I have a good AW auto transmission that I removed from a 1990 740. Less than 100k on the wrecked 740. It has the lockup converter.

I am looking into purchasing a 1992 740 with a bad transmission.

With the different shift points (and different rearend??) would the combination prove to be a disappointment? I am referencing this to performance, mileage, cruising RPM.

Randy

Looking at the numbers provided by John, I'd say that (compared to the original AW70) you will see somewhat reduced fuel economy in stop and go driving where the converter's higher stall ratio will have the engine revving a bit more on acceleration. And the acceleration will be a bit stronger if you want to get right on the gas at stoplights, merging, etc.

Assuming the AW72 shift points have been optimised for the higher-revving B234, you may find the B230 runs out of breath before upshifting, if you have the gas pedal floored. (Speculation: can loosening the trans/throttle cable give earlier upshifts?)

At highway speeds, with the converter clutch engaged (lockup) the difference between those OD ratios shouldn't result in more than about 1 MPG loss, all else being equal, ie: if you are keeping your original axle ratio.
--
Bob: son's 81-GL, dtr's '94-940, my 83-DL, 89-745(V8) and 98-S90. Also 77-MGB and some old motorcycles.

Thanks to both you and John for providing the information. I think I might give it a try if the owner of the 740 with the b230f would close the deal with me.

Randy

Randy,

If you've already seen the numbers set out, forgive me. But perhaps others who are interested have not. They suggest to me that an AW72L would impose a noticeable performance (and economy) penalty if stuck behind a B230.

per TP31642/1:

gearbox ratios AW70/71 -- AW72

1st 2.45:1 -- 2.83:1
2nd 1.45:1 -- 1.49:1
3rd 1:1 -- 1:1
4th 0.69:1 -- 0.73:1

Torque converter ratios:
AW71L: 1.72:1 OR 1.80:1 (green book shows 2 sizes, doesn't specify applications)
AW72L: 2.4:1

The rear end in the GLE should have been a 4.1:1, while the 1992 is likely a 3.73:1.

John

John,

Thanks for the information. I was not familiar with the comparison numbers. I understand the ratios for the transmission gears and the rear end, but am at a loss as how to interpret the converter numbers.

Randy

Randy,

The number given is the stall ratio for the torque converter. The TC is at its most efficient near the coupling speed, so a higher ratio means the TC will want higher engine revs to reach coupling speed.

If there's a chart showing power band for an unmodified B230F vs unmodified B234F, that might help you determine whether the AW72L torque converter's higher stall ratio will be enough to cause you grief.

john