Overdrive Trans trouble

[GH1]

My '84 has got the O.D. trans with the manual on/off on the floor shifter. One day I was driving down the road and it just downshifted and hasn't gone back into O.D. since, despite repeated attempts to switch it back.
It still runs & drives fine, but I'd really like to have the O.D. back.
Can anyone give me a possible starting point to figure this out? My Haynes manual is useless.
Thanks.
GH1

 

[tbplus10]

Step 1 is to check the OD fuse, Ive seen the fuse become a problem a few times.

 

[GH1]

I've done some diag work on this problem & everything is pointing to the OD solenoid on the trans. The switch on the shifter checked out, the relay seems to be doing it's job, so that only leaves the solenoid.
Now I just need to find one, it's proving to be quite elusive.
GH1

 

[tbplus10]

Give the crew at trdparts4u.com (toyota of dallas) an email, they just may be able to help you, they have great resources for oldr truck parts and a great track record of success.

 

[GH1]

Will do, thanks.
GH1

 

[toyotafan]

Let us know if you find one.

 

[GH1]

Still haven't found a solenoid. I wonder though, there must be some kind of speed sensor in the trans that tells the thing to shift, right? perhaps that is the problem, because occasionally it will shift into OD.