Mechanics

CAN'T GET A DECENT BRAKE PEDAL DESPITE ALL NEW PARTS

1979 Jeep CJ7 • 11,880 miles

I have a 1979 CJ-7, 258 cu. In, 4 speed, manual brakes, factory disc front, drum rear. I have replaced literally everything; master cylinder, hard lines, hoses, calipers, bearings, hubs, rotors, pads, proportioning valve, wheel cylinders, drums, shoes, hardware, EVERYTHING. And I didn't cheap out either, I got the "better" parts, not the cheapest. I cannot get a decent, sustainable brake pedal. We have bled, and bled, and bled, almost 4 quarts run through the system. If you pump the pedal about 30 times, the pedal comes up about halfway (halfway decent pressure, not great), but if you take your foot off the pedal, count to five, and step on the pedal again, it slams to the floor. It has no leaks anywhere. My first thought was a bad reman master cylinder. I have already tried 3 reman masters and 1 brand new master, same problem every time. It has damn good fluid flow to all 4 wheels. I have been working on cars for a long time, but I am completely lost. I don't know what else to do!
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Speedylube
May 17, 2012.




No air in the system. You can pump the pedal all day long, pressure bleed, and/or gravity bleed the brakes, no air bubbles at any wheel. And I have replaced the master cylinder 4 TIMES in the past 3 weeks, mainly because it acts like a master cylinder problem. 3 remanufactured master cylinders (from 2 different companies), and finally a BRAND NEW master cylinder. I run a repair shop, hence my screen name. I have been working on cars for 11 years. I have NEVER had a brake system be this problematic, not even new ABS brake systems. I have checked, double checked, and triple checked every line, hose, and part looking for ANYTHING that might cause the problem, I've found nothing!

Tiny
Speedylube
May 17, 2012.
I could see getting a bad master cylinder, maybe (and that's a big maybe) 2 bad master cylinders, but I very, very highly doubt I have gotten 4 bad masters in a row, especially considering that they came from 3 different companies now (1 NAPA, 2 Cardone, 1 Fenco).
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Tiny
Speedylube
May 17, 2012.
In case I didn't mention it, this is a bone stock factory disc/drum system, nothing altered or otherwise fiddled with.

Tiny
Speedylube
May 17, 2012.
Either the master cylinder is at fault or there's leakage somewhere in the brake system-brakes shoe adjusted properly and caliper pistons moves in and out-is the brake master cylinder push rod/adjusted properly-also investigate the inside mounting plate of the master cylinder

Tiny
Rasmataz
May 17, 2012.
Okay, here we go. Master cylinder pushrod is made to the master cylinder, it is NOT adjustable, but it is the correct length (no play at the pedal). There is NO VISIBLE leakage anywhere, trust me, I've been through this system many times. The shoes are adjusted tight to the point where they are dragging a little, and the mechanical parking brake works like a champ. The calipers are where this gets interesting; I did not originally plan to replace the proportioning valve (with internal residual valves), but when I first replaced everything else, despite that fact that it had no pedal, the front brakes locked up (even with new calipers). Changing the prop valve fixed that. But that also tells me the calipers and sliders are working. When you pump it up and get the half-ass pedal, it stops the front tires from turning; release the pedal, the tires spin freely. And back to the master cylinder. The odds of getting 4 in a row bad are astronomical. The odds are so incredibly high I'm almost willing to rule out the master cylinder as the source of this problem. Any other ideas?

Tiny
Speedylube
May 17, 2012.
Adjust your rear brake shoes. So they are just hitting the drum. This can be done by adjusting the star adjuster through the window on the backing plate and a adjustment tool or by removing the drum and turning the star until it starts rubbing the drum. Ill be hear

Cadieman
May 17, 2012.
They are already (and have been) adjusted correctly. When you spin the wheel by hand, you can hear the shoes rubbing the drums. At this point, if anything, they are probably a little too tight.

Tiny
Speedylube
May 17, 2012.
And when I say no pedal pressure, I mean NO pressure. Not even a little. The pedal slams down all the way to the floor. I did notice this: If you pump the pedal quickly, you get the half-ass pedal. When I say half-ass, it seems to have a little pressure behind it about halfway down, but it is so-little pressure that with a little muscle you can still MAKE it go all the way to the floor. If you pump very slowly, you never get anything, the pedal travels all the way to the floor every time. This thing has manual brakes, without this little problem I am having, the pedal should be leg-tiring hard (my manual brake 1968 Chevy C10 will wear your right leg out when city driving).

Tiny
Speedylube
May 17, 2012.
And again, I know it acts and sounds just like a master cylinder problem, but the same exact problem with 4 different master cylinders?

Tiny
Speedylube
May 17, 2012.

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