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Old 07-06-2008, 06:36 PM
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Default 80 rear end noise - got a spare diff?

So my 80 has this noise. Its a pulsing sound that is at the frequency of tire rotation. Its loudest at about 40 mph when your accelerating or at least using the skinny pedal to maintain speed. If you take your foot off the gas, the sound abruptly disappears. The sound was there when I bought the truck about 4000 miles ago. Maybe it wasnt as noticeable but it was definitely there. I thought it was a tire or a bearing. After replacing the tires, the sound was still there. I have since replaced ALL of the wheel bearings with no change in the sound. I think the sound is a bit louder or at least its starting to bug me more.

Todays experiment was to pull the rear drive shaft and the jumpered plug in the dash to engage the center diff lock in high range. I took the truck out for a drive and the sound is GONE or at least as quiet as when coasting without foot on the gas. Ill bet there arent many front wheel drive 80s running around. Anyhow now I pretty convinced that I have an issue inside my rear diff. Im guessing either some high runout in the ring gear, maybe a chipped tooth or maybe a loose or failing carrier bearing. A new ring, pinion and bearings would likely fix it but it seems a shame to go through a whole setup for a stock 4.11 gear set. So.. does anyone have a stock FZJ80 rear 3rd member with a locker that youd like to part with? Or perhaps youre thinking about regearing and are going to pull a perfectly good, already setup pumpkin? Sell it to me and use my core for the fresh gearset.

All ideas welcome. I know some someone will offer up, Why not regear your truck? Its the perfect opportunity? Maybe, Im really not planning to go to 315s from my current 285s but weve all heard that before. Would 4.56 be a good ratio for 285s? Im not too psyched to have to redo both diffs. Whats the cost to have someone reputable do a front and rear for an 80? TIA, Bruce.
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Old 07-06-2008, 08:19 PM
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Don't have a spare pumpkin but I do have a set of stock gears for the rear they are in good shape and they are yours if you want them. Ben, Bill and several others can hook you up on setting them up.
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Old 07-06-2008, 09:02 PM
JohnInDenver JohnInDenver is offline
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Hope you don't have to do a new diff!

Had a somewhat similar situation with a Tacoma. Mainly a loud vibration under hard acceleration and ok otherwise. It was not as bad when hauling a load but still there. Replaced the 8.4 rear axle with an elocker in an 8.0 rear axle. Same thing. Bought a $6.00 JOHNSON pitch and angle locator at General Hardware on south Broadway. Measured the angle of the drive shaft to the rear diff. It was off about 2 1/2 degrees due to the lift installed. Changed the angle by cutting and replacing the spring perchs at the axle. The drive shaft is now lined up at 1 degree off of the rear diff and no more noise.


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Old 07-06-2008, 09:15 PM
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So was it the same driveshaft with both axles? Was the noise at tire rpm or higher freq? Interesting but I think different than my noise - the truck was bone stock when I got it and adding the 2.5 OME heavy lift really didn't change the noise.

I'm open to paying $ to setup a set of gears or I would like to do it myself but it'd be nice to have a whole extra diff to assemble while the truck is still driveable. Anyone have a buggered spare diff in need of gears?
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Old 07-06-2008, 09:45 PM
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Maybe likely drive shaft. U Joints, balancing, maybe the phase isnt correct or too much old grease in the inner spline

Here is some homework for you

http://forum.ih8mud.com/80-series-te...oting-faq.html
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Old 07-06-2008, 09:55 PM
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x2 or 3 on just the driveshaft. If you want to do the swap work, you're welcome to borrow mine for a week or so to prove it out.. or just give yours a good R&R (especially pull it apart and clean all the gunk out from the spline area) and see if the sound changes. I bet it does..
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Old 07-07-2008, 12:28 AM
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No doubt, have the driveshaft checked by a good shop before you start tearing into diffs, what you are describing sounds like a driveshaft issue (including u-joints) more than a diff issue.

Of course, I do have a nice rear 4.10 R&P (not a complete 3rd) if you really want one
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Old 07-07-2008, 06:56 AM
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I'll likely take the shaft over to Boulder Driveline to have it checked out or rebuilt, maybe retubed in the process but the clue that steered me away from the driveshaft is that the pulse occurs at the same frequency as the tire rotation not at the frequency that the shaft is spinning at.
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Old 07-07-2008, 09:00 AM
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x5 or 6 on driveshaft. You're wise to take it to Ron at Boulder Driveshaft. Jerry stocks U-J's and can give you a better price on them than Ron can get them for.
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Old 07-07-2008, 09:36 AM
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If after this you are still convinced it is the Diff, changeout the gear oil and put 140wt in their. The sound will change just based on gear oil. That's how we diagnosed my bad tcase 3 years ago (Robbie's suggestion)

Still bet it's the drive shaft. Have you lubed the Ujoints to see if that makes a difference?

My ujoints felt fine when cold, but when heated up had excessive play. I used Toyota U Joints and had both shafts rebuilt and balanced.
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