Jack, see my comments, interspersed into your message below...
Amici,
Although I am still reeling from trying to absorb all the great information
from the bearing/brake thread, I have a gap in my gearbox knowledge I need
help resolving.
I am going to be building a full syncro A-type OD gearbox for my TR3. I
have a dependable A-type OD in the car right now, but it is connected to a
TR3 non-syncro gearbox. I've located two TR6 gearboxes which I believe are
suitable candidates for parts or transplant. They are gearbox numbers are
CD22490 and CD34961, which according to the TRF catalog are the third latest
of the four versions of the TR6 gearbox and have the following components:
1. 17 tooth first gear and closer ratio's in general
2. all 30 symmetrical dog teeth on the syncro's, versus the earlier only 8
of 30.
3. bronze top hats
4. The newer tooth profile (with greater engagement) on gears 1,2 and 4.
The big difference that I see with these gearboxes, as opposed to the very
late TR6 gearbox (which have no serial numbers) is that these have bronze
bushes instead of the steel top hat bushes, a desirable but not required
feature.
My questions are as follows:
1. With regards to gearbox cases, I was initially planning on installing
the
TR6 gears in a TR4 case, but have heard that the TR6 case is stronger. Is
this true?
[Jack Wheeler]
The big change was when they went to the TR-4A housing. Then they added a
little more strengthing material to the TR-6. I would say the TR-4A
housing is about equal to the TR-6, but either is going to be much better
than a TR-4.
I believe the TR6 gearbox will drop right into my TR3, but is
everything the same, ie., shifter location and can I keep my TR3 cover,
with
the dipstick?
[Jack Wheeler]
I have a TR-4A overdrive transmission in my TR-2. It fits, but I had to
elongate the holes in the rear mounting plate where the studs from the
bottom of the rear mount go through. I think I had to move the holes back
by about 1/4". The internal specs on all of the top covers were the same,
but the 1st/2nd and reverse shift forks are different. If you take all of
the moving parts out of a TR-4/TR-6 top cover and assemble them into your
TR-3 top cover you will be in business. I have lots of parts if you need
them.
2. Will the later steel bushed TR6 gearbox boltup to the A-type OD?
[Jack Wheeler]
Yes, with the correct mainshaft and adapter plate, they bolt right up.
I have
access to a TR4 OD mainshaft at a reasonable cost.
[Jack Wheeler]
I can provide the gears you would need to use this mainshaft, including the
input shaft. Or, if you decide to get a later TR-6 mainshaft, I might be
interested in buying this one (assuming it's for sale).
Is the steel tophat's OD
mainshaft available?
[Jack Wheeler]
The only difference in the mainshafts is the diameter of the nose of the
shaft which goes into the bearing in the input shaft gear. The later TR-6
transmissions (with the slide in bearings in the input shaft gear) used a
mainshaft with a nose diameter of about .835". All of the earlier models
(including early TR-6's) had a pressed in bearing in the input shaft gear,
and used a shaft with a pilot diameter of approximately .870". Both shafts
are available from John Esposito in Connecticut, or from England.
3. Aside from the steel versus bronze bush issue, are there any advantages
to the very latest TR6 gearboxes (those without serial numbers) versus the
post CD21769 boxes?
[Jack Wheeler]
None that I know of.
4. Also, the guy with the two TR6 gearboxes I anticipate buying has a
third,
with gearbox number CC83555, which he claims to be a TR6 box, but TRF
doesn't list "CC" numbers. Any idea what this is from?
[Jack Wheeler]
I know they used the TR-6 gearbox in some of the saloon cars in England.
It may have come from one of them. I believe the internals should be the
same as the TR-6. Or, it's possible that it got numbered to be put into a
saloon car, but ended up in a TR-6 from the factory. Hard to tell what
could have happened 25 years ago. Good luck!
Thanks,
Jack Brooks
1960 TR3A
1974 Norton 850 Commando
Hillsdale, NJ
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