Anyone know about shortening Propshafts?

[appletree]

For my E36 SMG box to fit my IS i have to shorten the Prop and have the larger type e36 flange welded on to the shaft to fit the SMG box.

My qestion is which prop do i base the conversion on?

I coulds either use the E36 prop and weld the IS diff flange to it or use the IS prop and weld the e36 flange to it

things ive though about is that the E30 prop has some adjustment on the splines if my measurements abit out but the e36 shaft is newer and id imagine made to take more power.

The other thing that i think will determine the above is the position of the centre bearing on each prop, as you can see from the below picture the universal joints are on different sides of the centre bearing, does anyone know the reason for this and therefore which shaft would be better for my conversion?

E30 left E36 right

[GeoffBob]

Matt,

Keep in mind that the location of the centre bearing will be super-critical if you opt to use the E36 shaft due to the fact that the UJ is on the outbound side. See what I am getting at? The bearing runs around the E36 shaft from the gearbox, right? And you'll want the bearing to run smoothly around the shaft, right? Hence, if the shaft from the back of the box box hangs at say exactly 5.5 degrees to the horizontal (for arguments sake) the you'll need to bearing mount to also be at 5.5 degrees else the axis of the shaft won't be true/co-linear to the axis of the bearing mount. Yes, I realise that there is some give in the mount, but you'll still want to get it reasonably aligned, and that may take a bit of work.

However, if you use the E30 shafts the same will be true of the aftward shaft. However, you haven't changed the position of your diff and so that part is already taken care of. The E30 rear shaft will thus sit neatly in place and be happy in general

If I were you I would thus use the E30 prop shaft, but have the front shaft modded to accept the flange to match the output shaft from your Getrag 420g. Simpler all around in my opinion. But whatever you do, get it welded up and balanced by a professional.

[appletree]

This is what I was thinking Geoff, keeping the ability to slightly adjust the length of the e30 shaft could be useful to. I was going to try and work out how long the length of the shaft will be by measuring the difference in length of the two boxes including guibos and then take the difference off the prop and have the new flange welded on and all balanced by a local company who build props from scratch.

[DanThe]

I used an E30 prop for my 6 speed, also measured the difference between the boxes to determine the length

[appletree]

Great stuff Dan sounds like a plan! what did it cost you to get it balanced? and where? if you dont mind me asking..

[Dave_M3]

I cut the E36 M3 96mm BCD flange off the Evo prop and welded it onto the E30 318iS propshaft.
Then got it balanced.

I measured the difference in length between the two boxes first and also when I had the box on the car to be certain as I wanted to see was there any difference in propshaft position anyway with the mountings by bolting the front prop section and Guibo up solid to the box (3 nuts and bolts through the whole lot) so there was no deflection and measured what I needed.

Ended up having to shorten the prop-shaft 110mm.

Shortened the gear linkages 90mm if I remember correctly.

[appletree]

Thanks for your help Dave, ill do the same measurements and see if I get the same, at least i'll have a rough idea of what I should get.

[DanThe]

It was about £65 at a propshaft/driveshaft specialists not far from me