eurotrans tech-talk -> BMW-transmissions -> Request help diagnosis BMW 850i ZF 4HP 24 problem
Post Info TOPIC: Request help diagnosis BMW 850i ZF 4HP 24 problem
Jan

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Request help diagnosis BMW 850i ZF 4HP 24 problem
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Dear all,

Two visits to the garage and a lot of research did not give consistent results, maybe you can help diagnosing an error in my 1991 850i transmission, it is a 4 speed ZF 4HP 24.  I would much appreciate it in order to decide whether a revision is in order or just a electronics / sensor replacement should do the trick.

Sorry for the long post, I am trying to give complete information. Please note there are some subtle clues in the behaviour of the 3rd gear directdrive locking system. Also, the main question is why this happens only cold when oil is thick and wear and tear problems should be less not more (I assume)

The problem started from one day to the other and the symptoms are very consistent every day:
1. At cold start (mornings and afternoons commuting)
   - Car starts, normal driving (E) gear in Drive (D)
   - Tranny will not shift up from 1st to 2nd
   - Tranny does not lock on 1st (rpm drops to idle when releasing gas pedal)
   - If driven a few minutes or faster (> 3000rpm) : Getriebenotprogram
   - In getriebenotprogram tranny will shift up to 3rd (or 4th?)
   - In getriebenotprogram tranny will lock on 3rd (or 4th)
   - After stopping and restarting engine tranny gives getriebenotprogram right away, locks on 3rd gear.
2. At cold start, to allow reasonable driving
   - Car starts, manual shifting (M) gear in 1, 2, 3 and D
   - Tranny shifts and locks normally 1st, 2nd and 3rd gear, not 4th (D)
   - In M 3rd gear, tranny will lock (the torque concertor) but will not engage the directdrive, also not above 3000RPM
   - Getriebenotprogram only once in a while, but usually not
3. After driving several about 15km
    - Stopping (at gastation) and restart of engine
    - All errors are gone, normal operation of tranny restored.
4. When driving in Manual 3rd gear (M3), after about 15 km
    - Suddenly the tranny will engage 3rd gear direct drive around or above 3000RPM
    - When this happens, normal (E) drive (D) can be selected without stopping and tranny resumes normal operation
5. A little history
   - I have driven this car 30.000km, it is now 275.000km
   - Tranny has been serviced when I bought the car (oil filter etc)
   - 3rd gear direct drive has always been "slow" to engage, upto a few seconds for instance when accelerating with kickdown
6. Computer readings
   - First visit: code 26 and 27 (ignition signal and torque convertor) on X431
   - Second visit (+1 week) only code 27 tranny speed signal (origal bmw readout)
   - Second visit with lifted wheels, 3rd gear drive idle, engine and tranny speed signal are ok (around 850rpm) (Car is warm!, no errors)
   - When car is warm no faults can be found
   - Plugs are checkd (8pin at tranny and EGS in trunk)

Al right, if you read so far, thank you very much. You may understand I have a hard time believing this is mechanical due to the fact it only happens cold. Maybe it is only the speed sensor in the tranny? Any advice is much appreciated.

Thank you, Jan (I can be reached at eurotrans@av-e.nl)

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herb

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Hello Jan,

I have read all of your explanation and it is very familiar to me. Many cars have the same symptoms specially cars with a lot of mileage on it.

The seals in the transmission get brittle and old, the hard, and the transmission have shifting problems when "cold"

After a few mileages the transmission runs normal again.
This means the trani is warm, the robbers seals get soft and everything goes back to normal.

You will see, when you take your transmission in parts, some of the seals turnt in to plastic ! is looks like.

herb


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