92 Accord LX 4 Door, with hard hitting automatic tranny. It shift into 1st and 2nd very smoothly, and when it shifts into 3rd at 45 miles perhour, it go clunk, bump into gear. I have replaced rear tranny mount, front dogbone mount, and changed tranny oil. Any thoughts would be much appreciated.

 

Probably the transmission starting to fail. I would drive it until it fails completely and then swap in a boneyard trans. Also if you change the fluid and neglect to use Honda ATF, it can cause shift harshness, but that would happen in all the gears most likely. Good luck.

 

I would add one can of lube guard for import cars.

 

The local autoparts, (Advance Auto/ Discount Auto) tell me that I should use Dextron III, the bottle also says for honda's. Is this not the right Oil ?

 

Honda ATF is different in it's formulation than Dexron III. Dex will not HARM your trans in any manner, but it can produce harsher shifts, such as you have complained of. IDK exactly what is in Honda ATF, but it's just different, and the dealer is the only place to buy it, which is why the parts store says dex 3.... they don't want to lose you to the dealer.

 

no no and no. anything other than honda fluid is bad. detron iii is thicker and not made for honda cars

 

After trying to locate honda atf on a saturday, to no avail. I thought flushing the system with Dex III might help. Then found Lubegurd at local Discount Auto Parts store. I have to say it is shifting in first and second extremely smooth, third still has a little bump, and 4th is also smooth. Now its tolerable to drive.

Again thanks for the advise.

 

Have you tried going to your local Honda dealership? Most Honda dealerships have their own products/retailing section where you can purchase Honda ATF.