BMW STUB AXLE CONVERSION FOR A LOTUS EUROPA
BACKGROUND
A
problem I've seen on S2 Europas is loosening rear hubs and stub axle breakages.
If the retaining nut is not tight enough, the hub works loose. Increased torque
on the retaining nut MIGHT work, but this seems to lead to failure of the stub
axle.
I
had suffered from loosening of the hubs for many years, as well as rapid
degradation of the driveshaft universal joints. I was determined to cure both
problems and decided to fit CV jointed driveshafts, upper suspension links, and
new stub axles. The following details the stub axle conversion for a Europa
using the driveshaft as the upper suspension link.
At
the time of the original conversion I had an Alfetta GTV 2000, and I notice
that the driveshafts were exactly the right length for my design (400mm flange
to flange, 420 extended, 380 collapsed). In the past I had seen CV joint
conversions on Elans, and these all used cut-and-shut VW shafts, or uniquely
machined shafts (very expensive!). I wanted shafts that I could pick-up
complete from a wrecker, in case I needed spares. These shafts unfortunately
use SPICA CV joints, which are not readily serviceable. Perhaps I should have
tried to find something which uses Lobro CV joints (VW or BMW). I purchased an
Alfetta rear end, intending to use the Alfetta stub axles as well, but these
proved to be too short.
My
next choice of stub axle was BMW. I had previously owned a 2002, and thought
they should be OK. In retrospect, I probably should have fitted BMW drive
shafts as well. I visited my local BMW specialist in Melbourne, and found they
had bucket loads of stub axles and hubs. I selected a pair of stub axles with a
30mm shaft diameter. This shaft diameter would press straight into the existing
outer bearing in the Europa. The inner bearing on the Europa is a bastardized
6006 bearing machined out to suit a 31mm shaft. New 6006 bearing with a
standard 30mm diameter are really cheap, and can be supplied fully greased and
sealed.
The
flanged end of the stub axle (that attaches to the driveshaft) is basically
flat.
I
think the original stub axles I used came from 2002Tii or 2000. The second set
came from a 320 or something similar. Anyway, take the attached sketch along to
ensure you get the right parts.
WHAT YOU NEED
This
conversion requires
-
a pair of BMW stub axles with 30mm shafts, matching hubs and nuts. Overall
shaft length approx 223mm
-
two new driveshafts (20mm shorter than original)
-
two new U/J flanges for the ends of the drive shafts (to mate to the BMW stub
axles)
-
two new standard 6006 inner wheel bearings
-
two new 6206 outer wheel bearings (only if required)
-
4 tubular spacers, 30mm ID
-
2 spacer rings to centralize the brake drum on the BMW hubs
-
8 x 5/16" bolts and Nyloc nuts to
attach the new flanges on the driveshaft to the BMW stub axles
-
adjustable lower links to fine-tune the rear camber. I assume all Europa owners
have already done this!
STUB AXLES
Please refer
to the two sketches. One is coloured in the help identify the different parts.
The other details the dimensions of the last BMW stub axle I used
The
stub axles will need two (maybe 3) modifications
1
- the flange of the stub axle needs to be machined to accept the new U/J flange
on the driveshafts
2
- drill the stub axle flange to match the bolt pattern of the new U/J flange
In
the last few cars that were modified the following had to be performed
3
- the surface where the outer wheel bearing mounts needs to be built up and
ground to 30mm diameter. This can be done by hard chroming.
HUBS
The
BMW drive hubs need three modifications
1
- knock out the old BMW wheel studs (approx 100mm PCD). Drill 4 new wheel stud
holes on 3.75" PCD. From memory these holes need to be 1/2", and you
will need to countersink the holes to ensure the studs are long enough.
2
- machine down the outside diameter of the hub so that it fits inside the
brakes. The hub will hit the brake shoes and wheel cylinder if it is not
machined down, and it will also be too big to fit against the mounting face
inside the brake drum.
3
- a spacer ring is required on the hub, to locate and centralize the brake
drum. I fitted a spacer onto the hub (with Loctite) and then machined the
spacer down so that the drum was a nice snug fit.
P.S.
during my recent restoration, I modified these spacers. Now they are also used
to act as a pilot for centralizing my Cosmic mags
The
BMW hubs are quite hard to machine and drill.
DRIVESHAFTS
These
need to be 20mm shorter than the original shafts. I highly recommend you get
new shafts made. The tubing used on the Europa drive shafts is quite small in
diameter, and very thin. This makes it very light, but eventually it may twist
if you have a half decent cross flow engine with twin Webers.
SPACERS
You
will need 4 tubular spacers (similar to the ones used in the original Europa
set-up). Two will be used between the wheel bearings (approx 65mm long), and
two will be used between the outer wheel bearing and the BMW hub (approx 24mm
long).
These
spacers should be just over 30mm ID so that they easily fit over the 30mm stub
axle. Make sure you use something with a wall thickness of at least 5mm.
You
can vary the length of the longer spacer to adjust where the flange of the stub
axle will sit. If your not sure, start with a longer spacer and do a dummy
build. You can always remove a millimeter or two. Use the original long spacer
as a guide. If the original spacer is OK – use that! Mark all spacers, stub
axles and hubs "left" and "right", so the same parts always
go back together in the same order.
You
can vary the length of the shorter spacer to adjust where the hub and drum sit
relative to the brake shoes. Start with a long spacer and do a dummy build.
On
my car with Alfetta CV joints, the O.D. of stub axle flange was approx 100mm.
This required moving the spring/shock assembly rearward slightly on its lower
mounting bolt. I think I used 2 or 3 washers, each one approx. 1.6mm thick.
If
you don't have adjustable lower links, then the rear camber can be adjusted
(more negative) by shortening the longer spacer between the wheel bearings.
This would require building up the rear end, taking the car for drive to settle
the suspension, then measuring the camber. You then have to strip out the stub
axles and machine down the spacers and repeat the measurement process – a very slow and tedious task.
Don’t
forget to do a rear wheel alignment and set the toe-in.
If
you need some advice or clarification, please fell free to contact me rmann5@ford.com.
Richard
Mann
7004100119Q
RH
drive S2
Melbourne
Australia.