Toyo_Master

:wtf: I have a 94 SR5 extra cab 4X4, 3.0, 4" suspension lift, 3" body lift. I just got the truck and finally took it for a drive down the highway. I live in the mountains and rarely have an opportunity to go over 50 MPH.

At around 55+ MPH, when I lightly let up on the accelerator I get a loud hum that sounds like an exhaust vibration (but it isn't. Makes the noise when at idle with the clutch in). On compression or under acceleration no hum. Only when there's no load on the driveline. It will also make the noise if I push in the clutch and coast when I'm over 55 MPH. Below that speed everything is as quiet as a mouse. The faster I go over 55 the louder it gets. Open the cab slider and the noise is quite loud.

I've been told it's probably one of the following: Bad center support bearing, bad U joints, too much rear driveline angle causing the other two problems and creating vibration. I've also been told it could be a bad rear carrier bearing or bad transfer case output bearing. Wouldn't you think that if one of the latter were true that there would be noise even at lower speeds?

Solutions suggested: Go to a one piece driveline or rebuild mine and replace the Center suppor bearing (that costs as much as a solid driveshaft and would wear out again soon anyway).

Trouble shooting suggestions: Pull the rear driveshaft and drive the truck over 55 in 4X4 to see if the noise goes away. Put the truck up on jacks and run it at 55 and try and determine where the noise is actually coming from (not going to happen with me under there!).

I've pulled and pried on the U Joints and there's no slop and there's no noticeable end play, nor is there any side play or excess gear slop in the driveline componenets. The center support bearing has quite a bit of eliptical play in it and seems to be in need of replacement. The driveline components seem a bit dry so I plan to lube everything up good to see if that helps (as soon as the California monsoon stops). Until then the truck is parked.

Anyone have any more suggestions or possible causes for this noise?

Thanks,

Toyo Master

Toyo_Master

Nobody has any suggestions?? Do ya'll think the previous suggestions will determine my problem? Man, I hate to spend the $300 for a new drive shaft if it isn't needed right now and then spend more $ to actually fix the probem.

Thanks

hillbilly

One (or more) of your wheel bearings may be going bad?!? Check each wheel for slop and ease of rotation. I've seen some that squeal only under load, others only when not loaded, and some that make noise under any condition.

Just a thought...

95_4X4Runner

Have you resolved this problem yet?

I think mine is doing the same thing. I just got done towing a Harley for a freind at 80 MPH for about 20 miles, and I noticed a new noise coming from the drivetrain when we were putting through his neighborhood. When I got home, I had the wife rev it, and when the engine is decelerating around 1800-2000 rpms, it would make a noise like a chain is slapping the case. Has anyone ever had problems with the chain in the transfer case? Does the chain always spin, or only on 4WD?

Toyo_Master

My intention was to change to a one piece drive shaft because I suspected the noise was the center support bearing. I also had a vibration about 55 MPH like an unbalanced tire and about 2" of play all around on the CSB. Well, I didn't want to spend the $269 just yet for the one piece so I went on the web looking for the best price for a CSB and instead of the going price of $160 to $230 I found one for $80. Looks to be good quality too. Had it pressed on today and replaced the front and rear u joints also (they were perfect (140K) when I took them apart but I damaged both in the process, my luck). Since the Cardan joint felt really tight and smooth I didn't touch it. I'm going to put it all back together tomorrow so we'll see. I'm also going to lower the CSB as much as I can space it (about 3/4" but every bit helps I guess) to help reduce the rear drive shaft angle.

Man, my original CSB was toast. Comments from the guy who pressed it on were something like, "and you say you were driving around with that thing on there"? "It's no surprise it was making noise and vibrating". Then he showed it to me and wiggled it around and little pieces started falling on the floor. I guess it was worn out.

Toyo Master

Toyo_Master

Noises gone with the installation of a new Center Support bearing, U Joints and spacing the bearing down about 1". Got the CSB for $80. Total investment $110 compared to $269 for a single piece drive line. Better for me now but the one piece is next if I have another failure. It took 140K for it to fail the first time (probably 30K after the lift which the previous owner said he put on about that long ago) so I have a while to save up.

Toyo Master