I have a 87' 22RE automatic 4Runner.
I get a slight vibration I mainly feel in the gas pedal itself. This happens only going on a down slope, meaning not on flat or uphill, it can be just a few degrees of decline or more. To make it happen I need to just feather the gas pedal a tiny bit accelerating or decelerating, but happens on both and can just keep it vibrating if I stay with it just feathered. Soon as I give it more gas or let off the pedal it stops. Not really sure where to look for it as I mainly feel it in the pedal, I can hear it but it sounds like it is everywhere.
I have changed out my motor and transmission mounts and all my U-Joints as well looking for this, nothing stopped it.
I have had this problem ever sense I bought the 4Runner about 3 years ago and been slowly fixing things but this one has stumped my big time for a long while so I figured I would just ask to see.
Any help on where to search for it more would be awesome, thanks.

 

Forgot to mention it is only when going 40+ MPH and at 70 MPH it vibrates and sounds the same as it does at 40 MPH.

 

You feel it mainly in the gas pedal because your foot is mainly on the gas pedal while driving. When this happens, how does the brake pedal feel? How does the floor/firewall feel? The shifter?
I don't know if you can force an auto 1987... When going down a slope at low speed, say 40MPH, try lower gear, say 3rd?

 

I could feel it some on the dash and the firewall, not so much on the shifter. If I took it out of overdrive it did not happen as well in 2nd.

 

Are your "stiffening brackets" in place? (These are attached to the under side of the engine block where it meets the transmission, they stabilize the lower section of the bell housing) Possible a red herring, but something to look for they get "misplaced" often.

Does it have a lift? Does it have original factory springs?
Pinion and output flange angle.. These need to match, be parallel, or they induce shaft speed variations. If it's lifted and not angle corrected, or the springs are not holding it in place it will have improper angles.

Look in the rear view mirror, can you see the image blur (double image) when the vibration occurs. If you can pinpoint a light it is easier to visually quantify the vibration, do it at night in a safe location or have a rider to it. A light that turns into a vertical line is probably tire balance. A light that turns into a circle or big "blob" is the drive line.

Wouldn't hurt to check and change your differential oil. I don't know off hand the physical/visual way to differentiate this one. Audibly its a grindy howling with "general" vibration.

 

The brackets are in place.
I do not have any lift is all stock.
I tried to look in the mirror it is raining here in Washington and rains for 9 months out of the year really. was hard to see but seemed to go all over just slightly, but our roads are crap here too so... I tried to feel the mirror bracket and didn't really feel any vibration at all there.
As for diff oil, have to get to that in a bit, wife has me all booked up this weekend on honey doo's.

 

This kind of suggests a wheel balance weight having been tossed. But the down hill only is kinda odd for that.

 

I thought about this last year when I got my new tires, but right after coming home it happened on the first downhill again.
It makes me think it might have something to do with the the flex plate to the pinion because it only happens when no load is on the drive train and I give it a feather to the accelerator to give it just enough to spin more but not put a load on it. Just like bad U-joints, cracked flex plate, worn yoke, pinion bearing or loose pinion nut would I assume. I have in the past had a bad new u-joint but just one in the many I have changed. but after I changed these it stayed the same.

 

So you've checked everything in/around the front and rear diffs?

 

Yeah, even dropped the front driveline to make sure on the front.

 

I believe dropping the driveshaft only eliminates the shaft and possibly the diff. There is still mass rotating at the front like the brake rotors.

 

I agree on the removal only for the shaft, but as it need no load and with the accelerator slightly feathered it vibrates. I can see no reason it would vibrate on the front end, I have however checked it also.

 

It has to be some rotating mass and/or loose component. You've checked and eliminated the wheels, diffs, u-joints, front drive shaft (but not the rear). That leaves the transfer case.

 

Yeah, going to check the transfer case out when I can. My friend owns a driveline business if the TC checks out going to have him check the shaft itself. I have seen some crazy stuff on his wall of shame with drivelines.

 

Let us know what you find.

 

Forgot to let ya all know what happened. The Transfer Case ATF was low, drained it and filled it up, no more vibration. Thanks for the help, it was driving me nuts.

 

Glad you figured it out,