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D type.


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Hmm. Had the d type in 20 odd yrs. works great. When it works. However it has always been a little slow to engage now even slower and often doesnt. Especially when working hard at motorway speeds. Drained it and changed the oli which was very clean with no bits. I assume solonoid adjustment ? Any tips ?

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some  things to check  now  ,youve done the oil levels.


take off the tunnel

remove the plate on the drivers side

operate the OD  

the lever inside is pulled a short distance by the solenoid  Yes ?

NO check 12v is at the short solenoid feed wire  YES ??

NO check the 3rd 4th inhibitor switch is working,

check the relay is clicking  


if solenoid pulls the arm you will see there's a 3mm? hole in it , when operated push a drill through this hole it should line up with a similar hole in the main case, if this is out of line adjust the nut on the solenoid shaft till its all lined up.


solenoids do suffer from corrosion, can be a pig to get at the lower fixing to remove it and clean the plunger and its bore


there is a switch on the end of the solenoid which once engaged reduces the coil amps from 10 down to a holding coil of about 0.5 amp

these switches can fail, most are sealed not repairable.


when all this drives you mad remove the hex cap nut on the top of the case gallery

inside is a spring and small ball and the spool valve with a very fine hole down its length  make sure the bore in the valve 'tube'is clear 

its through this little orifice the pressure is controlled



think that will do for a start,  Oh   dont forget some strong tea laced with something happy 



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a ha!!!    first you have to get at the bottom   screw  


may need to jack up the unit a bit or............... remove the chassis   Hmm  !!!!!


if you do.....

     get some allen key/socket cap screws as you can get a long extenion on with a hex bit ... makes for easy next time 

          i would look first and  not buy  till you have two,  check the setting , if its out a bit its a simple and cheap adjustment 



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  • 7 months later...

I have a similar issue apparently developing to that outlined above, but with slight differences as outlined below...


The D type overdrive on my GT6 has started engaging slowly, or struggling to engage under load. If I take the load off the drivetrain it engages smoothly and quickly, staying engaged under all conditions without slipping. My first thought was that the oil level in the gearbox was low (it does leak), but having checked it and topped up a little as required (100ml), the problem remains. I'm guessing it's a tunnel out and check the solenoid throw and clean the filters as the next step, unless anyone has any other pearls of wisdom?


Many thanks,



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