Mystery noise when off gas above 55mph in 4wd

[Dane Hauler]

Here's the situation:
2011 SR5 4Runner with ~90k miles and a 3in lift (about 10k ago). I get this noise in 4wd only, when I'm above 55ish mph, and only when I let off the gas. Then it sounds like a jake brake. Same speeds in 2wd, I don't hear it. Took it to a local mechanic shop, and they *think* it's the rear diff pinion bearing or maybe the drive shaft itself (put it up on rack, dropped the rear shaft and couldn't get the sound to recreate, and say they can get it to recreate in 2wd also). Then the estimate came and I choked ($1700). Anyone had similar issues or thoughts on this?

 

[hikenbike]

Should you be traveling over 55 in 4wd?


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[Dane Hauler]

Winter driving on mountain highways.

 

[Dane Hauler]

I think I fixed it!

When I installed my lift kit, I didn't do a very good job positioning my rear diff so the input axle was parallel to the transfer-case output axle. I had it set up closer to what one would use for a CV axle. Now that they are within a degree of each other, the noise is gone.

I figure that when I was 4WD, the front wheel and rear wheels were both driving the transfer case where the front driveshaft was positioned correctly, and the rear wasn't. The delta between these two was creating a rotational "pulsing" (not good) which was more evident under engine braking (probably there under HEAVY acceleration too, but never tried that).

Anyway, if anyone else runs into this, get an bubble level app on your phone, and check the angles at the flange yokes on either end of your drive shaft(s). Might help you find the culprit.

 

[Lemonblazer]

slow down.

Glad you fixed it but you may eventually do some damage as considering owner manual says your not supposed to drive past 50mph in 4WD MODE.

This is a part-time 4WD after all. Sounds like you need a full-time system. Something to consider for next time. :tea: