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Old 01-25-2010, 12:05 AM
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Recommended front axle swap for a 73 J2000?

I know the old saying "if it aint broke, don't fix it". More often then not, I usually don't follow that rule ...

Ok, so here is the brief story ... I have a J2000, it had drump brakes (which worked ok), I then decided to replace the drump brakes with a pair of junkyard ford/jeep disk brakes (I read somewhere online that it would be a good bolt on swap)

My problem now is that the brakes don't quite work, they do and they don't ... let me explain ... I'll start the truck, and it will drive, and it appears like the brakes work well, however after a bit of a distance, it seems like the calipers will start to stay in the compressed position, I really need to press the gas to try to move it, it will compress to the point where it no matter how much gas I give it the brakes are stuck.

Instead of fumbling with it, I would like to swap in a used axle in the front. I've heard that newer/similar models of the FSJs have open knuckles and disk brakes ... seems like an ideal swap over a closed knuckle axle.

Has anyone done this and what year/model axle should I be looking for?
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1973 J2000, AMC 360, TH400 (i think) Automatic transmission, D44 closed knuckle drums (front), D44 drums (rear)
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Old 01-25-2010, 12:17 AM
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to go with front disc stay with 70's diff passanger drop.then you have to modify leaf spring mounts,then deal with the correct springs.
their might be a disc conversion kit. look a bj's off road.
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Old 01-25-2010, 12:26 AM
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Any J-10, wide-trac Cherokee, 74'-79' would work for you but... isn't there always an exception, you have 5x5.5 lug pattern correct? all of these axles are 6x5.5, you could use the Ford rotors and hubs, I don't know if you have to swap spindals or not, or you could swap rears at the same time, the other issue is spring perches, I think they're in the same location but I'm not positive, someone will know for sure.
When you did your brake mods did you also swap in the disc proportioning valve and master cylinder?
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Old 01-25-2010, 12:29 AM
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Residual valve

You need to remove the residual valve in the master cylinder.
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Old 01-25-2010, 03:54 AM
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Under a '73 J2000 I believe you have the 5-lug pattern.

An '80-84 Dodge pickup/Ramcharger Dana44 front axle has the 5-lug on 5.5" pattern and open knuckles with disc brakes

JP Magazine did the swap on a '68 Gladiator.

http://www.jpmagazine.com/projectbui...all/index.html

Last edited by wickedwagon767 : 01-25-2010 at 04:02 AM.
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Old 01-25-2010, 09:10 AM
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Quote:
Originally Posted by wickedwagon767
Under a '73 J2000 I believe you have the 5-lug pattern.

An '80-84 Dodge pickup/Ramcharger Dana44 front axle has the 5-lug on 5.5" pattern and open knuckles with disc brakes

JP Magazine did the swap on a '68 Gladiator.

http://www.jpmagazine.com/projectbui...all/index.html

X2. And I did it on my '71 about 3 years before JP did it on their's. And the years are '80-'91. Mine's out of an '85. It's pretty easy as swaps go. I used the tire rod and drag link from a J-10, JP did something different.
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Old 01-25-2010, 11:48 AM
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Dr. E, can you explain how to remove residual valve in the master cylinder? and why this is necessary? thx
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Old 01-25-2010, 11:59 AM
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Quote:
Originally Posted by farinspace
Dr. E, can you explain how to remove residual valve in the master cylinder? and why this is necessary? thx

I'd recommend just replacing the stock drum/drum MC and replacing with a disc/drum MC and a proportioning valve. Disc MC have a larger resevior for the added volume a disc caliper needs.
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Old 01-25-2010, 10:29 PM
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The residual valve allows a certain amount of line pressure to be maintained even after you release your foot from the brake pedal. This compensates for the return spring tension on the brake shoes. This is not needed on a disc brake system and will actually cause the symptoms you are describing.
The valve is located where the front brake line goes into the master cylinder.
Josh D has a good point. In addition to the residual valve problem the size of the fluid reservoir may also be too small. As a general rule it is ok to have a larger reservoir just not the opposite. More fluid is needed to push the caliper piston far enough to apply pressure on the pad to the disc.
The next problem to address is brake bias. The proportioning valve is that brass distribution block that your brake lines are routed to after the master cylinder. It is usually mounted on the inside frame rail below the master cylinder. This is also a flow control valve which is engineered usually to provide for more pressure to the front brakes and less to the rear.
Upon hard braking in a non ABS equipped vehicle this causes the front brakes to lock up prior to the rear. This allows for better steering control.
If the opposite occurs the rear end of the vehicle will slide around the front. Have you ever seen a "jack knifed" tractor trailer?
Make sure you get the right MC and bench bleed it properly before installation. Bleed the system and test the bias in a safe area. If you find that the rear brakes lock up too soon then you need to find a proportioning valve for a disc/drum system or try an adjustable proportioning valve to adjust the bias so that the front brakes lock up just before the rear.
Keep in mind that most modern vehicles are designed to adjust bias to allow for increased load like when a pick up bed is full. Sadly our old systems don't have this provision and require more driver skill.
Class.... That is next weeks lesion on "threshold braking".
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Old 01-26-2010, 04:10 PM
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As dajeeps said and I will add, you will have to get or make new leaf spring mounts as the leaf spring mounts on the 1973 and earlier are riveted and welded on the sides of the frame whereas the 1974 and newer models are riveted to the underside of the frame. The springs them selves are the same size.
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  #11  
Old 01-26-2010, 04:24 PM
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Quote:
Originally Posted by jeepmeister
As dajeeps said and I will add, you will have to get or make new leaf spring mounts as the leaf spring mounts on the 1973 and earlier are riveted and welded on the sides of the frame whereas the 1974 and newer models are riveted to the underside of the frame. The springs them selves are the same size.

Not necessary with the Dodge axle I used. The stock post mount spring spacing places the spring pads wide of the diff housing. Easier to weld on new spring pads than to relocate the springs.

Here's what it looks like with the Dodge axle slung under.

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Last edited by Josh D : 01-26-2010 at 04:29 PM.
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  #12  
Old 01-26-2010, 06:16 PM
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Switch to a disc brake master cylinder. Sounds like it should solve your problem.
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1975 Chevy K20 8400lb GVW Camper Special
1971 Gladiator
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1970 Gladiator J3000 3407Z Camper Truck 350/T18
1968 Wagoneer Custom 327/TH400
1963 Gladiator J300 Townside 350/TH400

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