Rear-end noisy between 30-40mph, drive-axle?

Hi All,

Just got rid of my flowmaster muffler and installed a less noisy one. Ten years ago I would have gladly paid extra for the flowmaster, but my early morning noisy take-offs aren't really good for my relation with the neighbours (and my wife). Now everything is pretty quit again outside and inside the cabin, but with the loss of engine noise of course other noises step up. Now there is one in particular that I am unsure what's cuasing it. Driving between 30-40mph there is a whining sound coming from the rear end. When I let go of the throttle it's gone; when I press hard on the throttle it is much reduced. Between 40-50mph it is less and > 50mph it is gone. Like I said, since the whine is gone when I let go of the throttle, I suspect it to have something to do with the drive-axle. Any thoughts? How big a deal is this (whine is not terribly loud), how much work is it to fix it? Can I -- an enthousiastic but limited hobby-mechanic -- do this myself?

Thanks!

I'm not sure it's a problem. My '01 does the same thing, only in 3rd with TC lockup at about 40mph. At 50, it disappears. It will not do it in D with TC lockup. It's done this for 97K miles, so I'm thinking its just a weird vibration/harmonic in the drivetrain.

Willing to bet that you've got a 8.25 rear end as well.

You got it...

I'm guessing it's an 8.25 thing. I've got 2 XJs and a P/U with the 8.25 and find that the ring gears ALL make noise at certain speeds. The odd thing is, it's not the same speed on each vehicle.

Thanks guys. Very reassuring. It never sounded like a real problem but I just wanted to prevent it from ever becoming one. Great! Just to check I have that same rear-end, how do I identify that? Is that stamped on it somewhere?

Tim

Chrysler 8.25:
This axle came in non-ABS equipped Cherokees starting in 1988. It is identified by its flat bottomed casting on the center section. This is a c-clip rear end with 2 major variations:
1988 - 1995
These units were equipped with 27 spline axle shafts and about the same strength as the Dana 35. The only advantage is the housing is stronger.
1995 - 2001
These units are 29 spline equipped and are considerably stronger than a Dana 35 rear end.

mudpuddle said:

Chrysler 8.25:
This axle came in non-ABS equipped Cherokees starting in 1988. It is identified by its flat bottomed casting on the center section. This is a c-clip rear end with 2 major variations:
1988 - 1995
These units were equipped with 27 spline axle shafts and about the same strength as the Dana 35. The only advantage is the housing is stronger.
1995 - 2001
These units are 29 spline equipped and are considerably stronger than a Dana 35 rear end.

Click to expand...

I got an ABS-equipped XJ from 1992. Is that still equipped with 8.25? So in that case I should check for the flat-bottomed casting? Look, I know next to nothing about axles so I am sorry to ask (but that's the only way for me to learn). I came across "Dana 35" a lot on this forum, but what's that then? An earlier/later version axle? What's the difference between these different axles (apart from strength maybe)? Sorry for my retarded questions, just trying to pick up whatever I can.

dutchjeep said:

I got an ABS-equipped XJ from 1992. Is that still equipped with 8.25? So in that case I should check for the flat-bottomed casting? Look, I know next to nothing about axles so I am sorry to ask (but that's the only way for me to learn). I came across "Dana 35" a lot on this forum, but what's that then? An earlier/later version axle? What's the difference between these different axles (apart from strength maybe)? Sorry for my retarded questions, just trying to pick up whatever I can.

Click to expand...

Both the 35 and the 8.25 can be found on the same model year XJ's. As stated previously the 8.25 has larger axle tubes and larger gears and in the case of the later versions, 29 spline axles, all this making it a much stronger axle than the 35. But if you have the ABS system, as I do, then you have a 35. The axle tubes are smaller diameter and prone to bending if abused too much. The axles are 27 spline but can be upgraded to 30 spline with kits offered by Superior Gear or Randy's Ring and Pinion, for a price. Most people will tell you that upgrading a 35 is a waste of money since you'll still have the weaker gears and housing. But, if you have, and want to keep, the ABS system (as I have done) then it may be worth it. Besides, if you're going to keep your XJ stock and not totally thrash, it the 35 will probably do you just fine as it is. Hope this helps.

Yep, helps. Thanks for that one!

I won't be abusing my XJ so I'm perfectly happy with the 35's. But then I'm back to my original question: what about the whine coming from the back? It was suggested that this was an 8.25 issue and therefore not to worry about, but now it turns out I have Dana 35's. So is that also an issue with that axle? Or something more serious?

So all ABS XJ's were equipped with the (weaker) Dana 35? Why does the ABS requires a different rear axle?

Yeah, the ABS'ed XJ's all have the Dana 35 as far as I know. The why of that I can only guess as a money saving thing. (With the Dana already set up for ABS why spend the money to modify the Chrysler to do the same thing?) During any model year the only determining factor for which rear end an XJ got seems to be "what was available at the factory at the time" with the exception of the ABS XJ's.
As for the noise...Mine was always quiet before I changed gears, and still quiet after I installed 4:10's. With Heim joints and poly-urithane bushing everywhere, I get enough road noise to cover up any mild gear noise I might have with the 4:88's I have now. I doubt that it is a seriuos issue but you could always pop the cover just to make sure everything is wearing properly and all the parts are still securely fastened. (Or have a trusted shop do it for you if you're not comfortable/confident with it) In the process you'll be getting nice new gear lube in the rear-end, which is a good thing if it hasn't been replaced for a while, and hopeful catch any problems, if they do exist, before they cause you any real problems. Good luck.

P.S. Since we're not too far away from each other, if you find you need gears and don't want to spend money on new ones, I have the original 3:55 gears from mine you can have if you want them. I took them out at about 86,000 miles and they where still in great shape.

Thanks Rob. I will have the rear-diff checked. Actually I was planning on changing the fluid on the diff's this weekend, so maybe I'll do that first and see what it does. I guess I will have to have a shop look at it since I really don't know what to look for (I have no reference). Thanks for offering your gears Rob! If it turns out I need them I would love to come pick them up!

Tim