MG List Subscribers:
The topic of final gear ratios for the TD/TF has been debated frequently on
the list and from my research, this is what I can offer on the subject. The
8/41 (5.125:1) gear set was standard on the TD and an alternate for the TF.
The 8/39 (4.875:1) was standard on the TF and an alternate on the TD and
finally the 9/41 (4.55:1 was an alternate for both the TD and TF. The MGA
was apparently fitted with a 10/43 (4.30:1) as standard. Now that I've got
you wondering about the topic of this message, please read on....
An acquaintance operates a very successful Land Rover restoration and repair
business here in Salt Lake City. He works with older models only and over
the years has had the same problems with rear axle ratios that haunt the
MG-T series. Replacement ring and pinion gears are difficult to come by and
the available ratios are never ideal (sounds familiar). His solution was to
have the gear sets manufactured. Obviously, this is an undertaking that
requires time, connections, savvy and capital. He's now into his forth
batch of 100 gear sets and the venture has proved to be successful. The
details of how one goes about manufacturing gears is too involved for this
list but suffice it to say it's an undertaking that requires global
(European) connections.
During a recent British Car Club meeting we were discussing his business and
the subject of the gear sets came up. I asked how the new gears were
manufactured and was told all that is needed is an original set for the
overall pattern and the specifications for the new set (desired ratio,
surface treatment, finish). Obviously, the design of hypoid bevel gears is
not for the faint of heart and the real details (pitch circle, tooth
properties, offset, materials) are handled by the engineers. There are also
limitations to what ratios can be accommodated.
Now I was curious and asked if he would be interested in having gears for
T-series MG's (TD & TF) manufactured. He said he would consider such an
undertaking but first we would need to assess the interest. Which is the
purpose of my message on the list. The first question is "what would be the
level of interest in the perfect gear set given it would likely cost between
$300-$400?". Moss offers the 9/41 gear set ($250) and Abingdon Spares
offers the 8/41 ($365) and 8/39 ($265) sets. I understand that an MGA 10/43
(4.30:1) gear set can be installed in the TD/TF differential but I'm not
familiar with the associated costs or the skill required to do so (Carl
Cedarstrand will have to answer that one).
The second question is "if you could redesign the TD/TF rear axle - what
would be the perfect ratio?". What would be the merits and/or problems
associated with say a 9/40 (4.44:1) ratio (assuming the gear geometry works
out)?
I'll pass your feedback along.
Gregg Smith
1950 MG-TD #1844 (with 9/41 gears)
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