5 Speed Gear box into baby Elan Prop shaft length discussion

[mark030358]

So, almost getting there with my 5 speed conversion. One of the more curious aspects of this is the propshat length. So here are my findings...

BMC on the 11 Sept 2010 said he measured his at 30” flange to flange and had it made up at 29.25” compressed.

Aussie John on the 12 Sept 2020 measured his as 29” compressed.

Alex Black had to add 8mm spacers to his engine mounts when he did his build, thus too long. I am assuming he used BMC's 29.25" length as Alex's thread was very popular and I have referred to it mant times (thanks Alex).

Rohan measured his spare +2 prop shaft at 972mm centre to centre of the UJ’s. Now adding 30mm each end for UJ to flange, this gives 972mm+30mm+30mm = 1032mm. But the +2 chassis is 12” longer than a baby chassis thus baby prop shaft length flange to flange is 1032-(12*25.4)= 727.2mm = 28.6”

However, I have been very lucky to have had a friend measure his original Sprint 5 propshaft at 73cm/28.75". He stated that at this length the shaft was virtually fully compressed.

So I conclude the length, withe no plunge (extension of the sliding spline) is somewhere between 28.6"/72.7cm or 28.75"/73cm.

I will have mine made up at 72cm/28.34" so hears hoping all works out well


Comments welcome...

cheers
Mark

[nmauduit]

fwiw I went into the same rabithole circa 2014 and opted to a 29" compressed length propshaft (made by North West Propshaft, £150 VAT included - no affiliation) : it fits and no issue so far, only that at first the flange was not the one that I had sent originally which did not fit the gearbox, a second propshaft had to be made (FOC, no issue only a small delay)...

[mark030358]

Found something interesting today, when working on my gear box.

In the attached photos, there are two caps and two springs, one set from an Elan box, one set from the Elite box.

The longer spring and cap with a hole in it are from the Elite box. The Elite cap is also slightly shallower that the Elan one.

So two things, the hole in the cap acts as a breather for the box (some people have drilled holes in the casings ) but this is much much neater fix done by Lotus (I assume), as the pressure can vent here. Also the oil would have to propagate through the internal plunger in the assembly to leak out. All in all very happy with this.

Secondly and perhaps more interesting is that the spring is MUCH weaker on the Elite box. Even though the Elan box has a shorter spring it has much fatter coils, thus making it much harder to compress. I did a compression test on both and for sure the Elite spring is weaker. I fitted the gear lever and with the box on the bench I could make the 5th gate very easily. I didn’t fit the spring to return the lever to go back to 3rd/4th rail, as the pin didn’t want to come out and I was worried about damaging the case.

Cheers
Mark






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[mbell]

Interesting, the elan standard setup if far to stiff. So good they softened it.

It's there any difference in the spring and done but on the under side? This impacts the effort to get it out of 5th gear.

[mark030358]

That’s a good question, I haven’t looked, will check next weekend.

I’m 99.9% sure the Elite box had not been opened up before I got it. Will post on here what I find.

Cheers
Mark

[mbell]

Also notice that one of the covers had a small hole filled in it. Was that from the elite box?

Maybe lotus adding the missing breather? Probably a good spot for it being pretty far out of the way.

[mark030358]

I like to mention companies that do a good job and give credit where credit is due. Sent a +2 propshaft to Firow Propshafts, https://www.firowpropshafts.co.uk ( contact Mark Rowley 01477 535960)to have it shortend, balanced and painted. I have no affiliation whatsoever.

They had it just around 10 days and it came back today. I am delighted with the quality, finish and speed of service, just excellent. Even the return packageing was top notch.

By the way 72cm fact to face when compressed.

Here are a few shots

[mark030358]

So a quick question and favour.... Could you measure the distance from the bulkhead to the edge of the bell housing as per my photo below, just want to make sure I'm in the ball park so to peak.

Propshaft length no issue by the way.

cheers
Mark