How
In the end, Option 7 won and of course having
started, this rapidly got out of hand.
Somewhat to my surprise, I found a suitable outer
joint. Correct spline, correct length
the lot. It even came from a nice
common donor vehicle. I took the
attached drive shaft too, more as something to measure against than anything
else. However, with everything loosely
bolted into the car it became apparent that this very shaft would probably do
the job if I could find a suitable joint to go on the inner end, as the
original tripod inner joint was no use for this.
Now, the drive shaft joints need to be able to take
up angular variation and at least one has to be able to accommodate plunge
(drive shaft length-change).
Types of CV
joint a very rough guide
The joint found to fit the hub and upright was of
the conventional type, without any plunge capacity, so the inner joint had to
be able to accommodate it all. However,
as the rotoflex rear-end has relatively little plunge (I measured 11mm over the
full suspension travel), I hoped to get away with using a lobro type joint on
the inner end as these typically allow 18 20mm. So the search was on for a suitable one preferably one that
would fit straight onto the drive shaft.
I begged a drive shaft catalogue from my local motor factors, which
listed joints, splines, vehicle applications etc. This let me draw up a (very) short list of potential donors.
Armed with the drive shaft it was back to the scrap
yard. Having removed a joint, I tried
it on the shaft I had brought, and amazingly, it fitted, even the retaining
circlip groove was right. I was
astonished. Pausing only to rob the
gearbox output flanges from the donor vehicle I rushed home to offer it all up
again.
With it all back in the car, a number of things were
apparent, some good, others not so good.
The good (truly astonishing really) was that the
assembly basically fitted.
At the
Inner end you need to adapt the 6
bolt pattern of a 93mm lobro to a standard Triumph flange. My approach was to
get the flange from the donor vehicle machined so it sat snugly in the recess
in the stub shaft flange, grind the 'ears' off the diff stub shafts and weld
the two parts together (Flange modification). A better, reversible, bolt-on approach would be to have some
proper adaptors machined. As the drive shaft used was a little short it was
necessary to space the outside face approx 17mm outboard of the original mating
face. This leaves little room for a gaiter. I used racing gaiters (Formula
Fords and the like use these joints) available from Merlin Motorsport. Not especially cheap but they do fit in the
available space and look nice too if you happen to be lying under the car.
At the outer end there are
three problems:
1. There is a large radius on the CV joint between the splines and the body of
the joint, which interferes with the standard wheel bearing shims. I had some
minor machining done to place the shims between
the bearings instead. This makes setting the bearing preload even more
awkward than usual! I would hesitate to take this route again.
2. The standard shaft has a non-splined section, which is an interference fit
in the hub and presumably helps support the inner bearing, as the wall
thickness of the hub-spigot at this point is quite thin. The CV joint doesn't
have this. Don't know how much this matters. In fact, shimming the bearing the
way I have stiffens the whole thing up so I'm seeing what happens..... (The
Triumph 1500 FWD CV joint is reputed to match the original stub shaft exactly,
but it has a very unusual drive shaft spline so if you used this you would not
find a ready-made shaft lying around!!).
3. The area that the seal runs on is a larger diameter than the original.
Finding a seal that had the right inner and outer diameter was easy enough, but
it also needs to be very low profile. I had to grind the seals down to fit.
According to my parts book there is a CV joint that is identical apart from
having a smaller diameter sealing land (almost the same as the original Triumph
part) but I didn't find any - too lazy to take enough scrap cars apart!
It works; the car drives like before but without the
rotoflex wind-up and UJ clicking. Ive
done about 3500 miles so far, so have some way to go before Id call it
proven.
I dont have any worries about the shaft itself. However, I do worry a little about the inner flange adaptors (my best welding is it really good enough?). Also worry a little about the hub and bearing time and miles will tell!
Partially installed spring omitted for clarity.