I could use some help with a problem on my '91, 3.0, 5spd 4WD 4Runner that recetly developed.
I've got a very loud rubbing or grinding noise coming from the driver side front wheel area. Sounds much like a rubbing tire, but more metallic. This condition is not constant, but will present at any speed and in any gear, driving straight or turning. If it happens when driving straight, turning the wheel either direction slightly, will change the pitch and timbre of the noise. The noise did not appear over time, it went from not there to VERY loud overnight. Also, occasionally the vehicle will shudder violently for a fraction of a second, as if I hit something or ran over a good sized rock. When that happens the RPMs go down, as if an additional load is instantly put on the motor. It feels as if something is trying to engage that shouldn't. I'm also thinking that these two problems are related.
Otherwise the drivetrain seems fine. Motor runs great, tranny shifts fine, clutch is positive, transfer shifts smooth as well. I'm leaning toward a problem with CVs, U-joints, wheel bearings or the automatic hubs. There's definately some mechanical interference somewhere. Any ideas greatly appreciated. TIA.

 

How many miles? Sounds kinda like wheel bearings or CVs to me as well...

 

150,000 and change.

I'm in the process of moving, so it'll be a couple days before I can get under it. Inspecting U-joints is easy. For CVs, is there any other test besides jacking up the vehicle and rotating to test for binding?

 

Sounds like you might be down to the wear indicators on the brake pads. Get it checked ASAP. I let mine go a little too long and had to get (another) set of front rotors... :pat:

 

It's not the brakes, I replaced them all the way around just before hunting season. 100% sure they were replaced correctly. Thanks though.

BTW, the noise isn't a high-pitched scaping noise. It's more of a dull metallic thump.

 

Regarding your hubs, if it's the ADD system, you can rule out the hubs. The ADD system just uses a plate with no moving parts at the hub.

 

I don't believe that it's the ADD system, just the standard automatic locking hubs. (Or is that in fact the same thing?).

 

Should be the same thing. Does the cover on the hub say "Automatic Disconnecting Differential"? If so this is the ADD system.

 

Wheel bearing maybe?

 

cv's. relaced my left side 2x in 165,000. the first time i heard the clunking/grinding noise and sure enough, the boot was busted. must have been that way for awhile and got all sorts of grit inside.

2nd time, last month, i noticed the boot was busted, so i replaced them before the cv joint got bad.

i believe mine to be prone because i make a lot of u-turns. so i got the manual hubs to save the cv wear-and-tear.

BTW, i've never replaced the passenger side. boots still look good.

but if you're driving in 2wd, it won't be the u-joints, and shouldn't drop the RPMs (if it IS the cvs).

 

I've got to ask why??? Being chased?

 

Upon inspection, the cover does say "Automatic Disconnecting Differential".
I am starting to suspect a wheel bearing, as the sound semms to be located more outboard than inboard. As I understand it, with the IFS and ADD systems, the CV shafts are constantly rotating while the vehicle is in motion. If that is the case, then when shifting into 4WD, the engagement would occur at the inboard side between the front diff. and the CV, correct? So what is it that keeps the CV disengaged under normal conditions? Could there be a component here that can fail and allow the CV to try and lock in to the front diff.? Of couse, in 2WD, the front diff. isn't rotating anyway, but could the CV be trying to hook up to a static gear?

 

have you ever tried to park in san francisco? everything is street parking, and the 4runner won't fit in a lot of spaces (if you overhang a driveway, the residents will have you ticketed or towed). so if you see one across the street, you flip it quick or drive around for another 30 minutes looking for a space 3 blocks away from where you want to go!

there's a write up in 4x4wire i think about defeating the ADD vacuum system. you could try this, to eliminate the axle-diff source as problem.

you could jack the wheel up, and spin it to see if it;s bearings, brakes, or cv. are your boots intact?

 

The manual hubs will keep the CV's from turning all the time. Easy and cheap. You can get of Aisins for under $50 and it's easy to do yourself.

 

Thanks for all the input guys. As soon as I get into the new house, I'll be able to further inspect the vehicle. I have a set of Aisins ready to go on the bench as well. If the problem turns out to be a wheel bearing, I'll be able to take care of both at once.

 

Can't recall exactly what they are called but there is a bushing inside the hub that the shaft rides in. There is a replacement that is roller bearing if I recall correctly. I have not had to do these yet but I have read posts indicating others have had this problem.

Edit - check here
https://www.yotatech.com/~corey/tech...imrockford.htm