087 vs 089 autobox ratios

[Mike Arman <armanmik@n-jcenter.com>]

Marty Liggins wanted to know the differences between the 087 and 089
autoboxes. According to Haynes, the 089 gearbox was fitted to the four
cylinder cars, and the 087 that went into the five cylinder models.

Transmission ratios seem to be the same: 2.55:1 first, 1.45:1 second, 1:1
third, 2.46:1 reverse. Final drive (ahhh, the infamous disappearing
differential!) ratios are 3.45 to one for all 5s, and 3.9:1 for 80, 3.25:1
for coupe, and 3.73:1 for 4000. Gearbox fluid capacities are the same,
final drives vary slightly. There are very minor differences in the torque
converter and various tightening torques, but Bentley should have those.

Essentially, the transmission SEEMS to be the same, but the final drive
ratios and various attachment details are different - so it looks like he
can use his spare 4K tranny in the 5K which needs one - keeping the 5K diff
and housing, though.

Make sure the drive pump shaft (long shaft from torque converter to tranny
oil pump) at rear of tranny doesn't get reversed! It LOOKS the same on each
end, but it isn't - and reversing it accidentally will cost you the
transmission!!!! Illustration also shows some seal rings on the shaft which
will probably need to be replaced.

Best Regards,

Mike Arman