Shudder at shifting around 45-50mph

[uncletwodogs]

I've got an 03' 4x4, V6 automatic. A few months ago I noticed a shudder/vibration when the transmission is shifting from (I assume) 4th or 5th gear. The AT level is ok on the dipstick and I've noticed no leakage. Also, I replaced the U-joints which didn't fix the problem.

I found info in the forums that suggested it may be cross contamination of coolant and AT fluid. My coolant in the reservoir looks fine. I also found where some folks will just drain the fluid at the pan twice, instead of dropping the pan and replacing the filter and gasket.

Can I get some input or an update on this? For those who drained and replaced the fluid, did it stop the shifting issues?

[muadeeb]

A few corrections:
1st Gens have a 4 spd A/T.
The coolant/ATF mixing problem (SMOD) is more of a 2nd gen problem. I'm not saying it'll never happen with a 1st, but is very, very, VERY unlikely based on the number of vehicles on the road with the problem.

You haven't mentioned if the fluid has been changed or not. A 2003 will likely be approaching 150K, and that long on factory fluid is too long. Fluid changing would be very high on my list at this point. It's a 9 qt system, and approx half will come out with each drain, but be prepared the first time with plenty -- refill with new the same volume that comes out. Drain and fill about a week apart for 4 or 5 times to make certain all the old is out.

Changing the filter is optional as it's more of a screen mesh than a foam or paper filter. Dropping the pan is the only way to clean the magnet, however.

[uncletwodogs]

Thanks for clearing that up for me and I plan to change the fluid ASAP.

[emmdock]

The vibration is the torque converter locking up while surrounded by fluid that's lost its friction modifiers. It happens at 43-47mph under light load once the transmission fluid is warm. It feels like a 5th gear, but it's not really a gear. I had the same thing - change the fluid twice because you only get like half out each time, and you'll be good. I did it 3 times for good measure. It was still cheaper than having a shop do it.

[robbtemp]

I have a 2001 with around 120K on it and just noticed this exact same problem. She doesn't get driven much anymore, maybe 2-4K a year. I'll start with the fluid changes as it's the original fluid. Thanks for the advice from the posters and to the OP for a good description of the problem!!

I'll report back results.