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Overdrive solenoid

bob hughes

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Just had to replace my overdrive solenoid, it had been acting up for a few months, but after following all the checks in the good book - backwards as I thought that it may be a relay, I eventually had to pull the trans tunnel and sure enough the solenoid needed to be replaced, it was over ten years old so I guess that it had a good innings.

Being curious, I started to take the old one apart - that's a joke, it is like Fort Knox, but the top came off easily to show a set of points and a plastic rod that obviously connected the metal plunger back to the set of points to break them and that is as far as I have got.

Has any one else attempted to explore the innards of this device?

:cheers:

Bob
 

John Turney

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The plastic rod and points are to change from the high current pull-the-plunger-up mode to the it's-already-up steady state mode. The initial current would burn out the coil if left on continuously (unless you add a fuse).
 

Bob_Spidell

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... the solenoid needed to be replaced, it was over ten years old so I guess that it had a good innings. ...

I just replaced my original--AFAIK--still working solenoid at 60 years and almost 200K miles while I had the OD out of the car, so it sounds like there is a lot of variance in lifespans of these. I'm sure I just jinxed myself.
 

John Turney

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I just replaced my original--AFAIK--still working solenoid at 60 years and almost 200K miles while I had the OD out of the car, so it sounds like there is a lot of variance in lifespans of these. I'm sure I just jinxed myself.
Don't throw that old one away. You'll need it when the new one fails.
 

Bob_Spidell

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Don't throw that old one away. You'll need it when the new one fails.

Are the newer ones known to be lesser quality? They do look different. FWIW, David Nock told me recently that he replaces solenoids and the gear selector switch as a matter of course (of course, he sells them ;)). I think it would be a difficult swap on the side of the road--and a somewhat finicky adjustment to boot--but maybe it's possible to just replace the coil section and leave the plunger and its adjustment untouched?
 

John Turney

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The good news is that one doesn't have to replace them on the side of the road; you just drive without overdrive. Bob Hughes' only lasted 10 years, so it must be a replacement. Yours lasted 60.

The quality of new parts can be good or suspect. The Lucas name was sold, so it's unclear who makes the "Lucas" parts. Overdrive solenoids seem to come up here every couple of months.
 

Bob_Spidell

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I'd hate to drive a couple thousand miles without OD (impulse power only, no warp drive). The 3.54 diff would help some, I suppose, but knocking a few hundred RPM off the tach really aids the meat sacks in the seats on long highway runs. I bought this solenoid years ago from Mike Salter; IIRC it was the German brand (Limora?).
 

Bob McElwee

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We had an O/D that became stuck in O/D on our way to the Conclave in Burlington, VT. Once we arrived had to remove the tranny tunnel and smack the iron ring between the tranny and O/D per Bruce Phillips. From there we visited a niece and her family in Conn and then drove back to St Louis all w/o O/D. Fortunately we had a 3.54 rear end so it was tolerable and we just crusied about 5 - 10 mph slower than normal.
Once home I put a Toyota 5-speed in. Wish i had done that years earlier.
 
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bob hughes

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but maybe it's possible to just replace the coil section and leave the plunger and its adjustment untouched?

Bob - I tried that in the garage but murphy's Law prevailed and the plunger is a problem to keep located properly, in my case it dropped and the 'hook' of the arm was then located above the level at which it should be. So in the end the side plate had to come off, I guess that you could try to fiddle with it but I did not want to risk it. In my endeavours I also forgot that two gaskets were required so these were hastily made from gasket paper to replace the damaged ones.

:cheers:

Bob
 
Last edited:

RAC68

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Hi Bob H,

I am not sure which SU fuel pump you are using but I still have my original points unit and, a while back, designed (with 2 British car guys from Origin) an Optically triggered head that could replace an original points or transistor head. We designed the optically triggered unit during the time when SU was having quite a problem with their transistor unit and points availability was becoming an expensive issue as well. However, we decided not to follow into test production when we learned of Transient-Voltage Suppression (TVS) diodes which, when applied to the points head, allows sufficient power to run the pump and clean the points (23 Volts) but gate to ground all voltage above that was generated by the Pump's Coil effect (as much as 200 Volts).

Although todays transistor SU pumps are much more resilient then the original Points triggered pumps, when they fail .... they are dead and a points triggered pump can be resurrected in most cases. The use of the TVS diode has allowed me to continue using and keeping my pump performing, and at 54 years old, is running without hesitation.

I do have the spare optically triggered head to fit on the pump should something happen to the points but it has been so long since fitting the replacement (while testing) I would have to read my instructions by the side of the roads to make sure it is installed correctly.

I don't know how your pump is triggered but I am well pleased with the performance of the added TVS and have also added a slow blow 20V to protect power to the pump coil power as well.

All the best,
Ray(64BJ8P1)
 
Last edited:
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bob hughes

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Ray

I am a bit confused here. Easy I guess at my age but I was looking at the overdrive solenoid - not quite sure how the fuel pump fits in ?

However, there has been a break in the weather and I was able to try out the overdrive - works a treat, it used to hang about, kind of lazily drifting into overdrive just before it's demise, and now it is sharp as a razor.

:cheers:

Bob
 

RAC68

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Hi Bob,

Its the answer to your next question. Sorry I didn't wait till you asked it.

I remember responding to your OD Solenoid situation by describing the installation of a slow blow 20 amp fuse for protection. I also remember wondering if the installation of a 23V TSV diode, described in my pump response, could be used on the solenoid feed to aid in protecting the solenoid from voltage buildup by the coil. However, I obviously mixed the responses.

Enjoy your OD,
Ray(64BJ8P1)
 

RAC68

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I have been thinking about my last response and the use of a Transient-Voltage Suppression (TVS) diodes as added protection for the OD Solenoid. It is not uncommon for a coils, such as the one used in the overdrive, to induce high voltages (i.e. Lucas fuel pump, ignition coil). Over time, components within these devices will begin to deteriorate due to these voltage levels and cause the part to fail.

There are 2 discrete stages that the Overdrive coil passes through for normal operation. Stage 1 can be considered the initiation stage that requires a higher amperage draw to pull the OD's lever to initiate operation. Stage 2 is the low amperage maintenance stage that holds the lever in place to continue OD operation.

Although no electrical protection was originally installed on the OD coil, some have added a 15 or 20 amp in-line Slow-Blow fuse directly to the coil's power connection and others a standard 10 amp fuse on C1 of the OD Relay. Although either application would provide more protection for the coil then original supplied, I am wondering if the application of a
Transient-Voltage Suppression (TVS) diodes
that gates off excessive induced coil voltage to ground (above 23 volts for the diode I already have on the fuel pump) would help protect the circuit and coil device. As I see it, by limiting excessive voltage, and fusing excessive amperage draw, coil longevity and proper operation should be maintained indefinitely.

Thoughts?

Ray(64BJ8P1)
 
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