Shift between 3rd and 4th (Overdrive) rough in automatic All-trac

Can anyone provide some guidance on why our 93 Previa (All-trac, automatic transmission, non-supercharged) will often have a slight "shudder" or "thud" when it shifts from 3rd into 4th gear (aka overdrive)? All the other shifting is smooth and seems completely normal...it's just that thud from 3rd to 4th (aka overdrive). And it's not every single shift from 3rd to 4th that you can hear/feel the thud...it's only sometimes that it happens, but enough to be annoying!

Overdrive is turned on, of course, and there is NO flashing of the O/D light either to indicate an issue with O/D. In addition, there are no codes or CEL's at all. We have about 155,000 miles on our Previa and it has done this since we bought it used with 118,000 miles on it.

I believe we have the A46DF transmission because we have a 1993 Previa with AWD (non-supercharged).

My guess is that maybe the solenoid for the shift point between 3rd/4th is slowly dying? Anyone else have an idea?

Thanks!!

Timsrv, I saw that you had much the same issue back in 2010 (see your post: http://www.toyotavantech.com/forum/s...full=1#post954 )

Did you ever figure out what was causing the issue with the "vibration" going into/out of overdrive in your AWD Previa?

After troubleshooting/investigation I came to the conclusion it was most likely the torque converter. Considering the PITA in replacing that, I decided to live with it. I still have that Previa, and it still does it. It's not severe (most people would not notice). If it ever got severe, I'd probably fix it, but it's only for a second while shifting into OD. Whenever I think about pulling the transmission it suddenly becomes something that doesn't bug me anymore. :wnk:

I had a similar problem with my '93. When it shifted either in or out of overdrive, it felt like I was passing over a "rumble strip". Eventually I realized that there were no rumble strips around and that it occurred when the OD clutch pack was engaging/disengaging.
Draining and refilling the trans (you can only get about three quarts out) solved my problem immediately. I concluded that the fluid had lost its magical properties.
I used Valvoline "Max-life", I think.

Thanks y'all! I will be giving the ATF a shot for sure. I read through another post (see: http://www.toyotavantech.com/forum/s...smission+fluid ) and it looks like a very similar issue. "Rumble strips" is a good description of the shudder you can feel when going into/out of O/D in our Previa. The last time the automatic transmission fluid was changed was by the Toyota dealer back in early 2014; since then we've probably put 30k miles or more on our Previa.

I will give the Valvoline MaxLife ATF a shot once I get around to changing it. Sounds like it will take several "changes" to get the old stuff out as I do not intend on dropping the AT pan.

Thanks again!!

I've changed my ATF since the issue, but it made no difference. I run Amsoil synthetic ATF and that's supposed to be good stuff (I've run it for years in all my automatic vehciles). It's hard for me to imagine a fluid change eliminating a vibration, but I've seen stranger things. Good luck with replacing the ATF and by all means please post your results. Tim

This is specific to my automatic A45de trans. with 95,000km

I had all the shifting issues and each spill and fill (5) fixed one issue and another shifted in...
Intermittent problems are so frustrating!:pissed:
No local shops would touch it after a test drive, just rebuild it $$$$
I did the last 2 changes with castrol transmax extended life as the regular didn't help as much. The ingredients are similar to Lucas trans fix, which I didn't want to resort to using. and noticed improvement, but the problem became more specific (valve body is my diagnosis)
I found a killer deal on the Castrol at Walmart and bought 6 gallons.
I had it flushed on a machine and the old fluid looked good.
On the drive home there was no change. :wall:
The Lucas recommendation is to wait for 150 miles for results, and I just happened to go 160mi that weekend.
I have now driven it 2 weekends and have not had a single shifting issue.:dance2:
Off road test next weekend.