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Fitting an overdrive to a seires 3 Lightweight


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After reading the instructions; on here, I decided to give it a go.

My reason for delaying was not being sure that the pilot hole would be in the right position so I would end up with a tranmission tunnel resembling Swiss cheese (full of holes as opposed to yellow and hard) but with Billing coming up, I decided I could not wait any longer.

I started by removing the 6 nuts (15 mm AF) holding the transfer box gear cover, as seen in the middle of the photo.

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The top cover plate was then removed by undoing 4 nuts (13 mm AF) hmmmmm... looks like my guarantee is void!

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The reason for the removing the top plate becomes apparent since unless you have special tool 600300, you would use a drift to undo the lock nut but only after a flat blade screwdriver is used to knock back one of the tabs.

I used a Machine Mart punch to undo the nut (not the one shown in the photo since it was too long). The MM punch is just the right length to give enough room to swing a hammer, albeit holding the head sideways. This punch is also small enough to pass through the drain plug should you drop it (no guesses as to how I found that out!).

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The gear can be removed and replaced by the clutch sleeve. The same lock tab can be used but 2 of the tabs need shortening as they cover the gear teeth preventing the clutch sleeve sliding past it. I shortened two tabs as the longer one was used to lock the nut in place - by trial fitting of the nut, the lock tab can be fitted into a position where it will align with one of the cut outs in the lock nut.

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At this point I fitted the angle bracket in place; the two 8 mm bolts are already fitted so you don't need to buy them, like I did.

The nuts holding the bracket were done up tight so the bracket was in its proper position and then I drilled a 6 mm hole at the position given in the manual. I continued to drill so as to mark the bracket - no messing around with pencils for me!

The manual states to use an 8 mm hole, I didn't for reason that will become apparent later.

The seat box side on my lightweight is vertical whereas the manual show it to be sloping backwards. It is not totally clear how you are supposed to mark the hole: for the vertical measurement - do you measure along the tranmission tunnel or in mid air and then transfer the measurement across?

plus what do you use as the lower reference? - the driver's floor does not meet the transmission tunnel so depending on which you use, there can be a difference of a few mm!

I used the figures in the manual and it turned out it is not cirtical since the 50 mm diameter hole is more than enough to cover the pilot hole.

In my case the pilot hole was spot on vertically but 11 mm to far forwards.

The instructions are a bit confusing here about drilling the second hole counter-intuitively using X for vertical distance and Y for horizontal. What you are trying to do is to align the pilot hole with the centre of the welded nut on the bracket.

Once done, I used a 51 mm hole cutter (Machine Mart) for the hole, on a 6 mm pilot drill - an 8 mm

hole would have been too big! As the tunnel is aluminium, the cutter took no time at all to make a neat hole.

At this point I fed the operating lever through from below to get the pivot through the hole (the bracket has to be removed to give more room), refitted the bracket and done up the pivot bolt.

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This was followed by fitting the operating lever. I purchased both the rubber grommet and sealing plate from Craddocks but could have saved money by making the round aluminium disc myself and bicycle inner tube for the rubber grommet, oh well.....

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Likewise the lock tab sent had the same length tabs as the original so needed shortening - seems one part is used for both applications.

Now the overdrive can be fitted. I offered it into place but it stood proud by about 10 mm. After some head scratching, I found that it helped to pull it out and then push it in quite quickly for it to engage past whatever was stopping it. The nuts are done up by a couple of turns and the unit withdrawn to give enough room to fit 2 of the spring washers and nuts whose stud ends are blocked off by the casting. These are the lowest two and can only be done up using an open ended spanner. I found that the supplied gasket would catch as the overdrive was pushed in and out and after tearing 3 of them, I made one out of a Special K box although any other cereal box could be used but with a slightly larger centre hole. Time will tell if this will leak.

Lastly don't forget to refit the earth strap and do the nuts up tight. The final fiddly job was fitting the clevis pin and split pin to join the operating lever to the overdrive selector shaft; this had to be done by feel. The fiddly nature of the job meant I was not able to fit the insulator piece - these can be made from a plastic milk bottle saving some more pennies.

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Overall it took about 6 hours!

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Is that a Fairey OD or a spanish (Ribas or Toro) one? It looks a lot like mine and I have a Ribas.

Do you have more detailed pictures of the lever's sealing plate? Or a part number from Craddocks... I still have to seal the hole in the tunnel on my civy SIII :P

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Is that a Fairey OD or a spanish (Ribas or Toro) one? It looks a lot like mine and I have a Ribas.

Do you have more detailed pictures of the lever's sealing plate? Or a part number from Craddocks... I still have to seal the hole in the tunnel on my civy SIII :P

no, definitely Fairey and identical to the instruction manual (or Manuel! :rolleyes: )

Part numbers are in the overdirve manual - the underline bit "on here" is a link to the manual, place your pointer and then click.

No photos of the sealing plate but it is an extremely complex piece of engineering; imagine a disc cut from aluminium sheet with a smaller hole :lol: The rubber gaiter is similar but with a smaller central hole. I can measure them but you should be able to make one to be an exact fit. I forgot to mention three holes for self tapping screw, I've yet to fit them.

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Hi !!! Just wondering how the overdrive is working and is it noisy / whining ????..........Tell you why 'cos I was offered one like yours where the teeth on the small gear were worn to an uneven shape and a little blued off. I chose to hang off for a while and the bloke is holding it for me . Wondered if yours was ok 'cos if so then I would buy it and fit it. Hoping you could help me out and advise. Thanks. P.S. When fiting 'boxes put a liberal spread of grease on the gasket surfaces and the leaks will not come.

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ah, yes, special note B, didn't see that, oh well.... :rolleyes:

re: teeth - they look far worse than in the photo but they are a bit worn on one edge; still a triangular shape but the side of the triangle moved over to one side. Not driven it yet but should do by the w/end. Worst case is to replace the clutch sleeve, a mere £ 50 or so.

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Hi !!! Just wondering how the overdrive is working and is it noisy / whining ????..........Tell you why 'cos I was offered one like yours where the teeth on the small gear were worn to an uneven shape and a little blued off. I chose to hang off for a while and the bloke is holding it for me . Wondered if yours was ok 'cos if so then I would buy it and fit it. Hoping you could help me out and advise. Thanks. P.S. When fiting 'boxes put a liberal spread of grease on the gasket surfaces and the leaks will not come.

If you think about it, and I did, those teeth are "permanently engaged~" - if that is the correct term? so it is not like two gear wheels whose teeth mesh against each other and mesh with drifferent teeth hence there shoould be no movement of tooth against tooth.

Qnyway, took it out on Saturday and quiet as a mouse, well I couldn't hear any additional noise above the usual gearbox and diff howl :o, although it did soulnd more clunky that turned due to FWH being engaged -so quite please really - shuold get about 60 mpg now!

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