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Old 11-30-2019, 06:52 PM
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Slop in front pinion after re-gearing

Regeared a 2007 Rubicon about 3,000 miles ago with 5.13. I was just checking things over and notice I'm getting a lot of slop in the front pinion gear now and I see a small amount of moister that appears to have seeped from the seal. No parts were reused on the re-gearing and pinion preload was set at the recommended 20-40 in lbs.

I tried throwing a torque wrench on the pinion nut but I can't get enough range of motion on my back to get more than 200 ft lbs which does nothing. This project was originally done at my dad's shop 1400 miles away so tough for me to do in my garage now.

This is my first re-gearing so wanted thoughts from the experts here on what I should try to do next and how serious this might be if I do nothing. I can grab the driveshaft at the flange and move it enough to get a knocking sound.

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Old 12-04-2019, 12:49 PM   #2
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How much can you move the shaft back and forth? Have you drained the fluid and inspected for metal shavings/chunks?
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Old 12-04-2019, 03:47 PM   #3
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It might have too much back lash, which is in part from the distance between the pinion and the ring gear as I understand it. And cranking down on the pinion nut, no matter how hard you crank on it, won't change that.
You can pull the cover and check the backlash with a dial gauge.
Of course, I could be wrong.
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Old 12-04-2019, 03:57 PM   #4
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Originally Posted by GuzziMoto View Post
It might have too much back lash, which is in part from the distance between the pinion and the ring gear as I understand it. And cranking down on the pinion nut, no matter how hard you crank on it, won't change that.
You can pull the cover and check the backlash with a dial gauge.
Of course, I could be wrong.
Would help if OP defined "a lot". Difficult/Impossible to say without a better idea, or video, or something...
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Old 12-04-2019, 04:06 PM   #5
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Guzzi is mostly correct. You need to check 3 things though to guarantee a proper set up. 1) Backlash 2) Pinion pre-load. 3) Coast & Drive patterns These 3 things tell you if a diff is set up correctly.

1) Backlash is the distance between the pinion and ring gear
2) Pinion pre-load is how much pre-load is on the pinion bearings. This is measured in inch pounds and is just the force it takes to move gears with axles / tires disconnected. You have a crush sleeve between the 2 pinion bearings. The 200-300 foot pounds (gears don't turn) you would apply is simply "crushing" the crush sleeve. Pre-load (inch pounds just as the gears start to turn) is the critical torque you have to get applied to the pinion nut.
3) Coast and drive pattern gives you depth of the pinion into the ring gear (different that #1) If this is off, you have to adjust either / or the pinion and carrier shims and repeat until all 3 above are correct. Typically in a fresh rebuild you don't put the crush sleeve in until it's set up properly so you don't have to go through a bunch of crush sleeves. In that case, you would only check pinion pre-load. It would only take 60-80 ft-lbs on the pinion nut to achieve 20-40 in lbs pre-load.
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Old 12-04-2019, 04:46 PM
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It's not a backlash issue. Backlash was set within the .006"-.010" spec confirmed with a dial gauge. Pattern looked good after several tries with various shims on the pinion gear. We used the old crush sleeve and honed out the lower pinion gear on a metal lathe to use for mock up to get our pattern. Once we were satisfied with the pattern we used the new crush sleeve, bearing and locknut for final assembly. Pinion preload was set at 35 in lbs. You guys know it takes a lot to get that crush sleeve to start crushing but once it does you can run past the spec pretty easily.

The movement I am talking about is between 1/16" to 1/8" in a vertical plane at the flange. It's enough that the pinion flange is making a knocking sound against the inside of the differential. I'm going to drain the fluid this weekend to inspect for metal fragments. If I see anything significant I know it's a rebuild.

The mystery to me is how it loosened up so much in only 150 miles of offroad use and about 3000 miles total on the new gears. It seems implausible to me that the locknut backed off, especially with red loctite added. That means that one or both of the brand new bearings have worn out in a very short amount of time or one of the races cracked.

I appreciate the comments here. I was hoping someone had forged this path before and had good advice. I'm not eager to tear this down again since the first time I did it was in my dad's shop 1400 miles away with all the tools needed to do the job. FYI, the rear seems to be perfect so far.
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Old 12-07-2019, 05:43 PM
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I checked the fluid today and there was no metal in it. Everything looked good. I also pulled the diff cover and ring gear still looked new. I couldn't see the pinion gear but since there is not metal in the fluid I'm sure it looks good also. The going theory now is that perhaps a pinion bearing race didn't get tapped in all the way and later set. I'll get a new crush sleeve and pinion seal and reset preload. I'll double check the pattern also in case I need to add a shim. A PITA but at least I should be able to fix it with minimal expense.
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Old 12-08-2019, 12:51 AM   #8
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Using a honed out USED pinion bearing for a mock can also lead to problems as it will have more slack then a new bearing. I honed out a brand new set of bearings just to do gear swaps.
Now, there is also one other possibility... it is possible to hit the front end hard enough (hit a ledge a bit hard to bump up or drop in a ditch too hard) to actually push the driveshaft/ pinion in and compress the crush collar enough to create slop.


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Old 12-08-2019, 08:13 AM   #9
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It's also possible that one of the races was not fully seated in the axle housing which now has created a loss of tension on the crush sleeve. Bearing failure is also a possibility even though it was new. I have seen this before. Manufacturing tolerances can vary on each piece of the component by just a little and suddenly you have one bad assembly.
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Old 12-08-2019, 08:31 AM   #10
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When you took the cover off did you check the backlash again? The carrier might of shifted away from the pinion a bit. This could be from the bearing not getting seated on the carrier completely or not quite loaded against the case tight when you put the carrier back in. Did you lap the back of the ring gear prior to putting it on the center section? Did you recheck the bolts in the ring gear when you had the cover off?
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Old 12-08-2019, 08:39 AM   #11
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Assuming the crush sleeve install was done properly, which it sounds like, I'd be looking at the pinion bearing and race. A PITA and basically a complete tear down and re-install but I wouldn't drive it the way it is with that much play.
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Old 12-08-2019, 12:03 PM
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It's also possible that one of the races was not fully seated in the axle housing which now has created a loss of tension on the crush sleeve. Bearing failure is also a possibility even though it was new. I have seen this before. Manufacturing tolerances can vary on each piece of the component by just a little and suddenly you have one bad assembly.
I don't think this is the issue. My dad and I installed this is a team with me lifting the carrier, races and shims in together and he would tap the races and shims in until they were fully seated. You can visually see and hear the race and shims bottom out as you tap them.

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When you took the cover off did you check the backlash again? The carrier might of shifted away from the pinion a bit. This could be from the bearing not getting seated on the carrier completely or not quite loaded against the case tight when you put the carrier back in. Did you lap the back of the ring gear prior to putting it on the center section? Did you recheck the bolts in the ring gear when you had the cover off?
No, because this is a complete tear down and reinstall operation no matter how I look at it. I've got to get preload reestablished on that pinion gear so everything has to come out anyway and will be looked over more closely at that point. I just wanted to make sure I didn't need to order anything more than a new pinion seal and crush sleeve and I don't think I do. Backlash and pattern will be rechecked when I do the full tear down.

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Assuming the crush sleeve install was done properly, which it sounds like, I'd be looking at the pinion bearing and race. A PITA and basically a complete tear down and re-install but I wouldn't drive it the way it is with that much play.
I agree. Fortunately this is just a toy and not a daily driver. I just got in a new tie rod, track bar and drag link from Steering Smarts, transmission cooler lines and brake lines. All those will be going in over the holidays when I have more time to work on the whole project. I might replace the driver side manifold as well while I'm at it since I can hear it leaking. I'm trying to talk my dad into flying back out and doing it with me since this is a father/son project we started together and I'd like to keep it that way.
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Old 12-08-2019, 06:19 PM   #13
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[QUOTE=Chainringtattoo;34613507]I don't think this is the issue. My dad and I installed this is a team with me lifting the carrier, races and shims in together and he would tap the races and shims in until they were fully seated. You can visually see and hear the race and shims bottom out as you tap them.


I was referring to the Pinion bearing races. Carrier races would have no bearing on the pinion being loose.
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Old 12-08-2019, 09:40 PM
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[quote=nevrnf;34613883]
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I don't think this is the issue. My dad and I installed this is a team with me lifting the carrier, races and shims in together and he would tap the races and shims in until they were fully seated. You can visually see and hear the race and shims bottom out as you tap them.


I was referring to the Pinion bearing races. Carrier races would have no bearing on the pinion being loose.
Well I said in post #7 that I thought the problem was one of the pinion races didn't get tapped in fully so I assumed you were talking about the carrier races. Perhaps you didn't see my post. Sorry for the misunderstanding but yes, we think that is what actually happened.
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Old 01-05-2020, 11:42 PM
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I figure I’d follow up after the repair. I was able to complete the repair for the cost of a new crush sleeve, a new pinion nut, some diff fluid, a new pinion seal (the old one was leaking very slightly) and a few hours of my time.

After tearing everything down the ring, pinion and bearings still looked new with no damage. The pinion shim depth didn’t need changing as the pattern still looked perfect and the backlash was still at 75/1000”. The only thing I can think of is that we missed fully seating the driveshaft side pinion bearing race by a few thousands of an inch. I caught it early so no damage done.
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Old 01-06-2020, 08:11 AM   #16
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I figure I’d follow up after the repair. I was able to complete the repair for the cost of a new crush sleeve, a new pinion nut, some diff fluid, a new pinion seal (the old one was leaking very slightly) and a few hours of my time.

After tearing everything down the ring, pinion and bearings still looked new with no damage. The pinion shim depth didn’t need changing as the pattern still looked perfect and the backlash was still at 75/1000”. The only thing I can think of is that we missed fully seating the driveshaft side pinion bearing race by a few thousands of an inch. I caught it early so no damage done.
Glad to hear and thanks for the follow up!
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