[Healeys] (no subject)

John Rowe jkrowe46 at bigpond.net.au
Thu Jul 24 02:10:04 MDT 2008


Mike
Is the 100 a 3 or 4 speed?.The 3 speed has a speed switch that cuts out 
below 30mph (centrifugal mounted at the rear of o/d unit. The 4 speed 
doesn't have this unit
John Rowe  Qld Australia  BN1. BT7
----- Original Message ----- 
From: "John Harper" <ah at jharper.demon.co.uk>
To: "mike brooks" <hypercubic at yahoo.co.uk>
Cc: "Healeys" <healeys at autox.team.net>
Sent: Thursday, July 24, 2008 4:52 PM
Subject: Re: [Healeys] (no subject)


> Mike
>
> I don't believe that if an O/D drops out is a function of speed but more
> one of distance. The O/D pump works on the output shaft that drives the
> wheels, as you say. If you have been travelling any significant
> distance, say perhaps 100 feet then the accumulator will be fully
> charged with something like 400 psi oil pressure available.
>
> The manual advises working the O/D valve six or seven times before
> working on the O/D. This is to relieve the pressure from the accumulator
> that might still be there after many hours and is therefore dangerous.
>
> I suggest that if your O/D drops out around 30 mph the oil pressure has
> dropped, again as you suggest. On a correctly working unit this should
> not be the case. Either the control valve is being operated somehow or
> there is an internal leak inside the unit. The most likely cause is a
> badly seating valve but it could be leaks around the operating or
> accumulator pistons.
>
>
> Regards
>>I am by no means an expert on overdrives. However, I thought the hydraulic
>>pressure required to engage the overdrive was created by a pump driven by 
>>the
>>main propshaft, and that at road speeds below about 30 mph there is
>>insufficient pressure to engage the overdrive. That is certainly the case 
>>with
>>the overdrive in my Triumph based home build Lotus Seven replica. So even 
>>if
>>for some reason the gearbox switch is still providing 12 volts to the
>>solenoid, at low road speeds there would be no possibility of being in
>>overdrive and reverse. My 100 has the throttle switched bypassed, but the
>>gearbox switch is in circuit. If I leave the dashboard switch on, and 
>>reduce
>>speed, it always drops out of overdrive sometime before I come to a halt.
>
> -- 
> John Harper
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