Subject: [TR] TR Overdrive in reverse.

From: Jonas Payne <[email-masked]>
Date: Sat, 28 Apr 2012 20:13:38 +0000

I believe that one of my electic OD switches failed "not safe", and I backed
my car out of the garage in reverse with the OD engaged.  It is my
understanding from the guys on the healey web that this is "very bad".

I am now suffering some "binding/lurching" when in first or reverse, and have
been pushing the car around in fear of doing any damage.

It would appear that the unit is coming out again, but exactly what does
driving an OD in reverse do that is so bad?

Jonas Payne
PBR
Cell:   (702) 358-5084

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From: "Randall" <[email-masked]>
Date: Sat, 28 Apr 2012 18:14:47 -0700

> driving an OD in reverse do that is so bad?

There is a one-way roller clutch (aka sprag clutch) in the tail housing that
prevents the output shaft from turning any slower than the input (to the
overdrive).  However, when you try to back up with the OD engaged, the OD
clutch and gears force the sprag clutch to turn backwards.  

I've only seen photos of the resulting damage, but it looked pretty bad.
The outer race of the sprag clutch had broken, taking the tail housing with
it.

However, unless it felt like you were backing over a curb, or you felt a big
lurch, most likely the OD didn't have enough pressure built to force the
clutch backwards.

Before you pull the gearbox & OD, I'd check that there isn't something else
going on.

-- Randall