I've got a 2000 Honda Accord LX 2.3 with an automatic transmission. Every now and then, but particularly when its cold, I get a slight knock or thump when coming to a stop. It sounds like its coming from either the transmission or possibly the vacuum operated engine mount. I first noticed it over three years ago on a cold morning after switching from Z-1 to DW-1 Honda transmission fluid. Last Nov., I switched to Maxlife and it went away for two months, but now its back.

 

You can inspect motor mounts by setting ebrake and foot brake w/ trusted assistant, and blipping throttle to 1500-2000 rpm w/ car in D and R. Watch motor mounts (front, rear, sides) for evidence of excess movement or damage.

I've had brakes grab as car comes to a stop producing a thump. It was rear drum brakes on a Suburban.

good luck

 

Thank you Texas Honda. Also, if I very slightly hold the throttle (gas pedal) to keep the rmps up just a little above idle, there will be no knock or clunk sound.

 

On my wifes 99 accord it was a jerk as you come to a stop at a redlight.
It didn't do it every time,,but eventually it got worse and would do it all the time. This took a few years to get to this condition,,,,and she is rough on her car,,,like most women,,LOL. Judging from the details in your first post,,I would wager it is transmission related,,,it sounds just like our experience.
Her car eventually got to the point of slipping in gear,,from the low shift point.
It turned out that the clutches were bad in the first gear set. They seem to get hot and stick to the drum from excess clearance. There is a wavy spring in the first gear set,,I assume to act as a damper,,and as the spring gets old,,it collapses and causes too much clearance in the clutch set,,which creates heat and the clutches stick.
I had never done an auto tranny before ,,but I had no choice,,,we were broke. I bought a kit off of Ebay for about 150 bucks,,,,and got some drawings and info off the net. As it turned out,,the tranny worked great when I was done,,,the Honda BAXA transmission is an awesome design,,,I was really impressed with quality of the parts inside. While I was at it,,,I also replaced both axles for about 150 bucks too,,,,,so for less than 300 bucks,,I rebuilt her trans,,and replaced both drive axles. That was several years ago,,and about 50,000 hard miles since,,,LOL.
It is still working great to this day !


Tommy

 

Thanks for the feedback, Tommy. You must be quite the mechanical type to take on that project. It's great to only spend $300 for all that!

 

Thanks for the compliment,,,,but to be honest,,,I did it because I had no other choice. Yes ,,I do have a lot of car building knowledge,,but it is all old school hot rod stuff. Auto transmissions in an Asian design can be more than intimidating.
This experience did give me a lot of confidence though. I found out that the auto dealers give a lot of false info about the service requirements of their product.
When we bought our Accord new,,,,they told us that we really needed to keep the trans serviced regularly by having a complete flush done about every 90,000 miles. This cost about 180 dollars,,,,also,,they told us that there was no filter to service,,,so it was just a fluid change only. We were also told that there was no way to rebuild these transmissions,,,so we had better go the extra mile and keep it serviced well,,,also,that you can only use Honda fluid in it.
After having the second service,,,,,the trans had already started a slight clunk when stopping,,which eventually got worse as the miles went by.
After about 200,000 miles or so,,,,the tranny started slipping and I had no choice but to fix it. So I did some homework and got my plans in order and went to work.
Like I said,,,inside ,,the Honda trans is a work of art. The only thing wrong with it was the low gear set of clutches. The other gear clutch packs still looked like new,,they even mic 'd out almost the same thickness as the new ones I put in. (There is a filter inside,,but it can only be serviced by taking the transmission apart at rebuild.)
So,,,,,my discovery was this. The Honda car line is a great piece,,,great engine,,,excellent transmission,,,,,the only thing that caused the trans failure was the wavy snap ring. I used Valvoline Import Full Synthetic multi vehicle fluid from O'reillys,,,,,yes it works great. We have over 50,000 miles on it since the rebuild and it has no shift problems.
Also,,,there is a drain plug toward the bottom of the case,,,,you can drain your own fluid and replace it with 4 quarts you can buy at your local store and save some good money,,,,,just an idea there,,,,wink wink,,,LOL.
I hope I haven't offended some here,,but I am very skeptical about the info that some dealers give to the customers.
So,,don't believe everything salesman tell you,,some time it is just to drum up business and to get your money.
Honda makes a great product,,,we are gonna buy one again soon.


Tommy

 

Update: The problem seems to have been eliminated. Over the course of many years, I would manually downshift into 3rd and 2nd gear to better control the sometimes harsh BAXA Honda transmission; I would slightly blip the throttle before downshifting, which made for a smoother experience; it also allowed me to control unnecessary up and downshifts in traffic. Anyone who has driven a 9-speed Eaton transmission would understand this concept. So, I decided to stop doing this, and the clunk sound seems to have been eliminated. Apparently, this technique was altering something in the transmission, perhaps the torque converter? I don't have enough knowledge of the internal operation to know.

 

Update: Poured some TransTune by Seafoam in to the Trans. No more clunk. Perhaps it cleaned something hanging up.