Tranny problem on 1997 BMW 740iL

[akshatp]

Its an automatic transmission, 4.4L V8

This only happens from a cold start, and goes away once the car is warm.

The symptoms are as follows:

Start the car, begin driving down the road, everything is fine. Upon coming to the first stop which is less than a mile travelled, the car starts to surge like its shifting gears and is not sure which one to pick. Then when I come to a full stop, the car seems to want to "go" even though I've got my foot on the brake. From what I can tell, its still in 2nd gear at a complete stop.

Then when I start going again, I feel like I am driving a manual transmission and am in the wrong gear. Very little power, sometimes shuddering. Once I get on the highway it bounces back and forth between gears (I think) but then when I get up past 30mph or so, it kicks into the correct gear and is fine from that point on.

For the rest of the day, even if I turn off the car and let it sit for a few hours and then go somewhere again it is fine.

Does this sound like a computer problem or a mechanical problem? I am not sure how the auto tranny picks it gears, so maybe something in the mechanism that tells it what gear it should be in is not working correctly...

Anyone have any ideas?

 

[woodie1]

Originally posted by: akshatp
Its an automatic transmission, 4.4L V8

This only happens from a cold start, and goes away once the car is warm.

The symptoms are as follows:

Start the car, begin driving down the road, everything is fine. Upon coming to the first stop which is less than a mile travelled, the car starts to surge like its shifting gears and is not sure which one to pick. Then when I come to a full stop, the car seems to want to "go" even though I've got my foot on the brake. From what I can tell, its still in 2nd gear at a complete stop.

Then when I start going again, I feel like I am driving a manual transmission and am in the wrong gear. Very little power, sometimes shuddering. Once I get on the highway it bounces back and forth between gears (I think) but then when I get up past 30mph or so, it kicks into the correct gear and is fine from that point on.

For the rest of the day, even if I turn off the car and let it sit for a few hours and then go somewhere again it is fine.

Does this sound like a computer problem or a mechanical problem? I am not sure how the auto tranny picks it gears, so maybe something in the mechanism that tells it what gear it should be in is not working correctly...

Anyone have any ideas?

Have you checked the transmission fluid level?

 

[Zenmervolt]

Caveat: This is very vaguely remembered and applied to the 8-series cars, but I believe there was some commonality between the engine and transmission in the 7 and 8 series cars, but I may be wrong. I would suggest following up on it with someone who is an expert in BMWs to make sure that I'm not insane.

IIRC, BMW transmissions from that era have two transmission pumps and tend to run hot. One of the pumps shuts off at idle (intentionally) and this can cause the transmission to overheat, then the damage from that overheating starts to cause issues with the lower gears when the transmission is cold. If I remember rightly, the only solution is to rebuild or replace the transmission.

ZV

 

[akshatp]

Originally posted by: woodie1

Originally posted by: akshatp
Its an automatic transmission, 4.4L V8

This only happens from a cold start, and goes away once the car is warm.

The symptoms are as follows:

Start the car, begin driving down the road, everything is fine. Upon coming to the first stop which is less than a mile travelled, the car starts to surge like its shifting gears and is not sure which one to pick. Then when I come to a full stop, the car seems to want to "go" even though I've got my foot on the brake. From what I can tell, its still in 2nd gear at a complete stop.

Then when I start going again, I feel like I am driving a manual transmission and am in the wrong gear. Very little power, sometimes shuddering. Once I get on the highway it bounces back and forth between gears (I think) but then when I get up past 30mph or so, it kicks into the correct gear and is fine from that point on.

For the rest of the day, even if I turn off the car and let it sit for a few hours and then go somewhere again it is fine.

Does this sound like a computer problem or a mechanical problem? I am not sure how the auto tranny picks it gears, so maybe something in the mechanism that tells it what gear it should be in is not working correctly...

Anyone have any ideas?

Have you checked the transmission fluid level?

I would if I could. Need to get the car on a lift to do so though. BMW's (at least this series) dont have the ability to check the tranny fluid by yourself. (This would have been the first thing I did if I could btw)

 

[JulesMaximus]

How long have you had this car?

 

[woodie1]

Originally posted by: akshatp

Originally posted by: woodie1

Originally posted by: akshatp
Its an automatic transmission, 4.4L V8

This only happens from a cold start, and goes away once the car is warm.

The symptoms are as follows:

Start the car, begin driving down the road, everything is fine. Upon coming to the first stop which is less than a mile travelled, the car starts to surge like its shifting gears and is not sure which one to pick. Then when I come to a full stop, the car seems to want to "go" even though I've got my foot on the brake. From what I can tell, its still in 2nd gear at a complete stop.

Then when I start going again, I feel like I am driving a manual transmission and am in the wrong gear. Very little power, sometimes shuddering. Once I get on the highway it bounces back and forth between gears (I think) but then when I get up past 30mph or so, it kicks into the correct gear and is fine from that point on.

For the rest of the day, even if I turn off the car and let it sit for a few hours and then go somewhere again it is fine.

Does this sound like a computer problem or a mechanical problem? I am not sure how the auto tranny picks it gears, so maybe something in the mechanism that tells it what gear it should be in is not working correctly...

Anyone have any ideas?

Have you checked the transmission fluid level?

I would if I could. Need to get the car on a lift to do so though. BMW's (at least this series) dont have the ability to check the tranny fluid by yourself. (This would have been the first thing I did if I could btw)

I remember those now.
I bet you are gonna have to get it rebuilt too.

 

[akshatp]

Originally posted by: JulesMaximus
How long have you had this car?

Just over 7 years now.

 

[akshatp]

Update. I spoke to a German Car Shop guy, and he told me to try driving the car in "Sport" mode (which is basically in "4" instead of "D") and see if the problem happens.

Well, it doesn't happen in Sport.

Does this mean anything? I am going to call the guy tomorrow and tell him my findings and see what this means.

 

[Zenmervolt]

Originally posted by: akshatp
Update. I spoke to a German Car Shop guy, and he told me to try driving the car in "Sport" mode (which is basically in "4" instead of "D") and see if the problem happens.

Well, it doesn't happen in Sport.

Does this mean anything? I am going to call the guy tomorrow and tell him my findings and see what this means.

A quick note on "Sport" mode. It's not at all like driving in "4" instead of "D" (assuming a 5-speed automatic). Dropping the shifter down one position from "D" only locks out the top gear, that's all.

Sport mode changes shift mapping and firm-ness but still allows access to the highest gear. In Sport mode, an automatic will hold each gear longer during acceleration and will downshift more readily when throttle is applied.

As for what it means, there are a couple of things.

The first would be that this is solely a computer problem. That is, unfortunately, unlikely as the issue goes away after the transmission is warm.

The second is that the issue has to do with something in the hydraulic transmission controls that is masked when in Sport mode. Since Sport mode has firmer shifts, that means it does not modulate the line pressure inside the transmission during shifts. This means that the line pressures are higher, which could overcome slight problems that are more apparent with softer shifts.

Of course, these are just guesses. The guy at the shop should know best. Automatic transmissions are not a strong suit of mine other than basic operational theory.

ZV