Overdrive Throttle Switch

[bt7tricarb]

Overdrive Throttle Switch = Frustration!!

Well, I think I've tried everything, so do I have a bad throttle switch? For the sake of full disclosure, this switch was replaced about 1,000 miles ago and worked fine until these latest symptoms appeared (old switch had gotten to the point where the contacts always stuck together and OD would not disengage. This new switch was installed and OD worked just fine... for a while).

What it's doing now (and, also for disclosure, I do have a test light currently installed):

With the car running:

- Driving along in top gear, flip the dash switch. Overdrive will engage but will dis-engage when the throttle is depressed more than half way. (I've adjusted the operating shaft on the throttle switch to where this won't happen, but then the OD will dis-engage while the gas pedal is not depressed - i.e. decelerating)

Now before anyone tells me about the 3/16 (5mm) adjustment detailed in the shop manual, please know that I've tried this, BUT...

While the car is not running (ignition on, 4th gear engaged), when I turn on the dash switch the indicator light will come on and I can hear the OD "click" in, but when I turn off the switch to make the adjustment the indicator light goes out WITHOUT depressing the accelerator AND the OD disengages.

Also, with the car off, ignition on, 4th gear engaged, OD switch in the on position, the light will come on but if I press and de-press the throttle, the light will go on and off accordingly (just like when the car is running).

So, do I have another bad throttle switch? Please know that I've adjusted this switch to all points in the range of where it will engage and won't engage. I know that I can bypass the switch, but I really don't want to. I just want to make sure I'm not overlooking something else before I replace this switch AGAIN.

While I truly believe that I got a bad replacement switch (typical, as of late, as it seems all re-manufactured parts I've been getting seem so cheap either of poor fit or not working or lasting), I'd love to get some of ya'll's feedback. Please know that I'll check back later, but right now I'm still pretty frustrated.

Thanks,
Devin

 

[Keoke]

HI, Devin, I do notthink your problem is in the throttle switch since it is a simple on/off microw switch. I would give some attention to the OD Relay and it's associated wiring. -Fwiw--Keoke

 

[bt7tricarb]

Thanks Keoke. That was suggested by one other person (over the phone), but isn't that switch just an on/off switch? I'm not sure how it fits into the wiring, but I thought if it's "activating" with the dash switch, that would rule it out. I guess I'm wrong, but can you (or someone) please explain?

- Devin

 

[Keoke]

NO it is a relay which has been modified to perfprm in this application You need a schematic to see its total function.---Keoke

 

[roscoe]

Devin,
There is a wire that goes from fuse block terminal A3 to contact C1 on the OD relay. If this wire were broken, or not supplying power to C1 (you should have 12 V there at all times). Then the only way the power would be supplied to the OD operating solenoid would be through the OD throttle switch WHEN THE TOGGLE IS ON. As soon as the toggle is turned off that power supply would go away and the OD would disengage. Likewise, when the toggle is closed and you depress the throttle you eventually open the throttle contacts and there-by remove the power supply to the operating solenoid. If I had a clue how to post diagrams it would be easier. See if you have power at C1 on the OD relay when you turn on the ignition (running or not). If you don't, that is your problem.

 

[roscoe]

I need to add to my post. It is either what I said above, or it is that the contacts in the relay control (as Keoke said)are not ever closing. If the contacts weren't closing it would have the same effect as the A3/C1 wire being broken as C1 is one side of the relay contacts. The contacts could be left opened if the coil in the relay were bad, which would again have the same effect. If you do have power at C1 , then the problem is most certainly inside the relay box. Geez, I hope this is right.

 

[GregW]

Here is one of Dave Russell's diagrams.

 

[Andy65]

Devin,

I think the cam is facing the wrong way in the OD switch. There are two positions it can go in. Rotating the shaft will cause the points to open if set "ahead" of the cam or cause the points to close if set "behind" the cam. Easy mistake.

Your comments "flip the dash switch. Overdrive will engage but will dis-engage when the throttle is depressed more than half way. (I've adjusted...but then the OD will dis-engage while the gas pedal is not depressed" indicate the switch is working but just the opposite of what is desired.

By the way, moisture gets in these switches over time causing rust and crud which fouls the points. They are repairable. Clean and seal.

 

[John_Progess]

Devin,
One thing you can do is dissassemble your old switch, clean the internals and try it again. I agree with you on the quality of new parts so this is what I did to mine and it is very simple. Have a good day!

John

 

[Healey 100]

It is very easy to isolate and test the switch separately:

Turn off the ignition and disconnect the two leads on the switch.

With the throttle closed, the two lugs on the switch should be closed, i.e. zero resistance across the lugs.

If you crack the throttle open slightly (1/4 open or less), the switch should open, i.e. infinite resistance.

If you continue to open the throttle, it should stay open.

When you close the throttle, it should return to closed.

Adjust the throttle switch or repair it until it does these things.

If the system still does not work properly with the switch set up this way, then the problem is elsewhere.


Good hunting!

Bill S
Albuquerque, NM

 

[GregW]

To avoid confusion, I have deleted my post. I have removed my brain and replaced it 180° from where it was and all is better now.

 

[Healey 100]

Not according to the Dave Russell drawing or the shop manual. The switch should be closed with the throttle closed.

That throttle switch is rather odd in its function. As far as I know, its only purpose is to keep the OD from disengaging with your foot off the throttle -- as if that would create a big problem for your Healey.

If the switch is not adjusted properly, simply disconnect one of the leads to the throttle switch and your OD should work fine -- except when you turn if off it will disengage immediately regardless of the throttle position.

Bill

 

[Ed_K]

Hi Greg,

My turn to keep you honest.



The purpose of the throttle switch is to provide current to the overdrive relay pick coil after the dash switch is turned off which in turn keeps the o/drive engaged,
UNTIL the throttle is depressed enough to break open the switch, which in turn drops the current to the relay and thus disengages the operating solenoid and overdrive. If it is adjusted correctly, it is a normally closed switch.

Respectfully,
Ed

 

[GregW]

Thanks guys :thumbsup: , my error.

 

[bt7tricarb]

AAARRRGGgghhh!!

O.K. I looked at all the diagrams shared (thanks everyone), and decided to look more closely at the throttle switch to see if the cam was turned around as suggested. It wasn't, but in the process I discovered something new (by accident).

As I said in my original post, there is a test light installed on the throttle switch. Well, today after much adjustment and flipping the dash O.D. switch on and off so many times I lost count, I made a final adjustment, hooked the coil back up, and started the car. As I was revving the engine a bit and pushing the choke in, I noticed my test light from the throttle switch going on and off, and the car was not even in third or fourth! I had left the overdrive dash switch in the O.D. (up) position, and like I said, the light just kept going on and off with the throttle (gas pedal).

So, I'm beginning to think that it isn't the throttle switch, but the relay... of maybe this is what Bill was talking about and the relay is good and I should just by-pass the throttle switch for now? Gosh, I'm confused.

Anything else I should be looking at with this new information?

Thanks everyone!

 

[Healey 100]

Devin:

I am not sure how you have the test light hooked up, but assume for now that you have connected it across the two terminals on the throttle switch. BTW using a test light is not the best way to diagnose a circuit like this, a voltmeter is better and safer. Unless you know what you are doing, the presense of the test light can significantly change the behavior of the circuit you are testing.

It is probably normal for this test light to energize when you turn on the dash switch and the ignition even with the transmission switch open. You can see from the circut that the OD relay coil is energized whenever the dash and ignition switches are on.

To see if the relay works, put your hand on the relay when you turn on the dash switch with the key on. There should be a distinct click you can feel when you turn the dash swith on. If it clicks, it is probably OK though if the contacts are bad it could click without closing the c1 c2 contacts. (this is not likely in my experience). Note: if the system is wired correctly and adjusted, when you turn OFF the dash switch (leaving the ignition on), the relay will NOT click off -- not until you step on the throttle and open the throttle switch. This is the only purpose of the throttle switch, to keep the OD from disengaging unless the driver blips the throttle.

Before you do much more, I suggest you trace out the wiring to make sure your car is wired as per the russell drawing. Did this OD work before? If so, there is little that could go wrong except for solenoid, relay or throttle switch failure. On my Healey, the solenoid is usually the culprit, this gadget is nortorious for intermittant and sudden failures. Still, I usually check out all the wiring, switches and relays to make sure they are OK first.
Hope this helps...

Bill.

 

[Keoke]

Test light poses no ambiguous circuit operation as used here.

Because relay clicks does not mean it is functioning correctly
in the electrical sense.

 

[Andy65]

If I read your earlier post right, the OD is on when it should be off and off when it should be on. That cam can cause the OD switch to open when it is rotated OR can cause it to close when rotated. It is not a matter of the cam being backwards, it is what degree of rotation it is at relative to the linkage. I'd take a second look i.e. if it is currently set so the linkage closes the circuit when actuated, rotate the cam so the linkage opens the circuit when actuated.

 

[Andy65]

If I read your earlier post right, the OD is on when it should be off and off when it should be on. That cam can cause the OD switch to open when it is rotated OR can cause it to close when rotated. It is not a matter of the cam being backwards, it is what degree of rotation it is at relative to the linkage. I'd take a second look i.e. if it is currently set so the linkage closes the circuit when actuated, rotate the cam so the linkage opens the circuit when actuated.

 

[Andy65]

If I read your earlier post right, the OD is on when it should be off and off when it should be on. That cam can cause the OD switch to open when it is rotated OR can cause it to close when rotated. It is not a matter of the cam being backwards, it is what degree of rotation it is at relative to the linkage. I'd take a second look i.e. if it is currently set so the linkage closes the circuit when actuated, rotate the cam so the linkage opens the circuit when actuated.