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Thunk on take off


adamzan
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As the title states I'm having thunk noise when I take off, or when I let off the brakes after coming to a stop, it feels like something is loose. At first I figured, bad u joints. So I grabbed the drive shaft and found no play (I also checked them when I had the shaft off for the tranny swap). Then I checked the trailing arms, I could move them a tad, but I was really trying hard, but they didn't seem that loose. I also rocked the truck back and forth while it was in park and the pinion angle changes slightly (and I mean its hardly noticeable).

 

I am also getting a vibration in the rear end around 50mph. I thought it was the transmission, but then after the xterra swap it was still there.

 

Strange thing is, when it was really cold, it was perfectly fine, which made me forget about it for most of the winter...

 

Anyone ever had this before?

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Transmission mount is good to go? Didn't happen to break in the winter? Other than that sounds like a bushing somewhere. Rear arms, panhard rod. Especially if you say you can rock the truck and see the pinion angle change. 2* is a pretty big change that will be amplified inside the cabin.

 

Sent from my Moto X

 

 

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The tranny mount looks good, no cracks and it doesn't move when I push up on the trans...I did use the one that came with the xterra. I thought maybe my old one was bad so I used the one that came with the new tranny. It is the same as the old pathy one.

 

I will have a second look at the rear arms. Maybe just change the bushings anyways, they are 20 years old.

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I'm guessing the thunk is something you feel as much as you hear? From the rear area?

 

Check the lash in the rear diff (drive shaft rotation before gear/axle engagement), I've noticed our R50 has the same thing occasionally...

 

B

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if it was less in winter than I feel it has to be something in oil (which is noticeably thicker when cold) ... So I would check the end play of the pinion bearing ... or input or output shaft bearing of the transfer case...

 

Good luck..

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I'm guessing the thunk is something you feel as much as you hear? From the rear area?

 

Check the lash in the rear diff (drive shaft rotation before gear/axle engagement), I've noticed our R50 has the same thing occasionally...

 

B

I will do that. I assume there is some kind of spec in the fsm. Hopefully I don't have to take all that apart....

 

You might try brake standing it a tad to see if you can get it to replicate at a stop. Have someone under there watching and listening.

I tried that today and it worked! Just gotta get someone to watch it now...

 

Does this sound happen all the time you accellerate from a stop, or only after you have backed up in reverse, put it into drive, then go forward?

Yes it happens probably 90% of the time. Doesn't seem to do it when I put it in reverse though.

 

if it was less in winter than I feel it has to be something in oil (which is noticeably thicker when cold) ... So I would check the end play of the pinion bearing ... or input or output shaft bearing of the transfer case...

 

Good luck..

I'll do that too, I don't think the t-case is an issue as it started in the fall, then my tranny died. I replaced the trans and t-case at the same time so the case is new and it still does it.

 

I'll post up what I find.

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X2 on checking the control arm bushings (last time I had a similar noise it was a tennis ball rolling around in the back of my truck). I have seen rear bushings on similar setups (not on wd21s as their ain't many left around here) cause thinks and vibrations (have to figure if that bushing is moving, te rear end has some extra movement as well).

 

 

Solve all your problems, cut the converter off! :chairfall:

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  • 3 months later...

Bringing this back as I believe I figured it out. I went to change my diff fluid a few weeks ago and the fluid that came out was all nasty and grey, which leads me to believe water got in at some point. I changed it out with some 80w90 and a tube of LSD additive. All seems well at the moment.

 

FWIW the fluid that was in there was barely a year old.

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If there was water in the diff, I'd wait about a week and change it again. You will want to make sure your breather is in tact and not letting any water in the diff. H2O is a crappy lubricant.

 

 

Sent from my iPhone using Tapatalk

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Is your breather hose in place/intact?

 

B

!st time I had to leave it bottomed out in a mud hole, I checked this very thing. I know some trucks only have a small tube but my pathy had a long one, so it was safe. I was worried being in the water overnight I was sure water had got in. But all was good.

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