I recently bought a used 2011 Mazda6 4 cylinder. I bought it from a non-Mazda dealer and it had just under 39k miles on it. Within approximately two months (1200-1500 miles) my transmission began behaving abnormally.

When I decelerated without applying the break I could feel the transmission slip, or what I believed was slipping, specifically while downshifting from gears 4 to 3, 3 to 2, and 2 to 1. I am not positive if it was slipping but the whole car would shimmy/lurch forward and back when downshifting.

I took it to my local Mazda dealership and they could not reproduce the problem but did find that my fluid was dirty at 43k miles. They recommended a flush I passed wanting another opinion. I took it to several places but no one would touch it due to the fact that it was a sealed transmission etc. etc. A few places questioned the necessity of the flush with so few miles. One place even questioned the flush at all.

I took it to another Mazda dealership who drained my fluid and refilled it. They said they test drove it and said that it worked good. On the drive home the slipping, or whatever it was, was much improved but I could still feel it. Less than three days later the transmission is back to it's normal problems.

Does anyone have any ideas/suggestions as to what the problem is and what I should do. I've already wasted well over a dozen hours at various mechanics shops, not to mention money, trying to figure out/solve this problem. Any advice would be greatly appreciated! Thank you!

 

I'm assumming this is an automatic.
40,000 miles on a car is a lot especially if driven mostly in city. Basically overdue for fluid. The times they are a changing! We have hotter engines!
With an automatic, you must consider an extra external tranny cooler. After my transmission went @ 20,000 miles, this is what i did.
Also consider new transmission valve body.
READ: Flush it or Forget it |*MotorWeek

Tranny temps go up in stop and go traffic.
Check out this chart:

 

Thank you for your advice! My concern is that the majority of mechanics I have spoken to, including one from a dealership have told me that if I do a flush on my transmission the probability is high that it will damage it due to the sensitive nature of it.

I just spoke with another dealership how says they do a fluid exchange using only 2 psi in order not to damage the transmission. So...? Just curious if you or anyone know if my car's symptoms are due to dirty fluid or something more serious. I don't want to spend more time and money accomplishing nothing.
Thanks!!!

 

And yes it is an automatic. Sorry.

 

Generally, when a tranny has real dirty fluid and lots of miles, it's better to do a few fluid changes so passages won't get clogged. A few drain and fills are in order as each time you are only changing about 1/2 of fluid as lots of fluid still in torque converter.
With your mileage and previous issues, the flush is questionable and there is not a black and white answer. I would do 2 more drain and fills first. as well as external tranny cooler!

 

Thank you!!!