We just had the engine of our 2004 Sonata replaced (long story…), in the end we drove it home and noticed it doesn’t shift as well and my husband has noticed a “thud” sound. Called the mechanic who said, “ya, my test drive guy noticed that too”… and went on to say it’s not their fault, probably the transmission is going… Is this possible?
Anything is possible.
If the tranny is ‘harsh’ shifting, the fault MAY be a dirty or bad shift solenoid or pressure solenoid.
If you had to replace the engine on a 5 year old vehicle, that certainly makes me wonder about the type of maintenance that this car has had over that 5 year period.
Automatic transmissions need to have their fluid (and filter) changed every 30k or 3 years (whichever comes first), so this definitely makes me wonder when (if ever) the transmission fluid was changed. At this point, the fluid in that transmission should have been changed at least once, based on elapsed time, and if your driving pattern is typical of most Americans, it probably should have been changed at least twice already.
If your transmission fluid has not been changed according to “the book”, then it is very possible–bordering on likely–that your transmission is ready to join the engine in automotive heaven.
Hint: Proper maintenance is invariably cheaper than the repairs that result from lack of maintenance.
We are generally very good about maintenance; That said, we missed the timing belt at 60K and that was the problem with the engine. Otherwise, any time fluids etc have needed to be changed, I believe we have done it (I would have to check our records to be sure). Oil changes every 3-4000, any suggested maintenance at those appointments we follow-up on.
(as a side note, the steering rack was replaced because a known little leak was getting bigger, decided to fix it before it got worse, but in the meantime we had spoken with a mechanic who owns a Sonata who said his had the same problem and adding fluid regularly was his plan for his car…)
It appears the mechanic did not have a chance to test drive the car before they did the engine work (engine was destroyed). If he could have drove it before he did the engine work he probably would have noted the shift problem.
When someone “misses” something as vital as the replacement of the timing belt, that reinforces my thoughts about how well a vehicle has been maintained. I am glad that you are “generally very good about maintenance”, but you have still not told us about whether the transmission fluid was changed previously, and if so, when it was changed.
In the absence of any hard data, I have to conclude that the mechanic is probably correct about the transmission being on its way out, and I suspect that this was the result of a lack of maintenance.
Could be when they replaced the engine they left something loose where the engine connects to the transmission, flex plate etc. Or a motor mount/tranny mount issue.
The warranty on a 2004 Sonata is 5 year 60,000 miles on the car generally, 10 years, 100,000 miles on the drive train. Why not throw this problem at Hyundai?
Warranty coverage will depend on whether the OP can substantiate proper maintenance. Based on his/her lack of response to my request for substantive information regarding maintenance, it is likely that proper maintenance (such as the 30k and 60k fluid changes) cannot be proven with documentation.
If that is the case, goodbye warranty coverage!
Yes, the fluid was changed. Today they took the car in - they found that a number of bolts were loose. problem resolved immediately. Don’t always Assume.
It was our mistake. We accept that responsibility re: the engine. Also, since we purchased the car used, (bought it in 2004 with 7000 miles on it), only the 5 yr/60,000 mile warranty applies, and we are beyond that. Thank you for the suggestion though!
YOU GOT IT! Thank you!!!
Again, I had to look in my files for the records - I didn’t want to mislead anyone here. The proper fluids have been addressed!!!
Thanks to many of you for your comments! We took the car in today, the mechanic identified the problem as soon as it was driven into the shop - a number of bolts had not been properly tightened when the engine was replaced. We brought the car home, all sounds, “thuds” etc are resolved. 
To those who question the care of our car, we had fluids replaced at 37,000 and 67,000 miles by VIP and Valvoline, respectively. We have looked at the manual, and sad to say, the timing belt was the one mistake we made, all other proper maintenance has been completed.
Is this your normal mechanic? If so, I’m a little leery about his other work.
We moved recently and have not found a regular mechanic yet; The first place we went (for snow tires) scheduled our appointment, then didn’t order the tires, when they came in they threw away our all-weather tires before asking us. The second place put new all-season tires on, and got the car when the engine died, but their prices were substantially higher, and this third place had some good local reviews… In the end they did fix the problem and were very professional in their interactions with us, but we, too, wonder how one neglects to tighten the bolts?
I’m very glad to hear that the problem has apparently been resolved.
I am also glad to hear that you have been good about most of the maintenance.
I prefer to not assume things, but when details are not provided, we must make certain assumptions in order to reach conclusions. Sometimes those assumptions are wrong.
Try to remember that including as much detail as possible when requesting help is beneficial to both the person requesting help and those who are attempting to provide that help. Without details, suggestions will be less helpful.