Lotus Elan

Modifying a gearbox input shaft

PostPost by: worzel » Sun Apr 15, 2012 12:29 pm

Hi

I suspect I'm going to attract a lot of "don't even consider it" comments but is there any feasible way to alter the length of a gearbox input shaft- anybody out there done it already?

John
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PostPost by: mikealdren » Sun Apr 15, 2012 12:43 pm

Why? Are you looking at using a non-standard (non-ford?) gearbox or a different engine?

It may be possible to machine a little off the shaft making it a little shorter or to fit a smaller spigot bearing but the clutch splines will remain fixed.

You can look at different input shafts for some boxes.

Mike
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PostPost by: worzel » Sun Apr 15, 2012 1:18 pm

Hi Mike

Thanks for reply. It actually is a Ford box but the splines are wrongly positioned- they need to be about 0.626 inch further out. Alternative input shafts aren't available that'll do the job. My reasoning for asking was that the prop is welded and transmits the power so why couldn't an input shaft be altered and then re-hardened?

John
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PostPost by: c42 » Sun Apr 15, 2012 1:50 pm

Which gearbox are you using?

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John
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PostPost by: worzel » Sun Apr 15, 2012 6:16 pm

Hi John

It's a MCT75. I could solve the problem by altering the bellhousing but since the one I'm using is a Rocket item at ?450 I don't feel like carving it up. Anyway, as far as I know the input shafts on lots of boxes are hardened on the outer skin so I don't see why one couldn't be alterted for length, cleaned up properly on a lathe then case hardened again. A prop is only a tube transmitting all of the power and that has quite a bit of welding on it so why not a gearbox shaft?

John
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PostPost by: c42 » Sun Apr 15, 2012 8:55 pm

I see what you mean! The problem thet you have is that the input shaft has to cope with loads of torque, the propshaft although welded is a a larger diameter which gives the weld more ability to deal with the forces but the smaller diameter input shaft really needs to be solid with lack of weaks spots; the other issue would be to ensure that the shaft was true post welding and I fear that at some stage a welded input shaft would snap like as carrot.

A bit off the wall but I would consider how I could get the clutch plate nearer the gearbox, maybe a flywheel spacer or different flywheel for instance.

Sorry that I could not be more helpful.

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PostPost by: rgh0 » Sun Apr 15, 2012 10:50 pm

While it would be technically possible to modify and lengthen the shaft by cutting and welding it would be very expensive to get it done properly with the right welder, the right gear, the right weld procedure, the right pre and post weld heat treatment, Xray examination etc etc. And even then the strength will not be as good as an orginal shaft.

Modification to other components or getting a complete new shaft made seems a better bet.

cheers
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PostPost by: mikealdren » Mon Apr 16, 2012 9:59 am

If the problem is with the position of the splines, can you overcome it with a different clutch plate? That's certainly the approach that Spyder take with the Zetec and MT75.

Mike
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PostPost by: worzel » Mon Apr 16, 2012 1:44 pm

Hi Mike

Re your comment about the clutch plate. The problem is that the splines on the input shaft are about 0.625 inches too far back resulting in the friction disc splines overhanging. I know that custom friction plates can be made up but I'm not sure if they'd be able to resolve the problem of so big a discrepancy.

By the way- you mentioned Spyder have a similar problem- can you elaborate at all. No reflection on Spyder but they obviously don't wish to give away for free, info they had to research and pay for.

regards

John
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PostPost by: mikealdren » Mon Apr 16, 2012 4:07 pm

There are various different clutch plates and covers available and I think (but I don't know) that the position of the clutch boss can vary in relation to the friction surface.

I'm sure others here will know more.

Spyder recommend different combinations to suit the geometry of the various components.

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