[Fot] TR-4/6 trans top cover advice (won't go into 3rd gear)

[yellow04]

Tony,

I have been into many top covers, they really only have one fiddly bit, 
the interlock. Consists of two balls and one dowel. You need to 
reassemble in the right order to get it back together, but once you have 
done that once it's pretty easy. You can see the cavity on the outer 
rails (that's the reverse rail and the 1st/2nd rail) where the balls 
live, when everything is cleaned up and ready to go back together I 
apply a dab of grease to the cavity with a long screwdriver, hold the 
top cover on its side and roll the ball down the bore until it drops in 
the cavity. Using the long screwdriver you press the ball home in the 
grease/cavity, then slide the rail home assembling the shifter fork and 
spacer as you offer it home. Then repeat with the other outer rail. 
Finally, the center rail (for 3/4) has a drilling for the dowel pin. 
Grease it up, slide the pin into the rail, and install. The outer forks 
must be in the neutral position to get it to slide home. The Buckeye 
Triumph writeup on gearbox overhaul includes the top cover, worthy of a 
quick read before jumping in for sure.

The other tough part is getting the three tiny square headed tapered 
screws out of the shifter fork/rail, after too many years I finally 
broke down and bought a proper 8 point socket, made life much easier on 
that front. Be forewarned, a failure point on these gearboxes after 
overhauling a top cover is those tapered screws do tend to back out and 
fall into the soup, I highly recommend drilling the screw head for 
safety wire, and drilling the adjacent web on each fork to anchor the 
safety wire. I lost one on track in the TR250, I got lucky and it 
dropped down to the bottom of the gearbox without fouling any gears and 
I simply retrieved it with a magnet, reinstalled, and was back in 
business. On the race car, it was slightly inconvenient and caused a DNF 
for that session, in a street car it is a huge pain in the ass because 
you are pulling the interior to get the top cover off!

The only other thing that I can think of that might trip you up is if 
you have a top cover from a later TR6 that has never been apart, in a 
cost savings measure the Triumph decided they didn't need to supply 
threaded screwcap access to the fork detent spring and plungers, they 
simply used press in plugs. Not at all difficult to remove the press in 
plugs, but you will need to tap the bores you pulled the press in plugs 
from and source the screwcaps from an earlier gearbox to reassemble.

As to the possibility of your top cover causing the issue of not being 
able to engage third, if the tapered screw is tight so the fork is 
properly fixed to the rail, and the shifter feels OK with rowing through 
the gears with the top cover removed, the only think I can think of 
would be a bent shifter fork. I can't tell if a fork is bent by looking 
at it, the only telltale is the fingers that slide into the shifter hub 
will be worn.

Feel free to give me a jingle is you have questions.

Cheers

Henry Frye

On 2024-08-15 19:44, Tony Drews via Fot wrote:
> At my last race, I felt entry to 3rd gear have some resistance, then
> the resistance went away, but near the end of the weekend something
> happened that prevents me from shifting into 3rd gear. I can shift
> into all of the other gears just fine.  Didn't feel like a internal
> gearbox issue (I certainly hope not, I just replaced all the quaiffe
> goodies in there).  I've never taken the top cover apart / had to fix
> that.  It does still have the overdrive switches in the top of it even
> though I'm no longer running the OD.
> 
> So... I'm planning to remove the tranny top cover this weekend and see
> what's going on.  I probably have a spare from an unknown quantity
> transmission from my Dad's stash, but I'd like to fix the existing one
> if possible.  For those who have done it, how fiddly of a job is it to
> take that stuff apart?  Any ideas what would keep it from shifting to
> 3rd?  I have noticed increased resistance on the 3/4 shift rail since
> my rebuild earlier this year (but didn't have time to look into it at
> the time).
> 
> Looking for words of wisdom from those who have been there / done that.
> 
> In other news I have some pretty epic videos from last weekend's race
> at Grattan coming.  Here's a appetizer from the "Genius Garage
> Invitational": https://www.youtube.com/watch?v=_LWlZIFA_gg
> 
> All the best, Tony Drews