This is a very interesting question, I am in the process of the same
upgrade.
You are limited by the OD mainshaft that you need to keep from your
old transmission. The diameter of the "nose" on the main shaft where it
inserts into
the input shaft varies from time to time. You need an input shaft that will
mate properly
with your mainshaft.
If possible, you need a post 1973 (?) transmission that has the Stag internals
which are
stronger. I do not know if your mainshaft would be able to be used on the late
transmission.
But, the mainshafts may be different in the diam. of the "nose".
The steel bushings are better, but the "tophat" second gear bushing is not
available
for the "early" transmissions.
The selection of the "cluster" gear depends on the input/main gears you use.
I am about to experiment with a few new designs. (not my designs, but those
devised by
Brian Schlorff at Britcars@powerbritish.com). Ha has made for me an
experimental steel
bushing to fit my early TR6 (same as TR4/4A) 2nd gear.
The need for these experimental parts is interesting. There are 2 areas in the
transmission that
seem to fail prematurely. The 2nd gear top hat bush. The brim of the tophat
breaks off causing
problems. The "late" transmissions have a 2-piece steel bushing. Brian has
used made such a
bushing for my transmission. The other failure spot is the needle bearings at
the back of the
laygear near 1st gear. The great torque exerted there causes one spot of the
hardening on the
layshaft to crack and delaminate. Happens almost all the time.
Brian has a great idea, He will be trying on my transmission a new 21st
century answer to the
needle roller bearings. There is some sort of advanced plastic material that
will outperform
roller bearings by a large margin. Since the compressive force is spread out
over a "bushing" style
area rather than localized on needle rollers, the strength of the surface
hardening _ought_ not to be
exceeded, and failure should be prevented.
We will be replacing all 3 needle roller bearings with this new bearing
material. I can't see how it will fail
_faster_ than the stock method (remember, the TR2-3a transmissions used a
bushing between the
input shaft and the mainshaft), and may well be much superior.
Contact Brian Schlorff at the address above for more info. I am sure he can
make more of these things
for you if you were interested. Since I have messed with this stuff, I too
can help.
Use a caliper to measure the parts I.D., O.D., etc as the first step to judge
whether the exchange is
even conceivable.
-Tony
>From: bdoty@mindspring.com
>To: ArthurK101@aol.com
>
>I'm in the process of rebuilding my TR4 overdrive transmission. It kept
>jumping out of third gear
>and I had to hold it in gear to keep it from slipping out. After
>disassembling the box I
>found the main problem an some other interesting ones. The bushing for
>second and
>third gear was damaged and the end play was excessive. Also the cluster gear
>set
>thrust washer toward the rear had spun damaging the aluminum case. I
>realized the case
>is damaged beyond use.
>
>I had a later TR6 non-overdrive transmission that I also disassembled and
>found in good shape.
>There were some minor differences in the type of bearings used for the
>cluster gear set and input
>shaft.
>
>Well my questions are about what parts I should use. Do you have any
>recomendations about
>what parts I should use. There is a steel bushing to replace the bronze
>type. Is there any problem
>using this.
>
>I appreciate any information and recomendations that you could pass along. I
>have rebuilt many
>Spitfire transmissions and this is the first TR one.
>
>Thanks, Bill Doty
E-mail <billdoty@kemet.com> and <bdoty@mindspring.com>
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