I have owned and driven a 1988 740 with an automatic transmission for about 15 years and just bought a 1990 740 that is an automatic as well. The trans in these 2 cars act totally different... The newer one seems to glide or almost freewheel where the 1988 seems to slow or gear down when you let off of the gas. Overdrive is working fine on both so I was wondering if anyone knows if they may have used 2 different transmissions for these cars? They just feel like a completely different animals. The shifting even feels different... Weird...

Thanks!
Dan (in Tennessee)

 

those both should be AW70 or AW71 (unless one or the other car is a 16V, then it would be an AW72L, which has different gear ratios and a torque converter lockup).

The AW71 is a heavier duty version of the AW70, otherwise identical.

first thing you probably should do is check the 'kickdown cable' that goes from the throttle pulley under the hood down to the transmission. it has an adjuster at the ferrule of the cable sheath, and there;s a little 'stop' on the cable that should be about 1/16th of an inch from the end of the ferrule when the throttle is completely off, also with the throttle completely off, there should be just the slightlest amount of slack in the cable between the ferrule and the pulley.

2nd thing is to check the transmission oil... do this when the engine is fully warmed up from driving, but first, wipe off the top of the ATF dipstick and handle so its as clean as you can practically make it (thats easier when the engine is cold). anyways, with the system fully warmed up and the engine is idling, pull the transmission stick, wipe it with a CLEAN rag, and reinsert it then pull it again, and the oil level should be between the notches on the 'hot' side. also that ATF should be clear red or no more than very light brown, and it shouldn't smell burnt. if its dark or burnt, you're overdue for a ATF flush and valve pan clean and tranny filter.

actually, I just read what you wrote again...... these cars SHOULD coast with very little engine braking when the transmission is in "D" with OD enabled, maybe its the 88 that was misadjusted or needed a tranny service.

 

You may be right. The 1988 could be the problem as it IS the one with lots of engine braking.. OD is on and working but I have noticed when cold it is slow about up-shifting until you let up a little on the gas pedal AND it seems to downshift pretty quick with a slight press on the gas ANY time.... You now have me thinking that the kickdown cable may be too tight on the 88.. I also noticed that yesterday I was driving the 1990 and was going down a steep hill at about 30 MPH and turned the OD off. It STILL did not seem to engine brake much...(the engine idle is set low but can't remember what RPM) Weird... BTW the 1990 seems like you can't really feel when it shifts. In other words it is super smooth shifting but I don't think it is slipping or anything..
On the 1988 you have no doubt when it shifts and at 30 MPH if you turn off the OD you really feel the engine braking..(you really feel it with the OD on too). I'm now thing they both are not right with one being too "tight" and the other being too "loose" for lack of better words...
The 1990 has a small trans leak. 4 drops in a week on floor and it was only out of the garage about 6 hours in that entire week but the fluid could be low. (I'll check it) I found a paper in the glove box that shows it had a seal replaced in the trans right before I bought it to stop a leak so it may have been run low and could have caused some wear too..
Thanks for your input and I will be following up with this.. Sorry to get so long winded...

Dan

 

Also the 90 is a Turbo and the 88 in not.. I don't know if that could make any difference....

Dan

 

ok, the turbos have the AW71 heavy duty transmission, while the non-turbos normally don't. my 92 turbo wagon has very little engine braking unless I downshift, so what I said before likely applies. our 87 240 non-turbo (same gearbox and engine as your 88) is much the same, very little engine braking unless you downshift.

my sons old car, a 1991 940SE turbo, he had replaced the heater core, and when he did, he misrouted the kickdown cable, so it was being bent a little sharper than it should have, this resulted in it acting as though it was misadjusted, and the car was very reluctant to upshift, had to be going downhill with your foot completely off the gas before it would go from 2 to 3, which it would do rather abruptly. you can see that here



badly focused closeup...


make sure the cable sheath to the right is coming STRAIGHT out of the ferrule and not bent like that. make sure the sheath is pressed completely into the ferrule. the little bead just to the left of the orange protective cap should have the tiniest space between the bead and the cap, and there should be just a little bit of slack in the cable to the left of the bead. adjust the slack by loosening those double nuts on the bracket that holds the ferrule...

too much slack, and the engine will upshift early, and slushily, this is harsh on the bands.
too little slack, and the engine will upshift late, this is also not good.

 

The 88 'kickdown cable' was a bit too tight so I loosened it a little. It did help the slowness of upshifting but I didn't drive it too far so I am not sure about the coasting part..
I know the torque converter on the 88 seems to lock at about 47 mph. I can't tell on the 90 model though.. To be honest, I can't really tell at all when the 90 shifts..It does not seem to slip but it is weird that you can't tell when it shifts and with the 88 there is NO question when it shifts..I am wondering if the torque converter is never locking....Any thought on that... Like I said before, they act like two different animals...

 

i *thought* they only used AW7xL on the 16v models, but its possible they got used on others... I know the turbos never have lockup in the US as the torque of the turbo would eat up the lockup clutch.

 

I feel sure the 88 has the locking torque converter ans it feels like a 5th gear when I get to about 47 mph. The car is a 1988 740 (non turbo) GLE. I was wondering why I didn't feel it on the 90 turbo and now I know. Thank you again!!

Dan

 

is that GLE a DOHC 16V? would have a completely differnet looking wider valve cover than the turbo SOHC motor. the 16V's have different gear ratios, they like to run at higher revs. the turbos like to shift so they are running fairly low RPMs as they have a lot of torque down low.

 

Hmmmm.... So it looks like I DO have different transmissions
I am SURE the 88 IS a locking torque converter....

 

The engines look the same in both cars..

 

Any numbers on the cars that would tell us something??

Dan

 

if they have the same valve cover, then your non-turbo is a B230F, and the turbo is a B230FT. the AW70 provided on non-turbos did have a lockup version, AW70L, but the gear ratios are the same in the AW70(L) and AW71, only difference is the AW71 is heavier duty to handle the higher torque of the turbo.

the turbo cars do have a taller rear end ratio, which moves the shift points a little farther up the speedometer.

frankly, if neither car has had one in the last 5+ years, I'd suggest getting them BOTH a tranny service, flushing, a new filter, and fresh ATF does wonders for your transmission longevity.

 

Maybe the taller rear end ratio explains the "coasting" feel on the turbo. They sure do "feel" tons different though..

 

Auto trannies have a clutch system for coasting vs manual braking. To test this, roll down a slight hill in drive at 5-8 MPH where it's still in 1st, then slam it into low. You'll feel more engine braking even though it's in the same gear.

I'll only throw out there that the OD solenoid was going bad on my AW71; one symptom was *delayed* shift into OD at about 47 MPH. I hollowed it out and get shifts at as low as 35 now, both at 1% throttle. I figure it was blocking pressure/flow and the "hydraulic math" wasn't adding up the same.

Back on topic, IMO the typical setup is for OD and D to not engine brake, and 2 and 1 TO engine brake. Otherwise they'd call D "3".

I agree on the fluid service. IIRC these trannies just have a coarse screen filter and taking apart the dipstick tube to drop the pan is an undertaking so watch out. But draining the fluid couldn't be easier.

 

The ZF HP22 was used in the mid 80s behind the diesel and may have been used on petrol models. This one had a lock-up torque converter and had noticable engine brake effect. My '86 745TD had one.
Look on the trans tag, also the component tag on the 'B' pillar may show it.
Ed

That's ZF 4HP22.
Thanks for the correction Pierce.

 

eljefino, Mine definitely goes through 4 ratios before 47 mph and then it feels like a 5th ratio at 47 when driving easy. I am almost certain it is the torque converter locking.
I'll have to do the engine braking test the next time I drive it.

ed7, Can you tell me more about where to find the trans tag and what numbers I should look for?

Also I do understand the importance of servicing the trans for giving it longer life.
BTW I gave the 88 car to my daughter and the 90 is for me to drive. My daughter is just learning to drive so she drives the 88 to school some mornings and I drive it home.

 

Yup, you have lockup; I do not (I have the turbo/AW71 and miss lockup). But the shift to 4th and final was delayed by my OD solenoid before said solenoid died completely. I brutally fixed it with a 4" angle grinder cutoff wheel! If your car behaves like domestics the TCC unlocks at zero throttle.

I also have a non tubro 740 sedan waiting in the wings for when I get it street legal, so I can see how its trans behaves at speed.

 

left side of the transmission, just aft of the shift linkage arm pivot.

1208501 is a ZF22
1208334, 1208661, 1028642, 5003718 are AW71
1208563, 1208604 are AW70

extra fun, there's more possible numbers. I forget if the AW7x or ZF22 is stamped on there or not, but if its a AW, it will definitely say AISIN-WARNER

oh. ZF-22 cars have "P-R-N-D-3-2-1" on the shift quadrant and NO overdrive button on the shifter. AW7x cars have P-R-N-D-2-1 and the OD button.

 

I'll try to check whenever I get a chance. Both cars DO have the OD button... Thanks for this information..

Dan