Pardon my "poetic license". I've been running a TD for 17 years on the 5.125
rear axle ratio, and have crossed the country several times. I have no
problem doing it, but at 4400 RPM indicated, I'm doing just about 60 MPH.
How many other cars built after WWII rev that high for 60 MPH?
Don't get me wrong. I enjoy the driving, but I would like to be able to coax
a few more MPH out of the old TD, or at least drop 500 or so RPM off the
engine speed.
So this winter I am conducting a seminar on differential rebuilding using a
lower ratio gear set ( 4.3 or 4.55) from an MGA. If the rear axle ratio were
still so suitable for driving some 45+ years after the cars were built, rear
axle conversions would not be as popular a modification as they are.
Come to think of it, maybe I'M the one getting older, not the TD.
Lew
-----Original Message-----
From: Dave and Liz DuBois [mailto:ddubois@sinclair.net]
Sent: Thursday, January 07, 1999 3:01 PM
To: mg-t@Autox.Team.Net
Subject: Re: 5 speed question
I don't often jump into these discussions, however I think I will join
this
one. Bob Howard and Lew Palmer are absolutely correct. An overdrive is
either
an add on unit or a gear ratio in the gear box, achieved with extra gears
(ie. 5
speed or 6 speed) that gives a final ratio lower than 1:1 at the input to
the
rear axle. A lowered gear ratio in the rear axle is just that, a lower rear
axle gear ratio and affects the MPH/REV in each of the gear box's position.
There are trucks in use (or used to be) that have two speed rear axles that
are
controlled from the gear shift lever, but they are termed just that, two
speed
rear axle as opposed to overdrive.
Not to get into an argument with Lew, but I believe that the statement
"The
second problem is that with a 1:1 ration in top gear, the engine is running
at
much too high an RPM for comfortable cruising at 60 - 65 MPH" is a
subjective
assessment, based on the American preference for large displacement low
revving
engines. My wife and I have twice taken our TD, with standard gearing on
5000+
mile trips in the Western USA, traveling 8 to 10 hrs a day at 4200 RPM and
the
worst problem that we had was a fouled plug at the end of the last trip.
The
high RPM did not in any way damage the engine (other than to wear it
faster),
although I do admit to wishing for an overdrive just to make ME feel better.
Hope that this doesn't muddy the waters too much.
Sincerely,
Dave DuBois
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