Reverting back to Open diff

[Dillithium]

Hello All,

 

This will be a little long, I apologise in advance for this.

 

Since I bought my Comanche, I've left the front driveshaft out. I just never got around to putting it back, but I did replace the ujoint in it. The double cardan seems fine so I've left that untouched. This last saturday I decided to put it in, seeing as winter is coming. This has had some interesting consequences.

 

Whenever I drive my Jeep on the highway, I really do not dare go over 75 miles an hour. The reason being is that a very strange noise starts coming from the back of the cab area. It's a slow helicopter noise, but it does not come with any kind of vibrations. After installing my front DS, I now hear it around 55 miles an hour, but coming from the front.

 

Before I go on, a little background info is necessary. In both diffs, I have a kind of locker installed. This was done by the previous owners. I am unsure of the make and model, it resembles an aussie/detroit locker. It is a self contained locker, no air or cables, just worm gears. It is paired with 4.56 gears.

 

As a result of this, the yoke of my front axle spins in synch with my driving speed. In other words, my front DS is constantly spinning, even in 2WD. It is not powered by the transfercase, but by the front diff. I've been told this is not normal, that the front DS is only supposed to spin if driven by the transfercase.

 

After talking this over with my jeep mechanic, we've kind of agreed that I need to at least swap out my front diff for the traditional style of open diff. Basically, to revert back to a carrier and spider gears. He claims this should resolve the noise and front axle vibrations I've been having. It would stop the front DS from spinning all the time. To me, this makes sense. My front DS isn't meant to spin at 55+ miles an hour. I'd like to stop this.

 

But now I'm coming to my second part of this, the physical swap. My mechanic says I can take out the locker, take off the ring gear and install that on a traditional carrier. All I would need are spider gears, either new or used. Is this true? Will the ring gear swap over? Also, what is the difference between loaded and empty when it comes to buying a carrier? 

 

To summarize, I'm looking to revert back to a traditional style differential to eliminate the noise starting at 55 MPH, without having to shim or set backlash in my diff. Is this as easy as my mechanic describes? Can I really just swap everything over without ruining anything?

 

Any insight is appreciated.

 

Crap, wrong forum. Would a moderator be so kind as to move this to MJ tech? Thank you!

[Incommando]

Your front driveshaft will spin when the vehicle is in motion whether the transfer case is engaged or not. Your front differential is permanently attached to the front tires. It would be just like putting a rear wheel drive car in neutral and letting it roll. The driveshaft will turn. To prevent the front drive shaft from turning whenever the vehicle was in motion many older 4wd's used lock out hubs to physically disconnect the front axle, and therefore the diff, from the tires. Our trucks do not have these.

 

The diff you described sounds like a Detroit Truetrac. It is a type of Gleason/Torsen limited slip differential and not really a locker. You can Google pics to confirm this. As your driveshaft turning is correct this diff is not a problem and replacing it is not necessary. These diffs are pretty darn good. You can make them act nearly like a locker by dragging your brakes slightly. Your front drive shaft is just fine at any speed that your rear shaft is and certainly well past 55 or 75 miles an hour. If your driveshafts are in good order they are not your issue.

 

Generally you cannot change out a diff with another without setting it up again including shims, etc... But as nothing you describe indicates a need to change that diff.

[gogmorgo]

The MJ's 4x4 is designed to be used at any legal speed, just not on a high-traction surface. There shouldn't be any issues having it turned by the front wheels.

Most Jeeps came with a central axle disconnect (CAD) in the front axle, which disconnected the passenger side wheel from the differential in 2wd, meaning the driveshaft wouldn't spin. This system proved problematic, and if the CAD didn't engage, then you didn't have 4x4. A common fix is to permanently engage the CAD, which results in the front driveshaft being turned by the wheels. I have yet to see anyone who had issues because their front driveshaft spins.

It's a good idea to figure out exactly what kind of locker or limited slip differential you've got in there. Some of them require friction modifiers to be added to the gear oil.

I don't know how much snow you get in the Netherlands, but if that's why you're wanting your 4x4 for the winter, this brings up another good reason for figuring out what you have in that differential. A front locker or even a severe limited slip differential can lead to serious understeer tendencies. There are those who say it's manageable, but generally it's not recommended to run a front locker in a daily driver if you'll be seeing snow. I don't have enough experience in this area to comment much beyond that.

 

Figure out exactly what it is before you get rid of it. "Worm gears" makes it sound like possibly an Eaton/Detroit Truetrac, or possibly a more local (to you) Quaife ATB. If that's the case, I'd say leave it in.

[Incommando]

*If* it is Torsion style diff it does not cause the winter difficulties of a traditional locker or LSD but they would make the driveshaft spin even if the CAD is disengaged where an open diff won't, true. They are a good choice for on-road winter driving in the front or rear. I admit that I forgot about the CAD as I did not look at the year of his truck and my '91 does not have it. The CAD was only used by jeep for about a decade and personally I am not a fan. Luckily of the 14 jeeps I have had only my '88 MJ had it and I permanently locked it.

 

But if the front driveshaft is in order it should be fine at speed. That still leaves the noise. I would check all of the u-joints first

[Dillithium]

Thank you very much for your detailed responses. My desire to replace it was to prevent the DS from spinning. I've replaced every possible u-joint on my Jeep except for the double cardan joint, I think I may need to start there and try putting it back in. 

 

Concerning CAD, for me it still seems to be functional. 

 

It originally came from california, I assume it was set up over there and the PO picked a popular locker available in the US.

 

What puzzles me, is that I get the exact same noise coming from the rear of the vehicle but at a different/higher speed. Without the front DS in. If it is a detroit/eaton, are they normally well behaved at speed? Do they cause more vibration or something? In both diffs I have 75/140W diff oil in there, for future reference.

[Jeep Driver]

I don't think your lockers have anything to do with the noise. Bad Ring and Pinion or bad pinion bearing.

 

Even with an open carrier your R&P will spin....yoke will spin......DS will spin.......that fact that  your mechanic does not understand that, I would dismiss him and find another one.

 

 

More than likely who ever installed the lockers failed to set up the R&P properly and now you seeing the end result.

[Dillithium]

I know my front pinion bearing has a little play it in, I can make it click if I push on it hard enough. My ball joints are coming up, when I'm tackling those I will have to mark the R&P with some gear paint and see what kind of pattern it's making.  I really am getting quite tired of finding more and more things to fix or deal with. I keep pushing all the fun projects to the back because I find yet another mechanical issue that needs immediate attention. Maybe this is just what it's like trying to DD a 1986 car?

[gogmorgo]

Yup, that's the way it works. The running joke was that eventually I'd have a brand new MJ, having replaced my entire truck, one part at a time... But the Lada I'm daily driving is much worse. LMAO

*IF* it is a Torsen style diff, definitely keep it.

[Dillithium]

Haha, I'll just keep replacing it all until I've nothing left to replace. Good luck with your Lada!(Also, how the hell did you find a Lada in North America?)

[Eagle]

Thank you very much for your detailed responses. My desire to replace it was to prevent the DS from spinning. I've replaced every possible u-joint on my Jeep except for the double cardan joint, I think I may need to start there and try putting it back in. 

 

Concerning CAD, for me it still seems to be functional.

If the front drive shaft is spinning because of the locker, the CAD isn't doing anything for you. It WILL fail; it isn't a question of "if," it's a question of "when." Mine failed to engage on a below freezing day when I was trying to get to work through a heavy snow storm. Fortunately, I had a limited slip in the rear so by taking a different route I was able to get where I was going.

 

The vacuum harness had rotted, so the CAD shift motor wouldn't shift. Like an idiot, I replaced the vacuum harness. The next time it fails (or maybe before), I'll just lock it in the engaged position.

 

What puzzles me, is that I get the exact same noise coming from the rear of the vehicle but at a different/higher speed. Without the front DS in. If it is a detroit/eaton, are they normally well behaved at speed? Do they cause more vibration or something? In both diffs I have 75/140W diff oil in there, for future reference.

My Cherokees all have the factory Trac-Lok, which uses clutches. I have a TrueTrack in the '88 Comanche. It's totally transparent -- I don't even know it's there (except for the fact that I almost never need to use 4WD in snow). I think you need to check out your drive shafts.

[Incommando]

*IF* it is a Torsen style diff, definitely keep it.

I don't know for sure what diff it is but from the description that is my best guess.

[gogmorgo]

I don't know for sure what diff it is but from the description that is my best guess.

 

Same.

 

(Also, how the hell did you find a Lada in North America?)

They were sold domestically (in small numbers, 12000/year) in Canada until the late '90s. There aren't that many still around, but they have a small following of strange people like myself. I much prefer driving the MJ, though. But the Niva definitely attracts more attention than the Comanche as you don't see as many around, and it's not just another little old truck to everyone else. Just the other day, I spent five minutes trying to make a set of not-quite-as-universal-as-they-claimed wiper blades fit, and had three people come up and talk to me about it. Women in particular seem to like it. :teehee:  :shake:

[dasbulliwagen]

Not to get off track, but a pic of said Lada would be great for those of us who don't know what they are.

[dasbulliwagen]

I just googled it, it looks like a Yugo on steroids.

[gogmorgo]

 

Yugo on steroids, that's an interesting way of putting it. Couple pics I took on Sunday after the first decent snowfall we had this year.

[Parker]

 

Whenever I drive my Jeep on the highway, I really do not dare go over 75 miles an hour. The reason being is that a very strange noise starts coming from the back of the cab area. It's a slow helicopter noise, but it does not come with any kind of vibrations. After installing my front DS, I now hear it around 55 miles an hour, but coming from the front.

Going off your original post I would check the transfer case fluid level then drain it into a clean pan and check the fluid for signs of wear. the reason I say that is the speed change of the noise from when you had the DS out to when you put it in.

 

This is why. I have seen the front output of transfer cases spin wile in 2wd with no DS from resistance of the bearings but slower than the rear output and the vehicle speed. this would explain why with the DS in it happens at a slower vehicle speed because the front output is spinning the same as the rear while being driven by the front axle and not the resistance of the bearings which allows it to spin slower. The DS can also resonate which would explain the sound moving forward when you put it in.

 

If I'm wrong and its not coming from the transfer case all it cost you is the price of new fluid plus you will know whats in it and that its full.

[Rockfrog]

You also have to consider the gearing itself...

With 4.56 gearing, anything less than a 35" Tire will be spinning a lot faster than normally seen. With a 33" Tire your driveshaft will be spinning close to maximum balance speeds at 60mph... With a smaller Tire they will be spinning way faster than balance speeds. Meaning you may have a rotational runout in the shafts that isn't apparent at normal speeds but is now.

I had this problem with my XJ when I regeared to 4.56 and 33's... Had to get things rebalanced again, and still was unable to fully eliminate my front shaft vibes. Just had to live with some vibe. When I swapped to 35's it slowed the shaft speeds down and ended my vibes. A happy side effect.

May or may not apply.