Hi
I tried to mail to John Reed, but it bounced. This is my interpretation
of overdrives & TRs; I'm no expert! I've also include a rambling missive I
wrote earlier this year about my experiences.
John says:
>I don't think the gears will be a problem since they have the same
>part numbers, but I need to locate an output shaft. Since I don't have
>an overdrive gearbox output shaft, how can I verify one is correct for
>the TR4?
I dont know the answer to this; my advice would be to lay your hands
on a broken TR2->TR6 complete O/D box & strip it for bits. I *think*
the output shafts are the same, but I wouldn't stake my life on it.
Check out the part numbers. Be very careful in re-using gears; there
are subtle differences.
>I also need to buy an overdrive unit, something I have no experience
>with. What should I look out for when shopping for one? Is there a way
>to tell a good one from a bad one before buying? How much should I spend
>on one?
I think you will need $$$'s as they are hard to find & scarce.
The correct unit for your car is the Laycock "A" type, which I think was
uprated across its life; A TR2 unit will work fine but wont take as much
abuse as the TR4A type. A good one has a working oil pump & a non-destroyed
clutch system. I think the clutch liners can be replaced. Buying a busted
one & paying $$$s for a rebuild could be an option.
The TR6 used the Laycock "J" type which is stronger & a better (simpler)
design. As Teriann inferered, a TR6 `box can be made to fit (its actually a
shade longer), and a J O/D will mate to a TR4 box (I think), but you need to
modify the mounts. [ In the UK a B.L. Marina gearbox mount welded in is
ideal ].
I think you need to join your local club & talk to folks who have been
through this loop. Someone might just have the correct unit too!
here is what I scribed earlier this year.
_____________________________________________________________________________
Hi,
The modification to my TR4 that I've been promising myself for the past
couple of years has just been completed - an overdrive unit has been
fitted.
For some reason, it seems that the majority of UK TR's had the overdrive
option but the reverse was true for the US, about one in five I believe.
Any ideas why this would be so - with the US interconnected by Interstates
I would have though overdrive would be highly desirable? Comments?
Anyhow, now that the unit has been persuaded to function, I cant
emphasise just how great these things are. In the UK cars travel at 70mph
or above on motoways & dual carriage roads, and the engine noise & vibration
at this speed made driving the thing a bit tiring.
I have been asking people for years on "how to convert my gearbox to
an overdrive box" and have received various conflicting advice. Here's
how I did it: My gearbox was in good shape & is the only part of the
drive train that doesnt leak (more on this later!), so the conversion
requires the substitution of the output shaft, the gearbox extension
housing being discarded, and the replacement with the overdrive & soleniod,
adapter plate, plus the switch, wiring harness & relay. Sounds straightforward?
Well it is, pretty much. The main question I had (here in the UK)
was whether Laycock 'A' type units (ie: TR2->4A) from other vehicles would
fit; you can/could get units from Triumph 2.5 pi's, Triumph 2000's. They
are not as plentiful in breakers yards as they were, but they do show up.
The answer is, "yes" but part of the housing needs to be changed to
fit the TR mounts, otherwise you have to modify your car. The 'A' overdrive
did not change significantly across its life, although its innards
(eg; springs, accumulator pressure spring (?)) may be different
depending on application.
TR/Triumph gearbox parts are interchangable too, but Extreme Care is
needed to make sure the substitution is correct. I'm not sure where my
output shaft is from, but the o/d came from a Triumph 2000 and we
substituted half of a new casing. This produces a very close approximation to
the TR unit; the only difference is the position of the solenoid.
The other parts were "used" with the exception of the solenoid
& relay.
The gearbox was rebuilt with no problems; a new lay shaft being fitted
as the original was a bit worn, the output shaft went in ok, the
o/d bolted on in two halves to align everything taking care to make sure
the springs & oil pump cam were on ok. The o/d got some new seals
but was otherwise ok. Back in the car with the propshaft disconnected
the unit worked fine. On the road it was ok too, but then refused to
engage.
I drove it home & parked it, then realised I couldnt drive the car in reverse!
The unit had engaged owing to incorrect adjustment. If this happens to you:
undo the solenoid arm & briefly drive the car FORWARD in top; the unit
should disengage. If not ...
Saturday I drove it back for adjustment and by manually working it the
o/d started to work: on the motorway the propshaft oil seal failed
spraying hypiod onto the exhaust -> car fills with smoke .... I get to a
filling station, phone friend, buy hypiod, remove gearbox cover, fill up, etc.
I complete the journey & after some fiddling the o/d works just fine.
We had forgotton to clean the o/d filter, plus I think there was air in the
system and there isnt a way of easily getting it out.
So: If someone offers you an overdrive, even not the exact one for your
vehicle, its worth serious consideration. I understand that 'J' type units
will mechanically fit earlier TR's but a chassis bracket is needed. The 'J'
type is a better design too.
The usual disclaimers apply for the above - I had expert help, but its
certainly all worth it.
Regards, Adrian
asj@dsbc.icl.co.uk
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