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Axle ratios & Electrics TR3 and 4 - and a bit on 4A

To: <triumphs@Autox.Team.Net>
Subject: Axle ratios & Electrics TR3 and 4 - and a bit on 4A
From: "jonmac" <jonmac@ndirect.co.uk>
Date: Sun, 12 Apr 1998 19:23:40 +0100
It's clear that some of the technical publications at BMIHT (as produced
and printed by the factory) is scant in certain areas in terms of content
detail.
The detail I have obtained today and shown below was sourced from
Engineering Bulletins and then cross-referenced against some of the
company's press releases of the time and further cross-referenced against
respected technical publications of the day e.g. Automobile Engineer
magazine and some reliable trade magazines.
I've dealt with axle ratios and generators for both models because while
this wasn't queried on the list yesterrday, it occurs to me that there may
be someone out there who will find this data useful for their own or club
records. Nothing too startling but one or two variances between the two
cars that could be important.

TR3 (1957 model year) AXLE RATIOS
Axle ratio is 3.7:1 from chassis number 13046 onwards. What it was prior to
that is not stated and I couldn't find. Teeth on diff pinion =10, teeth on
crown wheel=37
This gave overall ratios as follows for a NON-overdrive car:
1st gear=12.5:1, 2nd gear=7.4:1, 3rd gear=4.9:1, 4th gear=3.7:1 
Overall ratios for a car WITH overdrive are:
1st gear=not quoted (obviously) 2nd gear 6.07:1 3rd gear=4.02:1, 4th
gear=3.03:1

TR3 (1957 model year) GENERATOR
Type Lucas C3PV-2
Brush tension 22-25 ounces
Field resistance 6.1 ohms
Max. output 19 amps @ 13.5 volts in an engine rpm range from 1900-2150
Replace brushes when worn down to 11/32nds of an inch

I also remember seeing something on the list recently when someone queried
the tyre size which would fit in the spare wheel well. Those fitted to the
1957 vehicle were specified as 6.40 x 15

TR4 (1962 model year) AXLE RATIO
It seems the car offered a choice of axle ratios, though whether these were
country specific I could not determine. Overdrive was available as well for
both ratios which possibly shoots in the foot any response that the lower
ratio was for overdrive only cars.
Axle ratios were 3.7:1 and 4.1:1 though I could not determine the tooth
count on either for the pinion or crown wheel. I guess its there somewhere
but none of the archivists were on hand to help. The overall ratios when
overdrive was fitted to these different diffs gave 3.04:1 and 3.36:1
respectively

TR4 (1962 model year) GENERATOR
Type Lucas C40-1
Brush tension 13-30 ounces
Field resistance 6.0 ohms
Max. output 22 amps @ 13.5 volts.
Cut in speed 1450 engine rpm @ 13.0 volts to 22 amps at 2250 engine rpm @
13.5 volts
Replace brushes when worn down to 9/32nds of an inch

I also had a look at similar aspects of the TR4A - but gave up owing to
lack of time. The generator is stated as being a Lucas C40 but whether a -0
or -1 is anyone's guess. Axle ratios have changed yet again with 10/41 and
10/47 pinion/crowns. Couldn't find out whether these were market specific,
overdrive/non-overdrive or beam axle vis a vis IRS. If this sort of info is
crucial to anyone in 4A country, let me know and I'll try to learn more.
I'm sure answers must exist somewhere on the web from sites submitted by
those in't know (Andy?). Don't think the excellent site of axle ratios on
the Amicale Spitfire site covers TR's.

Is all that of any help?
John Macartney
Now in the same museum as the cars he sold when they were new

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