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Propshaft alignment
pdm - 8/4/10 at 08:06 PM

Hi there,

Wonder if you can answer a question of prop alignment please ?

You might know I'm dismantling a BMW E36 and the propshaft input is not central in relation to the half shaft outputs - it's over to the drivers side when looking from the rear of the diff. I'm assuming at this point that the half shafts are the same length.

I'm guessing this is a normal "shape" due to the internals ?

Potentially when this diff is installed into a kit the output shafts would be centred, the propshaft input on the diff would be offset to the drivers side - meaning the prop would need to be angled via the UJs if the gearbox output was exactly centred.

Is this ok from an engineering point of view ?

On the Beemer, the prop is meant to be in line front to back according to the manual which suggests to me gearbox output, prop and diff input are all on the drivers side OR the passenger side halfshaft is shorter than the drivers side with the propshaft centred. I havent had time to measure it yet.

thanks
Paul

daviep - 8/4/10 at 08:23 PM

Yeah it'll be fine either way.

Davie

locoboy - 8/4/10 at 08:23 PM

As far as I know props should always run with some misalignment be it either horizontal or vertical.

RichardK - 8/4/10 at 08:29 PM

Yes mate, less wear on the uj's if they are that way.

Rich

pdm - 8/4/10 at 08:35 PM

Thanks folks - so this install

looks ok to you all then ?

NB - it's a picture I've copied from a build blog so apologies for it not being my own car.

skinned knuckles - 8/4/10 at 09:28 PM

quote:
Originally posted by pdm
Thanks folks - so this install

looks ok to you all then ?

NB - it's a picture I've copied from a build blog so apologies for it not being my own car.


it could probably do with a bit more metal in there to hold the diff, or is the tyre on the floor going to become an integral part of the chassis the alignment looks about right from what i can see

tony-devon - 8/4/10 at 10:29 PM

some run out is required, keeps the rollers moving

if you run it straight then you could flat the rollers

I have a similar scenario, luckily for me it works to my advantage

I am using a shaft drive bike engine, so the output is well left, I have to flip the sierra diff over, and when the diff is central, the input flange is slightly to the left, every little helps

[Edited on 8/4/10 by tony-devon]

[Edited on 8/4/10 by tony-devon]

pdm - 9/4/10 at 07:02 AM

Excellent - thanks for the input everyone.

Bluemoon - 9/4/10 at 08:53 AM

The input and output flanges of the prop should be parrell (in both planes), and you should run a slight angle on the prop as noted above to stop the rollers wearing flat. I have some details of the angles that you should run and how parrell things need to be (u2u if you want the details I would have to look them up).

Get this wrong and an whole lot of problems can occur.

It is possible to run with the flanges out of line in particular positions but the geometry is complicated and I can't remember the details.

Dan

bassett - 9/4/10 at 11:59 AM

Hi, sorry to hijack but sounds similar to a query i have. My diff sits central with the prob dead inline with the centre bearing sitting on the same plane(flat). from the centre bearing the prop goes at a 35-45 deg angle to the bike engine sprocket adapter. From the posts above should i angle the centre bearing to face the sprocket slightly? Also why purely out of interest.
pic - not attached to bike engine - would go upwards

Thanks
Adam

[Edited on 9/4/10 by bassett]

Liam - 9/4/10 at 03:48 PM

To the OP - I'd get your tape measure out and wave it at your driveshafts. The Sierra diff also has the input off-centre compared to the output flanges - as you say dictated by what's inside. But on the Sierra it's designed so that the input is dead centre in the car and the driveshafts are unequal length to compensate for the shape of the diff. BMW may be exactly the same.

Liam

MikeRJ - 9/4/10 at 05:46 PM

quote:
Originally posted by bassett
from the centre bearing the prop goes at a 35-45 deg angle to the bike engine sprocket adapter.


Are you sure? That seems like an extremely large angle for a single Cardan type universal joint?

pdm - 9/4/10 at 06:01 PM

Yep - plan to measure it in situ as havent taken it off donor yet.

My worry is that
a) Bentley and Haynes suggest in the BMW it should be dead straight from gearbox to diff
b) if that's right then the halfshafts must be different length OR the whole lot is off centre in the BMW

which either way means that the kit isn't aligning the prop as per the donor.

I'll measure it and post back tomorrow.

Thanks again everyone

pdm - 10/4/10 at 12:07 PM

Well my measurements show what you all thought.

The half shafts are the same length, the gearbox, gearbox output flange, front part of prop and centre bearing all run centrally down the car.

The rear of the prop is then angled from the centre bearing to the input to on the diff.

In other words although its harder to tell on the donor, the fitting is the same setup as the kit.

Thanks to everyone who replied.