[Healeys] Overdrive Deceleration

[Charlie Baldwin]

Greg,
It seems that Austin-Healeys are one of the few makes that used a system 
to allow the overdrive to drop out only on acceleration.  I've owned 
several Volvos with Laycock overdrives, both D and J type, and there was 
no provision for this on any of them.  One car that was in my possession 
for a while, an MG TD with Volvo B18 engine and D type OD trans. would 
actually chirp the tires if you flipped off the OD switch when 
decelerating, so using the clutch made it much less harsh.  The Volvo 
owner's manuals actually tell you to use the clutch if the engagement or 
disengagement of the overdrive was too harsh.  No mention of damaging 
the unit; they seemed to be more concerned about comfort.  The overdrive 
is, of course, is one of the main parts of the drive train and Volvos of 
that period were known for their longevity, more so than most any other 
brand.  There is a Volvo 1800 on Long Island, NY that has over 2.5 
million miles on it.  That car has a Laycock OD unit.  Volvo also 
probably put more Laycock overdrives into cars than any other manufacturer.
Perhaps there is something about the A type overdrive in an 
Austin-Healey that makes it more fragile, but I believe that it is very 
similar to a D type, though more robust.
Charlie

Greg Mandas wrote:
> John, 
>
> I just read your article on the overdrive on your site, healey6. Nice site.  You say the roller clutch allows the OD to drive the rear wheels but not the oposite, as it will damage the OD unit. 
>
> Knowing you can't possibly keep ALL deceleration force off of the OD unit, how much can the OD manage and how much is too much before it's damaged?
>
> Does one's driving style change when the OD is engaged? 
> Is engine breaking absolutely forbidden?
> What the minimum time the OD should be used before it's being engaged and disengaged too much, 5 minutes, 15 minutes, 30 or more?
>
> Greg
> 65BJ8
>
> Sent from my iPhone so please excuse typos and brevity. 
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