and see if that makes a diffeence. Anybody else got any suggestions? .

Did you try this?

Originally Posted by 69chevyshort

BTW I'm fully aware my MC and engine compartment for that matter look like chit.

Your Chit looks better than my Chit.

[Painter D]

I haven't tried swapping the lines yet, I'm gonna wait until the stainless steel lines show up and try that first.

[es67chevy]

I saw you got your lines. I'm subscribing to this thread to see how it all turns out. We're about to go through putting ours back together too and I'm worried about a similar outcome. Good luck!!!

[Painter D]

Originally Posted by es67chevy

I saw you got your lines. I'm subscribing to this thread to see how it all turns out. We're about to go through putting ours back together too and I'm worried about a similar outcome. Good luck!!!

It's probably going to be a couple of weeks before I get around to plumbing the new lines. I've got too much other stuff on my plate that I have to have finished by the weekend of March 18th.

After that weekend I'll probably have time.

[Painter D]

Problem solved.


After I finish with my motor swap I'm ordering a whole new big brake system. When I say "whole system" I mean a whole system. Not sure which one yet ,I'll keep you guys posted.

[87chevy.com]

ha, i just read a post about a guy having the same question... they were talking about the smaller brake line... quoteing from another forum
"Think of it as the effect acros the length of the tubing. With 3/16" tubing, 1/2" of pistn stroke is 1/2" of fluid movement into the atrium of the calipers (I am leaving the calipers themselves out of the equation as that is particular to the volume needed for any specific caliper). Now, use a 25% larger i.d. tubing from the dist block to the rear and going from 3/16 line out of the MC to the dist block (without doing exact math) 1/2" of piston stroke will be about 3/8" into the calipers. but the fronts will not experience this drop as they use the smaller i.d. lines.
This effectively increases the front bias already built in to the MC"

plus I dont think your supposed to run a proportioning valve + an aditional prop valve... is that what your running or a stock gutted one plus an adjustable... i also read on the site that thats no bueno...
clint