Overdrive

[JayGT6]

I've got a late model GT6 and the overdrive has started playing up recently. When driving along at low speeds the overdrive will work normally. If you're driving at say 40mph or above then it constantly engages and disengages. I've checked the gearbox oil level and it's fine, plenty there. I've checked the connections and all seems okay. Any ideas what I should be looking for?

[gt6power]

There is a filter and magnetic ring under the cover with 4 bolts this may be blocked.  

[CHRIS211083]

Maybe be a solenoid problem or even wiring catching on chassis as speed increases.

Chris.

[BrendanD]

All OD problems are electrical until PROVEN otherwise!!

[Velocita Rosso]

How do you know you have enough oil?

Generally its best to top up with the front end of car slightly raised, this allows oil to flow over the lip of the box/od joint.(allowing more oil to be kept in the reservoir at the bottom)
Then with the car slightly raised  the oil just dribble out the filler later than when flat on the ground
Your symptoms , knocking out when going faster, may relate to not enough oil getting to the pump

[Pete Lewis]

just a few ideas if the simple fails to resolve.
also make sure the inhibitor switch  is only just being operated and when hot  doesnt  make  contact,

if D type  remove square cover and operate OD solennoid, in the lever you see a small 3mm hole this should line up with a similar hole in the case, use a drill as a gauge.

there is in the top case a hex headed cap screw which will allow you to lift out the valve tube, this has a small hole in end careful cleaning if blocked


if J type remove solenoid with thin wall 1" af spanner and remove end circlip , tap out the piston and give a good clean up

both units rely on clean filters and oil up to  the correct level,  its not uncommon for the filters and magnetic rings to be covered  in a gunge and they are messy to clean up.

pete

[mjwman]

These are the same symptoms I had on my Spit less than a year after a new OD installation.
Yes it was electrical.
The inhibitor switch was making intermittent contact with the cam in the box.
Removing its washer and replacing it cured it.  :)

[Tim Bancroft]

Got to go with Pete on this one, the inhibitor switch ball bearing often wears and therefore will not press in when the gear is selected, I had exactly the same problem with my car years ago.

Also, have a look at the bracket that the inhibitor is mounted onto, these sometimes need a friendly tap to get them into the correct shape!

[Paudman]

Just experiencing the same problem in my MK1 Gt6, it’s wiring shorting out through a hole worn in the outer sheath. I’ll clean it up when I get time but in the meantime I’ll have to use plain 4th.. :(