If everything else is working properly, and it only happens at 40 mph, it is very likely it is the tourque converter locking and unlocking. Over about 40, it locks up so it transmits power more efficiently, under 40 it unlocks. Try driving a couple of MPH faster, or slower. It should stop.
bent drive axle or axles
replacing mounts on 1994 dodge caravan
109 mph with 3.1
The recommended tire size for a 1997 Dodge Caravan is P205 75R 14. These tires have a speed rating of 112 mph.
215 km/h / 134 mph
You don't need to change anything. Both speed ranges are on speedometer face.
all i know is my mechanic (a Great one) told me if my 6 cylinder dodge caravan sport is runnin at 3rpms and staying there it is running too hard. he said i should be doing 70-80mph for it to be at 3rpms
wheels off van raised engine shakes side to side at 40 kmh
Wheel balance, Worn steering parts, Worn suspension parts, Tire damage,
125 mph,,,,, still a feckin caravan though
Have you tries having the wheels balance.
Check or replace axles, worn axles are primary source of shaking when accelerating.