Bad Axle?

[77RHINO]

Hey guys, while getting the new engine dialed in, I think the power made what used to be a minor problem a much bigger one..:-X..while driving under light throttle or coasting, I can hear some grinding/crunching noises from the back end that I used to only hear on occasion with the old motor, but now it has turned into nearly a constant noise. It's similar to what you would hear if a lug nut was rolling around in a center cap, but a much deeper/heavier sound. I am not sure what/how to check if its an axle or R&P, bearing, or what. Has anyone heard this before? I have searched and seen similar situations, but not seen any remedies on ways to check it out. The transmission (nv3550) and driveshaft/u-joints aren't more than 3 years old, and it hasn't been offroaded hard at all, just muddy hunting roads. I am just trying to get ideas on what to look for before I can tear into it. Its a stock '77 rear end, hasn't had a gear change yet. Thanks in advance for any input ya'll may have!

 

[Apogee]

It could easily be an axle bearing (or two), u-joint or something in the diff, but my money would be one of the first two. If you get it muddy and don't grease things semi-religiously, a life span of 3 years or less isn't unheard of or even unreasonable.

 

[77RHINO]

as far as diagnosing, should I just jack 1 wheel at a time and try to wiggle and rotate it? what are the best methods for figuring out what could be wrong before cracking the diff open?

 

[Apogee]

You can do the wiggle-wiggle test, however I would start by jacking up the rear and spinning each tire by hand first to get a feel for the bearings. If they're growling/grinding/crunching, then you may very well be able to feel it by hand. If the bearings are that bad though, you would typically see an oil leak as well due to an inner oil seal failure, that is unless your oil levels are low.

Given the ease of changing the u-joint, I would pull it from the rear yoke and inspect the bearings inside the two u-joint caps. If there's any damage, you'll see it. Dry bearings or piles of crumbs and dust are not uncommon.

I wouldn't pull the diff until I was 99% confident it wasn't anything else. If the noise is constant, then I'd lean towards the axle bearings. If it's only under power, then I'd lean towards the u-joint(s) or something inside the diff, hoping it isn't something in the transmission or transfer case.

 

[Mac2Night]

Rhino,

Does it quiet up if you take your foot of the accelerator? I have a similar issue (roaring but no grinding or crunching really, just a roar). Mine is totally quite with my foot off the accelerator. I am in the process of having it looked at where it is headed is the ring and pinion are warn and under load they don't mesh but under coast, they quiet down because they ride without any toque. Is yours similar or is the noise constant? I'll let you know what I find out and I will keep an eye on your post as well.

 

[77RHINO]

Apogee, I will do that first, and hopefully something will show. I know I have a leak at the pinion, the seal is bad there but the fluid never really drops too much just a few small drops after a ride..I haven't driven it enough lately to lose all the fluid I don't think.

Mac, My problem seems to be the opposite of yours, in that when I am on the throttle I do not hear it (unless the engine is loud enough that it drowns it out), I hear it when I let off or am under little power, such as cruising 25-30 MPH. I haven't even driven over 40-45 MPH yet, as the engine is new. Laid into it a couple times in 1st and 2nd gears to check for pinging while trying to get my timing dialed in, and then when I let off I heard the noises from the rear end, actually could feel the clicking/crunching all the way up to the steering wheel. I will check these issues first of next week and hopefully figure it out. 4.56s are next on my list to do, it just appears that may happen sooner than expected! Thanks for the help guys!

 

[DuctTape]

Maybe a long shot but pull your drums and check for loose e brake parts. When strange noises appear I try to rule out the simple an easy things first.

Next I'd do visual inspection of ujoints, springs, etc just as a quick and easy check.

Sounds like bearing noise to me (I had same thing), pulling axles should come before pulling pumpkin IMO. Pulling the rear axles is pretty easy.

 

[77RHINO]

Bringing this back up, in case any searchers come across my symptoms - I knew I was going to swap the gears, so I ended up buying new gears and a master overhaul kit rather than the install kit, that way it came with new bearings, seals, and shims for the entire housing and 3rd member. I took up to my local shop, and had it installed. Mechanic told me as soon as he LIGHTLY tugged on my drivers rear axle, it slid out along with pieces of shattered wheel bearing! Said he couldn't believe it had even made it to the shop without walking a wheel off Inner piece was still stuck on the shaft, didn't deteriorate that surface, so I didn't have to replace the shafts. Passenger wheel bearing was roaring, and pinion bearing had deteriorated so bad my old ring and pinion had pitting on them from the metal bits. I'm glad I parked it for a little bit to save up for the parts because I could be fixing alot more if I had kept on driving it like I wanted to!

Also, I am loving the 4.56s so far, (only driven it for 30 mins) first is super low and 2-4 are alot of fun around town! haven't gotten it on the highway yet, but if 5th acts like it should then its going to be a great all around cruiser!

 

[RODRIG3911]

I'm kinda crazy, but if it were me I'd just pull the axles and inspect the it all up close, and while I had the axles pulls, I'd drop the 3rd member and inspect it too haha. That way you know what it all looks like and you can put fresh gear oil in it and re seal the i. It's really not that hard bro and you can make sure you check everything out and know it's perfect when you're done

 

[bronconut73]

I'm kinda crazy, but if it were me I'd just pull the axles and inspect the it all up close, and while I had the axles pulls, I'd drop the 3rd member and inspect it too haha. That way you know what it all looks like and you can put fresh gear oil in it and re seal the i. It's really not that hard bro and you can make sure you check everything out and know it's perfect when you're done

Look up a few posts before yours....he's done....it is all set up with good bearings and 4.56 gears

 

[DirtDonk]

If any of that noise ever comes back, double check your pinion angle too.
Those NV3550's like to make a lot of death-rattling kinds of noises under decel when the pinion drops below a certain point while under light or no throttle coasting.
Also when shifting between gears if the angle is really bad.

Glad you got it fixed though. That was a bad one waiting to get worse!

Paul

 

[77RHINO]

Thanks guys, and Paul I will keep an ear out for that as well. I am now saving up for a front driveshaft and D44 gears/kit, My old shaft is stock length and I ran it anyways with the lift, but knew it was worn out and will be getting replaced with a longer one. I had read that I can buy the thick-cut gearset and not have to replace the carrier, so that is probably the route I will go.

 

[DirtDonk]

A lift kit alone is not usually a reason to change the shaft (though it can be) but a worn out one is all the reason you need any time.

I mentioned the trans even though it didn't sound like your issue this time (because it went away with your other fix) but different setups do act different, and with you potentially changing the lift kit (rear springs specifically) you can run into the issue down the road too.

What happens is that with the thickness of the leaf packs (more so than the total amount of lift alone) your rear pinion angle can change. The lower your pinion yoke points in relation to the centerline of the driveshaft, the more likely you are to have a vibration during coasting and deceleration.
The NV's, being truck transmissions and a bit "looser" inside than the old 3-speed car trannies that came stock, tend to rattle a lot more than we're used to. Sounds just like an old-time truck tranny (like the SM-420 and SM-460) that have about a zillion miles on them with the original gear oil and are getting worn out. If you've ever driven an old 50's or 60's pickup/work truck, you'll know what I mean.

Easy to tell if your pinion angle is going to be a problem. The optimum setup for a Bronco with a double-cardan shaft (double joint at the transfer case end) is for the rear pinion shaft to angle up about 2° below the centerline of the driveshaft.
You can eyeball that angle when you get familiar with it, but a simple angle finder app, or digital level will do the job.
I've used the old floating needle type dial angle finders, but most of the cheap ones are not really consistent when you're looking for 1 or 2 degree differences. A really good one will work fine, but the cheapies tend to stick and act funky.

Have fun!

Paul