MyE28.com

I recently built an early 745i with a fair amount of boost. I've had several boosted m30 automatic cars that included 1 e28 and several 745's, so I figured it'd be fun to own a 5spd for once. I quickly found out with the 5spd when some say 1st gear is useless... This one was built with upgraded clutch & 3.07 diff. It's a fun car, but has me thinking maybe I should've kept it an automatic or converted it over to an EH tranny to take advantage of the faster/firmer shifts the 745 valve body is calibrated for. Couple that with 3.73 an stall torque converter to have a match made in heaven!
With this configuration I could stay in boost to enjoy rocket launches even more. I think Bill in MN said it best "this thing will accelerate until you let off the gas or see Jesus around the corner whichever comes first". In reference to boost/gearing/stall converter. Perhaps for simplicity I could've done a non-eh trans. It's still the early stages of the car & I have several other items to keep me busy in getting it up to par so I"m trying not to dwell on it. But dark winged angel of boost is on my shoulder whispering...

I'm running 3.45 with tall tires, and like it. The car will burn out and stay in gear long enough to get some pull before you have to shift.

I want an auto more than anything else at this point.

What parts do you have to replace from the standard 3HP22 or 4HP22EH trans to have a 'reliable' auto transmission for turbo?

Did the early 745i's have any difference in the transmission from the other auto 3 speeds?

tschultz wrote:What parts do you have to replace from the standard 3HP22 or 4HP22EH trans to have a 'reliable' auto transmission for turbo?

Did the early 745i's have any difference in the transmission from the other auto 3 speeds?

The trans lines & cluster shift lights are different in the 3hp equipped models. I could do a built 4hp22 non eh unit, or swap in the harness to run an eh model. I'd need to verify if the tcu is fully standalone or interfaces with the cluster lights.

Having driven several automatic 745i's and Vance's really sweet 5 speed car, I must say I prefer the automatic with the 745i's.

tschultz wrote:Did the early 745i's have any difference in the transmission from the other auto 3 speeds?

Piles.

Six clutch A drum (forward)
Five clutch B drum (direct)
Three clutch C drum (intermediate)
Taller C1/C sprag for the extra clutch
Five clutch D drum (low/reverse)
Different torque converter
Different valve body

The E32 750iL used the same clutch stackup, but a few different hard parts for an even beefier unit. I have full 4HP24 guts in my 4HP22 EH case in my 10/84 745i.

Nebraska_e28 wrote: or converted it over to an EH tranny to take advantage of the faster/firmer shifts the 745 valve body is calibrated for

Are you insinuating that the 745 EH valve body is different that the other EH VBs offered in the other models?

Thanks

four2zerohero wrote:

Nebraska_e28 wrote: or converted it over to an EH tranny to take advantage of the faster/firmer shifts the 745 valve body is calibrated for

Are you insinuating that the 745 EH valve body is different that the other EH VBs offered in the other models?

Thanks

It is different.

I have taken apart many 091 case coded 745i specific EH units. The 286 coded, I believe, just has increased lubrication to the overdrive planet via a different sized hole in the case and matching hole in the valve body's channel plate. If I can ever get my hands on one, I can confirm. That is an 08/85-05/86 only unit, very difficult to locate.

Hit Man X wrote:

four2zerohero wrote:

Nebraska_e28 wrote: or converted it over to an EH tranny to take advantage of the faster/firmer shifts the 745 valve body is calibrated for

Are you insinuating that the 745 EH valve body is different that the other EH VBs offered in the other models?

Thanks

It is different.

I have taken apart many 091 case coded 745i specific EH units. The 286 coded, I believe, just has increased lubrication to the overdrive planet via a different sized hole in the case and matching hole in the valve body's channel plate. If I can ever get my hands on one, I can confirm. That is an 08/85-05/86 only unit, very difficult to locate.

I did not know that. very interesting.

So how sturdy or reliable are the US spec auto transmissions for boost? Curious about a low boost setup.

I guess they would be okay, but putting boost into a 200,000 mile automatic transmission makes about as much sense as doing that to a 200,000 mile stock clutch. It simply will not last too long. 745i EH were built nearly identical to the US spec EH, the 745 just had one additional forward clutch and one additional reverse. Valve body different. You can also upgrade all with a simple spring to increase shift quality and TCC lockup. For $30 it is worth it. FWIW, a fresh trans shifts insanely different than a 30 year old unit...and most of the clutches internally could be reused, they have such little wear. I was really surprised. Borg Warner was the OE supplier.

The autos usually die from lack of maintenance, the hydraulics become soiled and shifting slows and slows. Internal o-rings on the pistons leak, resulting in slower and slower clutch application. The stock filtration really is laughable at best. It is a screen. Be 100% sure to use some heavy duty rare earth magnets in the pan and service it often. 50k intervals are unacceptable for this thing.

I have a few ideas how to build a non EH to shift firmer, LJ is going to be my guinea pig on that one. Hey, he was on my prototype drop in Tial conversion for the 745s

Hope it helps guys. Let me know if you have more ZF info, I am no authority but I know enough about the 745 spec ones, V12, etc.