Overdrive mk2 GT6

[Bob Horner]

Hi all

I wonder if any one can help with this one.  I have a mk2 GT6 that has been converted to overdrive (not by me).  I have noticed that recently, when the car is cold it behaves oddly in that it seems to be going into and out of overdrive.  Although, it may be more like a clutch slipping  - the revs rise but the speed does not - or rather does not straight away - if you apply power it seems to take up drive.  Once warm, it behaves normally - in and out of overdrive with no undue delay and no issue of revs rising or falling.  There is some vibration at higher speeds (70 plus) which I think is the prop - the UJs were changed and I think it needs balancing.  I don't think its electrical as all the wiring/switches were new (done by me) and checked and all seem to be working fine.  I know there are a couple of clutches in an overdrive and confess I don't fully understand how they work!  Oil levels checked and ok.  Its not long been back on the road (it was a part restoration that I finished)

Thanks in advance for any contributions.

Bob

 

[Pete Lewis]

as most has been refurbished i guess this is a D type ??

would start by checking the solenoid throw , under the plate on the drivers side inside is a lever  when energised you find a hole in the lever needs to align with a hole in the case  a 3/16 drill makes a easy tester you can adjust the give a tiny bit more travel .

on the top is a cap nut  undo and with care remove the ball and spring  pull the needle valve out  chech the very small hole in its tube is clear 

sorry as this all needs the tunnel off

as a simple test hold the gear lever to one side as the inhibitor switch may just need some simple adjustment especially with the cold/hot variations   often at fault  very cheap fix   its on the front of the gear  remote  

Pete

 

[NonMember]

From your description it sounds like poor engagement when cold, which is a little unusual (it's normally when it gets hot that the oil is too thin to maintain pressure past the leaks) but not unknown. As Pete says, it's worth checking the solenoid throw - if it's wrong then the thicker oil might be restricted by the valve not opening fully. If it were the inhibitor switch I'd expect it to be a harsh in-out-in-out, not the "clutch slip" symptoms you describe.

[Colin Lindsay]

1 hour ago, Bob Horner said:

Hi all

 I don't think its electrical as all the wiring/switches were new (done by me) and checked and all seem to be working fine. 

 

Hi Bob - I know you say the switches etc were checked but check again; I had this before on overdrive cars and the switches were not making full contact with the operating cam. One was half-worn away and the other was in a bent bracket. The O/d appeared to come on as normal but every so often would give a miss; revs up and down, but when it finally settled down it worked fine, maybe due to something expanding with heat and therefore keeping a better contact. Once I lined up the switches properly the problem went away. It's just a thought, but maybe worth a look at the operation. 

[Bob Horner]

Thanks chaps. One thing I should have said, which I observed today,  is that this slipping occurs when the overdrive switch is off.  It seems not to do it when engaged.  That would seem to rule out issue of it dropping in and out due to electric and/ or solenoid adjustment  issues?
Bob

[Pete Lewis]

ring dave twigger at OD sparea a call  always free to help 

http://www.odspares.com/phdi/p1.nsf/supppages/odspares?opendocument&part=2

there are some  test on their site to aid.solve some problems

read also daves   techy item 4   on slip

https://www.canleyclassics.com/?archive=the-d-type-overdrive

Pete

[DanMi]

35 minutes ago, Bob Horner said:

Thanks chaps. One thing I should have said, which I observed today,  is that this slipping occurs when the overdrive switch is off.  It seems not to do it when engaged.  That would seem to rule out issue of it dropping in and out due to electric and/ or solenoid adjustment  issues?
Bob

which type of switch do you have as it is a conversion, the ones on the gear knob can have wiring problems within the switch/gearstick that could cause the overdrive to engage when off, unlikely if you have the column lever of course

[johny]

Yes looking at the work shop manual it seems the OD clutch is slipping. When selected off the clutch is held engaged by springs but can slip if the friction material is worn (or contaminated with anti-friction additive), the springs are weak or hydraulic oil pressure is getting through to the operating piston even though the solenoid isnt energised.

The last of these possibilities is the simplest and the first thing to check is the adjustment of the solenoid arm as, if not returning to the correct position, it looks like it could cause this problem...

[NonMember]

1 hour ago, Bob Horner said:

is that this slipping occurs when the overdrive switch is off.  It seems not to do it when engaged.  That would seem to rule out issue of it dropping in and out due to electric and/ or solenoid adjustment  issues?

Not really.

My GT6 (when it was my brother's and still had a D-type) suffered from cracked insulation on the wire from the switch in the gearknob to the inhibitor. This would rattle around against the gearbox and ground out, pulling the solenoid in momentarily, irrespective of the switch. The result was partial O/D pressure - enough to disengage direct drive but not enough to go fully into overdrive - and a hopelessly slipping clutch effect on overrun.

It's also possible to have the solenoid misadjusted so that the valve never really fully closes, resulting in overdrive engagement without the switch. Again, that same GT6 had that problem when I fixed the wiring.

While I don't dispute johny's comment about weak springs being a possibility, it's rare. Hydraulic or electric faults (or maladjustment) are much more likely to be the cause.

[Clive]

Maybe a flush out (diesel works, but best with no load on the gears) plus a filter clean. Then refill with ep 80/90 GL4 would be my first suggestion if the solenoid is correctly adjusted.

Not had those symptoms on a D type, but did with a J type. That was a worn cone clutch in the OD.

 

[johny]

I was going to say, I know these units are pretty strong but after 50 odd years the cone clutch linings of some units must be coming to the end of their lives! 

[Clive]

3 minutes ago, johny said:

I was going to say, I know these units are pretty strong but after 50 odd years the cone clutch linings of some units must be coming to the end of their lives! 

A friend rebuilds boxes and od's.

He has had a few d types with broken up linings.

(And he has 2 that have been rebuilt, they are available, he usually takes some to Stoneleigh)

[GrahamB]

I only have experience of a J type on my Spitfire.  Is it possible to disconnect the 12 volt supply from the D type solenoid?  If this cures the problem then you know it is  an electrical problem such as an intermittent short in the wiring. If the problem persists then it is mechanical such as a worn clutch  or maladjusted solenoid.

[Bob Horner]

Thanks everyone.  A fair bit of food for thought from the above.   Time to take the bloody cover off and play around with it then!   
 

Bob

[johny]

Let us know what you find - for future reference👍

[Pete Lewis]

and we do need to identify it should be  a  Dtype soleoid on the rh side  but may have been converted to J type  solenoid LH side 

very different operational faults between the two models 

Pete

[Bob Horner]

Hi Pete

Its a D type - I should have cleared that up in my initial reply.

Regards

Bob

 

 

 

 

[Guppy916]

also first check your gearbox oil level it might be that simple 

[johny]

Always good to have the correct oil level but in this case, as it slips with the OD off, its the springs that keep the clutch locked not oil pressure☹️

[DanMi]

I would disconnect the electrics at the relay as a test and then drive the car. That can't cause any problems but would completely rule out electrical issues and is really zero effort. To be honest if it's not electrical/oil/actuator settings level it will mean a recon unit. I can recommend Mike Papworth in Coventry but have also heard good things about odspares and overdrive-repairs

[Bob Horner]

Update.  Disconnected electrics still had symptoms.  I’ve taken out the tunnel now (forgot what a git of a job this is compared to a mk3 spitfire).  Anyway, checked the throw of the solenoid and then removed cap nut etc to ensure all ok.  Unfortunately, still seems to be slipping when not in O/d..  Unless anyone has anyone has any other bright ideas looks like it’s a recon O/D.  If that’s the case, can I swap out the o/d with the gear box in situ?  

I had a vibration as well so removed prop to find it was out of phase by 90 degrees.  Sorting that has got rid of the vibration.  I wonder why it was set 90 degrees out on the first place?

 

 

 

[Pete Lewis]

you are sure its OD slip and not the main clutch ????

easy to get them confused .

you can lift the rear end and just about get  the OD off    refitting is a real faf as getting the splines aligned or getting two levers in the piston plates and opening the anulus lining to allow  spline alignment is darn difficult  " In Car "

Ive done this on my Vitesse   but would not  recommend it 

Pete

[Bob Horner]

Well, assumed must be O/d  issue rather than main clutch if no slip when overdrive engaged?

[Pete Lewis]

ring dave twigger at od spares to confirm your diagnosis    its free 

http://www.odspares.com/

Pete

[Bob Horner]

Dave has kindly got back to me - thinks its the Uni directional clutch so looks like a rebuild.   At least the tunnel is already off!  Will pull out the whole gearbox this week.   I've asked Dave for a price.  I see paddocks do one for £395 plus exchange surcharge.  Anyone any experience of their exchange units?  I'm in Yorkshire so spoke to ORS in Sheffield-  I've used them twice before for gearboxes and overdrives but 2 week wait minimum ( and slightly more expensive by £50 plus VAT).  

Bob