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7 Series - E38 (1995 - 2001)

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  #1  
Old 06-25-2013, 05:55 PM
wrficklin wrficklin is offline
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Mein Auto: 97 740iL
Shifty transmission gremlin

I bought my '97 740iL when it had 97K miles on it. Since then I've put 90K on it with no issues except one. I have searched forums here and there and found no threads that describe the behavior I've experienced with this car since day one. I've gone through the oil and filter changes several times with no affect on the behavior. It seems to matter not what the temperature is nor doing the adaptive reset procedure. The behavior persists with only rare occasions when it amazingly performs perfectly. I've been able to make no associations between when the tranny works correctly and any other factors such as driving it easy or hard, hot or cold engine and tranny, hot or cold weather, etc.

I changed out the valve body with a reman sometime back, hoping that would resolve this. No joy. It made zero difference in the tranny's behavior.

Symptoms A & B:

When I start the car and place it into reverse, it engages hard. Doesn't matter if it's hot or cold (the weather or the tranny). When I then place it into drive, it engages hard. (The RPM is about where I think it should be, 700 or so, but the hard engagement feels like what I'd expect if the engine were revved up higher than idle and slamming it into R or D. Sometimes it's more noticeable than at others, but always annoying.

Symptom C:

When I allow the car to coast down to about 38 ~ 40 MPH I will feel a thud when the tranny shifts out of 5th into 4th. If I drive with it in 4th (Sport) all of the time, there is no such behavior (I've seen a lot of guys use this method as a poor workaround). I also see this behavior if I'm coasting (foot off the gas) and pull the shifter manually into 4th before getting down to 40MPH. HARD THUD. A clue seems to be related to "coasting" verses not coasting. If there is even the slightest amount of acceleration, or just enough gas to keep the speed where it is when I pull it into 4th, it does so beautifully, every time.

Another scenario is when I'm cruising along at, say, 50MPH and I start up an incline but hold the throttle steady and allow the speed to decay, the car will eventually drop to 38 ~ 40 MPH and the tranny will shift down into 4th smooth as butter. Every time. The trick is to keep a slight amount of power to the tranny and it will shift down exactly as it's supposed to even though the car may be slowing when going uphill. If I am gently accelerating by applying more power, it shifts down perfectly when I manually pull it down into 4th gear.

As I mentioned earlier, once every blue moon I'll start the car and put it into reverse and it's perfect. It eases into reverse nicely. Ditto with shifting into Drive. I cannot figure out what is different at those times. I may then drive it 5 miles to the store, go in, come back out, start it up and place it in R or D, and THUD. Break time is over and it's back to bad behavior.

Recently I've started to wonder if perhaps the culprit is the torque converter (just a hunch, nothing solid to go on). Could the TC cause the R and D hard engagement at idle RPM as well as the hard downshifting from 5th to 4th when coasting only? There are no shifting issues in the lower gears.

Thanks for any info,
Del
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  #2  
Old 06-25-2013, 10:30 PM
ebida3's Avatar
ebida3 ebida3 is offline
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Location: High Point, NC
 
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Mein Auto: 2001 740iL
This is a earlier re-post

The TC could cause a bang going into gear but highly unlikely, the bang on the downshift could be a bad band/s and not the TC.



Remember that when the tranny shifts up it does so under high fluid pressure provided by the TC. A downshift doesn't use high fluid pressure. In fact, it uses the opposite to shift. A lack of pressure causes the valve to close causing the downshift. The abstinence of high pressure allows for a smooth downshift. Hence, what you describe as coasting vs. not coasting (under acceleration)


Sounds like you have more than one issue here.
One of them being a weak or bad first/reverse and 4th to 5th band. (gear)

This is a re-post from another tranny problem a member here has.
Read below.
------------------------------------------------------------------



The tranny sounds like it may be on the way out wear wise.

You need some basic tranny 101

The torque converter spins and depending on the speed it spins at, it pushs fluid thru different channels in the tranny body. These channels lead to valves located in the "valve body".

Now depending on the pressure of the fluid the valve is a gate that opens and pushes the clutches to engage and shift gears. There are no GEARS per se in the tranny, there are bands that tighten on the clutches to make the shift. There are different clutches and, "bands" for each speed except reverse and first which share valves and bands.

Now with that said if you had an electrical issue in the tranny a code and/or a "Transmission Failsafe Program", warning would be evident. If these are not present we may assume that it is a mechanical fault. I will also assume that there are sensors to monitor fluid pressures. If the pressures are low in any given area, that sensor should signal back to the ECM and show where the problem is.

I would tend to think it is a worn vs. low pressure problem you are having.

These are mechanical reasons for failure...

Slamming into first or any gear can be caused by:
1. Bands that are worn
2. Bad valve/s depending on which gear is banging
3. Low fluid pressure
a. low on fluid
b. bad torque converter
c. restricted screen
4. Clutches are worn
5. Faulty pump (indicated by a whining sound not unlike a F-22 Raptor taking off)

Pick one

Tranny problems usually start with a bad first/reverse shift because this shift demands the highest pressure to initially get moving. If any of the above are weak, we see it at this shift. Remember the reverse and first share the same mechanics.

Good Luck

P.S. You do know what assume stands for.......

Last edited by ebida3; 06-25-2013 at 11:03 PM.
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  #3  
Old 06-26-2013, 08:03 AM
Sharkymaheesh Sharkymaheesh is offline
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Me too

This is exactly what my 750il is doing.
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  #4  
Old 06-26-2013, 10:02 AM
wrficklin wrficklin is offline
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I'll throw a wrench into the scenario outlined before. Let's assume that the transmission, torque converter, and valve body have ALL been replaced, and the symptoms did not change in the least. What would likely be the cause of the behavior now?

I ask, because that's essentially what has been done to the car. The entire transmission is not the original. The original tranny had a catastrophic failure at 165K miles. I swapped it out with one that had 52K on it (and then later the valve body with a rebuilt unit on the assumption that perhaps this model of valve body had a known issue with stilling check valves, etc., and the performance behavior was identical to the original before it failed. The only thing I'm not certain about is whether I changed out the original TC because a one point I lost track of which was which during the swap. In other words, it's higly possible that the original TC is still in the car. This is why I'm know suspecting the TC as the source of the problems.

On the other hand, assuming that the TC in the car now is the replacement, is there any external input that could be feeding bad info to the TCU? Could a defective throttle posistion sensor do this?
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  #5  
Old 06-26-2013, 04:43 PM
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ebida3 ebida3 is offline
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The ASSUMTION is that the tranny you put in is good. This is not a valve problem either.

The torque converter is a fluid coupling. It transfers torque from the engine to the transmission. If the transmission has problems shifting then it's not a torque converter problem. You either have low fluid pressure from any of reasons I described or bad bands/clutches.

Last edited by ebida3; 06-26-2013 at 04:45 PM.
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  #6  
Old 07-14-2013, 06:54 PM
Podmore Podmore is offline
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Quote:
Originally Posted by wrficklin View Post
I'll throw a wrench into the scenario outlined before. Let's assume that the transmission, torque converter, and valve body have ALL been replaced, and the symptoms did not change in the least. What would likely be the cause of the behavior now?

I ask, because that's essentially what has been done to the car. The entire transmission is not the original. The original tranny had a catastrophic failure at 165K miles. I swapped it out with one that had 52K on it (and then later the valve body with a rebuilt unit on the assumption that perhaps this model of valve body had a known issue with stilling check valves, etc., and the performance behavior was identical to the original before it failed. The only thing I'm not certain about is whether I changed out the original TC because a one point I lost track of which was which during the swap. In other words, it's higly possible that the original TC is still in the car. This is why I'm know suspecting the TC as the source of the problems.

On the other hand, assuming that the TC in the car now is the replacement, is there any external input that could be feeding bad info to the TCU? Could a defective throttle posistion sensor do this?
The symptoms you describe are the same as the ones which were found to be caused by a failed 'A' clutch drum; in my case, the circlip which retains the clutch pack had let go when a couple of the sprags on the drum broke off. Extremely hard downshifts from 5th to 4th; slow to engage reverse; and progressively more erratic shifting. I was told it was a known weak point on the 5HP24, and replacement drums have stronger or thicker sprags where the circlip mounts. That was a $5000 rebuild .....
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  #7  
Old 12-29-2013, 10:13 PM
wrficklin wrficklin is offline
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I finally fixed the problem first described in this thread. It turned out to be none of the usual suspects or suggested causes. Rather, after the "TRANS FAIL PROG" message became more frequent, and especially in one instance where I was sitting in PARK with the engine idling, the TRANS FAIL PROG message appeared, I finally had a better clue that the issue was NOT with the transmission, per se, but with the computer or wiring. In every case prior to this I was able to pull over, turn off the engine, and let the computer reset. Restarting always gave me a functional transmission again. However, this procedure always cleared a code that I wasn't aware was there until the occurrence while sitting parked with the engine running. Before I cut off the engine this time I checked for codes on my Ultragage OBD2 reader. There was nothing in the engine code memory, but there was in the Pending Code memory: P0745. I was finally onto the trail of the gremlin that had been present since purchasing the car many years prior, even after swapping out the transmission and subsequently another valve body. The symptoms never changed.

For the BMW, the error code P0745 indicates that the TCM detected an improper voltage drop when it tried to operate Pressure Control Solenoid A. In other words, all this time I had been living with either an intermittent short or open connection issue between the TCM and the transmission valve body. But where? I checked both halves of the connector at the TCM under a magnifying glass and shot it with contact cleaner. No change in behavior. Then I looked through the wiring diagrams in the Bentley manual and saw that there were only two connectors involved in this circuit. One was at the TCM, which I'd already checked, and the other was at the transmission.

Under the car I found that the connector I was interested in is on the upper side (driver side) of the tranny housing right above the brace that fastens to the two exhaust pipes before the CATS. Removing that I could reach the connector just enough to disconnect it. I could visually check the female end of the connector and it looked clean and otherwise fine (I halfway expected to find corrosion, but didn't). I couldn't see the male pins up on the housing mounted connector from that angle, but assumed that they were also fine based on what I saw on the female side. I shot both connectors with contact cleaner, and reconnected the two, (in and out several times to be sure all contacts would wipe together for better contact along with the cleaner).

Voila! Since cleaning the TCM-to-Transmission connector (connector X8600 in the manual) I've had perfect performance out of the tranny. No more slamming into Reverse or Drive out of Park at idle RPMs, no more hard down shifting out of 5th into 4th at 40MPH while coasting, and pulling the selector into Sport mode while coasting above 40 doesn't shift hard anymore either. I've driven it now for a week, over 700 miles, and not one hiccup. Prior to this, I could count on the bad behavior 99% of the time every time I drove it.

Given that I experienced this behavior from the day I bought it (then it had 97K miles on it) I'm convinced the prior owner knew there was an issue and was told he needed a new tranny, and so he unloaded it quickly below book value. I'm also convinced that this shifting issue is what destroyed the original tranny at 165K.

Today it feels like I'm driving a new car. What a nice Christmas present and a great way to start the new year.
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  #8  
Old 12-29-2013, 11:02 PM
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ebida3 ebida3 is offline
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That's great! It is gonna be a Happy New Year!
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