dylansmith17

I am an idiot.

I have a 1995 Pickup, 3.0 3VZE 4x4 with manually locking hubs, 97,000 miles. I didn't know any better and I put my truck in 4WD on dry pavement. My goal was to turn the front diff because I wanted to mix up the gear oil before I changed it. I didn't realize that I could have done this simply by locking the hubs and driving around. Anyway, I basically just drove once around the block, probably about 1/10 - 2/10 of a mile, but did do some pretty idiotic 3-point turns and parallel parks (i.e. had the wheels turned a lot). It felt awful and jerky, as I now know it should. Like I said, I'm an idiot, but that's what I did.

I now notice a loud humming/whirring sound from the front end when I drive. It's possible it was there to a certain degree before this incident, but I swear it's a lot louder now. It happens in all gears, changes frequency relative to speed and NOT rpm (is higher pitched at higher speeds). It seems the loudest in the 10-20 mph range, and generally is not noticeable and high speeds (+50 mph), though this is probably due to the sound being drowned out by all the other sounds (3VZE is loud as ****, plus I also have transmission noise due to a bad input shaft bearing, plus wind, etc.). This morning I brought the truck up to about 30 mph and then turned the key off, driving in a straight line. When the engine shut off the sound didn't change, so I don't think it's engine or tranny related. The sound doesn't seem to change relative to whether I have the wheels turned or not.

I'm looking for help assessing how bad I screwed up my truck by driving it in 4WD on pavement, and figuring out where the noise is coming from now. Could I have screwed up my front wheel bearings? My hubs are NOT locked now, which I thought meant that my front diff shouldn't be spinning? So I would assume it's not the diff that's screwed up? I have a cursory knowledge of cars, though not much, and basic mechanical skills. I still haven't changed my oil in the diff anyway so I can check for obvious signs of damage by assessing how much metal comes out in the oil. I can also jack the front end up and try to rock the wheels back and forth to check for free play in the bearings. What else should I do? Was planning on taking this truck on a ~1000 mile journey in about a month, so I'd like to figure this out and replace anything before that. All advice/thoughts appreciated.

Thanks.

RJR

So you're saying the noise is there even in 2wd with the hubs unlocked. In that case it's very likely not the front diff or the front drive shaft. However, it could be a rear drive shaft u-joint. Running in 4wd on dry pavement stresses the entire drive train, not just the front section. You may have pushed an already weak u-joint to the failing point with your inadvertent stress test.

Don't feel too bad, though. A healthy drive train should handle what you did. People do the equivalent of that on Moab slick rock all the time. That stuff is easily as grippy as your street, and some maneuvers require tight 3-point turns while in 4wd. Usually things survive.

Noises under your truck often don't come from where you think. The fact that it's a hum suggests drive shaft to me, and since it does it in 2wd with unlocked hubs, it points to the rear. That's where I'd start.

If it's not that, check to be sure your hubs are really unlocking. The stress could have jammed one of them in the locked state. Just because you turned the dial to "Free" doesn't mean the sliding collar actually unlocked inside. Jack up the front end and rotate both wheels and make sure the CV shafts don't move. If one hub is stuck locked, the CV shafts will be rotating at highway speeds in opposite directions and can make some noise.

dylansmith17

Hey thanks for the reply RJR. With the panic of engaging the 4WD, I was only really considering the front drive line.

I did some reading about rear u-joints, and people mention that often you'll hear a metallic clicking or clanking sound when shifting into reverse when the u-joint is starting to go bad. As a matter of fact, that is exactly what my truck does. Whether I'm stopped or gently rolling, engine on or off, from any gear or from neutral, into reverse I get a "clank" sound. So you think if it is indeed failing it could cause that whirring/humming sound at speed?

If if I get under the truck and have my girlfriend shift into reverse, do you think I'll be able to see anything that could help me diagnose if the u-joint is failing? Is there anything I can do to save it (like re-greasing it?), or does it need replacing?

i will also check my front hubs just to make sure one isn't stuck in locked.

thook

when a u-joint gets to that point, there's no saving it. and, the only sure way i know of to really inspect a u-joint is to drop the shaft and rotate it. i mean, if you get under there and can wobble it by hand then it's obvious. otherwise, when they seize up it'll be as stiff as any other joint while in place. iow's, you won't be able to move it.

anyhow, for sure when they start seizing they can and do making that whirring sound.

RJR

A bad u-joint can certainly cause a humming. If the u-joint is failing, the only cure is replacement. Shouldn't be too expensive, but generally is not something you want to do yourself as a newbie. Be very careful if you are looking under the truck while the engine is running and someone is putting it into gear. Getting run over isn't a good experience.

The safest way to check is to put the truck into park or in gear, engine off, block the front wheels, and jack up one rear wheel. Then watch/listen to the drive shaft joints while someone turns that wheel hard forward and back. Any motion or clicking is a bad sign. Make sure you check the joints at both ends of the drive shaft.

You don't want to mess around with a bad u-joint. When they completely fail, one end of the spinning drive shaft drops to the ground and can cause all kinds of mayhem, up to and including a fatal accident.

If you have an experienced mechanic you trust, have him ride around with you for 10 minutes. He'll be able to tell you a lot more than I can over the internet.

scope103

Yeah, whatever the cause of your "hum," you should definitely check the driveshaft

I'm going to guess that you can crawl under your truck, put your hand on the driveshaft, and rotate it quite a bit. That's not good. But thook is correct; failure can also be NO motion (freezing). Once when I replaced a clutch (requiring the removal of the driveshaft, among other things) my more-experienced-than-me helper pointed out that the u-joints were Brinelled ("notchy" feeling, due to the roller bearings hammering ruts in the race).

Especially when it's your girlfriend at the wheel!

I never recommend that someone try a repair they're uncomfortable with. But I didn't find replacing u-joints to be that difficult. http://web.archive.org/web/201204171.../3propelle.pdf The manual tells you to match-mark every flange you disassemble, and I suggest you pay attention to that. We've discussed on this forum whether balancing is actually an issue, but since you have multiple u-joints PHASING absolutely is an issue. And match marks never hurt anyone.

The manual shows a special service tool for pressing the bearing out and in. A big C-clamp and a socket works well to install bearings. When I had to remove the bearings and pointed out the need for a special tool, my helper pooh-poohed that and reached for his "Mexican Speed Wrench." (a hammer) (I believe he was in awe of the resourcefulness of our friends to the South, but if you think this is offensive I will apologize in advance).

thook

scope... what i mean is drop the driveshaft and rotate the u-joint

dylansmith17

Thanks thook, scope, RJR, all. I called a place who said if I brought them the driveshaft they'd replace the u-joint for well within my budget, so it looks like I'll do that. I'll check the joint myself once I drop the shaft, maybe it'll be very obvious like you've pointed out. Even if not, I'll probably get a new one put on there, just so I know for sure if the whirring/humming persists it wasn't that.

Going to to try to tackle this tomorrow morning, fingers crossed that it fixes the problem.

And do do I assume that my idea about the wheel bearings wasn't a very popular one? Anyone think that my adventures in inner city 4x4ing could have damaged those to the point where I should check them out?

thook

reread what rjr posted about moab. unlikely you've damaged anything, i'd say. i've driven all the way to the post office where i live forgetting to take it out of 4wd. nothing was harmed. they have pretty robust equipment.

dylansmith17

I like your positive attitude thook.

OK, now for the REALLY noob question. I'm looking under my truck and I have what appears to be three different u-joints on the rear driveshaft? One right at the connection to the t-case, one in the middle (hard to see, has a guard on it, maybe just some other type of bearing?), and one at the connection to the rear diff? So in actuality am I talking about replacing all of these, or am I not getting something?

I do have the FSM, I'm staring at the diagram and I think they're called "spiders" in the FSM, but I'm not sure if I'm really reading this correctly.

Thanks for your patience and advice all.

dylansmith17

Hmmm OK I think I figured out my own question. One on either side of the shaft, the thing in the middle is a carrier/center bearing. And I guess I wouldn't know which or whether both are bad until I have the shaft down and can inspect for movement and free play?

thook

i don't have a pick up...rather a 4rnr. are you maybe looking at a carrier bearing?

what page in the fsm are you looking at? can you post the link?

thook

lol..okay. there you go.

i'm no expert on carrier bearing inspection. i only ever had a pick up once. when the bearing went bad, it simply snapped and i had no forward propulsion. no inspection really necessary

scope103

You must have the 3-joint type (and with 3 joints, you need the center bearing). Which type you have depends on the specific model (I have the 3-joint type, because of the extra frame length for the back seat).

The next question is, if you don't take the u-joints (spiders) apart yourself, how are you going to carry it to place that will replace it for you? (The drive shaft s pretty long.) Just remember: match marks!

Driving on pavement in 4wd is pretty hard on tires, but rubber is much softer than everything else. But I wouldn't rule out pushing a marginal wheel bearing until it failed. Jack up one wheel at a time, and turn the wheel with your hand. If you feel anything, you may have a bad bearing.

dylansmith17

GOOD question. Was definitely thinking I would take it in a backpack on a motorcycle until I got under there after work today and realized that it's three times longer than I thought. I have the three joint type, from what I could figure out. Also have the extended cab.

scope103

Not a problem.