Vibration after swapping in replacement rear end

[Gibbs]

About a week ago I bought a complete rear end from a TDR member in order to gain an OEM limited slip, as my truck came with an open differential. The axle supposedly only has about 140K miles on it and all the gears look good with no discernible play or roughness in the bearings, etc. I replaced the wheel seals and parking brake shoes, filled with fresh gear dope, and swapped in the axle.

With nothing else being changed, I now have a noticable vibration. I
It is a high speed rhythmic vibration that I can feel through my seat. Almost like the sound of agressive mud grips, a rhythmic wahh wahh wahh sound. At about 65 I can actually hear it. When I swapped my rotors onto this axle, I checked the runout on both sides and indexed the rotor for the least runout possible, which ended up being .002" on driver side and .004" on passenger side. I have moved the driveshaft to all four positions on the pinion flange and it doesn't affect the severity of the vibration. The rear driveshaft is a complete brand new unit from Mopar that's only been on the truck about a year/6000 miles as I had a BAD 70 MPH vibration in the past that got cured by replacing the (bent/out of round) driveshaft. The axle is bolted in securely with u-bolts torqued to 110 ft/lb. Everything appears to be good so I'm not sure what could be causing the vibration. This concerns me because I didn't knowingly change anything else and now I have this pretty bad vibe.

Any ideas?
Could it be caused by something internal in the axle?
I'm concerned that its noisy/rough pinion bearings, even though I can't feel it when I turn the pinion by hand.
Stuff like this aggravates me to no end.

Thanks

 

[NIsaacs]

Do you have a lift kit on the truck? It sounds like the pinion angle is off for some reason. One piece or two piece drive shaft, 4x4 or 4x2, year and model, auto or manual?

Nick

 

[rscurtis]

Why didn't you just swap the carrier with your open unit? All you would have to do is reset the backlash and bearing preload. Of course, you still have that option, but I would look elsewhere for your vibration. Another thing you could do is pull the axles and run the truck on the ground- that would eliminate any of the rotating components beyond the differential.

 

[Gibbs]

Not sure why my signature didn't show up. Its a 04.5 QCSB automatic 4x4 with no lift, stock driveline. Not sure how the pinion angle would change unless the spring perches on the replacement axle were welded on different from the factory. Nothing else was changed.

I didn't change the carrier because I didn't wanna have to set the gears back up. But I will keep that in mind as a possible option. I will try messing with the pinion angle, but don't have a good way to do it as far as having angled shims or the like. Thanks for the replies, keep em coming.

 

[Prairie Dog]

I would swap the rotors (hopefully you still have the old ones) as they can be seriously out of balance and hard to diagnose.

Scott

 

[rscurtis]

Why didn't you just swap the carrier with your open unit? All you would have to do is reset the backlash and bearing preload. Of course, you still have that option, but I would look elsewhere for your vibration. Another thing you could do is pull the axles and run the truck on the ground- that would eliminate any of the rotating components beyond the differential.

The AAM axle is very easy to do when it comes to carrier preload and backlash- it's not like a Dana in that respect. The difficulty comes with getting the proper pinion depth, but you're not messing with that dimension. Run the truck stationary with the axles pulled- do the easy stuff first.

 

[Gibbs]

I kept the rotors from my old axle as they had been turned recently and were in good shape. One of the bearing hubs had a lot of runout, over .015"! but between a .003 shim ( designed to go behind the rotor) and by indexing the rotor a certain way, I got the runout on the rotor face down to .004". I had this problem with one of the bearing hubs on my old axle and I had to shim it as well. And there was no vibration.

rscurtis, when I get some time I'll try running the truck with the axleshafts pulled. That's a good idea I hadn't thought of.

I just realized the AAM 11.5 is similar to the old GM 14 bolt as far as setting the backlash--and I've messed with axles those a couple times. As a last resort, I'll put my old axle back in and put my original ring gear onto the anti-spin carrier and set the backlash.

 

[sag2]

You now have the dreaded 68-72 mph drone. Pull the drive line at the rear, turn it 180 degrees and reinstall.

 

[RCMerrill]

How can you tell if you have limited slip rear end !

 

[hcole]

Did you put that special lube additive in the rear end for the limited slip? I've been told that the rear end will do strange things if you don't add the mopar additive.

 

[sag2]

American Axles do not use additive.

 

[Prairie Dog]

You now have the dreaded 68-72 mph drone. Pull the drive line at the rear, turn it 180 degrees and reinstall.

I have a similar issue with my Mopar 1 piece (or it could be something totally different) - can they have the same problem and need to be rotated 180?


Thanks Sag,
Scott

 

[Gibbs]

In my original post, you can see where I tried the driveshaft in all four positions on the pinion flange with no difference in vibration. I ran the truck on jackstands with axleshafts pulled and not only was there the vibration, but a lot of noise coming from the differential. I've got it all pulled apart and the carrier bearings show some wear, but nothing too bad. But there is practically no preload on the pinion bearings. About 2 in/lb on my torque wrench...So far haven't been able to tighten down the pinion nut to increase preload, but it won't matter anyway, because I'm swapping the LS carrier into my original rear end, which had no noise and no horrible vibration before all this went down. Maybe when the "holidays" finally get over with, I can have enough time to get everything done. I'll try to update when its all said and done.

 

[Hoefler]

Do not increase the preload!!!! Preload is for new bearings!! After the unit has some miles on it, the preload will disappear and the bearings wear in. This is totally normal! And expected.

 

[rscurtis]

Two inch pounds is way too low, even for used bearings. The FSM calls for a pinion preload of 10-20 inch pounds for used bearings, 15-25 for new. Total preload for the pinion and carrier bearings is 25-35 for the original bearings, and 30-50 for new. IIRC, that preload on the carrier is achieved by tightening the adjusters four notches past zero clearance.

Gibbs,while you have it this far apart, run the DS with the pinion only, and that will eliminate anything but the DS as the source of vibration. I'm assuming that your QCSB still has a one-piece DS, so you can't remove the rear section and run the front half in the hanger bearing to eliminate it as a source of vibration. Regarding the noise you hear, running it on the tires as opposed to jack stands may make a difference there, but it's a moot point if you're going to use your original rear end. My signature truck had a slight deceleration whine when new, and I virtually eliminated it by tightening the pinion nut about a 1/16 of a turn. The companion flange holder and a 4' breaker bar will come in handy for that job.

 

[Gibbs]

Well, this evening I removed the open carrier assy from my original rear end. I decided to check the pinion bearing preload and it was the same as the other rear end, approx. 2 in/lb. So obviously the bearings wear in over time, or maybe the nut may back off slightly? Who knows. But I do know that it's out of spec. And that my old wore out 3/4" IR impact wouldn't tighten the pinion nut (held the flange with a 3' pipe wrench but plan on making some kind of pinion flange holder). And I broke my 3/4" ratchet in half with a 3' cheater pipe and still didn't get it to tighten! Dang it's stubborn. Not sure what my next attempt will be, but I definitely think it needs to be tightened some. I have a small 1/4" drive beam type torque wrench that measures up to 60 in/lb so I have a pretty accurate way to measure preload. As far as carrier bearing preload, you're right-- 4 adjuster holes for used bearings and 6 adjuster holes for new bearings.

I figure between the tires and the diff being under load, some noise may be dampened or unnoticeable. But this was really loud and I could hear it inside the cab with the doors shut. I have new carrier bearings and races I'm going to install on the LS carrier before I put it my original axle. If nothing else, at least I'll have peace of mind when it's all back together.

Hopefully I can get it back together Saturday because the starter died again on the Beemer (affectionate name of my 1984 Nissan Sentra diesel commuter car) and now I'm driving my '72 Chevy trail truck on 42" Swampers back and forth to work! If it goes down, I'll have to start borrowing vehicles from somebody else...

Thanks for ya'lls help so far, I appreciate it.

 

[Hoefler]

Any bearing that is set with a preload when new, will have very little, if any, measurable preload after run in. If it has not been disassembled, do not tighten it any. You will cause it to go through a new break in/wear in, and after that you will be in the same spot as before, except you have caused premature wear and heading for failure. I have been building gearboxes for 30+ years, trust me, you do not want to tighten it at all!

 

[S.Morris]

+1 on what Hoefler said.

 

[Gibbs]

Thanks for the advice, Hoefler. I don't think it has been disassembled, but I bought the truck with 143K on it. And it's not that I doubt what you say, it's just that the FSM gives a certain range of preload for used bearings. Reckon why? Do you think it only applies for when you change gearsets and and put in a new pinion gear with the same old bearings? It does say when the pinion seal is changed, you measure rotating torque before disassembly, tighten pinion nut until there's no endplay, then keep tightening in small increments until rotating torque is 3-5 in/lb above what it was originally. Maybe only tightening a slight amount doesn't hurt anything?

Since both of the rear axles I have have about the same bearing preload, your logic seems sound. But don't you hate it when there's conflicting information?

 

[Hoefler]

Large trucks have several 100,000 miles on them. I have never increased the preload when changing the pinion seal. They use a spacer and shims with a torque value for the nut, which will not increase the bearing preload when changing the seal or yolk. In our trucks, instead of a spacer and/or shims, there is a crush sleeve. When tightening the nut to the specified value, whether torque or preload, you will crush the sleeve to achieve the desired value. When changing the seal or yolk, you will be disturbing its original set. That is why you have to be careful not to over tighten the nut and crush the sleeve further. When new, there is a certain amount of wear in expected, hence over tightening when doing a yolk swap or seal replacement is critical. If over tightened, you will in a sense, start a new break in procedure, causing excessive wear on the bearings and premature failure. The yolk, pinion, and nut should be indexed before disassembly, then assembled back in the correct orientation. As long as the bearing is smooth, tight with no up and down or in and out movement, let it be and run it.