I have an '86 4runner, automatic trans. I just installed new leaf springs on the back end to give 2" of lift over stock height, wondering if this somehow caused my issue.

Now I get a metallic grating sound coming from behind the driver's seat every time I press or release the gas pedal while driving. The sound does not occur at any other time, but consistently every single time I fully release the gas pedal and then again when I depress it. It makes no difference whether I am abrupt or gentle. The sound is more prominent the faster I am driving, and is not audible unless I'm going at least 20-25.

I tried revving the engine with the car in park and cannot reproduce the issue that way. It only happens when the car is moving. I just checked the transmission oil and it is full and clean. My hope is that it is not a transmission issue...

 

Did you check the u-joints? Any clunking noise when shifting to/from reverse?

 

I'm with Paul, I would strongly suspect ujoints need to be inspected and probably changed.

 

are you thinking that the lift has put more strain on the u-joints and now its somehow rubbing? If it was the u-joint making the sound then wouldn't it be continuous whenever the car was moving? Last, if it turns out that it is the issue, would an OME u-joint be the right thing to replace it with since the suspension is no longer stock?

 

After I lifted my POS s-10 blazer the same thing happened, it was more of a lift but the same symptoms. Accelerate= horrible noise and same with the decel. Ended up having to add another custom ujoint and all was well.

 

Yes, changing the angle will put more stress on u-joints. When is the last time they were greased? It would be more noticeable with abrupt accelerating/decelerating or shifting to/from drive to reverse.

 

I dont hear any sound when shifting to or from drive/reverse. I crawled under and greased both ends of the drive shaft today. No effect. Maybe it's time for them to be replaced altogether.

 

Besides the driveshaft, there should be a zerk fitting on each u-joint that needs to be greased. If it was never done, you may have a small bolt in place of the zerk fitting but I think that was only done from the factory for the ball joints. If any u-joint was replaced, it may be a non-greasable one.

You should have a total of 3 fittings for the rear shaft/u-joints & 4 fittings for the front shaft/u-joints.

 

Sorry to be vague, that's what I meant. I greased the u joints at both ends of the drive shaft as well as the slip yoke. Tonight I am going to change out the diff oil and see what I can see.

 

Pinion bearings will make noise on accel or decel as well.

 

Last weekend I replaced the u joints on the rear drive shaft, which had no effect on the grinding noise. While I had the shaft off I took measurements of the angle of the flange on the differential and the transmission. My next move is to order shims for my leaf springs, but I admit that I'm not really sure what to do with the measurements I took. The drive shaft angle measured 14°, the differential pinion flange measured 82.5°, and the transmission flange measured 87.5°. I want to try leaf spring shims before pulling the trigger on opening up the diff. How do I determine what angle I need to correct the rear axle?

 

OK, you have some angle problems.

You want the differential and pinion flange angles to be within about 1.5 degrees of each other. You've got a difference of 5 degrees, which is for sure going to cause vibrations and nasty stress on the drive line.

Second, your driveshaft angle is 14 deg from horizontal, or 76 degrees from vertical. That puts the angle of the individual u-joints at 11.5 degrees at the transmission, and 6.5 at the pinion. Anything over 7 degrees can be problematic at high speeds.

You may need to rotate your pinion up to point straight at the tcase output (making the rear u-joint angle ~ 0), and replace the front u-joint with a double-cardan joint, which is (essentially) constant velocity.

Here is a good tutorial on drive shaft angle issues from 4crawler.com

Drive Line 101

 

Probably like everyone else said, your joints. could be the pinion angle is wrong now since adding the leaf springs and it's highlighting the worn out u joints.