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<p>I've been pulling 136HP though FIS6's (might be down around 125
now)? GT6 MKIII box for nearly 12 years now.<br>
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.<br>
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? <br>
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__.</p>
<p>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.<br>
</p>
<p>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!<br>
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.</p>
<p>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,<br>
</p>
<p>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.<br>
Mike Ross (out in Ohio) did a great write-up on them years back.</p>
<p>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</p>
<p>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.</p>
<p>ptegler<br>
</p>
<p>ymmv ...only yacking from personal experience?? :-)</p>
<p>ptegler<br>
</p>
<div class="moz-cite-prefix">On 5/26/2019 7:06 PM, David Templeton
wrote:<br>
</div>
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<p class="MsoNormal"><o:p>?</o:p></p>
<p class="MsoNormal">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.?
<o:p></o:p></p>
<p class="MsoNormal"><o:p>?</o:p></p>
<p class="MsoNormal">Looking at all these parts etc and now I
have a bazzilion questions, first the points I know<o:p></o:p></p>
<p class="MsoNormal"><o:p>?</o:p></p>
<ol style="margin-top:0in" start="1" type="1">
<li class="MsoListParagraph"
style="margin-left:0in;mso-list:l1 level1 lfo1">I know the
input shaft is matched to the depth of the bell house and
has less but thicker splines.? All good<o:p></o:p></li>
<li class="MsoListParagraph"
style="margin-left:0in;mso-list:l1 level1 lfo1">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 )<o:p></o:p></li>
<li class="MsoListParagraph"
style="margin-left:0in;mso-list:l1 level1 lfo1">The input
gear has a different number of teeth than the MKIV ?<o:p></o:p></li>
<li class="MsoListParagraph"
style="margin-left:0in;mso-list:l1 level1 lfo1">The
mainshaft for the OD is different, I need to get one of
those still to attach my OD unit.<o:p></o:p></li>
</ol>
<p class="MsoNormal"><o:p>?</o:p></p>
<p class="MsoNormal">Nowwwww, for the questions <o:p></o:p></p>
<ol style="margin-top:0in" start="1" type="1">
<li class="MsoListParagraph"
style="margin-left:0in;mso-list:l0 level1 lfo2">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 )<o:p></o:p></li>
<li class="MsoListParagraph"
style="margin-left:0in;mso-list:l0 level1 lfo2">What is the
mechainical difference of the MKII ( KC ) and the MKIII ( KF
), is there any in reality that make a difference?<o:p></o:p></li>
<li class="MsoListParagraph"
style="margin-left:0in;mso-list:l0 level1 lfo2">The laygears
look exactyl the same between the MKIV and the MKII, are
they really the same?<o:p></o:p></li>
<li class="MsoListParagraph"
style="margin-left:0in;mso-list:l0 level1 lfo2">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<o:p></o:p></li>
<li class="MsoListParagraph"
style="margin-left:0in;mso-list:l0 level1 lfo2">In the end,
what can I mix and match? does it matter? Is it OMG don?t do
this?<o:p></o:p></li>
<li class="MsoListParagraph"
style="margin-left:0in;mso-list:l0 level1 lfo2">Can the
bushings on the laygear, can anyone with a machine shop do
this?? I john at Quantum still doing this??
<o:p></o:p></li>
<li class="MsoListParagraph"
style="margin-left:0in;mso-list:l0 level1 lfo2">Has anyone
replaced the needle bearings with roller bearings?? Or not
strong enough?<o:p></o:p></li>
</ol>
<p class="MsoNormal"><o:p>?</o:p></p>
<p class="MsoNormal">I need to be educated by the masters of
this list.? <o:p></o:p></p>
<p class="MsoNormal"><o:p>?</o:p></p>
<p class="MsoNormal">Thanks<o:p></o:p></p>
<p class="MsoNormal">David Templeton<o:p></o:p></p>
<p class="MsoNormal"><o:p>?</o:p></p>
<p class="MsoNormal">?59 tr3a ? damn she is fast and wonderful
to be driving again.? In shakedown mode.<o:p></o:p></p>
<p class="MsoNormal">?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
<o:p></o:p></p>
<p class="MsoNormal"><o:p>?</o:p></p>
<p class="MsoNormal"><o:p>?</o:p></p>
<p class="MsoNormal"><o:p>?</o:p></p>
</div>
<br>
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<pre class="moz-signature" cols="72">--
Paul Tegler
<a class="moz-txt-link-abbreviated" href="mailto:ptegler@verizon.net">ptegler@verizon.net</a> <a class="moz-txt-link-abbreviated" href="http://www.teglerizer.com">www.teglerizer.com</a></pre>
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