Well, looks like I’m keeping the 4Runner (1990, 4WD, 3.0 v6) for a while. Time to address the strange sound that’s coming from the underside. It started a couple weeks ago.
At 35-40 MPH or so, it seems most audible. It seems to get louder when I slack off the accelerator some and the car is decelerating slightly. At 35 MPH it’s about 2 beats per second, a soft scuff-scuff-scuff sound that makes a slight vibration in the floorboards. It gets faster and slower with the speed of the car. With the car in park, there’s no sound at any RPM. The problem is somewhere in the drive train.
I just had the entire rear-differential reworked. New pinon seal, front flange and axle seals (there was slung oil around the underside of the car lined up neatly with the front of the diff). I also had the drums turned and the brake fluid replaced but that’s probably not important. Sadly, the scuff sound persists. I can’t think of anything that spins that slowly at 35 MPH.
I’ve also greased the entire length of both drive shafts. This seemed to reduce the sound at first but I think I was just damping it.
So, I was thinking about removing the front drive shaft to see if it would stop. That might indicate if the problem is in the front differential. Anybody know if I can run this truck without the front drive shaft?
If it were me, I’d get the thing up on jack stands and (carefully) listen underneath the vehicle while running it in gear. The usual “don’t be stupid!” caveats to heed when working around heavy running equipment apply. You ought to be able to narrow it down to the general area, at least.
Well, I know zilch about cars but I have a 1990 4Runner too. I love it. It has 250K on it and pulls my horse trailer with no problems.
Anyway, you reminded me of when a flap inside my wheelwell came loose and made that same scuff scuff sound as the tire brushed it and I could also feel it underfoot through the floorboards. But that is probably too silly and if you already know it is something to do with the drive shaft then I should just pipe down.
A wheel bearing can make a sound like that when it goes bad. Since the sound gets faster and slower with the speed of the car and does not happen when the car is not moving, it’s most likely something at the wheels, not earlier in the drivetrain. The only trick is figuring out which bearing it is. Mechanics are able to pinpoint it after driving a very short distance, while I have never been able to pick the right one even after they told me which one it was.
I don’t know for sure, but I doubt there would be a problem with driving it without the front driveshaft, so long as it’s in 2WD and so long as the driveshaft has a flange at each end (as opposed to a slip yoke that goes into the transfer case which would allow leakage if removed).
My first thought was a universal joint. They can make a variety of noises/vibrations, and it’s usually different between accelerating and coasting. If there’s any detectable play in a U-joint with the driveshaft installed, it’s definitely worn. Sometimes it’s necessary to remove the driveshaft to detect play or stiffness, either of which is a problem. I can see greasing a U-joint making it temporarily quieter. I can’t see how greasing anything on the driveshafts would affect any other type of noise.
I greased the U-joints and the slip yokes on both shafts. That’s what I meant by “the entire length of both drive shafts”.
I’m not sure about the flanges on the front drive shaft. I’ll have to crawl under and look. Lifing the car on jack stands has been mentioned by a friend but I haven’t tried it yet.
I was considering a bearing but the wheels turn so much faster than the sound itself. I caught a piece of duct tape on my tire and had it slapping the wheel well for a moment. Even at 15 MPH, it was significantly faster than this sound.
If I jacked the car & spun the wheels by hand, do you think that’d be enough to identify a bearing?
The Haynes manual says not to operate the vehicle without the front shaft but it also covers about 12-years of pickups & 4Runners so all their advice might not apply to all models. It does warn not to disassemble the front shaft for some reason.
Coincidentally, I currently have a bad wheel bearing and a stone stuck in the tread of a tire. I can hear the scuff-scuff sound up to about 60 mph, at which point it becomes hard to distinguish the individual scuffs. The sound of the stone hitting the pavement occurs more frequently than the scuffing sound, and the ticks become indistinguishable well before 60 mph.
That’s what I thought you meant. What I’m saying is that greasing those things won’t change noise from a differential, or wheel bearing, or anything else that’s not actually part of the driveshaft.
Probably because the U-joints are swaged in and are not replaceable. It’s a common design on Japanese cars, and it bites if a U-joint goes bad, because the fix is replacing the driveshaft for a gajillion bucks.
Two aspects of your symptoms - the noise changing with accel/coast, and the vibration - are not at all typical of wheel bearing noise. They are fairly common with a worn or sticking U-joint. They’re less likely, but not impossible, with a differential problem. I would suggest checking the driveshafts first.
Unless I am mistaken, the front drive shaft and does not rotate when the truck is in 2WD and the hubs are unlocked. So if the noise is present in 2WD with the hubs unlocked, I would remove the rear drive shaft, put the vehicle in 4WD and go for a drive. If the noise is gone it is the rear driveshaft. If it is still there it is in the rear axle. Either the pinion bearings, differental bearings, or the axle bearings. Or just possibly the output shaft of the transmission/transfer case (unlikely)
My personal bet is the rear driveshaft.
So, I had this idea yesterday on my way home. “Scuff Scuff” means friction. Friction means heat. So I slid under ther car after my 10 mile commute & felt up the universal joints.
Unfortunately, the results were inconclusive. The rear U-joint was pretty much cold and the front was a little bit warm. The front, though, is only inches from the transfer case and that was pretty hot.
So, given that I thought the sound was reduced after I greased the shafts, I re-greased only the front joint. I think the car is quieter again. I’m going to go ahead and replace the front joint’s spider & bearings & see if that cures things.
Just thought I’d drop an update. I had the ujoint in the main driveshaft replace a couple days ago. The noise persists.
I took it in because of a recent jump in noise, including the occaisional “Clank”.
The shop that did the joint suggested the transfer case, there’s some play on the output shaft. The tranny shop I talked to, though, said a little play was normal and that he’d suggest getting the drive shaft looked at, especially the slip joint.
So, a week to payday. Then I’ll haul the drive shaft in (the shop has no bays, gotta bring it in already removed).
I took the car to a mechanic to have the valve cover gaskets replaced, I was getting to the point where the joke was to “fill the oil and check the gas”. (Boy, there’s a reference that newer generations probably won’t get. Any full service stations left?)
Anyway, he eyeballed it, wiggled stuff, and suggested the transfer case again. I stopped by the tranny shop on the way home and had the guy there inspect it. Yeah, there’s a bit of a wiggle he says but unsure if it means anything. He then turned on the engine and engaged the wheels while up on the lift.
The noise was very obvious. Left rear tire. A quick inspection showed a line of differential oil leaking out along the tire, too.
Bearings
blankity-blank bearings.
I’m holding them now - they’re very pretty, all scored and gnarled like glass marbles banged together for too long.
The gear oil ruined the brake shoes on that side so they had to be replaced too. I had the other side inspected, the bearings are good but the seals were bad. Had those replaced, too.
The rear u-joint “whirrs” pretty loudly so that’s next on the hit parade. That was also obvious while wandering aimlessly beneath a running vehicle.
well - in my defense, there is a missing piece of information.
I had the diff’s front pinion seal had been replaced and at that time I asked the shop to inspect all the diff and I thought they told me they had replaced the seals.
So, all this time, I thought these seals and bearings were fine because of this work.
“All new diff, must be something else”, thought I
Using the tranny shop to jack the car up and run the wheels was a lot easier than contemplating doing it myself - that terrified me.
