engine and drivetrain AutoTrans ? for PatA

[Guest Anonymous]

PatA:

I have been reading your many posts on auto transmissions for the 02. It seems many of the ZF auto transmissions would be adaptable to many different m10 and m30 models and probably share many of the same internal components. Naturally, the 4 speed auto would seem a better choice than a 3 speed, if one had the choice and the correct length drive shaft.

For basic understanding, what is the major difference between the3 speed auto transmission used on an 02 (3hp12) versus the e21 320; (3hp21)? Is one transmission different than the other? Is one better than the other? More durable? Lighter? Different stall speeds or ratios? All things being equal, is the newer 3hp21 somehow better or considered an upgrade?

How about the zf auto's found in some of the big sixes? If size weren't a consideration, would these 3 speed or even 4 speed AUTO transmissions be more durable (take more abuse or last longer) than the auto transmissions found in the lighter and less powerful M10 equipped vehicles?

Merci!

[PatAllen]

Hi. the 3hp22 from a e21 is an upgraded version of the 3hp12. the governor and valve body is quite different and it no longer uses ravigneux planetary gearing (noisy). the design of this transmission dates back from the arly 60's. Its the first automatic transmission manufactured by ZF.

Its lenght is different and with some driveshaft work could be fitted to the 02.

The big sixes transmission can be a substitute, and yes the 4HP22 found on a LOT of other cars with the M30 engine is almost a bolt-on and quite desirable for an 02.

the driveshaft needs to be shortened

the rear support needs work/relocation

exhaust needs to be modified to clear the pan

shifter selector is different altough i think it could be adapted to use the original 02 part.

note that there is two kind of 4hp22. one is the H type, hydrolic only, and the other one is EH, electronic-hydrolic. the electronic one needs to be wired to the motronic dme to monitor the TPS, speed signal and a bunch of other signals, so for an 02 it is far from the good choice, altought, i am lurking at a 5HP22 EH type, adapt a bell housing for the m10 and do my own electronic shifter box....

[Guest Anonymous]

Hi. the 3hp22 from a e21 is an upgraded version of the 3hp12. the governor and valve body is quite different and it no longer uses ravigneux planetary gearing (noisy). the design of this transmission dates back from the arly 60's. Its the first automatic transmission manufactured by ZF.

Its length is different and with some driveshaft work could be fitted to the 02.

Thanks Pat!

Since I have put 200k miles on a 3hp12, I am convinced it is a decent workhorse transmission. I never noticed anything about the noise although the e21's always seemed much quieter. Do you think the 3hp21 with its improvements is equal to the earlier model in strength and longevity? How about efficiency? Does one have greater friction or parasitic losses than another or are they all the same?

Thank you again!