[TR] Finally some progress

Sun May 26 18:53:01 MDT 2019

I've been pulling 136HP though FIS6's (might be down around 125 now)? 
GT6 MKIII box for nearly 12 years now.
Long distance road trips to, and laps on, then driving home from Road 
Atlanta, Watkins Glen, Mid Ohio and Lime Rock ....have never had a 
single issue with that tranny.
It's not a week box.... it's the way the driver dumps the clutch, 
attempts to power shift, or shocks the gears shifting the O/D under 
heavy load? that will kill those boxes,,,and
having been rebuilt with the improper (too much) clearance between gears 
usually resulting in the third gear circlip jumping it's groove from too 
much side load, letting the whole box go to sh__.

note:? spec'ed use... slip the clutch with a D-type o/d when 
shifting...not needed on the j-type, but neither is supposed to be 
shifted in or out under load.

The GT6 has a larger (than the Spit box) tip on the main shaft that 
rides in the end of the input shaft.? I rebuilt a tranny for a friend 
that had that tip sheared off the end of the main shaft!
The half rings and collar were destroyed, Shifting was super hard but he 
still drove it for awhile. That's how it was when he bought the car.

BUT.... after examining the break, you could see is was a stress riser 
at one of the cogs on the shaft... it had been slowly cracking for quite 
some time before it sheared . You could see 1/3 was totally different 
metal texture...the other 2/3rd was the crystalline structure you'd 
expect from a crack vs the slow 'rip' of the first 1/3rd of the break. 
So actually...it was a defective or mis-machined shaft,

I've never seen a box (have rebuilt at least 12 now Spits and Gt6) with 
damaged needle bearings...although I've seen massive wear on the shaft. 
Simply stated...they were run with the improper volume of oil, plain and 
simple.? Years back there was a massive issue with the supply chain, as 
replacement needle bearings were slightly oversized causing all kinds of 
problems.
Mike Ross (out in Ohio) did a great write-up on them years back.

Early and late boxes had different diameter synchros. At least the Spits 
did, so assume too the GT6 boxes? (have never personally rebuilt a 
MKI/II GT6 box)? I'm fairly certain the gear ratios never changed. The 
other variance is a 17 or 22 tooth reverse gear configuration. 
early/late..can't remember off-hand which is which

And believe it or not.... you CAN mount a J-type o/d to a three rail GT6 
box. main shafts are avail...usually cheaper than the more common d-type 
shaft.

ptegler

ymmv ...only yacking from personal experience?? :-)

ptegler

On 5/26/2019 7:06 PM, David Templeton wrote:
>
> For the longest time, it really seems like decades, oh hold on 15yrs ( 
> really long story, a long boring story ).? I have been searching for a 
> replacement gearbox for the spitsix.? Namely the gearset and main 
> case.? Well, a number of weeks ago I picked up a MKIV-non-OD gearbox. 
> Pristine shape.? Yesterday, got ahold of a MKII GT6 ( KC series ) and 
> today got another MKII GT6, again KC series.
>
> Looking at all these parts etc and now I have a bazzilion questions, 
> first the points I know
>
>  1. I know the input shaft is matched to the depth of the bell house
>     and has less but thicker splines.? All good
>  2. I know that the input/first gear of the GT6 box is a different
>     ratio than a spitfire.? I can scream a GT6 in first for a while (
>     younger year stunt, but still sounded cool )
>  3. The input gear has a different number of teeth than the MKIV
>  4. The mainshaft for the OD is different, I need to get one of those
>     still to attach my OD unit.
>
> Nowwwww, for the questions
>
>  1. The GT6 box is considered ?weak?, I know the needle bearings on
>     the laygear are generally crap and that Quantum will put bushings
>     in ( we will come to that )
>  2. What is the mechainical difference of the MKII ( KC ) and the
>     MKIII ( KF ), is there any in reality that make a difference?
>  3. The laygears look exactyl the same between the MKIV and the MKII,
>     are they really the same?
>  4. With the stated diffference of the input and first gear, what are
>     the differences in the spit MKIV and gt6 MKII/III?? Again visually
>     they look the same
>  5. In the end, what can I mix and match? does it matter? Is it OMG
>     don?t do this?
>  6. Can the bushings on the laygear, can anyone with a machine shop do
>     this?? I john at Quantum still doing this?
>  7. Has anyone replaced the needle bearings with roller bearings?? Or
>     not strong enough?
>
> I need to be educated by the masters of this list.
>
> Thanks
>
> David Templeton
>
> ?59 tr3a ? damn she is fast and wonderful to be driving again.? In 
> shakedown mode.
>
> ?74 spitsix ? there is a light forming at the end of the tunnel, a 
> light where the engine and rear diff may talk to each other again
>
>
> ** triumphs at autox.team.net **
>
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-- 
Paul Tegler
ptegler at verizon.net  www.teglerizer.com

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