In a message dated 96-05-21 10:49:43 EDT, you write:
>I'm probably wrong but I believe there were slight differences in the A-type
>O/D fitted to TR4s and those fitted to TR4A onwards. Something to do with a
>gentler engagement for the IRS cars?
Well, I rebuilt the OD in my '71 TR-6 (bought December of 1970). The OD
self-destructed in 1971, at maybe 20,000 miles. I bought a '64 TR-4
transmission/OD for parts. The only difference I discerned between the two
OD assemblies was that the mainshaft front spigot, which goes into a pilot
roller bearing on the back or the input shaft, was smaller on the later
(TR-6) model.
Not wanting to mix gears on the relatively new -6, (and in fact I didn't
disassemble the trans at that time), I needed to modify the input shaft to
fit into the TR-6 trans. Nothing to lose, I chucked it in a lathe, trued it
up, and turned the area down and polished it. There was a noticeable pattern
to the surface when I was done, because I had apparently cut through the
outer case-hardened area and into somewhat softer steel. I worried about how
long the repair would last, even though it's a roller contact and not a plain
bearing. Then I examined the original part, and saw the same exact pattern!
Hardness "felt" similar with a file. Since then, I always wondered if
Triumph (or Laycock, or whoever actually made the part) hadn't done just what
I did to convert some older parts for production.
The modified part worked fine, as did the entire OD unit, and still worked
fine when I sold the car at 36,000 miles.
BTW - Just a few weeks before the OD went out, I had the trans out to replace
what I thought was a weak pressure plate (Laycock diaphragm). I had
experienced a slipping problem, particularly when starting off from cold in
the morning. I put in a Borg & Beck pressure plate & disk, and was REALLY
disappointed when I put everything back together and the slipping was still
there. I re-checked hydraulics, etc., and everything was OK with the clutch.
I kept driving the car daily, and was just beginning to suspect some
slippage in the OD when it blew up.
Moral ?? If you think it's a slipping clutch, don't forget to check the OD
too !!
>Anyway, I have found slight use of the clutch to be useful. Mine comes in
>with a real jolt, but that could be expected as the whole drivetrain is
>original and 33 years old. With practice just a very slight pressure on the
>clutch pedal as you flick the switch is enough to give silky smooth changes
>as you roar away from the stoplight.
>
>
A properly-operating OD, even an older model, won't really lurch when
engaging/disengaging, but you should lift your foot off the gas to ease the
shift -- declutching doesn't hurt, and will likely lengthen the OD's life
somewhat, but shouldn't be necessary. The OD operates by engaging
organic-faced cone clutches riding in the oil along with the gears. The
Healeys have a switch system to ensure you don't engage/disengage under heavy
throttle, but on my Healey 100-6 racecar I just wired direct to the switch
and was usually careful. Worked fine, never slipped or blew up. I used to
run 50W Valvoline racing oil plus STP in the Healey's trans/OD, on the advice
of other racers. Never seemed right, (no EP additives) but it didn't cause
any problems in my years with the car.
Good luck
-Karl
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