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OD only when it's cold

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S

spritenut

Luke Skywalker
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Having logged about 500 miles on the Healey since I (almost) finished it, I notice that the overdrive only works once and only if the engine/tranny are still cool, like it a few miles from home. I have tried the switch and know that the solenoid engages all day long if the car is not started. It will work once, maybe twice it it is just idling in the driveway.
The solenoid is clean, greased, grounded, etc.
My only guess is something expands with the heat in the tunnel. I can also manually engage OD via the lever on the other side even when hot. But as soon as it kicks down, no more OD.
Any ideas?

Frank
 
Hi Frank,

I can think of a couple of possibilities.

1- The solenoid has two windings. A high current (about 14 amps) pull in coil & a low current (about 1.5 amps) holding coil. The high current winding is switched by a set of contacts under the top rubber cap. Once the solenoid reaches full travel, the high current winding is switched out of the circuit by these contacts. It usually happens too quickly to see on a meter. If the contacts get too dirty, only the low current coil will operate & there may not be a full solenoid stroke.

On the other hand, if the contacts are good but the solenoid doesn't make a full stroke to open the contacts, the high current winding will burn out in short order. Either problem can cause a failure to operate the OD. The two windings can be roughly checked with an ohmmeter. Separate the contacts with a piece of paper & measure the winding resistance individually. The operate winding should measure about one ohm. The holding winding should measure about 12 ohms.

2- On the RH side of the OD, near the back, & at the top is a small hex plug, Under this plug, in order, are a spring, a short spring plunger, a ball valve & a long plunger. The OD operating lever at the solenoid on the left side must be adjusted on it's shaft (loosened & rotated) so that this ball valve is lifted .040" when the solenoid is operated. If you operate the solenoid with this ball uncovered, it will be shot into orbit, never to be found.

OR

There is a second lever on the right hand end of the OD operate shaft that is "supposed" to be used to gage the LH lever adjustment. The LH operate lever is loosened on it's shaft. The RH (gaging) lever is moved to it's operated position & a drill bit is inserted through a hole in the lever end to engage with a similar hole in the OD housing. This holds the RH lever & thus the ball lift at the correct operated position & The LH lever is tightened on it's shaft with the solenoid in it's fully operated position. This is the factory recommended method of setting the valve. If there is wear on any of the parts, this method sometimes doesn't result in the correct ball lift, so I prefer the first method.

3- There are a few other possibilities, but check these first. BTW - I don't think that I would grease the solenoid plunger. It can collect dirt & make the plunger bind.

Good luck,
D
 
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