I recently replace the AW 70L tranny in my 89 740 with a used one with less than ½ half the miles, per the bone yard. The transmission shifts fine, (smoothly) AFTER it’s engaged into 1st gear. Intermittently when shifting from park to drive there is a delay before the transmission engages the first time. There is no problem after this and all shifting is fine unless I go to neutral or park, wait a few seconds, then again shift into drive. Then the hesitation, and depending on how much throttle is used on start-up, a clunk into gear and then all is fine again. I did flush the system through the cooler outlet line using about three gallons of fluid after the first episode. The problem disappeared for about 200 miles then re-occurred. I haven’t removed the pan again, since I did replace the screen before installing the transmission. There was no visual indication of a problem at that time. I ran another 6 qts of new fluid through it but this time no change to the condition.
The problem is intermittent so I don’t think it is a plugged screen. I’m guessing there must be a valve which is hydraulically shifted when starting in drive that might be sticking thus causing a slow fill on the forward clutch. If I manually shift directly to first the problem doesn’t seem to occur. It also doesn’t seem to occur in reverse.
I am under the assumption that DexronIII is the correct fluid, however is there any chance that at some point this transmission took something different? Maybe my bone-yard tranny falls into a different fluid type requirement.
I thought about replacing the valve body with the one from the removed transmission but I’m not anxious to do this without knowing they are the same.
I’ve read through many of the FAQ’s, and files on transmission difficulties but haven’t seen anything quite like this.
Can anyone shed some light on this please?