Subject: [TR] 4:10 diff

From: Brad Kahler <[email-masked]>
Date: Tue, 17 Jul 2012 14:00:08 -0400

Listers,

Now that I have the TR4 street worthy and have been driving it I've come to
realize that the differential in the car is a 4:10.  I've verified this by
comparing tach readings with road speeds via GPS.

So that leaves me with the problem of the speedometer being way off.  This
is the speedometer that was in the car when I got it so either the
speedometer was replaced at some point or else the diff was swapped out for
the original 3:70 diff.

I'm looking to find out which speedometer would be correct for the car,
i.e. what numbers would I find on the front of the speedometer that would
indicated it is for a 4:10 diff?

Thanks,

Brad

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From: [email-masked]
Date: Tue, 17 Jul 2012 18:20:46 +0000 (UTC)

Jack up one rear wheel, turn the wheel and count the wheel revolutions.

Have Susan count the driveshaft bolts going by.

Do the math.

Phil Ethier West Side Saint Paul Minnesota USA
1973 Triumph Stag LE22439UBW "uncle jack", Sapphire Blue
2004 Suburban 8.1, Sport Red, the only automatic of the bunch
2005 Lotus Elise, Bordeaux Red Pearl
2007 Saturn Ion 3 2.4, Berry Red
pethier [at] comcast [dot] net
http://www.flickr.com/photos/pethier
http://www.triumphtransamerica.org.uk
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From: Brad Kahler <[email-masked]>
Date: Tue, 17 Jul 2012 14:43:11 -0400

That method involves higher math...

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From: "Randall" <[email-masked]>
Date: Tue, 17 Jul 2012 12:38:30 -0700

> indicated it is for a 4:10 diff?

I don't know the exact number for a TR4, but the first two digits should be
13xx rather than 11xx for the 3.7 diff.

I had the same problem with TS13571L, which didn't even have an overdrive!
(When I got it, of course.) Frankly, I didn't like the 4.10 gears on the
street even with overdrive (behind a relatively stock motor), the 3.7 I have
now suits me much better and I'm planning to go to 3.45 as soon as I get a
spare axle built up.

If you want to change, I'm sure there would be lots of racers more than
willing to trade a 3.70 gear set with you.

-- Randall

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From: Brad Kahler <[email-masked]>
Date: Tue, 17 Jul 2012 15:48:45 -0400

> 13xx rather than 11xx for the 3.7 diff.
Hmm, I wonder if 1384 might be the number.  I don't know that I have one
with that number in my box of spares.  If I can find the box I guess the
smart thing would be to compare numbers and see if I have an odd ball one :)

> now suits me much better and I'm planning to go to 3.45 as soon as I get a
Living in LA like you do I can see where a 4:10 would not be of much use.
 Here in Kentucky there isn't a straight road to be found.  Heck even my
driveway has twists and turns!

I've got a 3:70 diff that I can use if I want to but I do have an OD to
install this winter so until the 4:10 proves it's not suitable for my
driving style I'll probably stick with it.

> willing to trade a 3.70 gear set with you.
That's for sure.