Very Loud and Noticeable 'Thunk' When Downshifting at Speed

Hi all,

I have been experiencing an issue when downshifting at speed in my 2007 Tacoma (4.0L; automatic). If I'm cruising along the road around 70+ km/h (also happens at highway speeds) and I need to accelerate quickly (i.e. going for a pass, speeding up to catch a green light, etc.), as the vehicle downshifts in conjunction with my depressing the accelerator, I get a noticeably loud thud noise and a somewhat violent jerk of the vehicle in the process. I'm not 100% sure where it's coming from - is this something from the transmission or could this be from axle wrap of some sort? It's worth noting that I have had the rear leaf spring replaced by Toyota recently, and also have had my transmission re-furbished/re-built by Mr. Transmission (tranny chain in Canada) as a result of slipping early last summer. I'm not really sure why this happens, as it doesn't happen when accelerating gently or when decelerating either - only when I need to speed up quickly. I haven't been able to recreate it when accelerating from a standstill either.

Any ideas? Your input would be greatly appreciated!

Cheers,

John

 

Sounds driveline related obviously, so trans, transfer case, drive shaft (center bearing mount, u-joints, etc), rear diff, axle shafts....A good rule of thumb is to revisit anything you recently touched in that department. So trans rebuild and leaf spring mounting.

If it were me, I'd find a way to safely raise the truck and just check for abnormal slop in any of the aforementioned areas. If that doesn't yield anything obvious, run the truck in drive while it's lifted (if you can safely secure it to do so) and try to replicate the jerk while someone watches those components and see what moves. If you can't do that, or can't verify anything visually, the next best bet might be to just revisit the dealership and complain that 'since you replaced the leaf pack, it's been doing this" as that seems like the most recent change before this started happening. They stand a decent chance of diagnosing it, possibly even for free as they touched it most recently.