Slight buckle when reengaging accelerator at highway speeds

Have a 2010 SR5 that thumps/buckles slightly when I’m coasting at highway speeds and then reengage the accelerator. Typically starts happening at 45 mph or so. Any ideas on what’s happening?

 

Could be so many things. When was the last time the driveline was greased/serviced? How many miles on the truck? What is the service history? See, without a lot more information, it's all guesses. Maybe even a video would be helpful.

 

And by 'buckles' do you mean 'bucks'?

 

230k miles. Just had driveline lubed. Still doing it. Trans last drain and filled at 190k. Shifts perfectly. Maintained by the book.

Bucks, buckles, slight thump, whichever adjective you prefer.

 

Driveline, has it been lubed regularly about every 15k miles? If it was neglected for an extended period, and bearings got dry/worn, lubing now won’t recover that. It’ll still bind.

 

I know this may be difficult to answer, but does it feel more in the transmission or the drive train of your runner?
Knee jerk wondering if may be describing a converter issue.

 

Wondering the same. Maybe the use of a obd-2 app that show when the TC lockup happens. If the thunk happens when the TC locks or unlocks, that would be my suspect.

 

Very helpful thoughts. Didn’t think these were related so I didn’t include this in the original post, but I also get a thump/clunk when I do a hard stop. At times, the clunk happens a second or two after I’m completely stopped. Does that point to the TC?

 

Motor mounts?

 

@RkyMtnMan that makes a lot of sense too. Will ask a technician to check that out as well

 

Can you replicate this clunk easily when stopping hard? If so, next time you go to stop hard-where it would normally clunk, throw it in neutral a few seconds prior. See if it still clunks.

Did you grease the slip yoke yourself? Did you over grease it?

 

@Rocko9999 great idea to rule out the trans! The dealership did the lube, which also makes me wonder if they actually did it.

 

I'd crawl under there and see if you see fresh grease at the zerks.

 

Check the transmission mount(s) near the driveshaft. If it's broken, it will separate when you slow down or stop. When the energy dissipates, it goes back together, usually with a clunk. Not unusual for them to fail.

 

Thanks @Toolguy73! Very helpful lead.
Will look into that as well.

 

I have gotten a quiet thunk when stopping that is more felt than heard. Kinda felt like somebody rear ended me very lightly (i actually looked in my rearview mirror lol). It was a sticky slip yoke. Sometimes they need a ton of pumps on the grease gun before it gets into the length of the splines. Even if the dealer greased the zerks regularly, it might just be only a few pumps. That’s what I did with mine, a few pumps every oil change, but I got the thunk.

The danger here is that if you over-grease the slip yoke, it can effectively hydro-lock it, which blows out an end cap on the slipyoke that contains the grease. I pumped mine full till the yoke shaft extended very slightly, then I removed the zerk fitting, bounced on the rear bumper to compress the yoke, this forces excess out, then I cleaned up, drove it down bumps in my driveway, cleaned up, and put the zerk fitting back in. It got rid of the thunk, but it does seem to reappear after 15k miles or so. That grease has to travel a long way down the shaft, which might be why some of the slip yokes are dry.

Also, Good idea on checking the transmission mount as well.

 

Thanks @McSpazatron! Appreciate the context. Helps to have this information for my conversation with the technician.