[Healeys] BN6 Overdrive

[Bob Spidell]

The OD and gearbox share fluid supply.  Take the car out for a run to 
get the fluid warmed-up, then get it up on a rack--preferably--or SAFELY 
on jackstands, as high as they'll go. There is a dipstick on top of the 
gearbox; check your fluid level before emptying--if it's low that could 
be at least part of your problem.  There is a drain plug on the bottom 
left side of the gearbox, and a big brass disk on the OD.  Older cars 
had a sensible square 'nut' on the OD plug, which can be turned with a 
big crescent wrench, and newer ones have a notched disk that requires a 
tool to be undone properly, but you can use a brass punch and hammer or 
other method.  When you drop the brass plug, there should be a 
cup-shaped screen and, possibly, a couple of soft, circular magnets.

Let the fluid drain completely, then re-install the gearbox and OD 
plugs, being sure to a) place the magnets inside the plug and b) place 
the screen on top of the magnets.  It's difficult to stop leakage from 
the OD plug; use a new fiber washer and, possibly, some teflon tape on 
the threads of the plug (being careful to not get any inside the OD).  
Top off with the fluid of your choice--'book' is 30W non-detergent, but 
most motor (20W-50) and synthetic gearbox oils work well--checking the 
level often with the dipstick.  Should take about 3.75 quarts.

Don't know how you 'persuaded myself that the OD electrics are fine,' 
but my money's on the electrics--esp. the relay.

Bob


On 1/2/2017 10:56 AM, Neil McDonald wrote:
> One of my New Years resolutions, before I put the car back on the road after sitting in the garage for several years, is to fix the overdrive so the car is comfortable highway driving. It once (and once only) went into OD once very briefly - which suggests that nothing mechanical is broken.
>
> So far I have persuaded myself that the OD electrics are fine and there is adequate hydraulic pressure - around 390 psi if I recall correctly. I have also checked the hydraulic valve adjustment using the "drill through the actuating lever" method but not the direct "is the valve ball lifting by at least 1/32 inch when the solenoid is actuated?" method.
>
> Somewhere I read that there is a small passage around the hydraulic valve area which can get blocked and thus needs cleaning out with a wire. Is there an internet link elaborating on this?
>
> Online research also suggests that I should change out the OD fluid which is certainly old and a significant amount could have leaked out. I assume that the gear box has a drain and filler plug but have yet to find them. Should I refill to just short of overflowing or ......?
>
> I don't have the resources to pull and strip the OD myself so am hoping that I can get it working without hiring a professional. Does anyone have any words of wisdom and/or comfort?
> _____________________
> Neil McDonald
>
> Email: nmcd10 at gmail.com
>
>
>