Won't go into overdrive when hot.

J

jackson

Member
50 Mercury, stock drive train. BW overdrive. 12 volt with 12 volt solenoid.

When starting out cold, it works as it should.... when I lift the gas pedal, it shifts into overdrive.

After driving for a while.... 20 or so minutes in stop and go traffic, it then will not shift into overdrive.... regardless of speed. It has to sit for several hours before working again.

I do have dual exhaust, and the "added" (drivers side) pipe comes close to the solenoid side of the overdrive unit. Thinking maybe excess heat is causing the problem, I wrapped the exhaust with heat tape, but that doesn't seem to help.

Any ideas ?
 
make sure the wire from the relay to the solenoid is 12 ga wire. smaller gauge wire may overheat and increase resistance in that wire causing the symphonic you are having.... dont ask how many hours i spent tracing that down....
 
donald1950 said:
make sure the wire from the relay to the solenoid is 12 ga wire. smaller gauge wire may overheat and increase resistance in that wire causing the symphonic you are having.... dont ask how many hours i spent tracing that down....
Click to expand...

Thanks..... I built a new OD wiring harness, but “downsized” wires for 12 volt system. I’ll try your suggestion.

Jackson
 
also a suggestion is to tap the 12v off the battery post with a 30 amp fuse inline to the relay. i had a bad ignition switch on one car that was probably corroded internal contacts and would not let the OD operate
 
Check for loose connections. Also it is possible the relay is failing when hot. When it is not working ground the terminal with the wire headed to the governor and listen for it to click. Check for voltage at the out put if it does click or if you do not hear the solenoid engage.
 
Wanted to post this to thank you all for the help. I did get my overdrive working, using the info supplied in this post.

Frank Miller.... my relay was failing when hot. I ended up installing a new 12V relay, one with four posts, rather than the stock three-post, that had just an ignition wire to the fuse, no battery wire. That one wire to the coil was #14.... maybe OK for a 12 volt system, but seems small for the overdrive relay.

Since I now had a four-post relay, I took Donald1950's advice and ran heavier wire I went with #10 from the starter relay to the fuse, and again used #10 from the coil + to the IGN terminal on the relay. I realize #10 is overkill, but I had some available, and it can't hurt.

While under there, I pulled the governor.... it was dirty and gummy. It appears that to disassemble the governor you have to drive a small pin out of the drive shaft. I wasn't prepared to do that, so instead sprayed it full of WD40, which cleaned a lot of gunk out, and dried it with air. I may have ruined it... don't know, but for now it runs perfectly.

Thanks again for the help.
 
The governor can be checked without pulling that gear. Taking the cover off and you see the points for the switch. Underneath that is just spinning weights that engage the switch. Just file that. If it is working leave it alone.
whether it is 3 or four post on the relay makes no difference about performance. The three post just splits the incoming power internally. Glad you're up and running and thanks for the update.
 
Frank Miller said:
The governor can be checked without pulling that gear. Taking the cover off and you see the points for the switch. Underneath that is just spinning weights that engage the switch. Just file that. If it is working leave it alone.
whether it is 3 or four post on the relay makes no difference about performance. The three post just splits the incoming power internally. Glad you're up and running and thanks for the update.
Click to expand...

Thanks. I did assume there would be no difference in performance between a three or four post relay...... one of those odd things that keep me wondering. Apparently only FoMoCo used the three post relays. The BW Overdrive manual shows four post in the printed schematics. Wonder why Ford took a different route?

Another overdrive mystery........ if the rail switch can be bypassed without penalty, (it was discontinued altogether in 1951) why was it there in the first place?
 
Had that same problem with my 50 cpe finally figured it out and it was the solenoid took it apart and had to file and align the points and replaced the leather washer works great now hope this helps
 
jackson said:
Thanks. I did assume there would be no difference in performance between a three or four post relay...... one of those odd things that keep me wondering. Apparently only FoMoCo used the three post relays. The BW Overdrive manual shows four post in the printed schematics. Wonder why Ford took a different route?

Another overdrive mystery........ if the rail switch can be bypassed without penalty, (it was discontinued altogether in 1951) why was it there in the first place?
Click to expand...


Ford just used the high current wire to switch the relay, thus 3 terminals. If you use a low current circuit to switch the high current you need the 4 terminals. They just made a cheaper or simpler version of what was needed.
 
Jackson, I would encourage you to continue this thread with your observations. I too have a 1950 Merc and recently converted to 12v, rewired the pedal switch, bought a new 12v solenoid (not yet installed) but awaiting new engine haven't gotten to experience the overdrive yet. So, yes, I'm gathering information here as well. Thanks all.
 
The current reproduction relays (whether 6 or 12 volt) are all made with the 4 terminals. The usual Ford overdrive applications normally use just three of the four terminals. We keep these in stock.
 
I have found many stock relays with as much as a two volt drop on the output going to the solenoid, due to bad connections inside the relay. If you remove the cover you will see that all connections are made with rivets and over the years corrosion sets in and you get a voltage drop. The rivet connection where the fuse holder connects is usually a place to start. I clean all rivet connections and using a good flux, solder all these connections. You can also have a drop through the ignition switch. I have a test setup with a battery and sol. that I can use to check the voltage going in and out of the relay and after doing the above, if you have proper output from your charging circuit it will work every time. Another thing that helps is to go with an alternator, even if you are running 6v.
 
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