View Full Version : 80 rear end noise - got a spare diff?

07-06-2008, 06:36 PM
So my 80 has this noise…. It’s 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 wasn’t 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.

Today’s 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. I’ll bet there aren’t many front wheel drive 80’s running around. Anyhow now I pretty convinced that I have an issue inside my rear diff. I’m 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 you’d like to part with? Or perhaps you’re 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? It’s the perfect opportunity?” Maybe, I’m really not planning to go to 315s from my current 285s but we’ve all heard that before. Would 4.56 be a good ratio for 285s? I’m not too psyched to have to redo both diffs. What’s the cost to have someone reputable do a front and rear for an 80? TIA, Bruce.

07-06-2008, 08:19 PM
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.

07-06-2008, 09:02 PM
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.

97 tacoma reg cab 3.4 v6, chev 63' rear springs.

07-06-2008, 09:15 PM
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?

07-06-2008, 09:45 PM
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


07-06-2008, 09:55 PM
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.. ;)

07-07-2008, 12:28 AM
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 :D

07-07-2008, 06:56 AM
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.

Uncle Ben
07-07-2008, 09:00 AM
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.

07-07-2008, 09:36 AM
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.

07-07-2008, 10:16 AM
I greased the shaft joints a few weeks ago and noticed no changed in the sound. the ujoint bearings feel tight enough to me but they're not hot. The spline may have a bit of wear in it. I'll drop off the shaft today at Boulder Driveline and see what they say.

The thicker oil is a good idea. I'm not positive but I think the noise took a while to become noticeable when driving in cold weather. Maybe the 75-90w had enough of a viscosity change as it came up to temp in February to impact the noise.

07-07-2008, 10:50 AM
Did you notice any change in sound when you put on the lift? I can't remember when that was... was it February? Testing the steeper driveline angles=more sound hypothesis..

07-07-2008, 11:48 AM
I had the exact same issue...there is a thread somewhere here about it...pulled the front driveshaft and I had a bad u-joint. It is at Englewood Driveshaft right now getting both u-joints replaced.

07-07-2008, 01:39 PM
I read the timmbuck2 thread and yes its sounds similar. I hope its the driveshaft but I doubt it. I took the shaft over to Boulder Driveline. Ron said the ujoints feel like they should. He's going to go ahead and retube the thing with some thicker material. That should make it more durable and might improve the balance.

After I get it back on the truck, I'll try some 140wt oil in the diff. One drawback to the full floater axle is the lack of an inspection cover. I'd reall like to be able to examine the ring gear. Anyone got a bore scope that I can poke in the fill hole?

The significant question for anyone whose had a driveshaft related noise, was the noise at a low enough freq to match up with tire rpm? i.e. did it sound like a rock stuck in the tread at 7Hz or was it more of a rumble at 28Hz? (at 40mph)

07-07-2008, 01:46 PM
I'm coming into this late, but even with the rear driveshaft pulled your rear diff is spinning, so if the noise is gone then I would say, like everyone else, that it is a driveshaft issue. But then like you say if it was a driveshaft issue it wouldn't follow the frequency of the tires, it should be 4 or 5 times the rotational frequency of the tires.

07-08-2008, 12:34 AM
I read the timmbuck2 thread and yes its sounds similar. I hope its the driveshaft but I doubt it. I took the shaft over to Boulder Driveline. Ron said the ujoints feel like they should. He's going to go ahead and retube the thing with some thicker material. That should make it more durable and might improve the balance.

After I get it back on the truck, I'll try some 140wt oil in the diff. One drawback to the full floater axle is the lack of an inspection cover. I'd reall like to be able to examine the ring gear. Anyone got a bore scope that I can poke in the fill hole?

The significant question for anyone whose had a driveshaft related noise, was the noise at a low enough freq to match up with tire rpm? i.e. did it sound like a rock stuck in the tread at 7Hz or was it more of a rumble at 28Hz? (at 40mph)

The 80 rear driveshaft can make a nice grumble at low speed, say 40-50, and then run clean at higher speeds. It makes no sense to me, but I finally pulled mine and had it rebalanced and it was like a new rig for $50.

Having worked with just about every driveshaft configuration imaginable on my old XJ, including a double double-cardan, I thought I could diagnose a driveshaft in my sleep, and this one was so much like the tires at low speed that it took me about six months to wake up and take it to a shop (Driveline Services in the Springs).

The tech said it all felt fine, just a balance tweak was required, but it was night and day rumble to smooth. Good luck :cheers:

07-10-2008, 04:51 AM
The rebuilt shaft is back on the truck and the noise is reduced. Its not totally gone but its not as loud and seems to no longer be tied to the gas pedal. Now it sounds more like a mild tire sound that is constant whether you're on the gas or coasting. I'm shocked. I'm still trying figure out how rebalancing the shaft could do what it did. I think the spline was also cleaned and greased but the ujoints and the spline were not replaced, just the main tube. So far I've only driven it to the airport, (business trip to NY) but it'll be interesting to see if the improvement is permanent or maybe due to fresh grease in the spline. Thanks for all the advice pointing to the driveshaft.

07-10-2008, 07:23 AM
Take the front shaft off and see what it does. I had to do both shafts to get my noise completely fixed

07-12-2008, 07:05 AM
I spoke too soon. I drove home from the airport yesterday and the noise just as bad as it was and most definitely still tied to the load on the drivetrain. Now I'm groping for an explanation as to how it could be so different driving to and from the airport. It was really hot yesterday which might make the diff oil a bit thinner than on a cool day but I would expect the gear and bearing action in the diff to create much more heat than simply baking in a 100 deg parking lot. Maybe the tires developed some flat spots from sitting for three days in the heat? They're not bias ply tires but I'me really reaching here. I'll likely still try the 140 wt oil and maybe try pulling the front shaft just to see what happens.

07-21-2008, 11:30 AM
The latest.... Noise is still there, definitely unchanged with the front shaft removed. I've got 140 oil in the rear diff. The operating temp went up to 150F from 120F, noise unchanged. As before, the noise is gone when running with only the front driveshaft. The rear shaft has been retubed and balanced. I'm thinking about sticking a vibration analyzer to the diff housing to see if I can measure the vibe - mostly because its easy. I'm leaning towards pulling the rear diff and having the gears and bearings replaced. What's the consensus on used gears? Do they tend to make noise when installed in another housing? Also, would a basic Cruiser diff (FJ60?) fit in there? Would the drive flange match an 80 driveshaft? I sold my 60 spare a while ago but if one like it would fit, that could be a temp fix while the locked diff is out being rebuilt. 3.73 would be fine as I'm in rear wheel drive at the moment. Suggestions appreciated.

07-21-2008, 11:33 AM
You said re-tubed and balances, what about the Joints. Mine seemed fine when cold but had an issue when warm. How is the Yoke?

My suggestion, before all that. Borrow someone elses rear drive shaft just to be sure.

You can come on down to my house take it off, drive around a bit and then you can put it back on.

07-21-2008, 02:06 PM
I might take you up on that. Is yours a double cardan shaft?

07-21-2008, 03:34 PM
I might take you up on that. Is yours a double cardan shaft?


08-01-2008, 02:23 PM
As I continue to obsess over the noise, I'm pretty sure its not the driveshaft. I'm collecting rebuild parts and will be pulling the diff out one of these weekends. I was digging around on MUD and found a link to this guys site, ZUK. One of the writeups had an interesting comment that mentioned a whistling noise. http://gearinstalls.com/rob2.htm Oddly, I too have noticed a significant whistling noise. I had written it off as an exhaust noise but now I'm wondering if its actually the diff. Maybe some of the other whistles attributed to the removal of the resonator are actually gear noise? I'm hoping to find a chewed up carrier bearing when I get the thing out. Stay tuned.

08-01-2008, 02:58 PM
IIRC, a basic Cruiser diff should work in the rear of your 80 Bruce. It seems like people swap the 80 series e-locker diffs into 40s etc., so I would imagine it would work the other way around, maybe?

As long as the ring and pinion have been wearing together since new, I don't believe they should have any noise just by getting installed in a new carrier. But I don't know?

Before pulling the rear diff, maybe you could put locking hubs on the rear end (and unlock them) to keep the rear from spinning as you drive in front wheel drive down the road. :confused:

08-31-2008, 11:18 AM
So I finally pulled the pumpkin and found what I hope is the problem. The first pic is the forward drive side of a buggered tooth on the ring gear. 2nd pic is the reverse side of the same tooth - yes that's a crack. There is also a pretty noticeable scuff on the tooth behind it. What's wierd is that all of the other teeth look fine. Do you think this is an impact failure or a manufacturing defect?

I tried a bit of prussian blue on some teeth to check the engagement pattern. There's probably still too much gear oil on the pinion to get a good check but it didn't look too bad. pic 3 and 4 are the blue test.

I've got all the rebuild parts collected including new bearings and seals. The one thing I don't have is the big diff gasket. I know some folkes prefer to leave the gasket out and seal it w/ rtv but I was surprized how thick the stock gasket is - 0.020" compressed. I'm wondering if that thickness could possibly impact the squareness of the axle fit in the diff?

08-31-2008, 12:33 PM
And some measurements to add.....

The ring gear backlash is 0.009" - not too far out of spec, but it is out.

Now the ring gear runout measured on the flat side opposite the teeth, is 0.035". Wow! Thing is really tweaked. What's also odd is that it is flexed/bent towards the carrier mounting surface, the backside of the gear. Maybe the damaged tooth relieved some stress and the thing sprung out of flat? I hope the carrier isn't messed up.

edit..... Rebuilding this one isn't an option unless can find a replacement carrier housing. The carrier is cracked between the ring mount flange and the body of the housing.

08-31-2008, 06:52 PM
Yikes - well just be glad that it didn't blow up on you. My friend's CJ just had has carrier break in half and it locked his rear axle solid (luckily he was in a parking lot moving slow). Land Cruisers always wait until they know they are safe to let loose or wait until you have the time to check them out :D

It sounds to me like a new carrier and ring and pinion are the safest bets - wonder what would happen to make everything tweak/crack like that?

09-02-2008, 09:51 AM
Wow, sorry Bruce guess you were right all along.. can you see any marks at all on the pinion gear? I wonder if someone tried to ram it into gear at high RPM's, or did a reverse to drive move, or something like that.. can't really think of how else that could happen.

But I believe I've got a good used R&P, let me know if you want it.

09-02-2008, 01:52 PM
I've got a new carrier (case) on order from CruiserDan. I'm actually surprized that its available. It should be here next week. Hopefully it'll fit properly without needing to change the bearing shims.

As for how it broke..... As mentioned above, the noise was present when I bought the truck. Keep in mind that it wasn't a loud noise, just a subtle one that sounded like a tire needed to be balanced. When I got the truck, I got a folder full of service records. Most of the receipts were oil changes, brake jobs and other regular maintenance. The one reciept that was odd was for "replace rear axle." There wasn't any body work or other repair work to indicate an accident so I just wondered what happened to the original axle. Anyhow, I'll bet my current axle came out of a truck that was in accident and that is what chipped the ring gear and cracked the carrier case. I've gone over the rest of the axle housing and can't find any damage. It tracks fine, the brakes are wearing evenly. What's funny is that the pinion seal wasn't leaking at all.

Thanks for the offer on the gears but I'm all set on parts - hopefully.

09-13-2008, 09:48 PM
So I'm finally back in 4 wheel drive. I got the diff reassembled and installed and after 20 miles, so far, so good. No noise, no leaks. Hopefully its the last time I get to see the inside of the rear end. It was a pain to do but was quite educational - way more difficult than a simple ARB install. I had to reshim the pinion and the carrier bearings to get the thing in spec. The pic below is the original case with the cracked flange.