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Unread 02-25-2014, 07:45 AM   #1
leon1017
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1979 CJ5 
 
Join Date: May 2012
Posts: 35
Intermittent spongy brake pedal

So here is the story...

Last week I had some new tires put on my '79 CJ5. I am now running 33/12.5/R15. When I went and picked up my jeep, the guy told me that my right front wheel bearing(s) were loose. So, this past weekend I went ahead and replaced both sets of wheel bearings (as we know, two bearings per front wheel + new bearing seal) and put everything back together.

As we also all know, I had to remove the front brake calipers to get the hub off. I did not break the brake system (crack any lines that would necessitate to bleed again). So, I take off down the road and notice that my brake pedal went to the floor the first time I tried to stop. After pumping the pedal a few times, the pedal came back and I was able to stop. I take it back to my garage and pull the front hubs off again thinking at I didn't seat the bearing races properly causing the rotors not to spin evenly, thus pushing the front caliper piston in upon rotation. I double checked all of that, put both front hubs back on and tried to drive again. Same problem. First time hitting the brake pedal, it went to the floor; pumped it up and I can stop. This happens every time I try to stop.
Back to the garage I go, and decide to change the master cylinder thinking that could have something to do with it.

Still nothing. Every time I have to stop now, I have to pump up pressure with the brake pedal a few times to build up enough pressure to get the jeep to stop.

It is worth noting that I have an entire new brake system. Less than 6 months ago, I put in all new lines, proportioning valve, front calipers, all new rear brake hardware.

I am stumped. Considering that this is a manual brake system, it is a seemingly system but for the life of me I cannot figure this one out. Any help/suggestions are greatly appreciated.

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Unread 02-25-2014, 07:52 AM   #2
leon1017
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also worth mentioning

Upon noticing this problem, I bled the brakes at least 10 times. I used a vacuum to ensure that I was pulling fluid through all 4 wheels, as well as had someone help me pedal bleed all 4 wheels in the proper order. There are no visible leaks from any of the brake lines, wheel cylinders, calipers, prop. valve, master cylinder, etc.
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Unread 02-25-2014, 07:59 AM   #3
Balvar24
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New crush washers when you re-installed the calipers?
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Unread 02-25-2014, 08:02 AM   #4
leon1017
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I never broke the lines to the brake system (especially the front brake calipers) so I didn't see a need to replace the crush washers, or anything in the brake system initially upon simply putting the calipers back on the rotors.
All I did to the front brake calipers was to simply take them off and lay them over so that I could easily get to the front hubs.
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Unread 02-25-2014, 08:20 AM   #5
silentmike29
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Did bleeding the brakes do anything? Is there enough fluid in the resevoir? I went up a steep hill in my yard and got some air in the system
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Unread 02-25-2014, 08:34 AM   #6
leon1017
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bleeding the brakes multiple times did nothing. that is why i thought it necessary to replace the master cylinder. this one has gotten me baffled.
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Unread 02-25-2014, 10:00 AM   #7
JeepHammer
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Taking the front calipers off, and re installing them *USUALLY* means pushing the piston back into the caliper.
This means the piston has to be pushed back out against the brake pad/rotor when you are finished putting things back together, and a 'Mushy' pedal the first few times is standard and expected.

You usually do this pressing the piston out VERY SLOWLY, both down stroke of the pedal, and back up so you don't suck air into the system from the top side.
Heavy/quick strokes can suck in air, so you push the piston out SLOWLY...

Once you get an air bubble in the master cylinder or proportioning valve, it's VERY hard to dislodge and will cause the issues you are talking about.

I usually DO NOT start the engine for the first few strokes, just muscle the pedal down and slowly let it back up,
And I usually leave the lid to the tank open so I can keep an eye on the fluid level...

If you have sucked an air bubble into the master cylinder, it will be very hard to dislodge it since there is no direct path for that bubble to take to the surface.
Bench bleeding the master cylinder might be in order,
And I'd check the safety valve while pumping brakes to see if it's coming off center which would indicate you have a bubble trapped in the valve somewhere...

Remember, it's not the first 'PUSH' that gets you into trouble, it's the let up of the pedal when the master cylinder 'Gulps' more fluid. A quick return of that first pedal push will allow the master cylinder to 'Gulp' fluid/air, so let the pedal up SLOWLY and make sure the tank is full each time you press the pedal...

You can 'Bench Bleed' in the vehicle, but it's more difficult than doing it in a vice on the 'Bench'.
Since the pedal has a stop to keep the piston from bottoming out in the cylinder, it's very hard to dislodge/expel the air in a master cylinder on the vehicle...
When you have it in a vice, you can use a dowel rod to COMPLETELY bottom out the piston in the master cylinder which expels the air faster and more completely.
Once the lines are broken at the master cylinder for 'Bench Bleeding, it's just a matter of two bolts or nuts to remove the master cylinder and get a good bench bleed... Don't know if you have a bench vice or not, but if you do, it's easier on the bench...

I would also check to make sure you haven't popped a rear wheel cylinder...
That first push to get the front pistons out to the rotor is REALLY HARD on the rear if you used the power booster to do it.
Much more pressure applied to the rear than the front, and you can easily pop rear cylinders if they aren't adjusted up or are worn a bunch...
Just a suggestion from experience, since I've done the front and over pressured the rear, then have to do the rear before I got pedal again...
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Unread 02-25-2014, 10:11 AM   #8
ScroungerLee
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Also check the adjustment on the rear brakes just in case.
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Unread 02-25-2014, 10:29 AM   #9
leon1017
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I did bench bleed the new master cylinder before I installed it. After reading all the posts (and thanks to all), I am going to pull the rear wheels and make sure that the wheel cylinders aren't goofy. After this, I am going to be out of options I believe.
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Unread 02-25-2014, 11:55 AM   #10
leon1017
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More information -
So, I just got in my jeep to head to lunch. I pressed the pedal and I hand a firm pedal. I turned out of the parking lot and then head down the road and the pedal goes back to being soft again. Makes no sense. Especially considering it is not a powered brake system. The whole time I am driving, I have to pump up the pressure to get it to stop.

Very confusing to say the least.
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Unread 02-25-2014, 01:56 PM   #11
Mike Romain
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That is a perfect description of what happens with a loose wheel bearing or maybe a blown ball joint. Something is allowing the rotor to push the caliper back in.
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Unread 02-25-2014, 02:19 PM   #12
leon1017
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That is what I thought as well. So after I had replaced the bearings, I pulled the hubs back off again and double checked to make sure that the bearing races were seated properly and that the new bearings, seal, etc were properly installed and packed.

The only thing I can think of is that I can pull the wheels back off again, pull the bearings and races and get new ones (and new seals) and make sure that the locknuts are torqued to the proper spec and then cross my fingers.
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Unread 02-25-2014, 02:49 PM   #13
LumpyGrits
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Remove wheel and brake caliper.
Reinstall wheel-NOW ck for wheel bear'n play.
The caliber can hide 'loose' bearings.
Tell us EXACTLY-how you set the 2 nuts.
I tighten the inner nut to 50-60ft/lb. Then back it off and snug down by hand(the socket with no wrench). Then torque the outer to spec and bend the tab over EACH to loc'em in place.
LG
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Unread 02-25-2014, 02:58 PM   #14
leon1017
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thanks for the advise LumpyGrits. I will do just that and let you guys know how it turns out.
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Unread 02-25-2014, 03:03 PM   #15
LumpyGrits
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Quote:
Originally Posted by leon1017 View Post
thanks for the advise LumpyGrits. I will do just that and let you guys know how it turns out.
You really need to get a copy of the REAL, FSM. Haynes/Chilton and the like are way lacking in details.
LG
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