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Discussion Starter · #1 ·
Hello All,

I have 1995 325IC at ~89 K miles. The car has both automatic and manual options. I have a problem and would like to ask your suggestions or opinions. Thanks in advance!

When I am driving in automatic mode (D), [regardless of cold or warm engine / regardless of A/C running or not /regardless of my acceleration is gentle or aggressive], sometimes, I lose power (i.e., the RPM suddenly goes down from 2000 to 1000 for 2 seconds) and I feel a rocking (or, back and forth) movement and I can actually hear cranking from the transmission as if it is trying to engage to a lower or higher gear. Then RPM picks up, if I keep my foot on gas pedal and the gear change is back to normal. If I need to stop at a sign or at the lights, I get the same inconsistent RPM when the engine is running idle (RPM suddenly goes up to 1000 several times -whereas it should be around 500) and the transmission makes that cranking sound.

When I am driving in manual mode however, everything seems to be perfect.

I took the car to three different services, two of them are certified BMW service centers. The diagnostic computers did not pick up any codes, my transmission lamp is not lit and the trip computer's check mode comes clean every time I run systems check. I know it works because it recently gave a warning about the coolant level and it was accurate!

One of the mechanics suggested that the chip, which is controlling the timing of the automatic transmission (?), may be faulty since the problem is intermittent and occurs only in the automatic mode.

I will appreciate your insights!

Cheers,
barikan
 

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Discussion Starter · #3 · (Edited)
Thanx

Thank you! Do you think the fluid has gone bad and causing slippage?!

EDIT: I checked the records of the previous owner; the trans fluid (along with the filter) was changed at 81.400 miles, exactly 8K miles ago. I am sorry, I have no idea, does it mean it is about time?

barikan
 

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I'm not entirely sure that this is a problem in regards to transmission fluid, particularly now that you say it was changed 8K miles ago and this is only something that happens in automatic and not manual mode.

This could be a computer related problem as your mechanic suggested and I especially believe that because you say it only occurs in true automatic mode. I'll see if I can find additional information on this.
 

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Discussion Starter · #6 ·
Up-date

Hi and thanx for your help. I just got back from the service; they flushed and changed the transmission fluid but the problem persists.

I could not convince the mechanic to check ICV or MAF; from what I have been reading here, people with similar problems found solution when they are cleaned.

I still think that it is a chip-related issue for the exact reasons you mentioned; the problem is not there when I am controlling the gears. But why do I not get an error code when it is hooked up? This is frustrating.

I looked at the link you put on your reply. I am not really into cars, so it is difficult for me to tell, but my car is not 325 is, it is 325i Convertible (I only have 1st-2nd-3rd gears on manual and -D-) -I am not sure if it will make any difference.


Also, when I was talking to the main BMW service here, I was told that the BMW code for the type of transmission I had was THMR-1.

I will appreciate any suggestions.
 

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The transmission should be the same regardless of the model and based on the fact your manual has 1,2,3 gears in manual is telling me that you have a 4 speed automatic.

It is definitely a GM transmission and the BMW service code definitely helps me verify that on this document on Google Docs

The ICV should not have an effect on the way a transmission shifts. If your engine was idling erratically at stop lights I would definitely recommend cleaning the ICV for sure but I think this problem goes beyond that. If your MAF was faulty you would also have eengine problems as well.

You could always have the transmission software updated or reloaded.

This problem also doesn't indicate that an error or transmission light would be triggered because it doesn't seem to be an actual problem with the transmission itself. I'm still trying to find some info on this to see if someone else has had the same problem.
 

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Discussion Starter · #8 ·
Hi Bimmer E39,

So, please correct me if I am wrong; you are thinking that the transmission is mechanically (i.e., the hard parts) OK [because the manual is functioning] but the controlling unit (i.e., the chip or whatever it is called) may be faulty/going bad.

I discussed re-programming the chip yesterday and I was told that for the chips I had re-programming was not an option but replacement was. May be it is the next step!
 

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Yes, I believe the mechanical parts of the transmission are in working order based on the fact that manual mode works correctly and automatic mode seems to be an issue. If both modes had a problem I would definitely be look at the mechanics of the transmission itself.

I'm not entirely familiar with the electronic system of the E36 itself, but yes, the module might have to be replaced. I know on my car the actual transmission control unit can be reprogrammed/updated so that's why I suggested it.

You could always opt to have the transmission inspected first before replacing the control module itself. Lets see if someone else has an opinion on this.
 

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Discussion Starter · #12 ·
Up-date on the problem

Hi,

Finally, I had the existing chip replaced at the mechanic today. It seems that the one on the car did not have BMW emblem and probably was an after-market Asian (Singapore) product. The new chip is made in Germany by BMW.

Although the transmission shifts smoother (and definitely the intervals are different) and there is some improvement in the gas consumption (or the trip computer's estimations are more accurate), the transmission issue (i.e., slippage in low gears during acceleration) is still there.

Manual is still functioning properly.

Now, it seems to me that the problem is either related to the transmission (i.e., the hard parts) or the high gear discs are somehow already damaged and causing slippage.

I still cannot understand why I am losing torque (RPM suddenly drops and picks up) when the slippage occurs.

I will appreciate any comments/suggestions.
 

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Wow...I'm really shocked in all honesty. I'm also dissapointed for you as well. Your problem definitely seemed like a program issue with the transmission but it seems odd that the unit you pulled out was not a BMW spec unit...

In all honesty, I am at a loss for real answers at the moment. I'll ask my friend tomorrow what he thinks about your problem. He's an ASE Master Certified Technician so at this point I'm thinking he would be able to give me some better ideas about possible reasons for your tranny problems.
 

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Discussion Starter · #14 ·
Hi Bimmer E39,

I was shocked too. I am really curious what it will come to at this point. I just feel fortunate to have some kind of service coverage on the car.

I really appreciate your efforts and I am looking forward to hearing from you.

One strange thing; when I am driving in manual mode, I treat D as the 4th gear. May be I am wrong but the car should have at least 4 forward gears. But in D, there is no further acceleration, it is not any different than 3. It does not seem right to me!
 

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One strange thing; when I am driving in manual mode, I treat D as the 4th gear. May be I am wrong but the car should have at least 4 forward gears. But in D, there is no further acceleration, it is not any different than 3. It does not seem right to me!
Hmmm, I'm not too familiar with the transmission in your car but my guess is that D is the 4th gear and it probably acts like an over drive. I am like 99.9% sure your automatic is a 4 speed.
 

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Discussion Starter · #18 ·
BMW says...

I took the car to the only BMW dealer/service here. I drove with a service professional. He thinks that this is a timing issue (the engine and the transmission cannot agree on the timing of the gear shift) and that is why I lose torque and then I have the rocking movement from the transmission. And, this is why I don't have the problem in manual mode, because I am changing the gears and determine the timing. He said it could have been an issue with the programmable chip but mine is not one of these programmable ones.

He thinks that the part in the transmission, which is supposed to push gears (provide the actual change of gears)-and I cannot remember the name- may be faulty. However, he says, in some cases BMW prefers to change the whole transmission rather than replacing the problem part only.

Since I have so little knowledge of automatic driving, I also learned that I could drive my car in sports mode (keep the stick in 3 -rather than in D- in the automatic mode)!!! It seems that the problem goes away in this mode but I need to drive it some more to make sure.

So in summary; the problem is there only in Auto-D; it seems to go away in the sports (Auto-3rd) and it is definitely not there in the manual.
 

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Interestingly enough, my friend came up with a similar theory but he couldn't be 100% certain without actually driving/inspecting the car.

However, it is usually true that BMW replaces the entire transmission rather than rebuilding it as it is easier and more cost effective just to swap a new one in. There are plenty of places that rebuild transmissions however and seeing as it's a GM/BMW transmission I don't think it's going to be too complex or difficult for a qualified technician to do it right. I think this was will be cheaper for you because I think we can both agree BMW will destroy your wallet on the price/install of the new one (unless you have some sort of coverage).
 

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Discussion Starter · #20 ·
Thanks for keeping me informed about this. I am in the grace period of a warranty, so I will just wait a little more. And, at least I have the manual and the sports mode functioning right now.

To tell you the truth, reading so many horror stories about the transmission issues of later year models in 3 Class, I am a bit worried having my whole transmission replaced. But I guess, these transmissions are different than mine.

I will give an up-date once the repair is complete.

P.S. do you remember the name of the part in the transmission that may be the problem?
 
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