Transmission thunk and grind?

Ok...so I barely have 1000 miles on my new 2017 Tacoma and something strange and startling happened to me last night. I was coming to a stop at a light on a slight uphill gradient when suddenly I felt a thunk and lurch from my own vehicle. I honestly thought I'd been tapped from behind. Since nobody was back there I then check to see if somehow I'd stalled (although how that would happen on my auto trans is beyond me). THEN, I took my foot off the brake and started rolling backwards while still in drive. wtf? Ok. So I shifted briefly into neutral then back into drive and gave it gas again. I heard and felt this unnerving grind, then the engine/trans engaged and I was able to drive normally from the stoplight.

I have zero idea what this is about. I was in 2WD on normal, dry pavement. I've been reading up on the transmission TSB on the forums, but have seen nothing mentioned with these characteristics.

Any ideas?

 

The thunking I've felt on occassion. Seems like most logical explanation is the driveshaft's slip yoke sticking

 

So you was rolling backwards and put the transmission into drive?

 

You can roll backward while in drive if the slope is sufficient. The clunk sounds extreme-something to watch out for, have checked out if you can find a procedure that reproduces it. Without being able to reproduce it, you'll just get frustrated at the dealer.

 

Feeling like you're getting tapped from behind when you come to a stop sounds like axle wrap to me, there's a ton of info on it if you search for it up top. Common problem with 1st and 2nd gen Tacomas. The grinding you heard was likely from shifting into drive while you were still rolling backward (if I'm reading that right).

How steep was the hill? Been awhile since I've driven an auto trans but isn't it normal to roll backwards some if you're in drive on a steep enough hill?

 

Thanks for all the quick replies....gotta love this community. Herniator....no, i was not rolling when i put it back into drive. Once i felt the rolling i hit the brake to stop, and then shifted from D to N and back again.

eon_blue: the hill wasn't very steep...normal city hills and curves (not like SF, but not Kansas either). Is axle wrap something 3rd Gen's have had problems with?

 

No fun, maybe, but totally normal. Force of gravity has to exceed applied force (force of engine idle), then Newton tells us vehicle will roll downhill.

 

honestly I haven't read much about it with the 3rd gens but then again, I don't really look for it since I don't own one. But it was common throughout the last 2 generations so I wouldn't be surprised if it carried over again.

 

Low transmission fluid

 

The intermittent thunk and resulting "Did I just get rear-ended?" does seem to be a characteristic of these trucks. I don't even check my mirrors anymore, you'll get used to it.

The other issue of rolling backwards while in drive and grinding sound sounds like a different problem that should be checked out (if you can replicate it!!)

 

I've backed up down a slight slope, went from R to D and heard a clunk/grind with the VSC light flashing, I assume it was some sort of hill start assist, but do these trucks even have that?

 

The rear ended feeling is something I can't explain, but it happens randomly. I have read about this happening to 2nd gens as well. It is definitely not as strong as being rear ended, but a little bump can be felt on occasion.

The click, pop, thump, grind(?) noise is a protective feature so your truck tries to stop if it rolls backwards while in drive. It is the brakes/solenoids actuating, kinda like when you run the crawl control. I have had this happen off road several times, and rarely on a few on-road hills when my gas input (foot) is weak.

 

@BGXtobe and I seem to be having the same issue especially when cold

 

https://www.tacomaworld.com/threads/bump-after-stop.456356/