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  #1  
Old 07-05-2018, 03:33 PM
440sixpack 440sixpack is offline
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New Brakes Work Terrible

I have all new brakes on my '78 J10 and they're awful. it's like you have a 10 tone gooseneck hooked to it when it's actually empty.


So I have turned drums and rotors , new pads and shoes, new slaves and calipers, new hoses, new MBM booster and master.

I've rechecked the rod lengths per MBM specs. re-bled the system. checked the vacuum source and performed the start up test on the booster and checked the check valve.


The ONLY think I haven't messed with is the combination valve. I just ordered a new master and I'm going to change it on the off chance it's defective. my next move is to swap the combination valve out with one off my parts rig. could this cause my problem ? any other ideas ? I'm about to take it to a pro and tell him I don't know WTF is going on.
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  #2  
Old 07-05-2018, 04:38 PM
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airman airman is offline
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How did it stop before the brake job.

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Old 07-05-2018, 07:05 PM
440sixpack 440sixpack is offline
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I wish I knew . I hauled it home and did a full restoration.
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Old 07-05-2018, 08:09 PM
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Kali Kali is offline
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Quote:
Originally Posted by 440sixpack
I wish I knew . I hauled it home and did a full restoration.

If you're going FULL restoration, maybe consider upgrading to hydroboost. BJs has the kit. Unless you want to keep it stock.
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  #5  
Old 07-05-2018, 09:00 PM
440sixpack 440sixpack is offline
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Yes I'm trying to keep it as stock as possible. the vacuum booster should do a decent job if I can just find where the problem is in the system.
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  #6  
Old 07-06-2018, 10:18 AM
ShagWagon ShagWagon is offline
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Does your foot hit the floor or do you have pedal?
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  #7  
Old 07-06-2018, 10:54 AM
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Quote:
Originally Posted by 440sixpack
the vacuum booster should do a decent job if I can just find where the problem is in the system.
Unless the pedal is rock hard, doubt it's the booster. The booster doesn't give you better, more powerful brakes. All it does is make the pedal easier to push.
Seems not necessary on all vehicles but often the prop valve(combination) button depending on what type you have type-W, or type-D needs to be either held-in or held-outward when bleeding the front brakes. Is it possible on the rear drums you mixed up the leading and trailing shoes? Even if you botched the rears the front discs should still pull you down "somewhat fair".
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Old 07-06-2018, 10:56 AM
Ristow Ristow is offline
 
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are the shoes on correctly? primary shoe facing forward?


does the MC seem to have excessive stroke?
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  #9  
Old 07-06-2018, 10:58 AM
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what size tires?
rear drums adjusted correctly?
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  #10  
Old 07-06-2018, 02:39 PM
440sixpack 440sixpack is offline
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Shoes are on correct, adjusted until they dragging pretty good.

This booster/master set came from MBM. I looked and now they don't list anything for full size Jeeps. I called their tech line and they said if I didn't have all the paperwork including the date of purchase they won't talk to me. I can't find it ,I bought this stuff over a year ago. so they're useless.


I'm wondering if I have a master with the wrong bore size. since nothing makes sense on this I'm going to put a new master I know is correct on as soon as it's out of the shop getting the new gears installed and see if that does it.


If that fails it almost has to be the combination valve or the booster. and I doubt it's the booster it passes all the normal tests.
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  #11  
Old 07-08-2018, 10:35 AM
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rang-a-stang rang-a-stang is offline
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can you lock any of the tires up if you mash the pedal hard? Did you replace all the soft lines? Does it feel like the only the front or only the back are biting?
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  #12  
Old 07-08-2018, 10:45 AM
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Does it make a difference if the booster is connected to vacuum or not?
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  #13  
Old 07-08-2018, 10:47 AM
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Quote:
Originally Posted by joe
Unless the pedal is rock hard, doubt it's the booster. The booster doesn't give you better, more powerful brakes. All it does is make the pedal easier to push.
Seems not necessary on all vehicles but often the prop valve(combination) button depending on what type you have type-W, or type-D needs to be either held-in or held-outward when bleeding the front brakes. Is it possible on the rear drums you mixed up the leading and trailing shoes? Even if you botched the rears the front discs should still pull you down "somewhat fair".




Don't vehicles without power brakes often have master cylinders with a smaller bore to allow for lower braking efforts (at the expense of more stroke)?
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Old 07-08-2018, 10:55 AM
joe joe is offline
 
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Quote:
Originally Posted by Mikel
Don't vehicles without power brakes often have master cylinders with a smaller bore to allow for lower braking efforts (at the expense of more stroke)?
Mikel w/o some research I'm to lazy do do, you could be correct. I don't know the specific differences between std and PB masters but they are different.
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  #15  
Old 07-08-2018, 03:33 PM
77Deepj20 77Deepj20 is offline
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I've had a few bad out of the box master cylinders the last few years. You never did mention if the pedal was firm or sloppy ect.

Was the master bench bled before installation?

Unless the proportioning valve is clogged with rust or something it should work, never really had one go bad.

Is the pushrod between the booster and master in place and the correct length?
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  #16  
Old 07-08-2018, 06:36 PM
yossarian19 yossarian19 is offline
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Like others have asked... How does the pedal feel?
If you hit the brakes a dozen times or so with the engine off, does the pedal feel different?
When you hit the brakes, is it like stepping on a rock or is there a lot of motion in the pedal and inadequate stopping power?

By far the most common issue after a brake job is air in the system. This can be due to an inadequate job of bleeding the MC on the bench, having caliper bleed screws pointing down (instead of up), stubborn lines, etc.

I've also had an issue where while I was bleeding the brakes the combination valve did it's thing and shut off flow to one side or the other. It's been long enough I can't remember all the symptoms but "no stopping" was definitely one of them. I used a small screwdriver to push a little pin at the nose of the valve to reset the thing and went on with life - bled it again and problem solved.

If your problem isn't hydraulic and performance still sucks, have you done anything special to break in the brakes?

When I worked at a garage, we'd punch the gas and check the rear view - when there was nobody behind us, it was HARD on the brakes and off again before a full stop. Repeat 3-5 times while we made our way around the block. You'd be surprised what a few heat cycles and some HARD hits on the pedal would do for the performance of new friction.

Conversely, a "come back" I had, was a time I neglected to install the "shims" between caliper and brake pad + didn't break the pads in adequately. I drove it around the block, felt fine, but customer claims she damn near lost it while going down a pretty gnarly hill. I wasn't there and am in no position to say much about it - except that in commercial auto repair, it is standard operating procedure to cover your butt and if you get some smoke out of the wheels on a test drive, mission accomplished.
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Old 07-08-2018, 06:44 PM
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Another easy thing to test - While having someone step on the brake pedal, if you open a bleeder, does the pedal go to the floor?
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  #18  
Old 07-08-2018, 06:51 PM
440sixpack 440sixpack is offline
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Pedal feels pretty normal, an inch or so of travel and you can feel and hear the booster kick in, pedal gets firm well off the floor and then not much happens.

Rod length is correct , non adjustable but very close fit.

If the new master doesn't do it I will bleed them again with extra care to check the combination valve pin and make sure it's centered.


I feel like this has to be a defective or incorrect master after exhausting every other scenario. I should get it back in the next day or so and I'll know.
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  #19  
Old 07-08-2018, 11:07 PM
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PlasticBoob PlasticBoob is offline
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Not trying to insult your intelligence, but did you bed them in?

I just did the Tundra brake upgrade on my 4Runner (new rotors, calipers, and pads) and it took a 50 mile round trip freeway drive late at night doing around 30 hard stops, one every 1/2 mile, to get them nice and blued. These were the instructions per Brembo, btw.

On a couple of past cars, I failed to properly bed-in new brake components and had terrible performance the whole time.

For anyone else lurking and learning about brake jobs:

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  #20  
Old 07-09-2018, 09:40 AM
RamJetFSJ RamJetFSJ is offline
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I couldn't find if it was mentioned above, but make sure you bench bleed your master cylinder before installation.
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