67 122 with J type overdrive. Driving on the highway yesterday, after about 15 minutes, My overdrive dropped down into 4th, stuttered back into OD and then back into 4th. I switched it off and proceeded in 4th for awhile before trying OD again. On a slight decline, in OD it held for about 5 minutes, and then dropped back into 4th again. This was a somewhat progressive process, where it would hold for less and less time before dropping into 4th gear. Eventually I just kept it in 4th for the rest of the trip.

The only time this has happened to me before was in a different car (444 with B18 and D type OD) it was due to a slow leak from the front of the OD case -(one of the studs was broken) and topping up the trans cured the problem. I added some oil to the tranny yesterday, and it didn't change things at all.

So I thought maybe an intermittent short, but it seems not to be that. It's not intermittent.

Solenoid failing?

Seals going bad and so it's not generating enough pressure?

Filter needs cleaning?

I'm lost but am open to others hypotheses. OD Guru, please give me your 2cents.

thanks