Transmission help needed

[52 Muntz]

In my Darrin I seem to have lost the ability to get it into reverse when the car is warm. The other gears all work and shift fine. Any suggestions where to start looking?

[Fid]

Is the overdrive control pushed in or out?  If it's in, try pulling it out (with car not moving of course) and see if it will go into reverse. I had the same thing happen. I could actually pull the lever into reverse but I had to hold it there. If I let got, it would bounce right back to neutral. I could use reverse, I just had to hold the lever in that position while backing up.  If I pushed the overdrive cable in, the car would then stay in reverse when I shifted it there.  There is a lock out switch on the transmission which breaks the overdrive circuit to prevent the overdrive from engaging when the car is in reverse. When you put the car in reverse, there is a rod that slides back and pushes this button in to break the circuit. If anything impedes that rod from moving all the way back, it will not allow the transmission to fully engage the reverse gear.
I've heard others claim this was caused by the return spring for that rod being broken.  I also remember a '51 Frazer where the owner installed a backup light and mounted the switch down on the transmission. The switch moved forward slightly over time and eventually prevented that rod from moving all the way back- same symptom, car would not stay in reverse.
Unfortunately for me, when this symptom occurred on my Henry J, it was due to a piece of the casting on the overdrive adapter plate breaking off allowing the large snap ring to come loose and that blocked the rod from going all the way back. This required tearing the transmission apart and replacing that adapter plate which I was very fortunate to find. 

[52 Muntz]

You guys might be right. When the car is not running it goes into reverse fine, which suggests that it might be related to the OD circuit somehow. It doesn't seem to be affected by pulling the OD cable in or out, but I have had another problem with the OD solenoid? clicking in and out rapidily when the car is running. Sounds like maybe a problem with the OD solenoid, OD governor, or the connected wiring.

[52 Muntz]

I just reread the repair manual page that Jake posted, and the  one item hit the nail on the head with relay clicking and  reverse lockout. Excellent.   What shop manual is that from?  Thanks.

[Fid]

I have had another problem with the OD solenoid? clicking in and out rapidly when the car is running.

This additional information is helpful. What may be happening is the overdrive solenoid is not releasing. If the solenoid is remaining engaged, this  will prevent the transmission from shifting into reverse.  You shut the engine off, power is no longer applied to the solenoid and the solenoid releases and now you can shift into reverse.
You may have a sticky overdrive relay. I had that happen once too and it can be a problem because the car will be in overdrive when you start out from a dead stop - not good.  Shut the engine off, pull out the OD cable, start the engine and see if it will go into reverse.  If so, you know the problem is with the overdrive. 
When I had this happen it was a sticky relay which would not cut out and kept the solenoid energized all the time. If you have a spare relay, swap it out and see if that does the trick.
Otherwise, on the Darrin the solenoid mounts differently and uses linkage to push the pawl into the gears so check that linkage and make sure something isn't binding somewhere and preventing the solenoid from releasing.
 
 

[Aeroman]

I seem to remember John Parker fixing my Aero's overdrive by removing the big electric cylindrical thingie (my technical term, not John's) on the side of the tranny. There is a shaft that sticks out of it that retracts or extends as needed. Make sure this is freed up. He called it a "Parking Pawl." This was over 30 years ago, so my memory may be a bit faulty.

[52 Muntz]

Thanks guys I will start the check through in that order, and report on my success (positive thinking here).

[Terry T]

You should get a Henry J repair manual since the Darrin is basically a Henry J with a different body.
Get a 50's Motor Manual for additional repair information.

[Terry T]

BE AWARE WHEN SOMEONE GIVES ADVICE AND STATES " NOT SURE"
THE TRANSMISSION TAKES GL1 90W!

[52 Muntz]

Just an update and thanks to the forum, I have the reverse on my Darrin working again.  It would appear the problem was that the overdrive cable casing was rubbing up against the O/D rail switch contacts causing the O/D to lock out reverse. It was intermittent as it only occurred when the cable casing contacted both terminals. Thanks to all.

[Fid]

Sorry I never came back and read this update. Good info. If the OD cable rubs against the reverse lock out switch then the car will be in overdrive all the time. This would certainly produce the symptom you described. I'm glad it was something that simple.