Lotus Elan

Chassis geometry - gearbox output shaft height

PostPost by: Giff » Mon Jan 17, 2022 7:00 pm

Hi,

Would anyone know the correct gearbox output shaft height within the chassis?

I guess it is quite high to allow a straight run to the diff?

Thanks.
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PostPost by: rgh0 » Tue Jan 18, 2022 1:27 am

The height is mainly set by the height of the GB mounting bracket and the spacers the Lotus used and the standard Ford Rubber GB mount. Unless your are changing one or more of these components the height is what they give you. I have never actually measured what dimension this gives you from chassis bottom to output shaft centreline


The end of the GB tail may go up or down a little also depending on what if anything you do to raise or lower the engine mounts if doing things like trying to fit a tall block motor under the hood.

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PostPost by: Elanman99 » Tue Jan 18, 2022 3:31 pm

Giff wrote:Hi,

Would anyone know the correct gearbox output shaft height within the chassis?

I guess it is quite high to allow a straight run to the diff?

Thanks.


Most (maybe all) transmissions using Hardy Spicer type UJ's are designed to have some angulation at each end of the prop shaft so that at every shaft revolution their is some movement in each needle roller bearing to ensure the needles and grease do not fuse in to a rigid mass.

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PostPost by: Giff » Tue Jan 18, 2022 3:39 pm

So almost arbitrary? I can work with that!
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PostPost by: snowyelan » Tue Jan 18, 2022 4:41 pm

Not arbitrary. It is important to have the gearbox output axis and the diff input axis parallel. a couple degrees out is probably acceptable, but I'd try and keep it within that. There are some good videos out there explaining u-joint phasing that will explain it better than I.
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PostPost by: Giff » Tue Jan 18, 2022 6:47 pm

Wow ok - well that was a learning experience - thanks - I can now be specific in the positioning to align it in parallel with the differential output - think I need to get the string and the laser level out
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PostPost by: 2cams70 » Wed Jan 19, 2022 12:27 am

snowyelan wrote:Not arbitrary. It is important to have the gearbox output axis and the diff input axis parallel. a couple degrees out is probably acceptable, but I'd try and keep it within that. There are some good videos out there explaining u-joint phasing that will explain it better than I.


Yes there's definitely more to tailshafts than meets the eye. A good reference as to how to design / modify is the Australian VSB6 modification code for trucks.

Do a google "VSB6 truck modification code" and read the section relating to tailshafts. Although it's specifically about trucks the principles applied to anything else are the same.
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PostPost by: rgh0 » Wed Jan 19, 2022 12:54 am

I still don't understand the problem behind the question - why not just build to the original design using the original components ? Is this for something that is not a standard Elan / Plus 2 in some way ?

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