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RE: MGB Rear End Ratio

To: "'Richard A. Boris'" <borisri@earthlink.net>, mgs@Autox.Team.Net
Subject: RE: MGB Rear End Ratio
From: "Unger, Larry G" <larry.g.unger@lmco.com>
Date: Sun, 05 Jul 1998 11:31:34 -0400
Richard A. Boris wrote:

> I validated that my tachometer is reading correctly and checked the
> speedometer to a MGB traveling next to me. The condition I have is in
> forth gear, 4000RPM at 60 MPH. Does anyone know what the rear end ratio
> is? In the next few weeks I will be installing the entire banjo axle
> with a 3.909 ratio.

                  60000
        -----------------------  = MPH/1000 RPM
        Axle ratio * (revs/mile)

                                                MPH/1000 RPM (4th Gear)
TIRE                            -------------------------------------------
SIZE            REVS/MILE        4.55             4.3            4.1
3.91
-------------------------------------------------------------------
560x14     853  15.459  16.358  17.156  17.989
165x14     854  15.441  16.339  17.136  17.969
560X15     814  16.200  17.142  17.978  18.852
165x15     820  16.081  17.016  17.847  18.714


Rich ... assuming 165X14 tires, you have a 4.55 diff fitted ... just a WAG
on my part, as tire diameters and hence REVS/MILE vary ... but, it does
provide a ROM.

The ratio is stamped on top of the diff ... 

                BANJO REAR GEAR RATIO
-----------------------------------------------------
4.55:1    9 pinion/41 ring gear teeth
4.30:1  10 pinion/43 ring gear teeth  1500/1600 'A'
4.10:1  10 pinion/41 ring gear teeth   1622 'A'
3.91:1  11 pinion/43 ring gear teeth   'B'

... if its a 4.55 ratio you should find 9/41 stamped on the diff ...
however, it is possible that someone fitted a new set of gears to the
carrier so ya may want to count the teeth.

Give me a shout if you'd like to part with the 4.55 diff.

Safety Fast! ... larry.g.unger@lmco.com
'61 MGA 1600 MkII

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