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-   -   Driveshaft bouncing at the rear diff. (

igids1 10-05-2013 09:23 PM

Driveshaft bouncing at the rear diff.
Hi all, this is my first post here. I have been reading for a while and will try not to ask what has already been asked numerous times.

My issue is mainly with a vibration which occurs predominantly on acceleration, at speeds of 30-40mph or so. If I let off the gas it seems to go away. At higher and lower speeds it seems to go away as well. It vibrates the steering wheel, as well as what feels like the body/seats etc.

I already removed the front driveshaft, there was no change.

I jacked up and inspected the front end as best I could, wheel bearings, hubs seemed ok.

I jacked up the rear of the vehicle, and placed jack stands under the rear axle and had someone else put the vehicle in gear and get the speedo up to 30mph or so. I could hear some grinding noises coming from the driveshaft/rear diff area. Looking at the driveshaft where it joins the differential, it rotated normally at first, but as the speed increased, it took on more of a football shaped rotation, and I could see it bouncing around.

I turned the vehicle off, and grabbed the driveshaft at the diff, and pushed side to side and up and down. Up and down there was some movement, but none side to side.

Oddly, when I lowered the vehicle and tried again, there wasn't really any movement.

Am I looking at a bad pinion bearing? Bad U-joint? Driveshaft?


If it doesnt list elsewhere, this is a 1997 Grand Cherokee, with a 242 Transfer case, 4.0 engine.

newfieZJ 10-05-2013 10:42 PM

Should be zero play in the pinion . I bet the bearings are bad .

igids1 10-06-2013 08:34 AM

If I was to pull the Pinion, is it essential to take out and install new races also?

Could I just get a pinion and carrier from the junkyard, with bearings already installed, and just put those in?

I've watched enough youtube videos where I feel comfortable pulling everything out.

gearheadnick 10-06-2013 09:46 AM

I wouldn't trust junkyard pinion bearings, and the bearing is worn to the race, so you'd have to swap that over also. You could swap the whole axle out, or install a new bearing and race. If you opt to replace the bearing, since you'll have the axles out anyway, it would be the right time to change out the axle bearings and seals. And the pinion seal as well.

stageninja 10-06-2013 03:46 PM

You can't easily just swap carrier & pinion from 1 axle to another. Proper shimming must be done as the carriers & cases will be different. It would be the same as setting up new gears with lots of measuring & checking pinion depths, backlash & of course pre-load on the bearings.

If you are truly experiencing end play in the pinion there may be damage to the gears also. A rear end from the salvage yard that you or a shop changes bearings in might be the way to go.

Rikoshay 10-06-2013 09:33 PM

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Perhaps it's time to swap out the entire axle. If you don't have the tools or experience to set up a diff then that's the way I would go.

Or get a Ford 8.8 and swap that in.

My brother called once many years ago and said that one of his in-laws had driven his mother-in-laws pickup thru a barbed wire fence and of course the wire had gotten into the pinion seal and cooked the rear axle when it lost all the oil. He wanted to know how hard it would be to rebuild it??? Told him to get one from a junk yard.

igids1 10-07-2013 08:21 AM

Is it easier to swap out an entire axle? How much would one weigh? Can you do that in a regular garage at home?

Rikoshay 10-07-2013 12:22 PM

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Uh? I would probably do it in my driveway. Only suggesting the idea because people litteraly give these axles away for cheap.

And yes, axles are heavy, really freaking heavy.

igids1 10-08-2013 10:16 AM

Wow. It seems you are absolutely correct! I found one for sale for $50, which is less than even the bearings cost.

Do you know if there are any write ups on swapping out the entire axle>?

Any timeframes on how long it would take?

My first concern is that the brake lines are probably all going to start snapping once I try and unbolt them.

dnuccio 10-08-2013 11:00 AM

just a random guess here, but id assume a dana 35 would weigh somewhere in the neighborhood of 150-200lb. make sure you get an axle with the correct gear ratio. there were 2 offered in ZJs, 3.55 (common in 4.0s) and 3.73 (all V8s and some 4.0s with tow package). you can check by looking at the tag on the diff cover. if the tag is gone, the gear ratio should be marked on the ring gear. or you can count the teeth on the ring gear and divide by the number of teeth on the pinion (IIRC, mightve got that backwards)

igids1 10-08-2013 11:56 AM

Thanks for pointing that out. I didn't even realize the gear ratios would make any difference. Is that only due to the front differential? This had a tow hitch attached, so maybe it has the 3.73. Ill have to try to find if I can see the numbers. If the front drive shaft is not hooked up, would it make a difference what the gear ratio was?

dnuccio 10-08-2013 12:39 PM

if the front driveshaft was not hooked up, the different gear ratios would not matter. hell, theoretically you could drive it with the transfer case in 2wd and you would be fine with different ratios. not ideal, but it could be done. if you had different ratios, you could never use 4wd because it would bind and break things. i remember an episode of xtreme 4x4 where they had a (i think) 4.11 rear and a 4.10 front, and they said theyre close enough that it didnt matter. but 3.55 to 3.73 is too big of a jump, so better to find the right one and not have to worry about it

igids1 10-09-2013 10:16 PM

I've worked on other vehicles before, but never a jeep. Are the lower control arms kind of like leaf springs? In other words, when I pop out the bolts, are they under a lot of pressure and will they fly out? Also, with the frame on jack stands, and the rear axle hanging, does that take most of the pressure off of the rear coil springs? Coil springs can be dangerous, but in my searching, it doesn't seem to be a big issue on these.

dnuccio 10-09-2013 11:20 PM

the control arms will not shoot out. with the rear sway bar and track bar disconnected, the coil springs will decompress enough that they will be under very little, if any pressure.

igids1 10-13-2013 04:43 PM

Well, I went ahead and ripped the rear diff apart. First problem was just getting the Diff cover off....I had to get an air chisel to get it off...Guess it was siliconed on or something?

1) Don't they normally have gaskets?

I removed the carrier, races, and shims. When I took the Yoke/Pinion nut off, the Yoke and pinion both just fell out.

2)Is there a washer on the yoke? Everything just fell apart, so I couldn't see if there was a washer, but I thought there was supposed to be.

Just to be clear, i am talking about a washer between the nut and the yoke. The nut almost seemed to be widened out at the bottom to begin with.

So, I ordered the rebuild kit, and I will be trying to just rebuild it!

The take apart wasn't that terrible. Took about 1.5 hours or so

The time now is 07:07 AM.

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