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post #1 of (permalink) Old 07-02-2001, 07:37 AM Thread Starter
 
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Need brake help-pedal goes to the floor

My brake pedal goes to the floor at the most inopportune times. I have made two runs on my new setup and can't figure this out. I have bled them twice personally, once having a friend depress the pedal for me while I do the bleeders and once with a hand held vacuum pump. I have had two different brake shops bleed and check adjustments on everything.

I have a Scout 44 rear with all new brake parts including wheel cylinders. Front 44 uses '76 FSJ calipers (new). After the first go around with a brake shop last week, the manager pointed out some discoloration (not wet) on the power booster and said my MC was leaking. I bought new MC (not remanufactured), put it on, bench bled it, bled brakes with vac pump; didn't cure problem.
That's when I took it to a different brake shop; $55 bones to them to flush bleed and adjust, and on this weekend's run same problem.

Brakes work great, pedal is stiff, and I'm a grinning cuz I'm a Jeepn', and then out of nowhere the pedal goes to the floor. One or two pumps, and the pedal is back to being stiff and brakes are working great. I don't get it. No signs of leakage anywhere, wheel cylinders, calipers, nada. MC is full. Can air be pulled in around a fitting but fluid can't escape out? Maybe the MC is bad?
Only parts I haven't replaced were the power booster and proportioning valve.

Thanks for the read, I know it's long.

Max

82 CJ, some stuff stock, some stuff not
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post #2 of (permalink) Old 07-02-2001, 08:26 AM
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Re: Need brake help-pedal goes to the floor

I don't know if it makes a difference in this case, but was the metering valve on the proportioning valve depressed while the system was being bleed? I was having trouble bleeding my system and it got much better after I found out about this. On the type W proportioning valve you remove the rubber dust cover on the front and insure that the pin stays depressed through out the bleeding process. The D type valve appears to be similar. The way to tell the valves apart: W type is boxy looking and the D type is rounded with no sharp angles. Hope this helps.

post #3 of (permalink) Old 07-02-2001, 08:30 AM
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Re: Need brake help-pedal goes to the floor

I posted this last August:

It's not necessarily the master cylinder. What happened to me (after I replaced the master) was I found some air still in the calipers. My brakes would work fine, just spongy, pumping them up worked, and everything was new, so I naturally assumed it was the master. We bled the brakes, bled them more, and even used a venturi to bleed them (what a slick rig). I was convinced there was no air in there. A trick I did is to take the top off the master cylinder and have the caliper off the rotor but all lines attached. Now open the bleeder screw and let the fluid gravity drain out of the caliper, any air will travel out with it. I always bleed my calipers this way now and have never had it fail, just make sure the master doesn't run out of fluid.

And this later on:

The problem turned out to be the front calipers. I tried everything, even a Venturi bleeder, all with no luck. What I found was the bleeder on the calipers was not on the top, it was a little to the side. What I did was take the caliper off, and removed the top from the master. Next I held the caliper low, and opened the bleeder screw. This allowed the fluid to drain down by gravity. It'll come out a little slow, but it will come out. Move the caliper around to different angles and try to get the air out. I had bled mine so many times I ran 1/2 gallon of brake fluid through it. Like I said, even the Venturi didn't help. The good thing is you can even do this by yourself. Here's a test to see if that's the problem, but only if you have rubber lines in the front, take and pinch one off with a vise-grip. Next check the pedal. The gravity bleeding made the pedal rock hard, and it was so simple to do. Good luck and let me know if it doesn't work.

JEEPN
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'81 CJ-8 Scrambled, It's a Jeep, Chevy, IHC kinda thing!
'88.5 Zuki, 5" Calmini, Locked, Swamped, Rolled, and just generally broken in right!
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post #4 of (permalink) Old 07-02-2001, 08:33 AM Thread Starter
 
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Re: Need brake help-pedal goes to the floor

I don't know if it would make a difference or not. What is the difference between the valves, functionally, I mean. And why would it make a difference? When you bleed you are pushing fluid through the valve, cuz it is coming out the bleeder, right? Is the only way to do this have a third person there to depress the pin.

My pro valve doesn't have any round edges, it is squareish and boxy looking.

Also, could air cause the symptoms I am describing. The pedal is pretty firm and brakes work great most of the time.

Max



82 CJ, some stuff stock, some stuff not
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post #5 of (permalink) Old 07-02-2001, 08:48 AM
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Re: Need brake help-pedal goes to the floor

The boxy one is the type W. There is a tool to hold the metering valve in, p/n J-26869, but the Jeep (Chrysler) guy said it wasn't listed. I had a threesome going for my brake job. As far as air. It would seem to me that the problem would be a full time thing since the air in the system would be compressed every time you pushed the pedal, not intermittently.

post #6 of (permalink) Old 07-02-2001, 11:38 AM Thread Starter
 
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Re: Need brake help-pedal goes to the floor

Thanks for the info, Jeepn, I need to replace the front axle seals, and have to tear everything apart for that, so I will try a gravity bleed.

My pedal doesn't feel spongy at all, it is either rock hard or wet-noodle-to- the-floor. No rubber either, stainless steel braided lines.

Max

82 CJ, some stuff stock, some stuff not
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post #7 of (permalink) Old 07-02-2001, 11:48 AM
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Re: Need brake help-pedal goes to the floor

My buddy had a similar problem! It had nothing to do w/ the brake lines at all...

Here's the symptoms: You get normal resistance on the pedal and then all-of-a-sudden while you're pushing it, it kinda pops and drops to the floor. If you hook your foot under it and raise it back up... you can start getting resistance again.

What was happening was the pedal was popping out of the rod that goes thru the firewall. It would pop back into the rod after raising it back up. Some previous owner didn't put a pin back in or something. So stand on your head and check the pedal and see if it can wiggle away from the connecting rod.

We bleed brakes, and started messing w/ the master cylinder before we figured it out. Hope this helps!

Sam88Jeep

'88 YJ 4.2L, 32/36 Weber, HEI, 2.5" spring lift, 31" BFG ATs.
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