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rear brake line size


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to find out what size plug I need

I was afraid you were going to say that. So you haven't read any of the threads about how to remove or eliminate the rear height-sensing valve, I take it?

 

What you DON'T want to do is plug it back at the valve itself. If you do that, you still have two lines running the full length of the chassis, which doubles the probability of a leak or rupture. Why keep two lines if you're not going to use the height-sensing valve? And how are you going to close off the line you remove from the rear height-sensing valve?

 

The right way to do it is to remove the bypass line completely, starting at the master cylinder, and then run ONE new line directly from the master cylinder to the upper end of the flex hose at the rear axle.

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Ok thank you no I didnt look into it at all I just assumed I would get rid of the one line, plug it and get a new junction that doesnt have the T in it going to the porpoising valve, hook every thing up and go from there. If you say thats not the way to go then ill just do what you said. Thank you very much

 

Brandon

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He still needs to find out the thread and size of the threaded inserts for our brake lines for the plug that gets inserted into the MJ proportioning valve by the master cylinder. Trust me I have searched through everything on here and other forums about the rear height sensoring valve. I ended up keeping mine for now and just repairing the rear lines, but in the future I will remove it. In all of the threads on here one person talks about the size being a standard size. The best thing to do, is to go to a parts store get a piece of 3/16 brake line, take the threaded fitting on the brake line and match it up to a bolt or brass plug.

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Ok thank you no I didnt look into it at all I just assumed I would get rid of the one line, plug it and get a new junction that doesnt have the T in it going to the porpoising valve, hook every thing up and go from there. If you say thats not the way to go then ill just do what you said. Thank you very much

 

Brandon

 

You take the front "nose" line from the metering block beside the master cylinder and run a new line the whole way to the rear axle rubber hose. Then you remove the other rear line and put a bolt or brass plug in the metering block losing the bypass line. My previous post I was talking about the plug you need to buy for the metering block. Search proportioning valve on here, there is some nice diagrams and pictures. Is there anything wrong with your valve?

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He still needs to find out the thread and size of the threaded inserts for our brake lines for the plug that gets inserted into the MJ proportioning valve by the master cylinder. Trust me I have searched through everything on here and other forums about the rear height sensoring valve. I ended up keeping mine for now and just repairing the rear lines, but in the future I will remove it. In all of the threads on here one person talks about the size being a standard size. The best thing to do, is to go to a parts store get a piece of 3/16 brake line, take the threaded fitting on the brake line and match it up to a bolt or brass plug.

You plug the BOTTOM front outlet on the front metering block. The thread is 1/2" fine thread. The shortest bolt I was able to find in a 1/2" fine was 1-inch -- I cut it to the length that allowed it to just seat with an O-ring under the head, then I put a glob of RTV on the end before I installed it.

 

Discussed in this thread, toward the end: viewtopic.php?f=2&t=22773&p=235043&hilit=bolt+proportioning+block#p235043

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He still needs to find out the thread and size of the threaded inserts for our brake lines for the plug that gets inserted into the MJ proportioning valve by the master cylinder. Trust me I have searched through everything on here and other forums about the rear height sensoring valve. I ended up keeping mine for now and just repairing the rear lines, but in the future I will remove it. In all of the threads on here one person talks about the size being a standard size. The best thing to do, is to go to a parts store get a piece of 3/16 brake line, take the threaded fitting on the brake line and match it up to a bolt or brass plug.

You plug the BOTTOM front outlet on the front metering block. The thread is 1/2" fine thread. The shortest bolt I was able to find in a 1/2" fine was 1-inch -- I cut it to the length that allowed it to just seat with an O-ring under the head, then I put a glob of RTV on the end before I installed it.

 

Discussed in this thread, toward the end: viewtopic.php?f=2&t=22773&p=235043&hilit=bolt+proportioning+block#p235043

 

And, Brandon -- it's "proportioning" valve, not "porpoising." No aquatic mammals were harmed in the manufacture of the MJs.

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I wasn't trying to be insulting, just inject some humor. But the search only works when you type in the right word. There won't be many discussions of MJ brake systems if you search this site for "porpoise."

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He still needs to find out the thread and size of the threaded inserts for our brake lines for the plug that gets inserted into the MJ proportioning valve by the master cylinder. Trust me I have searched through everything on here and other forums about the rear height sensoring valve. I ended up keeping mine for now and just repairing the rear lines, but in the future I will remove it. In all of the threads on here one person talks about the size being a standard size. The best thing to do, is to go to a parts store get a piece of 3/16 brake line, take the threaded fitting on the brake line and match it up to a bolt or brass plug.

You plug the BOTTOM front outlet on the front metering block. The thread is 1/2" fine thread. The shortest bolt I was able to find in a 1/2" fine was 1-inch -- I cut it to the length that allowed it to just seat with an O-ring under the head, then I put a glob of RTV on the end before I installed it.

 

Discussed in this thread, toward the end: viewtopic.php?f=2&t=22773&p=235043&hilit=bolt+proportioning+block#p235043

 

 

Thanks eagle I did not see that when searching. I would of already of removed mine but it was still functional so I left it.

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Thanks eagle I did not see that when searching. I would of already of removed mine but it was still functional so I left it.

10-4.

 

I know Hornbrod disagrees with me, but I try to learn from experience. The height-sensing valve in my '88 MJ was functional, too ... right up to the day the old man in the Buick cut me off and I had to make a panic stop.

 

The height-sensing valve exploded.

 

Considering that 1992 was the last year for the MJ, that means the NEWEST of those gilhoolies is now a minimum of 19 years old. I don't trust them. I'm a bit funny about brakes -- when I stomp on the peddle, I sort of prefer that the system not blow up. I grew up in the era before they had proportioning valves -- I can deal with too much brakes a lot better than I can deal with standing on the peddle with both feet and not even slowing down very much.

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I could be mistaken but I believe my rear valve was replaced in the 2000's by the Jeep dealer. You figure they had or maybe even still have a supply of them laying around. My valve looks new. I left it on when I did my 44 swap but I don't like the bleeding procedure that you allegedly have to follow in order to get a proper bleed so I will likely remove it and plug up the proportioning valve or get an XJ valve.

 

Thanks eagle I did not see that when searching. I would of already of removed mine but it was still functional so I left it.

10-4.

 

I know Hornbrod disagrees with me, but I try to learn from experience. The height-sensing valve in my '88 MJ was functional, too ... right up to the day the old man in the Buick cut me off and I had to make a panic stop.

 

The height-sensing valve exploded.

 

Considering that 1992 was the last year for the MJ, that means the NEWEST of those gilhoolies is now a minimum of 19 years old. I don't trust them. I'm a bit funny about brakes -- when I stomp on the peddle, I sort of prefer that the system not blow up. I grew up in the era before they had proportioning valves -- I can deal with too much brakes a lot better than I can deal with standing on the peddle with both feet and not even slowing down very much.

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I could be mistaken but I believe my rear valve was replaced in the 2000's by the Jeep dealer. You figure they had or maybe even still have a supply of them laying around. My valve looks new. I left it on when I did my 44 swap but I don't like the bleeding procedure that you allegedly have to follow in order to get a proper bleed so I will likely remove it and plug up the proportioning valve or get an XJ valve.

 

Good, I'll take it off your hands when you do. :D I'm aware of the extra bleeding step in the FSM for the load leveling valve, but have never had to do it. I do a good gravity bleed before I start at the wheels, and it always works; firm pedal and great brakes. Not saying don't do it, just that I haven't found it necessary.

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Good, I'll take it off your hands when you do. :D I'm aware of the extra bleeding step in the FSM for the load leveling valve, but have never had to do it. I do a good gravity bleed before I start at the wheels, and it always works; firm pedal and great brakes. Not saying don't do it, just that I haven't found it necessary.

Well, here's the thing about that -- I don't know how the height-sensing valve relates to the bypass circuit under normal conditions, so it's possible that your brakes work fine normally, but if you were to lose the fronts you might not have any rears.

 

What's supposed to happen is that normal operation routes brake fluid from the master cylinder to/through the rear proportioning valve. But if you're running with no load so the valve is allowing very little force to the rears, if you lose pressure to the front circuit you're then stuck with maybe 10 percent braking power.

 

So, those clever engineers engineered a bypass circuit that's activated by the shuttle valve in the master cylinder. If you lose pressure to the front circuit, the shuttle valve (in addition to triggering the "You got no brakes, Dummy!" light) opens the port to the bypass port. That sends brake fluid past the rear height sensing valve and directly to the rear axle, so you get the full benefit of however much braking your rear wheels can produce.

 

However -- if there's air trapped in the bypass circuit, activating will NOT send full force to the rear wheels, because the air will compress and negate the bypass circuit.

 

As I said, I'm not 100 percent certain just what the rear valve does internally, but I am of the opinion that good rear brakes under normal conditions does not provide any evidence that the bypass will function as advertised if there's a problem.

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Maybe, maybe not. I don't know either. I do know that the older Toyota pickups used to have a similar mechanical load sensing valve and it was piped like the MJs. There was no special bleed procedure for it, according to a Toy dealer mechanic I know. I was discussing with him the possibility of swapping one of the Toy valves out if and when mine failed. He said at the dealership they do a gravity bleed for the valve, nothing else. :dunno:

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Maybe, maybe not. I don't know either. I do know that the older Toyota pickups used to have a similar mechanical load sensing valve and it was piped like the MJs. There was no special bleed procedure for it, according to a Toy dealer mechanic I know. I was discussing with him the possibility of swapping one of the Toy valves out if and when mine failed. He said at the dealership they do a gravity bleed for the valve, nothing else. :dunno:

If you look at the photo of the cut-away front distribution block, the bypass port is blocked by the shuttle. You can open rear lines and let it drain by gravity for a week, but there won't be anything flowing (or dripping) through the bypass circuit.

 

That be the problem.

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