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Unread 07-01-2013, 08:42 PM   #1
Dr. Marneaus
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Slow brake pedal return.

Okay!

First off, a good note:





First time it's been in the light of day in almost 2 months. Did the axle swap on May 12th.

That being said, she's runnin' like a champ, as always.

So, no the not so good, brakes are still messed up. 2 issues that may be separate may be related.

1. Pedal is soft when the truck is running. Still goes mostly to the floor.

2. Pedal is SUPER SLOW on the RETURN.

Now, In my mind, the pedal may7 be slow to return simply because it's moving so far.

I assume I just need to give it another bleeding, and make sure all is good. I bench bled the master while on the vehicle, using a bench bleeding Kit (the little rubber hoses) until no bubbles showed. I then bled everything 1 wheel at a time, starting at the furthers. Had my girl slowly pump the brakes, hold the pedal, I opened the valve, closed it, repeated 3 or 5 times per wheel. However it seems entirely possible i may not have done enough.

So. I've also been searching and i've read that its possible the booster can not be right, and can be fighting vacuum on the return stroke if the pedal check valves or something arent working.

It the truck is off, pedal returns with normal speed. Regardless of how far its pressed (it doesnt press all the way to the floor).

With the truck running, it presses to the floor (obviously because of the boost), and takes a few seconds to return. I've never driven a vehicle that acts like this. basically as seen below icannot "pump" the brakes because its too slow to return.



If i disconnect the vacuum line while running, it returns like normal.

What could this be and what shall I do? I figure step one is making sure they are bled properly?

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Unread 07-01-2013, 10:16 PM   #2
lucdog
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About how many time did you pump the pedal, when bleeding the master cylinder? It can take 60 or more pumps to get all the air out. Have you girlfriend pump the brakes, slowly while you a watch for bubbles.

Second is the proportioning valve. On one end is a little pin, this may have popped out when you changed the front axle. There is a clip a available to hold the pin in when bleeding the brakes.

Third, can you pull the pedal up quicker with your foot to bring it up quicker? Use both feet. and pump the brakes. If you get a better pedal I suspect air in the lines.

Right know I haven't looked under the dash of my '73 and '79 J trucks, or the '84 GW. I do know my CJ's have a return spring on the brake pedal.
Like you I haven't experianced this problem.

I'm also not a fan of bleeding the master cylinder in the way you did it. I prefer off the vehicle in a vise. That is the proper way. There is a proper procedure for this. I don't have the time to explain it at this time. If you would like to know, ask.

Bill
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Unread 07-01-2013, 10:32 PM   #3
pleontks
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I had a very similar problem on my 77 chief. It was ait in the lines. I had let all the fluid drain, and was refilling the whole system. It's taken 3 full bleeds so far, and she'll get another before hitting the highway. I had to bleed at the master cylinder, then at the prop valve, then the wheels.

When my booster went bad (76 j10), she would run good, then run bad when I had the brake pedal pressed, like a humongous vacuum leak.

When my MC went bad (76 j10), I had no brakes.


BTW, glad you got it all in. Lopoks sweet.
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Unread 07-02-2013, 09:19 AM   #4
super98lsc
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You need a one way check valve inline with the brake booster. Usually they are on the booster as part of the 90 deg fitting the vac line connects into. Make certain yours is working and installed the right direction. Bleed them out as the hydraulic pressure on the system is part of what helps the pedal return. From what i remembered you also upped to a double diaphragm J20 booster right? Start bleed at the passenger rear, then driver rear then passenger front then driver front in that order. Make certain back drums are adjusted properly too or the pedal will feel weak. Looks great man!
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Unread 07-02-2013, 10:34 AM   #5
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Quote:
Originally Posted by super98lsc
You need a one way check valve inline with the brake booster. Usually they are on the booster as part of the 90 deg fitting the vac line connects into. Make certain yours is working and installed the right direction. Bleed them out as the hydraulic pressure on the system is part of what helps the pedal return. From what i remembered you also upped to a double diaphragm J20 booster right? Start bleed at the passenger rear, then driver rear then passenger front then driver front in that order. Make certain back drums are adjusted properly too or the pedal will feel weak. Looks great man!
The check valve is installed and working right. I checked it with my mouth
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Having a Full Size Jeep is likehaving a hot wife. When you take her out in public it turns heads, they can insight jealousy, you could look at them all day, they require a lot of attention, cost a lot to get them to do what you want them to do, but when they're not happy you'll be cussing, throwing things, and constantly weighing how much you'll lose if you divorce her.

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Unread 07-02-2013, 09:37 PM   #6
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Here's a trick we use on the military vehicles I work on.

Besides just pumping the brake and letting it go through the system. Also look at turning the steering wheel 30-60 times in opposite directions to bleed it. Make sure it's on jack stands when your doing this and. Have someone or yourself check it every so often, basically turn that wheel till it stops the air bubbles. You should be sore after this.
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Unread 07-02-2013, 09:38 PM   #7
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some of you and thers have mentioned this pin on the prop valve.

what is it and how do i need to do something to it?
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Quote:
Originally Posted by revelc View Post
Having a Full Size Jeep is likehaving a hot wife. When you take her out in public it turns heads, they can insight jealousy, you could look at them all day, they require a lot of attention, cost a lot to get them to do what you want them to do, but when they're not happy you'll be cussing, throwing things, and constantly weighing how much you'll lose if you divorce her.

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Unread 07-03-2013, 07:20 PM   #8
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Start here.

http://auto.howstuffworks.com/auto-p...ter-brake2.htm

On the picture you can see the small rubber boot. The pin is behind the boot. The pin needs to be held in while bleeding the brakes.
There is, on power brakes a spring inside the booster that helps the pedal return to the "up" position, so there could be a booster problem as well.

B
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1957 WILLYS pickup, needs work.
1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac trail Jeep.
1979 J20
1980 CJ5 trail Jeep.
1983 CJ7 pretty weekend and sometimes to work Driver in the summer, My first rebuild, if the Q-trac and 5 are broke, this one is the one to take. its just as capable as the other 2, except nice paint.
1984 Grand Wagoneer, 1 ton axles, great 360/727, and a big a$& tree fell on it .
1989 YJ the CJ to YJ conversion.
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Unread 07-03-2013, 10:07 PM   #9
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image-2281018638.jpg



image-1877750666.jpg
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1957 WILLYS pickup, needs work.
1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac trail Jeep.
1979 J20
1980 CJ5 trail Jeep.
1983 CJ7 pretty weekend and sometimes to work Driver in the summer, My first rebuild, if the Q-trac and 5 are broke, this one is the one to take. its just as capable as the other 2, except nice paint.
1984 Grand Wagoneer, 1 ton axles, great 360/727, and a big a$& tree fell on it .
1989 YJ the CJ to YJ conversion.
2005 TJ Rubicon.
2011 Grand Cherokee Laredo 4x4, Mrs. LUCDOG's DD.
Lots of parts not for sale, i'm a hoarder.
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Unread 07-04-2013, 04:18 PM   #10
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So I replaced another line and tried to bench bleed the MC again. The MC was seeping from the piston. BAD

Went and got another reman MC. Bench bleeding it the rear reservoir would keep bubbling no matter what. I must have run the piston 150 times. BAD

On my way home now with a NEW MC. Hopefully this will work
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If guns kill people, then pencils misspell words, cars make people drive drunk, and spoons made Rosie O' Donnell fat!

Quote:
Originally Posted by revelc View Post
Having a Full Size Jeep is likehaving a hot wife. When you take her out in public it turns heads, they can insight jealousy, you could look at them all day, they require a lot of attention, cost a lot to get them to do what you want them to do, but when they're not happy you'll be cussing, throwing things, and constantly weighing how much you'll lose if you divorce her.

The Beast Build Thread: Marns '73 Wagoneer Thread ----- The Camper Build Thread: Marns 1980 Jayco JayFinch6 Build Thread

Gone but not Forgotten: 97 TJs Build Up.

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Unread 07-04-2013, 05:19 PM   #11
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That's a real pita! where were these coming from? Chinese castings,Cuban pistons and seals assembled in Guatemala & only rated up to 10psi using vegetable oil.
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Unread 07-04-2013, 06:48 PM   #12
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Quote:
Originally Posted by Dr. Marneaus
So I replaced another line and tried to bench bleed the MC again. The MC was seeping from the piston. BAD

Went and got another reman MC. Bench bleeding it the rear reservoir would keep bubbling no matter what. I must have run the piston 150 times. BAD

On my way home now with a NEW MC. Hopefully this will work
I can take that many times to bleed the master. Just to make sure your doing this correctly, the plunger gets pushed in until a little resistance is felt, release and push again, each push of the plunger will result in less distance traveled for the pistion. Continue until you are only pushing less than 1/8". I like to wait for the air to come to the top after 20 or so pushes. This gives the air a chance to work it's way up.

This is the only way to properly bleed a master cylinder.

B
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1957 WILLYS pickup, needs work.
1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac trail Jeep.
1979 J20
1980 CJ5 trail Jeep.
1983 CJ7 pretty weekend and sometimes to work Driver in the summer, My first rebuild, if the Q-trac and 5 are broke, this one is the one to take. its just as capable as the other 2, except nice paint.
1984 Grand Wagoneer, 1 ton axles, great 360/727, and a big a$& tree fell on it .
1989 YJ the CJ to YJ conversion.
2005 TJ Rubicon.
2011 Grand Cherokee Laredo 4x4, Mrs. LUCDOG's DD.
Lots of parts not for sale, i'm a hoarder.
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Unread 07-25-2013, 04:41 AM   #13
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Hi Doc
Didn't want to join the bantering on the mothership, thought I would try over here. Sounds like your running on rear brakes, front is not getting good pressure. Yea fix the leak, don't clamp the brake line, but do clamp the caliper to help you isolate the issue.
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Unread 07-25-2013, 07:50 AM   #14
Dr. Marneaus
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Quote:
Originally Posted by super98lsc
That's a real pita! where were these coming from? Chinese castings,Cuban pistons and seals assembled in Guatemala & only rated up to 10psi using vegetable oil.
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Andrew - Landscape architect in training. Not landscaper

If guns kill people, then pencils misspell words, cars make people drive drunk, and spoons made Rosie O' Donnell fat!

Quote:
Originally Posted by revelc View Post
Having a Full Size Jeep is likehaving a hot wife. When you take her out in public it turns heads, they can insight jealousy, you could look at them all day, they require a lot of attention, cost a lot to get them to do what you want them to do, but when they're not happy you'll be cussing, throwing things, and constantly weighing how much you'll lose if you divorce her.

The Beast Build Thread: Marns '73 Wagoneer Thread ----- The Camper Build Thread: Marns 1980 Jayco JayFinch6 Build Thread

Gone but not Forgotten: 97 TJs Build Up.

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Unread 07-25-2013, 07:51 AM   #15
Dr. Marneaus
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Quote:
Originally Posted by lucdog

I can take that many times to bleed the master. Just to make sure your doing this correctly, the plunger gets pushed in until a little resistance is felt, release and push again, each push of the plunger will result in less distance traveled for the pistion. Continue until you are only pushing less than 1/8". I like to wait for the air to come to the top after 20 or so pushes. This gives the air a chance to work it's way up.

This is the only way to properly bleed a master cylinder.

B
Yup. I did varying long and short strokes. Made sure there was zero air coming out too. The most recent time I had it off as mentioned above the piston is rock hard.
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If guns kill people, then pencils misspell words, cars make people drive drunk, and spoons made Rosie O' Donnell fat!

Quote:
Originally Posted by revelc View Post
Having a Full Size Jeep is likehaving a hot wife. When you take her out in public it turns heads, they can insight jealousy, you could look at them all day, they require a lot of attention, cost a lot to get them to do what you want them to do, but when they're not happy you'll be cussing, throwing things, and constantly weighing how much you'll lose if you divorce her.

The Beast Build Thread: Marns '73 Wagoneer Thread ----- The Camper Build Thread: Marns 1980 Jayco JayFinch6 Build Thread

Gone but not Forgotten: 97 TJs Build Up.

Dr. Marneaus is online now   Reply With Quote




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