The automatic transmission gave out on my 1999 Accord earlier this year on a trip from VA to FL and I had the tranny replaced with a reman automatic at a Honda dealership in Brunswick, GA. I picked the car up after hours, (I had cranked it and let it warm up a bit as I was transferring my stuff from the rental) and drove several hours north before stopping at a motel for the night. In the morning I fired up the Accord and immediately put it in reverse, which it responded to with a definite "thunk" as reverse engaged. Hard enough to make the car buck a little bit. I put it in drive when I had backed up enough and it responded with another thunk. I drove a few miles to the interstate and stopped at a station to fill up before getting on with my trip. After fueling I started the car and put it into first and the transition was as smooth as butter, with no discernible shift at all. By this time the car had warmed up to operating temperature, although the outside temperature was in the 40's.

I drove it home and it continued the same pattern for the next few days so I decided to garage it until I made my next trip to FL with the intention of having the Brunswick dealership check out the hard shift. I made that trip a few weeks later, and by then the daytime ambient temperature in VA was in the upper 60's and the hard shift had disappeared. I had them check it out anyway, and they could not duplicate the problem over the next few days. The temp in GA at the time was 70's and 80's.

The car made it back to VA with no issues and was fine until the temp once again dropped into the lower 50's. Again, it shifted hard going into gear until the car had warmed up a bit.

I began to suspect that the transmission might have been filled with the incorrect transmission fluid, and that the temp of the fluid might be affecting the viscosity.

I called the Honda dealership and was told that the techs there filled the tranny with fluid themselves prior to installation. I was thinking that maybe the reman shop had filled the tranny with the wrong fluid, but the service tech pulled my records and said that the tranny was filled with 5 qts. of the proper Honda fluid.

So I'm back to square one.

My question for those knowledgeable about transmissions is this: am I on the right track with possible fluid contamination, or is there another possible reason for the tranny to hard shift when it is cold and shift fine once it warms up?

 

I'm no expert, and in fact, hate automatic transmissions. You are likely on the right track with the temperature relationship. Cold fluid is thicker and will therefore achieve a greater pressure under the same pump actions.

What I'm saying is, I doubt there is a serious problem.

Regarding the temperature, you also have to consider that the valve body and the rest of the transmission are also subject to the same thermal dynamics as the fluid. IE, aluminum expands when it heats up. This can be the source of the perceived problem.

Fluid in a valve body has to travel through narrow winding passages and pass through tiny orifices to seat or unseat check *****. Now, if a check ball is tightly fit in its bore, and requires slightly more pressure than when warm to move, then obviously the piston being operated on that circuit will move with slightly more energy than when warmed to operating temperature. This will produce a pronounced "thunk" or "clunk" when operating. Valve body image:


Another possibility is that some swarf from the machining process during the re-manufacture may be present and causing some minor restriction when things are still cold. Once warmed up, the passages are larger and the restriction eased.

As I stated above, I doubt you have a serious issue. Over time, the transmission will "break in" and you'll notice smoother operation sooner in the cycle. If you are really **** about it, just have the filter and fluid replaced and see if there is an above average amount of swarf present in the filter or in the bottom of the pan......sean

 

Thanks for the reply and the advice, I was thinking of having the fluid and filter replaced, but it's good to hear another suggest it.