driveline slack

[blistovmhz]

98 xj - np231 - sye

I've got a few driveline issues that I'm investigating today and hoping for some input.

Issues:
* Rear right axle seal leaking. Bearing sounds fine but gear oil leaking out of axle into drum brakes.
* Driveline slack in front and rear. Not so bad in the rear, but it's enough to be annoying. Front is terrible. When in 4x4, the jeep lurches violently when I hit the gas or let off.

The axle seal should be easy enough, but I'm not sure where are the most common points to look at for driveline slack. The rear gears seem fine, but not really sure how to verify. I'll have the diff cover off today so I can give the DS a spin and watch the gears, but if that's not it, there's the DS slip yolk, the SYE, the T-case, and transmission. I suspect the issue originates at the t-case because the front and rear both have slack, but that could be incidental. Could be worn or improperly shimmed gears on both front and rear axles, or it could be something internal to the t-case.

Suggestions on how to find the source of this slack?

 

[yossarian19]

Put it in park & put the E-brake on. Engine off.
Climb under the car & grab the driveline - any of them.
Twist it & see if there is any play relative to the input / output shaft. You will be able to move the differential pinions a little bit owing to the (minor, factory designed) slop in the gears but if you can move the drivelines relative to the pinion, that is slop in the U-joints and you shouldn't have much if any at all.

How many miles are on the T-case? It could just be worn but I suspect U-joints instead, as they seem to be the more common wear item.

 

[RCP Phx]

Difference front to back would suggest a worn chain/sprockets.

 

[blistovmhz]

Thanks guys.
The u-joints and CV's are definitely good. The SYE has a little movement if I grab it and shake the joint up and down, but that's on the rear where the problem doesn't seem as noticeable. The front is real bad.

I had the rear axles out yesterday so when I put them back in, I left the diff open to look for gear slack. Everything was tight. Put the t-case is 4L and turned one of the back wheels and the drive shaft moves in perfect syncronicity with the wheel/axle, so I'm also guessing it's the T-Case.

How much work is it to replace the T-case chain/sprockets? I've pulled a T-case before, but never cracked one open.

 

[blistovmhz]

Opened up my front diff (D30) and found this:
https://picasaweb.google.com/lh/photo/5ZUt_RtHcgGk-WBT1LzzANMTjNZETYmyPJy0liipFm0?feat=directlink

Seems to be a tonne of slack in the spider gears. Never taken apart a carrier, but I assume there's some sorta bearing inside each spider gear and the bearings are toast? When I crank the pinion, the ring gear seems to be tight, but the carrier is slow to respond, and if I really crank on it (by hand) it slips further before catching while making some violent sorts of sounds.
Idea's?

 

[Flyfisher]

If the carrier doesn't move with initial movement of the ring gear, the ring gear-to-carrier bolts may be loose. These two are bolted together and should not move relative to each other.

 

[blistovmhz]

If the carrier doesn't move with initial movement of the ring gear, the ring gear-to-carrier bolts may be loose. These two are bolted together and should not move relative to each other.

Nah, Ring gear is moving super tight relative to the pinion. The slack is all in the top and bottom spider gears, relative to the center pin. They both seem to be loose on that center pin, so as the carrier turns with the ring gear, the spiders take a while to engage cause they just sorta hang out until the carrier's been spun far enough. Seems like the center pin or the inside of the spiders are worn, but as I've never had a spider apart, I've no idea how they connect nor what "normal" slack looks like.

 

[bails85]

The front axle shouldn't have much wear compared to the rear axle. You don't drive in 4 wheel as often as 2wd. I would suggest a stretched chain in the transfer case. Which is usually the more common wear item.

 

[akelts]

Subscribed. I too have a lot of slack in my front driveshaft...I replaced the carrier bearings last year before I installed this axle too so doubt its those. The rear has hardly any slack at all.

Could worn pinion bearnings be the culprit?

 

[blistovmhz]

Subscribed. I too have a lot of slack in my front driveshaft...I replaced the carrier bearings last year before I installed this axle too so doubt its those. The rear has hardly any slack at all.

Could worn pinion bearnings be the culprit?

Well like I said, the slack I'm seeing is right in the top and bottom spider gears. the whole pin shifts front to back relative to the carrier, and I don't think that's normal, but... I just don't know. Hoping someone will chime in.

 

[Tim_MN]

Lurching violently compared to what ? Have you checked the motor and transmission mounts for excessive wear and movement ? Do you have axle wrap from weak or damaged leaf springs ? Are you experiencing an engine performance/operation issue that is mistaken for a drive line issue ? Have you measured the current ring and pinion gear set up and backlash and checked against the readings new differentials should have ?

Slack in the drive line is normal, and tends to increase with age. None of my 5 XJ's have "lurched" not even the current one with 178,532 miles on it.

 

[blistovmhz]

Lurching violently compared to what ? Have you checked the motor and transmission mounts for excessive wear and movement ? Do you have axle wrap from weak or damaged leaf springs ? Are you experiencing an engine performance/operation issue that is mistaken for a drive line issue ? Have you measured the current ring and pinion gear set up and backlash and checked against the readings new differentials should have ?

Slack in the drive line is normal, and tends to increase with age. None of my 5 XJ's have "lurched" not even the current one with 178,532 miles on it.

I've actually got a few different places where I know I have slack, I just don't know what is normal for each part. I know what is normal for overall driveline slack from my other 6 Jeeps, but for individual components I've no idea.
The T-case front output definitely has more slack that I think is normal, but either way there's still excessive slack in the front diff as well and it's not from the pinion/ring gear (verified). The slack seems to be just inside the carrier/spiders, but as I've never taken a carrier apart, I don't know how much slack is normal. The video I posted above shows what I'm talking about. That center pin definitely isn't tight to the spider gears. No idea if that much slack is normal. I certainly wouldn't think so as I've never had that much slack in any of my other d30's.

 

[Tim_MN]

You can certainly start installing new parts in the belief that you may reduce the drive line slack slightly. The real questions are: is the current state of the drive line a problem that needs to be dealt with, and how much are planning to spend and what actually benefits do you hope to achieve ? My point is, since you really have no other points of comparison, there may be no actual problem only some honest wear.

My 1986 CJ-7 has 148,952 miles and the original gears, transmission, and transfer case. The only new stuff is the u-joints. Some drive line slack, no problems.

 

[blistovmhz]

This slack is the worst I've seen in any of my Jeeps, and most of my Jeeps were above 500,000 km
The Jeep in question is only 220k, and when it's in 4x4 and you hit the throttle, the front end makes a loud bang and you can feel the front wheels don't get torque till long after torques put to the back. Then when you let off the gas you get the bang again as the spiders line up against the other side of the carrier. I don't 'know if you can see this in the video I posted a few posts up, but in real world driving, bystanders actually look over to see wtf just made all that noise .

I'm not terribly anal about my Jeeps being 100%. I'd let this slack slide if I didn't think it was going to result in a broken spider gear somewhere out in the middle of the sticks.

 

[blistovmhz]

I gave up for a while on the driveline slack and did some other stuff.

Pulled the t-case to check for slack between the input and rear output. No slack at all. Lots in the front output but that looks to be part of the design.
Rear DS is tight, rear gear feels good as well. Pretty much anything from the wheels forward to the t-case should be good.
I jumped under the jeep today. Left it in first gear and pushed the jeep forward and back to listen for clunk and it really sounded like it was coming from the transmission (ax15).
Is there anything from the input shaft of the ax15 to the output shaft, that could be the source of this slack?

 

[blistovmhz]

Resurrecting old thread !

So the slack just got a little worse (noticeably) but I couldn't think of anything I might've done to change it.

Triple checked the entire driveline again from the trans output, through the t-case, to the SYE, to the new driveshaft, and discovered the source (I think).

When I disconnected the DS again, I tried to wiggle the diff yolk. It's dead solid laterally, but torsionally it has some give. I think the nature of this give is probably telling, but I don't know what it says Perhaps someone else does.

With brakes locked and DS disconnected, I try to spin the pinion. It'll wiggle a little bit with no resistance. This, afaik, is normal. But if I really twist hard, it'll move another 1-2 degrees, and it'll spring back to the original position when I let go. Feels like I'm twisting against a heavy spring or lifting something fairly heavy.

When I try to play out the mechanics in my head, I imagine the pinion engaging the ring gear normally, but when I apply more force, it feels like I'm lifting the carrier about 1mm, and when I let go it drops back down. I can definitely hear the clunk when I let go.
When I release the brakes and lift one wheel up, when I spin the pinion, the wheel will spin a little bit and stop, and again when I reef on it, the pinion spins further but the wheel doesn't move. This diff does have posi, and I originally thought it was just slipping, but the fact that the pinion returns to centre when I let go suggest something else right?

So, my top suspect at this point is a bad carrier bearing, probably on the driver side (though possibly both, but I figure the ring gear is on the driver side so that'd be the first side to lift if the bearing was bad.

I do get some whine when gearing down hard, which also makes me suspect rear pinion bearing, but I'd think i'd be able to move the pinion side to side if that were the case.

Anyone think I'm on the right track with the carrier bearing?
If so, is it worth repairing, when I fully intend to drop in a D44 or similar as soon as I can find one?

 

[blistovmhz]

After thinking about this overnight, I remembered that the "lifting" feeling happens when spinning both directions. If it was a carrier bearing or loose carrier bolts, I'd expect it to only lift when spinning counter clockwise as clockwise should just push the carrier down further.

Is there anything anyone can think of that would explain this? Don't wanna crack that cover again without at least having a solid theory.