Overdrive Bench Test Help

[jamie31888]

Hi guys,

So ive finally gunked down by MK3 1970 gearbox and have it on my bench, I wanted to test the overdrive.

I applied power direct to the overdrive solenoid via a 12v battery , positive onto the solenoid wire and negative onto the metal casing, a loud clunk then happens so i guess the solenoid is good?

Then the mystery part, i put the gerarbox into 1st 2nd 3rd & 4th and applied the positive to the red wire going into the reverse switch, the solenoid operated in all the gears.

This confuses me isnt the overdrive only supposed to work in 3rd/4th?

Please help!!!   :-/

[GT6 M]

So your by pass is shorted out, !!!

its at the front  of the remote  on the side.

[jamie31888]

Hey thanks for the reply,

Im not to sure what you mean by the bypass ? whereabouts should i be looking ?

[AngryBaldMan]

Ah this has answered a question of mine. If I apply 12v direct to the solenoid, I get no sound :(

[npanne]

4457 wrote:

Hey thanks for the reply,

Im not to sure what you mean by the bypass ? whereabouts should i be looking ?

It's a switch, operated by the square cam thingy (technical term) on the end of the selector shaft.

It's the same type switch as the reverse light one - two terminals, hex shaped.

[rotoflex]

The bypass swittch is external to the solenoid.
So if you're applying power to the wire directly attached to the solenoid, the bypass switch function is not tested, & it will go clunk no matter what gear it is in.

If you have an overdrive, you will have a reverse light switch like always, but also an additional switch used as the overdrive bypass/inhibitor switch.

The bypass switch on Mk3s was mounted on a sort of spider bracket over the front end of the selector shaft (i.e., opposite end from the gear lever).
In the illustration below from the Canley Classics website, the bypass or inhibitor switch is 147471, the bracket which holds the switch is 133770 or 158002 (depending on when the kit/assembly was built).

FYI, the single wire hanging down from the overdrive wiring harness in the illustration is the one that connects to the solenoid.

[nang]

To b e clear, because you put 12v directly to the solenoid you've bypassed the inhibitor switch on the gearbox. To be sure it's ok put the power on to one terminal of the gearbox switch. and run a wire from the other terminal to the solenoid, then try it through the gears'
Tony.

[jamie31888]

Thanks for the replies, it has answered allot of questions.

The inhibitor switch (147471) is missing from my bracket and because it looks similar to the reverse light switch i thought they where the same thing.

I thought that the mounting bracket (133770) was a lifting point for the gearbox haha.

The wiring could be an issue i shall post a picture later today.

Thanks again

[jamie31888]

Ok so ive put some pics up, it looks like the previous owner has wired up the reverse switch to the overdrive solenoid  ??)

Can anyone confirm this or give me some guidance?

Thanks

[jamie31888]

reverse switch left and right view

[Nick Jones]

Does look a bit like it, although the wires aren't joined just taped together.  It's wrong anyway.  Looks like it's wired to blow a fuse whenever you engage reverse......

You'll need to get an inhibitor switch but at least the bracket and cam on the selector rod are there.

Nick

[jamie31888]

Thanks nick , do you know if the reverse switch has its own harness or is it linked in with the overdrive harness?

[bob dunn]

http://www.tcoc.ie/wiki/item/367891                       hope this helps.

[TimW]

4457 wrote:

Ok so ive put some pics up, it looks like the previous owner has wired up the reverse switch to the overdrive solenoid  ??)

Can anyone confirm this or give me some guidance?

Thanks

I may be wrong but that bell housing doesn't look like a GT6 one to me.  

[npanne]

You're right there - that's not a GT6 housing - they have the slave cylinder mounted on the side shown.

[npanne]

It's a Spitfire bellhousing.

Pretty sure of it.

[rotoflex]

4457 wrote:

Thanks nick , do you know if the reverse switch has its own harness or is it linked in with the overdrive harness?

The reverse light switch is connected to wires that are coming from the wiring harness already in the car.  A green wire connects to one "side" of the switch, & a green/brown wire connects to the other "side" of the switch.  

A copy of the wiring diagram for a version of the US GT6 Mk3 is attached.  Yours will be different in some respects, but the part around the reverse light switch #57 should be the same.  It also shows in the box marked A how the optional overdrive is wired to all the cars.

From the impression I've gained here, bellhousings can be swapped.
If that's the case, you may be in OK position for trading, since that appears to be an aluminum Spitfire bellhousing which seems to be more sought-after than the steel Spitfire bellhousing.

[jamie31888]

Thanks for the info , my car is a MK3 1970 Spitfire 1300.

When i striped the car down there was no relay, the od is operated by the stalk on the steering column .... should there be a relay on a mk3 spitfire?

[HMaze]

Yes, definitly a relais. D-Type needs a relay, because the solenoid draws a lot of amps to switch on.
Relay next to horn relay on bulkhead.

Cheers
Harry