Hi Karl,
Very interesting turning down the shaft. I assumed it was too hard to machine
and would have to be ground down. Also, I didn't want to risk ruining a
mainshaft that might cost a couple hundred $ to replace.
I installed that gearbox this spring and have put about 1000 miles on it. It's
in my TR250 that I only drive to special Triumph related events (historic
license plates).
It works great and seems to be very quiet. I have however secured another early
gearbox that has a full set of gears that I'll be able to use in the future if
necessary.
Current task is to document procedure to overhaul A type ODs. That should be on
website in a few weeks.
Thanks for your interest & input. Next time I go back and update those articles
I'll mention your experience.
Nelson
----- Original Message -----
From: "Karl Vacek" <
To: <
Sent: Thursday, August 09, 2001 4:47 PM
Subject: Gearbox mainshaft
> Just looked at your gearbox tech articles on the Buckeye Triumphs web site.
> I have no idea how old the article is, but in browsing the first "overhaul"
> file, I noticed your discussion of the differences in the nose of the
> mainshaft and the pilot bearing inside the input shaft.
> May be too late to help you in your quest for a proper mainshaft, but here's
> how I solved the same problem nearly 30 years ago.
> In 1972, my then nearly new '71 TR6 upchucked its overdrive while just
> rolling down the Interstate in Indianapolis. Made it home to the Chicago
> area OK, but after disassembling the unit, I have no idea how!!
> Being semi-impoverished (from making the payments on the car and racing a
> Healey), I sought a used overdrive. I lucked into an OD transmission from a
> '64 TR4, with only a slightly broken bellhousing - accident damage. The OD
> was like new inside - still had hone marks on the mating surfaces of the
> gears. Looked like I was home free.
> Then I discovered the same problem you mention. It was Saturday afternooon,
> and I didn't thiunk I could afford a new shaft anyway, so after some
> consideration and half-hearted seat-of-the-pants hardness tests, I turned
> down and polished the nose of the older shaft to the new, smaller diameter.
> In examining the machined area, I noticed a pattern in the finish, I assume
> from the varying hardness, in the portion I had turned down. Will it work?
> In looking at the machined portion, I noticed a pattern in the finish with
> part being shinier than the rest. I assumed that the part was
> case-hardened, and that due to the shape the hardening had not gone to a
> uniform depth across the same journal, and hence in places I had cut through
> it completely and in other areas some hardness remained.
> Upon examining the original TR6 part (the end in question was fine - the
> overdrive end was what was all torn up) believe it or not, I saw that it had
> the exact same pattern in the finish, almost as if perhaps Triumph had made
> the original part by turning down an old-style mainshaft.
> I installed the mainshaft and hoped for the best. The transmission and
> overdrive worked perfectly, and the parts gave no trouble in the next year
> or so that I owned the car.
> What did you ever do with the transmission you described in your article?
> How did the non-matched gears work out? Were they noisy, as I'd expect if
> they had some miles on them?
> Thanks for some great articles !!
> Karl Vacek