New To Mj's Looking At One This Week.

[01yellowxj]

Guys and gals, I'm new to Mj's but have owned 6 Xj's. Is there anything I need to look for that is different on a Mj?

 

Is the 4.0 / autos still running D30/D35's with 3:55 gears? and the 4 cyl / 4 speeds D30/D35's with 4:10 gears?

There is a local one cheap and two others not so cheap. Rather have one with 4:10 gears to pull a medium trailer. if its 4cyl I can assume a 4.0 swap is like the Xj's. Or maybe get the 4.0 mj and look for axles.

 

My wifes xterra pulls it fine but my xj don't really like it with the factory 3:55's

 

 

Any help or pointers to look for will help as I'm looking at one tomorrow and another one thursday.

 

Soon will add a Mj to the flock...........

[airspeed]

I'm not sure about the 4.0L Auto.  My 88 2.5L 4spd has 3.55, the 2.5L 5spd would have 4.10's.  Comanche's would not be the ideal tow vehicle, they are light and have a short wheelbase.  When you say "pull a medium trailer" what weight are you talking about.  You are right with the D30 & D35, there was an option for the D44 in the rear.

[01yellowxj]

6x12 utility trailer with a zero turn mower. My XJ pulls it but not well. I have 31's and no frame with 3:55. Our Xterra with a frame and 3:73 or 4:10 pulls it awesome.

[Oyaji]

6x12 utility trailer with a zero turn mower. My XJ pulls it but not well. I have 31's and no frame with.55. Our Xterra with a frame and 3:73 or.10 pulls it awesome.

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Pulling is never the issue - you could pull a much heavier trailer with a 4-banger (just don't get in a hurry).

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STOPPING a load is an altogether different proposition, though... especially if you add bigger diameter tires and/or a significant load. I think the best bet would be to look for 10" rear drums, and that means a D44 rear, right?.

[airspeed]

It will be hard to find a receiver hitch for the MJ.  You can use the bumper, not sure what that is rated for?

[Oyaji]

It will be hard to find a receiver hitch for the MJ.  You can use the bumper, not sure what that is rated for?

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I think a bumper hitch would handle  the light load he mentioned (lawnmower and 6x12 trailer) just fine, though a receiver hitch is highly desirable.

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On the extreme end (and I surely don't recommend it), many times I  pulled  several tons  (3+) of agricultural implements  by the simple steel step-bumper hitch of an old light 1985 Toyota mini-pickup with the ~100HP 4-cylinder 22R engine and a 5-speed on 20-mile hauls down rural farm-country roads. Careful loading, attention to tongue weight, and low speed carried me through season after season. Pulling was not the problem - I never had a prayer  of being able to stop in any sane distance, so I never went faster than 30 MPH.  I drove so carefully I pretty much never had to use the brakes.

[HOrnbrod]

It will be hard to find a receiver hitch for the MJ.  You can use the bumper, not sure what that is rated for?

 

Factory rated @ 2000 lbs. Of course, that's if the bumper is in tip-top shape and structurally sound. You don't state where you are from, but if the MJ rear step bumper is a 20+ year old original and you are from a rust-prone area, I wouldn't tow a bicycle with it. These bumpers rust out fast.

 

I tow a similar sized trailer with motorcycles occasionally with no problems towing or stopping, but have a frame reciever hitch, rear disk brakes, 31s and 4.10s with the D44 and an AW4. The key is the receiver hitch, and as airspeed says, very tough to find now for an MJ. 

[Oyaji]

As an aside...

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Which has a higher factory tow rating - MJ with 10" rear drums or whatever donor vehicle the rear disc brake swap comes from?

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More importantly, which has superior load-stopping power on an MJ, the disc swap or 10" drums? Has it been objectively tested? test results posted? if so, where?

[mnkyboy]

I would suspect the disc brake equipped rig would have more stopping power, typically with the disc brake swap the rest of the system gets upgraded as well.

 

My rear D44 has 11" vented disc brakes and I'm running a dual diaphram brake booster, it feels like it has a lot more stopping power then it did stock.

[danbyrambler]

FWIW - - - If it's not Factory/OEM/Dealer installed/WTF ever & something bad happens involving others, just look out - Exactly the kind of thing lawyers have wet dreams about  - - Best to call your insurance agent - read policy fine print - Get something in writing concerning mods being covered & then rethink  - - - Wish I didn't know this.

[Oyaji]

FWIW - - - If it's not Factory/OEM/Dealer installed/WTF ever & something bad happens involving others, just look out - Exactly the kind of thing lawyers have wet dreams about  - - Best to call your insurance agent - read policy fine print - Get something in writing concerning mods being covered & then rethink  - - - Wish I didn't know this.

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This man is dead-on correct... which is exactly the reason I was asking the questions I asked. I know about the process for certification and the exhaustive testing required to document it, and was wondering just what (if any) has been done, and where to find the results.

[01yellowxj]

This thread went totally left field....................

 

Anyhow, I now own a 1990 MJ 4 cyl, 5 speed Ax5, 4x4, 4.10 axles D30/D35. Trans is a brand new unit 6 months ago and motor was installed 7 months ago from a TJ with 94K miles. MJ has 199 on the clock but other than shocks, brakes, and to figure out the emission light it all seems to be in good shape other than floor boards have a small hole. Will need to find a donor XJ or MJ to grab all the AC crap as this one was a non ac MJ. My wrecked 01 XJ out back has the dash and all AC parts so might need to look into adding that ac stuff.

 

here was the sale thread if it stays up long enough to see pics.

http://westky.craigslist.org/cto/4133939828.html

 

And I'm in Nashville TN.

[Minuit]

 

It will be hard to find a receiver hitch for the MJ.  You can use the bumper, not sure what that is rated for?

 

Factory rated @ 2000 lbs. Of course, that's if the bumper is in tip-top shape and structurally sound. You don't state where you are from, but if the MJ rear step bumper is a 20+ year old original and you are from a rust-prone area, I wouldn't tow a bicycle with it. These bumpers rust out fast.

 

I tow a similar sized trailer with motorcycles occasionally with no problems towing or stopping, but have a frame reciever hitch, rear disk brakes, 31s and 4.10s with the D44 and an AW4. The key is the receiver hitch, and as airspeed says, very tough to find now for an MJ. 

:agree:

 

My bumper is completely rusted through on one part of the bottom 'frame'. I have no idea how that happened but I wouldn't trust it in a situation involving potentially mine or others' lives. I might see about modifying a Fey bumper to have the same end caps for a more original look.

 

Good to see another TN MJ guy! If the light is 'MAINT REQD' (not sure if the 90 and older have those) it's just a warning saying you need to replace your oxygen sensor which comes on at about 82k. The best way to fix it is to just remove the bulb next time you have the cluster off. Post pics of your own! We like pics here.

[gogmorgo]

I also have zero faith in my rusty bumper. Mine flexes enough that I'll only step on it near the brackets, and I advise other people not to stand on it at all.

 

As far as the "Maint Reqd" light goes, in my search on how to shut it off on my, I recall that the timer can be replaced on the Renix models, or possibly even removed and reset, but you're not so lucky on the '91+, like mine, which require an incredibly rare and expensive OBD1 (Chrylser DRBII?) scanner to reset. Either way, though, it seemed like the best bet was just to pull the bulb out.

[01yellowxj]

not sure how to post pics right now.

[Eagle]

I would suspect the disc brake equipped rig would have more stopping power, typically with the disc brake swap the rest of the system gets upgraded as well.

 

My rear D44 has 11" vented disc brakes and I'm running a dual diaphram brake booster, it feels like it has a lot more stopping power then it did stock.

 

Your disc brakes may or may not have more stopping power than a D44 with 10" brakes -- but I doubt it. I suspect yours feels better because of the change to the dual diaphragm booster. Stopping power essentially comes down to swept area, and I very much doubt that the disc brakes have more area than 10" x 2-1/2" drum brakes.

 

Back when I was crewing on stock cars (local, short track stuff, not NASCAR), just about everyone was still running drum brakes front and rear. They were usually from full-size Lincolns, and they were basically the same brakes on the MJ D44 axles. They worked well enough that even with big racing slicks those cars could lock up all four wheels at speed.

 

Keep in mind that the MJ braking system is designed such that you never get to use all the braking power in the rear anyway. If you could, you'd be locking up the rear wheels in wet conditions, or when stopping going downhill, or in panic stops. That's what proportioning valves do -- they reduce the available braking to the rear wheels. If you want more rear braking, even with the D35 and the smaller 10" drums, just remove the height sensing valve in the back. That will give you 100 percent braking power to the rear wheels at all times ... and I guarantee that you'll be able to lock up the rears and spin out in a panic stop.

 

I don't mind that -- I grew up and learned to drive years before we ever heard of proportioning valves, so I don't miss having one. For those who have never driven anything that didn't have one (or have never driven anything without ABS) it can be a life-changing experience the first time to stomp on the brakes, and suddenly find yourself going backwards.

 

The first rear proportioning valve I encountered was in the original, 2-seat AMX. Curiously, the AMX had a proportioning valve, the Javelin didn't. (I guess the shorter wheelbase made a difference.) When a proportioning valve failed in the AMXs, we just by-passed it. To offset the tendency for premature rear wheel lockup, we substituted wheel cylinders from 6-cylinder Gremlins, which had a smaller diameter so they transferred less overall braking power at the same pressure.

[Oyaji]

I wonder how much of the touted improvements to braking I hear are merely  greater pedal sensitivity. Real braking performance is  measured as stopping distance, not how little  foot pressure needs to be applied at the pedal. Ultimately, the limit is being able to lock the wheels on a non-ABS brake system, so if you can lock them with a given brake system, it is not possible to improve beyond that. As vehicle weight increases, it becomes harder to lock the wheels, so it is with increasing vehicle weight (ie, increasing payload) that  increased pedal sensitivity would show improvement in stopping distance.

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Depending on how much a pickup is used as a truck (and not as a passenger car), proportioning valves can be very important in maintaining control/avoiding rear wheel lockup without ABS because  the weight distribution changes dramatically with  any load  change in the bed.

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An aside comment: Eagle, you are off base about braking being dependent on swept area (it has an influence, but very small).  Braking is instead dependent on force applied. All other things being equal, area determines the life of the friction material.

 

[zagscrawler]

I agree with Oyaji the disc can run much higher pressures at sustained intervals because of the design of the disc, not even the master or caliper.  the disc in my opinion is the important part.  The hydraulics has been available a long time before the disc part was invented.  Think of the size of the caliper piston.. Its huge and can be because of the disc needing so little clearance to work proper. You can translate much more squeezing power with much lest foot travel if you have the added bionic foot called a booster. The booster just makes your foot weigh 100% more is all.  Small masters + huge pistons + tight tolerences + pedal force multiplication = massive stoping force. There are ways to make specific situaltions seem better than others while using older tech but it usually means that the newer tech wasn't used to its potential. Disc is the best hands down if you have the other parts to make it work like designed is all. On a side note as long as you load the trailer and set the tongue height to create the least amount of tow rig rocking when brakes are applied I bet youll be ok with that load..  Also I just did the 99 wj master and booster swap in my mj with 35's on it and holly crap..   I can lock up all four if I want.  My good friend has a xj with 35's also and I let him drive mine to show him and he $#!& his pants when he stabed the pedal.  I know I am affectively overworking the front and rear brakes but till I see how things wear in the real world I couldn't be happier.

[HOrnbrod]

No, you are being fooled by these stellar braking results only because you have to apply less pedal pressure. Maybe I am too. Didn't someone say that?  :yes: 

[Eagle]

An aside comment: Eagle, you are off base about braking being dependent on swept area (it has an influence, but very small).  Braking is instead dependent on force applied. All other things being equal, area determines the life of the friction material.

 

 

 

You're right, of course. It's a combination of area and pressure, which together result in force. That's why the trick of using smaller wheel cylinders on the AMX was a tolerable work-around when removing the proportioning valve from an AMX -- the brakes themselves remained the same (same swept area), but the smaller cylinders at the same peddle pressure transmitted less overall force to the drums.

[Oyaji]

 

An aside comment: Eagle, you are off base about braking being dependent on swept area (it has an influence, but very small).  Braking is instead dependent on force applied. All other things being equal, area determines the life of the friction material.

 

 

 

You're right, of course. It's a combination of area and pressure, which together result in force. That's why the trick of using smaller wheel cylinders on the AMX was a tolerable work-around when removing the proportioning valve from an AMX -- the brakes themselves remained the same (same swept area), but the smaller cylinders at the same peddle pressure transmitted less overall force to the drums.

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Still off, and I too was  off in  that I was incomplete in what I said:   it isn't only force applied, but also the moment  via which it acts. In the case of brakes,  the moment is the distance from the center of the drum or rotor to the centroid of the area of the friction material (for drums, this is the radius of the drum, but for rotors it is the intersection of  the lines of an "X" drawn from the corners of the  brake pad, or the average radius of the friction portion of the rotor). Area has no influence on force; measured in PSI on  the friction material, adding area reduces pounds per square inch but does nothing at all to the total amount of pounds of force applied. Zagscrawler was  dead on target when he spelled it out thus: "Small masters + huge pistons + tight tolerances + pedal force multiplication = massive stopping force." A small master cylinder adds mechanical advantage, as does a larger slave (the  compliment of which you mentioned in your example of using a smaller slave to reduce force on the AMX to delay rear wheel lockup). Tight tolerances are required for this because although force is multiplied, the distance  through which it acts is reduced (as it is on the short end of a lever). Pedal force multiplication comes from either a longer pedal (not practical) or from power assist (a brake booster).           

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Adding bigger tires adds another variable: the torque moment that road force acts through is increased with increasing tire diameter, which makes brake upgrades important if it is impossible to lock wheels under braking after adding bigger tires. Another related braking problem that comes with bigger tires (and the lifts that so often accompany them) is that the center of gravity of the truck is raised, which changes nosedive and weight distribution  under braking and would require a change in proportioning valve bias in order to avoid early rear-wheel lockup. 

[gogmorgo]

You're right, of course. It's a combination of area and pressure, which together result in force. 

 

I'm assuming you're still referring to braking force and contact area of the braking surfaces. If that's the case, let it be heard that area plays no part in friction, and I've done several labs demonstrating this.

Force due to friction is dependent on only two variables; the force pushing the two surfaces together, and the coefficient of friction (a constant which is determined by the material(s) of the surfaces).

[Oyaji]

 

You're right, of course. It's a combination of area and pressure, which together result in force. 

 

I'm assuming you're still referring to braking force and contact area of the braking surfaces. If that's the case, let it be heard that area plays no part in friction, and I've done several labs demonstrating this.

Force due to friction is dependent on only two variables; the force pushing the two surfaces together, and the coefficient of friction (a constant which is determined by the material(s) of the surfaces).

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Simple experiment to  demonstrate this:

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For the mass shown in red, use a brick. Measure the force needed to move the brick with it laying on its side, then stand it on end,  repeat, and  compare the results. The force needed will be the same no matter what the contact area.

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This holds true for non-deformable surfaces; it goes out the window when the surfaces are deformable. That's why I mentioned there is a very small contribution from area - in the case of brake  friction material it is negligible though.

[Oyaji]

No, you are being fooled by these stellar braking results only because you have to apply less pedal pressure. Maybe I am too. Didn't someone say that?  :yes:

http://www.youtube.com/watch?v=NrVCjnRdB_k

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[HOrnbrod]

Yuk-yuk. Family videos perchance? If so, this should be posted in the Pub forum.