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Testing OD with Car on Jack Stands

nevets

Jedi Knight
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My OD has not been engaging for some time and I determined that the problem might be the transmission switch because I could not hear the solenoid click when moving the shift lever into 4th, with ignition on and the dash switch in the OD position.

So I removed the old switch and installed a new one, and bingo, I could hear the solenoid click! When I examined the old switch, I could see a very pronounced flat spot on the spring-loaded ball. I'm guessing the flat spot was the reason why the solenoid was not being energized.

But, before I do a road test, I was wondering if it is considered ok to try it out with the car still up on jack stands...as in start the engine, shift into 4th then flip on the OD switch? I'm tempted to try but a bit concerned about safety.

Oh, and a shout out to John Turney, who in another post, pointed out that access to the OD transmission switch is possible from below, eliminating the need to remove the transmission tunnel. Yuge time and bother saver!
 
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Re: testing OD with car on jack stands?

... But, before I do a road test, I was wondering if it is considered ok to try it out with the car still up on jack stands...as in start the engine, shift into 4th then flip on the OD switch? I'm tempted to try but a bit concerned about safety....

I've done this. Obviously, you need to be very sure of your jack stands--no Harbor Freight!--and you need to be on a flat, level concrete surface with the stands positioned so they cannot move (I usually put the front under the lower A-arms by the king pin trunnions, and the rears under the springs on the flat spot behind the axle). Note when the OD engages you probably will not see the usual engine RPM drop--unless you put your E-brake on a little--but your speedometer should tell the tale.
 
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nevets

nevets

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Re: testing OD with car on jack stands?

Bob, thanks for the response. My jack stands are good quality and on a flat concrete garage floor, however the stands are positioned fore and aft under the main frame members that run the length of the car. Close to the axle in the rear and A-arms in front. Moving the jack stands to the points you suggested would probably be as much trouble as taking the car off the stands and doing an actual road test. Hmmm...

attached is pic of old switch showing flat spot
 

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blueskies

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I would opt for the road test. The thought of a car running in gear on jack stands brings images of disaster to mind. I recently sorted various overdrive issues on the 100-6 and the BJ7 by using road tests after each step and don't see any problem with doing that.
 
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If the OD was working before and you're (pretty) sure a new switch fixed it by all means take it on the road. I'd rebuilt my OD and gearbox and wanted to be sure they were functioning before putting it on the road (and IIRC I hadn't yet connected the propshaft).

There is risk in all things. Testing a drive train when on jack stands involves some risk but if the car is stable--i.e., you can't move it--IMO the risk is manageable. I've done this several times.

Edit: There is some 'spec' about setting the depth of the switch in the gearbox cover. The Moss catalog shows fiber washers 'A/R' (As Required). IIRC I didn't find any instructions in the shop manual--they may be in there somewhere--but, obviously you want to set its depth to close the contacts in 3rd and 4th, but not so deep the contacts remain closed when out of those gears.
 
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nevets

nevets

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Bob, thanks for the additional input.

I'll probably take it off the jack stands and road test it, just to be safe. Interesting point about the depth of the switch in the gearbox cover. There was just one fiber washer used previously, so that's what I used. I suppose I can test if the contacts are closed when not in either 3rd or 4th by flipping the dash switch with the gear lever in 1st or 2nd and listening for a solenoid click. Think I'll try that while the car's still up on jack stands.
 
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...I suppose I can test if the contacts are closed when not in either 3rd or 4th by flipping the dash switch with the gear lever in 1st or 2nd and listening for a solenoid click. Think I'll try that while the car's still up on jack stands.

I think that's what I did (it's been a couple years). I wonder if the wear on your old switch's plunger was due to it being too embedded in the shift lever 'cage?' As best I can remember, my old switch didn't have that much wear; of course, you want the plunger inserted deep enough so it'll still work as the plunger wears some.
 

blueskies

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Those switches can appear good and not be so. On the BJ7 (with center shift transmission), the switch bench tested OK and the ball remained round, but once installed it did not activate the overdrive without pulling sideways on the gearshift lever. A new switch cured that problem. The contacts inside the new switch likely required less travel for the ball than in the old switch. It's possible to visually see more of what's happening with the switch ball on the center shift models, at least with the transmission tunnel removed. In case anyone is wondering, both the side shift and center shift transmissions use the same switch, even though they are placed in different locations on the transmissions.

The switch on the 100-6, possibly the original one since it still has the original style side screw connections, still works well.
 

Guido36

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I have visions of the scene in Ferris Bueller’s Day Off where the Ferrari California Spyder falls off the jack stand and exits the garage into the canyon at the back of the garage. I would recommend the road test....
 
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nevets

nevets

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A final note on the trans /OD switch replacement - Road tested the car and OD is working as it should. Fingers crossed it stays that way. Thanks for the help.
 
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