I don’t know the transmission in this van - but the only plausible thing can think of that would be connected to driving it would be if the TCC lockup is solenoid controlled and the solenoid got sticky and gummy from sitting and then cleaned up a bit from having been driven.
As far is disconnecting it goes - if I had an old beater truck that wasn’t going to spend a lot of time in highway/+45mph steady cruising then I would disconnect it. However, this is exactly the kind of vehicle that will probably do that kind of thing a lot and does have a lot of weight to drag around. So in that case I’d go along with transman and say not to disconnect it. I would, however, install an external transmission cooler if there isn’t one. And if there is one I’d think about a bigger one.
Change the fluid a couple more times and keep rolling.
Cig, I like the sticky solenoid theory. New fluid/filter coming soon…
Personally, I doubt the problem is the TCC.
My Brother put a switch inline to his GM tranny and it made it tolerable.But do run the ATF+4 in it and make sure you are not experiencing some carrier bearing trouble or tires on the verge of disintegrating.Some vehicles have an inherent roughness in them as I discovered with my brandnew Nissan Frontier-99 model the harmonics from certain roads make things seem worse(found out I could figure out which asphalt certain companies laid down) anyway the Nissan has 111K on it now and is still going strong-Kevin
Jesmed, a filter and fluid is definitely a good thing to do. It has been known to cure issues in automatics and I hope thats all it is for yours. Sitting for a year can definitely cause issues. Was it doing this before it sat?? (I dont remember reading this in your posts). If the problem subsided when you tapped the brake pedal above 45mph then the converter clutch is slipping and chattering. Try the fluid and filter change, make sure you clean the pan out real good. Note the debris in the pan and let me know what you find and by all means, please do not disconnect the converter clutch and drive it this way. You will very likely kill it fast. Automatics do not like heat and this will overheat it. Its not a matter of whether it would kill it but WHEN it kills it. I have been aquainted with the shudder fix Tester told you about and I have seen it work in some cases but before going there lets get some fresh fluid and a new filter in there and start from scratch with it. Let me know what happens.
transman
I remember everyone saying the same thing before my 8+ year experiment. I’ve proven it’s not definitive. BTW, I did a number of drain refills initially to get rid of the trashed fluid but never changed it again after that. I lived in a rural area where driving above 50mph most of the time was normal. Towing, plowing… There were long stretches of time where I drove 80 miles round trip to work each day, 75% expressway. But driving halfway across the country, overloaded, in the summer seems contrary to this inevitable destruction theory. And this was a 700R4. Personally, I don’t buy into the prediction…
Thats wonderful that yours held up, some do. The fact of the matter is unplugging will raise the heat in the transmission. We all know that heat damages transmissions. If you want to take the risk, thats on you, go for it. To prove it not definitive, you need to test a heck of a lot more transmissions in a heck of a lot more situations with the converter clutch unplugged. I base my statements on proven facts and 29 years being inside these things. I have nothing to gain by telling people this, in fact if everyone listened on this subject I would be hurting my business. I, personally would never risk this. Especially in an older transmission such as the OP’s.
transman
TWIN TURBO, I am with you.
Transman, in several Dodge vehicles I have experienced, tapping the brake petal does nothing except blink the brake lights. It surprizes me that after 29 years of working on tranmissions, how little you know!!
Applying the brake, not tapping the brake. Some controlers will momentarily disengauge the torque convertor (if the throttle remains open), others will stay disengauged while the brake is applyed. You should see a 200-300 RPM flare if you hold the throttle open while appling the brake on an old Dodge truck.
Transman, previous owner had the van for 2 years and took only 2 roadtrips in it. It probably hadn’t been on the highway in a year when I bought it. Previous owner did not have the bad shudder problem, which from the advice on this forum seems likely to be torque converter clutch slippage.
I drove the van home after purchase and had thebbad shudder problem for the whole trip, about 40 minutes highway driving. But a few days later, when I took it tothe shop for a state inspection, the problem had disappeared.
I will have the fluid and filter changed tomorrow, and since the shudder has disappeared, I don’t expect it to come back, but if it does I have the Dr Tranny’s stuff on hand to try. And I promise not to unplug the clutch…
Thanks for all the expert advice. This forum is a great help with so many knowledgeable people, especially the pros like transman.
jesmed,
Let me know how it reacts to the fluid and filter change. If it is acting better now, it could have been due to a sticky TCC control because from what you have said, the converter clutch is chattering. the clutch material here is very thin and easily damaged. Now, if the control is the problem then the Dr. Tranny wont do much good since it is mainly a friction modifier. You would need to put a cleaning product in there such as seafoam or Berrymans. Thank you for not unplugging the converter clutch, your trans is a little up there in age and needs some TLC to keep it running properly.
transman
Transman, I’m certainly not as experienced as you are but I have a firm grasp on how transmissions work and have rebuilt a number of them. My point is, one not self destructing IS definitive evidence that disconnecting will not always result in failure. When you made the statement that disconnecting WILL result in failure, I felt compelled to respond. Some may fail but I’ve proven not all will. In fact, my example is an extreme case of usage under those conditions and not babied so I think it serves as a valid example.
Personally, I suspect most could be run that way if one maintained a shorter interval for fluid change to counteract the degrading effects on the fluid. Naturally some designs are going to be more sensitive to such “abuse” and that’s partially what surprised me about the 700R4. It’s not known for being robust 
I wouldn’t advocate doing this except in cases like the OP’s (or mine).
Applying the brake does not release the TCC on any dodge I have driven including my '09 Letting up on the throttle will not either. Now I have had 2 S-10 s that would act that way.
Well, back to the original issue…the shop just called to say the rear u-joint is bad, too, so that’s being replaced in addition to the trans fluid/filter.
Oh yea, that should clear up the remaining vibration. That might have been most of the vibration itself. U-joints will cause drivetrain vibtations. I remembered last night of one I had come in the shop months back with the same thing as yours. It had sat for a year and a half. The lockup solenoid was not venting properly and it was due to the long sitting. This one ended up clearing itself out before I was able to service it but I was still able to see the solenoid blocked up. Your symptoms are identical and could be from the same thing. Let me know how it drives after the fluid change.
transman
Transman, interesting…that gives me hope this will all be cleared up…I would be interested to see what a lockup solenoid looks like…having a hard time imagining why/how an electrical (?) solenoid vents…can you refer me to a diagram of what it looks like?
Let me try to find one online that looks good enough to give you an idea.
transman
On May 22 I said I doubt if the problem is the TCC. I would like to repeat that statement. As a mater of fact, I don’t know a soul who has had a problem with the TCC. Maybe some do but they are few and far between.
Jesmed,
Check your PM inbox, I left you a message. Let me know if it didn’t come through, I had a glitch and it might not have made it.
Transman
I can’t believe you’re going to leave us hanging like that transman.