BW55 transmission overdrive is electrically activated, what activates it?

The automatic shifts seamlessly 1-3 but doesn't go into OD.
This transmission does not have the external solenoid.
There is no OD button for operation
again, what activates the OD?

(1981 245 DL)

 

The AW/BW 55 transmission is a 3 speed transmission. If you want 3+ overdrive you need the longer aw70/71 (with a solenoid on the left side of the transmission and the longer bellhousing, the shorter driveshaft, shorter shift linkage, and try to get a speedo gear that reads close. The diff ratio is different in a 3 speed car)

To answer your - what activates it question - a button tells a relay to send power to the solenoid. When the relay goes bad (or wiring or any other fault) you simply grind a grove between the 2 oil ports in the solenoid to allow oil to flow all the time. And then it will shift into 4th when needed and you spent 0 to make that happen.

 

I believe I have a Laycock OD unit mated to the BW55.
Researching I understand the single 12v wire has voltage present whenever the car is on and is hydraulically activated.

Thanks for your input and knowledge

 

The laycock overdrive is pictured below. It's part of a M41 manual transmission. (fixed many of both the m41 and Od units a long time ago) Solenoids for those 2 styles pictured below also

If you have a bw55 automatic, (with the short bellhousing and no solenoid on the left side) - you have a 3 speed transmission. The solenoid for a aw70/71 is pictured below also.

 

I finally got my old bod under the car and found the BW55 does not have a Laycock OD.
As Hoonk stated earlier I have a 3-speed only.

Thanks for your effort explaining this to me.

 

welcome