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TR2/3/3A DIDN'T BLOW the OD up [yet]

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doc50

doc50

Jedi Trainee
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Everything I've heard about the A type OD is that one NEVER should back up with it engaged. I've screwed up several times and gave myself the dope slap afterward.
The other day I was on a gravel incline and spun the wheels backing up for about 10 seconds....when I suddenly realized I was still in OD.
Any comforting thoughts as to why I didn't 'window' the OD...or is that just another urban myth? If it's true, is there any forewarning just before it spirals in?

Thanks for any feedback.

Thom
1959 TR3
#TS34909L(O)
 
I don't think it was in overdrive. If your shifter interlocks are working, it should drop out as soon as you come out of a forward gear, irregardless of your cockpit switch position.

If your interlocks are bypassed or broke, then your roller clutch is worn out.
 
Exactly. The interlock switches prevent the OD from being engaged in reverse, regardless of where the dash switch is set. There is a distinction between the switch being "on" and the OD actually being engaged.

The problem is definitely not an urban myth, but it (mostly) only applies when there is some malfunction, like the OD clutch is stuck in overdrive. The warning sign (if you are stopped or nearly so), is that it feels like you're trying to back over a curb. Pretty obvious (IMO) that there is a problem. The real danger is if you are already moving backwards and the OD engages (as might happen with a bad switch or shorted relay but no pressure in the OD before you started backing up).

The only scenario that I've found, that doesn't involve some sort of previous failure, is stopped at the top of a steep hill with no pressure in the OD. Turn the switch on, select a forward gear (so the OD solenoid pulls in), then roll backwards down the hill. As the OD builds pressure and starts to engage, it will try to stop the car abruptly. If it fails, BANG goes the sprag clutch (and probably the rear housing as well).
 
The other scenario I have pondered is that in a 180° spin the drivetrain can be abruptly forced to rotate backwards.

The traditional mantra -- "In a spin, both feet in" -- would possibly save the day.
 
Geo Hahn said:
The other scenario I have pondered is that in a 180° spin the drivetrain can be abruptly forced to rotate backwards.

The traditional mantra -- "In a spin, both feet in" -- would possibly save the day.
Click to expand...
Actually, I think that would make it worse. With the clutch out, the engine is going to keep the drive line from turning backwards. But with it in, if you got traction while moving backwards, it could force the OD to turn backwards.

Good point though, I hadn't thought about spinning out and potentially getting traction while moving backwards. I wonder though if the locking effect wouldn't just keep the tires sliding and save the OD that way. Don't think I'll try it to find out!

Likely doesn't matter though, if you're that badly out if control. If sacrificing the OD keeps me off the wall or another car, I'd call that a win!
 
Thanx, all. The system is all newly redone so I'll not worry so much if I forget to flip the OD switch down. No more dope slaps for me.

(Randall, I'm really liking the hard top!)

Thom
TR3 #TS34909L(O)
 
Glad to hear it, Thom.
 
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