Bob,
See my answers below:
-----Original Message-----
From: BobMGT@aol.com [mailto:BobMGT@aol.com]
Sent: Monday, August 09, 1999 5:07 PM
To: mg-t@autox.team.net
Cc: mgs@autox.team.net
Subject: Changing Rear End Ratio in a TD
I've always shied away from highway driving in my TD. The engine just
doesn't
sound too happy at 4000rpm. I've finely decided to take the plunge and
change
the rear end ratio. My mechanic has an MGA parts car, and is ready to sell
me
any parts I need from the rear end. Are the ring and pinion gears the only
two parts I'll need from the MGA?
No. If you choose to use MGA ring and pinion, you'll also need the driving
flange, the pinion distance tube and spacer. Bearings for at least the
pinion will also be required. But it's better to buy those new. Optionally,
as long as you are in there, you'll probably want to replace the carrier
bearings if they aren't brand new. (By the way, I have a full set of
bearings for sale, if you need them.)
==================================
Also, what is the recommended ratio for highway driving? Here are the
options
I've found:
Standard TD 5.125 3900rpm @ 55mph (What I have now)
TD option 4.875 3700rpm @ 55mph
TD option 4.555 3470rpm @ 55mph (Gears available from Moss)
MGA 4.3 3300rpm @ 55mph
MGA 4.1 3120rpm @ 55mph
It depends upon the type of driving you do. If all you do is freeway driving
across nice flat states, the 4.3 is good. If, like me, you do a bit more
hills, I find the 4.55 ideal. Don't consider anything lower ratio than 4.3.
Since the TD transmission gearing is different than an MGA, don't expect
that you'll get the same RPM/Speed combinations as the MGA. I find that with
a 4.55 rear end, I do just about 60 MPH at 4000 RPM. I can also happily do
65 MPH, at about 4250 - 4300 RPM. All this with a slight reduction in hill
climbing ability. I know find, with a 4.55 ratio, that hills I used to take
in 4th gear, now require 3rd.
=========================
My mechanic claims the MGA parts car has a ratio of 4.5, but I only see 4.3
and 4.1 in the literature. Is he mistaken?
No, a 4.55 ratio was available. I know, because I'm running one in the TD.
Carl Cedarstrand wrote a very good booklet on the subject of rear end
conversions some years ago. It is still available from Moss Motors. I highly
recommend you get a copy and read up on the theory and practice. I used it
as the basis of a workshop I conducted for our local club last winter. We
did 6 conversions in one day. To a person, everyone is very happy with the
4.55 ratio.
Regards,
Lew Palmer
Bob Donahue (Still stuck in the '50s)
EMAIL - BOBMGT@AOL.COM
52 MGTD - under DIY restoration NEMGTR #11470
71 MGB - AMGBA #96-12029, NAMGBR #7-3336
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