J type o/d odd behaviour

[AlanT]

Hi All,

The OD in my Spit 1500 resto has suddenly decided to self engage when the engine is hot. Works perfectly fine then, out of the blue, decides to engage. Flicking the switch does nothing. Any ideas? Obviously I've gently nursed home so as not to wreck things in 1st and 2nd. After sitting it's fine...until hot again! 

Thanks

Alan

[NonMember]

Not too much risk of wrecking things in 2nd, or even 1st. It's reverse you need to beware of!

Three possible causes - electrical, mechanical or hydraulic. It's unusual for any of them to exhibit self-engagement - more usually the opposite - but not impossible. My GT6 used to partially self-engage due to a bit of exposed wire hitting the gearbox casing, but that's a D-type problem, where there's a low-side switch to the relay. You could have a sticky switch but I think it unlikely. Hydraulic is possible if the small return drilling is blocked. The oil pressure then builds even with the solenoid disengaged. I would expect that to happen when cold, though. Mechanically, the solenoid could be sticking, although I'd expect that to exhibit as a failure to disengage rather than a self-engagement.

I assume you've not got any bizarre add-ons or strange wiring?

[AlanT]

Thanks. No oddness that I’m aware of. Will try it again after work but truly hope not internal. Was flushed and refilled before I fitted to the car. 

[johny]

Sounds like a wiring fault to me which is quite common as the environment around the gearbox is hot, oily and subject to movement so the plastic insulation can break and earth the circuit down intermittently thus bypassing the switch+interlock and operating the OD...

[Badwolf]

I have just come across a couple of metres of that bendy, slit down the length cable protector stuff. I may try putting some over my overdrive switch cable before I refit the tunnel cover, but would it melt next to the gearbox? It just looks like a flexible plastic compound.

[AlanT]

Thanks @johny Guess it’s back up on the axle stands to take a look…irony of it is that it was only taken off them yesterday after changing 2xUJs! 

[johny]

Depending on your wiring I would have thought the only earth fault to give you the symptoms described would be between the OD relay and the gearbox interlock switch. Could be a yellow/green wire and a short to earth here would erroneously pull in the OD relay to operate the unit in all gears (including reverse)...

[NonMember]

Just now, johny said:

between the OD relay and the gearbox interlock switch.

That's where my GT6 had the problem but the thread title says "J type" which ought to mean no relay and all the switches on the +ve side

[AlanT]

Yes, J type. No relay. I’ll see what I can see and report back (may be a day or so as have lots of work on).

[Pete Lewis]

J type with a mind of its own has all the sounds of the solenoid piston/plunger is sticking or the0 rings have worn out  

unscrew the sol  needs a 1" af thin spanner  dont use grips on the casing  you can wreck it   some oil will escape

give the sol a good shake  it should rattle as the plunger  moves back and forth   

cure is remove the small 10mm circlip and get the spool plunger out may need a good tap on the bench   

0 ring kits available from various places should be quite cheap  James Paddock Limited - Triumph Stag, Spitfire, TR6, TR7, GT6, Vitesse, Herald Parts and Spares Specialists. OVERDRIVE SEALS SET J TYPE(JPS287)

Pete

 

[Colin Lindsay]

1 hour ago, Badwolf said:

I have just come across a couple of metres of that bendy, slit down the length cable protector stuff. I may try putting some over my overdrive switch cable before I refit the tunnel cover, but would it melt next to the gearbox? It just looks like a flexible plastic compound.

Shouldn't melt unless it's touching the exhaust; it's usually good stuff. I have it on my own overdrive gearbox to protect the cables.

 

[AlanT]

3 minutes ago, Pete Lewis said:

J type with a mind of its own has all the sounds of the solenoid piston/plunger is sticking or the0 rings have worn out  

unscrew the sol  needs a 1" af thin spanner  dont use grips on the casing  you can wreck it   some oil will escape

give the sol a good shake  it should rattle as the plunger  moves back and forth   

cure is remove the small 10mm circlip and get the spool plunger out may need a good tap on the bench   

0 ring kits available from various places should be quite cheap  James Paddock Limited - Triumph Stag, Spitfire, TR6, TR7, GT6, Vitesse, Herald Parts and Spares Specialists. OVERDRIVE SEALS SET J TYPE(JPS287)

Pete

 

Thanks @Pete Lewis tunnel out pain! 

[Pete Lewis]

used to be called Kopex   any search will find it 

can be slit or not all diameters are available 

Pete

[johny]

3 hours ago, AlanT said:

Thanks @Pete Lewis tunnel out pain! 

Certainly sounds now like its got to be sorted before being driven again due to the risk of OD engaging when reversing😲

[AlanT]

I’ve now done an extensive internet search and can’t find any references to J type self actuating, which leads me to think the problem must be electrical. Loads of threads about them stuck on or slow to engage, none about them suddenly switching on and staying so.

What’s baffling is that it’s stuck in first and second. Implies that power is getting to it despite two switches being off.

Was working perfectly-fast to engage and disengage - so filter and flow issues would, I hope, seem unlikely. 
Will look at the solenoid wires from underneath and see if there is an obvious issue before taking out the tunnel (groan!). 

Alan

[johny]

If you disconnect the electrical supply completely from the OD control circuit and it still has the fault then its definitely mechanical😁

[NonMember]

47 minutes ago, johny said:

If you disconnect the electrical supply completely from the OD control circuit and it still has the fault then its definitely mechanical😁

Good point and a very easy test - there's a pair of bullet connectors between the main loom and the gearbox loom which are accessible from the engine bay.

[AlanT]

Ah! Not that easy! Mine is a conversion with the power borrowed from the reversing light switch. Tunnel out…I can just about reach the solenoid connectors so will disconnect that way.

[johny]

Think thats the standard way to supply the OD, certainly shows that in my WSM for late GT6. In fact as an aside the OD wiring diagram shows no relay which is interesting if that signifies a J type as theres been a long running argument about whether any GT6 got the later type OD....

[NonMember]

10 hours ago, AlanT said:

Mine is a conversion with the power borrowed from the reversing light switch.

As johny said, that's the standard way for J-type. Just unplug the feed to the reversing light switch - you don't need reversing lights for this test - which is a bullet connector in the engine bay.

[AlanT]

Thanks. I’ll do that. 
Having researched more, I suspect a blocked valve. The initial feeling (once hot) is of the unit being half engaged (can see the rev counter moving about) before becoming locked engaged after a few more hundred yards. The pressure seems to be building up? Not sure how easy this is to clear. Found this but may be for D type. Symptoms are same http://www.triumphspitfire.com/Over.html

[AlanT]

Will do the electrical test first. 

[johny]

Your blocked valve idea is something I was wondering Alan as my WSM talks of cleaning out a small hole in the valve operated by the solenoid (admittedly D type but must be similar) which I think if not clear could allow pressure to build up and engage OD unexpectedly...

Remember when testing car, pick a route where reverse will never be needed!  

[AlanT]

Thanks @johny Only reversing is when cold to get out of garage! 

[johny]

🤞