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GT6 OD slipping


Jim A

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Hi. Quick question. My Mk1 is finally on the road. I got an OD gearbox installed. We’re still shaking it down and we’ve found the OD slips out at times. It’s a bit like kickdown and happens mostly when you hit a hill and put some power on. Any thoughts? 
Thanks,

Jim

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If the gearbox oil is unknown and you don't know if any additive has been added by the previous owner, i think I may be tempted to drain all the oil and clean all the filters, refill  and see if it makes any difference? If not, as it has been mentioned, it sounds like the cone clutch  is slipping and needs replacing/relining....   

Edited by Martins Stag
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On 17/08/2023 at 19:26, Jim A said:

Hi. Quick question. My Mk1 is finally on the road. I got an OD gearbox installed. We’re still shaking it down and we’ve found the OD slips out at times. It’s a bit like kickdown and happens mostly when you hit a hill and put some power on. Any thoughts? 
Thanks,

Jim

My underline.  That is NOT a slipping clutch cone on the O/d!  As Nick says, probably an electrical connection.

John

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Great, while driving it try to get a feel for whether your losing drive (OD slipping) or its just momentarily dropping out into non OD. Unfortunately the symptoms will be very similar but perhaps the first actually causes a drop in speed while the second not? Also the second shouldnt be related to engine load so youll see the revs go up momentarily while just cruising on the flat....

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Have you checked the solenoid adjustment. If its not pulling the actuating leaver all the way you could have low oil pressure not fully holding the OD in. 

It's quite easy to do on a D type I have no experience of other types of OD but I would expect it to be similar.

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  • 8 months later...

I have a similiar problem. When driving at 60mph (3000 rpm) and engage the OD, initially nothing happens. If i take my foot off the accelerator slightly, the revs drop to 2000 rpm as if the OD has engaged. However, as soon as i touch the accelerator the revs jump back to 3000 rpm as if i have switched the OD off. I have a 73 mk3 GT6. I assume the gearbox oil / fluid is shared between the gearbox and the OD unit. The gearbox oil is full. I have read somewhere the OD has its own transmission fluid.......

I can hear the solenoid click when engaged (stationary with engine running) in 3rd and 4th gear, no click in 1st or 2nd which is good.

Thanks in advance for any tips

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1 hour ago, PaulGT6 said:

I have a similiar problem. When driving at 60mph (3000 rpm) and engage the OD, initially nothing happens. If i take my foot off the accelerator slightly, the revs drop to 2000 rpm as if the OD has engaged. However, as soon as i touch the accelerator the revs jump back to 3000 rpm as if i have switched the OD off. I have a 73 mk3 GT6. I assume the gearbox oil / fluid is shared between the gearbox and the OD unit. The gearbox oil is full. I have read somewhere the OD has its own transmission fluid.......

I can hear the solenoid click when engaged (stationary with engine running) in 3rd and 4th gear, no click in 1st or 2nd which is good.

Thanks in advance for any tips

Oil is shared between OD and box. So that is the easiest possibility crossed off.

Have a read through this 

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

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To me it sounds like the friction surfaces are slipping so that OD doesnt grip until the power is taken off and then slips as soon as it returns. This can be worn friction material or low hydraulic pressure. The oil filter, which if blocked might explain the latter, is accessible from the underside of the OD...

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