Gearbox / Overdrive questions

[npanne]

Got a couple of gearbox questions for you kind people:

I have a GT6 overdrive gearbox of unknown provenance that I will be dropping into my Spit6 conversion - I have weighed up the option of getting it rebuilt, but for the cost of getting it done properly, I'll take my chances and drop it in - it's got two chances. It came from a car scrapped due to rot rather than mechanical failure, but that's all I know.

Whilst it's still out of the car, and currently unattached to an engine, is there anything I can check to make sure that it's not obviously faulty? I've turned the box by hand (in each gear), and it seems to turn over okay, and draining the oil revealed no metal filings or suchlike - anything else I should do / check to give me the best possible chance?

With regards to the overdrive, I have two units. One came with the 'box (so is equally unknown in terms of condition) - the other I got from the widow of a GT6 owner, and this one is nice an clean, and in a box wrapped up in packaging - which suggests to me that it's a refurbed item that never got fitted, but equally could be a faulty item that was removed and cleaned prior to being sent for refurb... is there any way of checking the condition of either? If I have a refurbed one on the bench then I'd rather fit this now, but don't want to take off a potentially good unit to fit a bad one.

Thanks as ever chaps.
Neil

[Nick Jones]

Presumably one of the overdrives is actually still attached to the box at this point?

You've already done the oil test and you've already checked you can get all the gears - so far so good.  You can also give the input shaft a wiggle. 3 - 4mm movement side to side at the tip is good.  Much more than this indicates a tired spigot bearing (between mainshaft tip and input shaft) which is a major weak point on these.

If you refill the box with oil you can spin it up with an electric drill (going the right way!) and using a 12v supply (battery) you can energise the OD solenoid and see if it kicks in. Actually, you'll more likely hear it as the drill will find the job quite hard and as the OD kicks in there is a momentary drop in hydraulic pressure which lightens the load briefly.

If all is good up to that point, I'd be inclined to pop it in as is and give it a go.

Beyond that it's take the top off and look for chipped teeth and checking how close the synchro baulk rings will go to the engagement dogs as a measure of their wear.  Can't go alot further without a complete strip down.  This is perfectly possible DIY if you are so inclined.

Nick

[npanne]

Thanks Nick.

Yes - one of the overdrives is still attached.
No real appetite for stripping it down myself - I have a history of getting halfway through jobs and running out of time / money / patience, and then not remembering to go back to it - hence the stripped engine in one corner of the garage, and diff in the other, no real wish to add a gearbox in yet another corner!

[nang]

In my experiences with 2.5 J types I've never struck problems with unknown used units mechanically. Any problems have been electrical and relatively easily fixed. Hope yours is the same  :)  Tony.

[hypoid53]

Check the relief valve on your D or J type overdrive as they can seize solid over long periods of storage (Ask me how I know!)

[npanne]

Okay, quick update.

Checked the input shaft for movement - very little play.
Checked the overdrive pressure relief valve - all free and clear.
Checked the overdrive filter - clean and clear (although gasket looks shot)
Checked the solenoid - working fine
Checked the reverse light switch - fine
Checked the o/d gearlever switch - fine
Checked the o/d inhibitor switch - busted (have plenty sitting around somewhere, so will just swap for a known good 'un)
Will stick new oil back in there later (didn't fancy doing that in the living room - might have been a liberty too far), and then spin it up with a drill.

Just waiting for my new slave cylinder and associated gubbins to arrive now, so passed the evening repaint wishbones instead, and remarkably cleared some space in the garage too.

[bob dunn]

http://www.tcoc.ie/wiki/item/367891                this is how i did mine, good luck

[npanne]

Just been changing over the inhibitor switch, and I noticed that I didn't have to press down on the lever to get reverse - in fact, on inspection, the lever was permanently "down" - so the spring on the gear lever joint has presumably gone.
Luckily I had another lever/linkage/casing in a box (how many times have I said that?), so I swapped the o/d switch over, and middle linkage bush (old one had disintegrated), and now I have a nice positive gear linkage, an inhibitor switch that works, and a gear lever that won't crunch into reverse every time I go for 1st.

Better to find these things now rather than when it's in the car, I suppose.

[npanne]

Nick_Jones wrote:

If you refill the box with oil you can spin it up with an electric drill (going the right way!) and using a 12v supply (battery) you can energise the OD solenoid and see if it kicks in. Actually, you'll more likely hear it as the drill will find the job quite hard and as the OD kicks in there is a momentary drop in hydraulic pressure which lightens the load.

Nick

Got a chance to bench test the 'box and o/d today - works like a charm.

Think it's ready to drop in now, and will see how it goes.

Cheers for advice.

[npanne]

Ok - next stupid question - if I may.

I have now tested the functionality of the solenoid, the in/out switch and the inhibitor switch, and managed to bench test that the o/d drops in and out with a direct application of 12v.

What I would like to do is assemble the whole o/d wiring rig on the bench, and test that it all works together. I have both parts of the o/d loom, and the relay, and I've worked out how it all connects together - so now I'm left with the two wires that (according to the wiring diagram) both go to different terminals on the ignition switch (one white, one brown). Can anyone advise what the purpose is of each wire, and which one (or both) would I need to feed to a + supply to test? I presume there's no problem with testing this set-up directly on a battery, and also presuming that the earth just goes to the o/d outer case?

[Richard B]

Presumably you have a relay for a D' Type?

If your relay pins have numbers this is easier.

The white wire is ignition switched so that the O/D can only be engaged when the ignition is on, goes to 85.

The Brown wire is permanently live and goes to 30. If you are customising your setup its worth putting a fuse on this wire before the relay. (I burnt out a loom on a MkIV Spitfire through a short circuit in an O/D where the wires had fratyed).

86 goes to the 3/4 inhibitor switch.

87 goes to the solenoid.


Its quite easy to test this in the car. nb if you are leaving the ignition on during testing disconnect the coil to prevent it overheating.



ps to test they both need a +  :)