4hp22eh gear hunting

Specific conversations and info for the BMW E28 M5 and M535i.
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sanships
Posts: 20
Joined: Jun 09, 2021 11:36 PM
Location: Cebu Philippines

4hp22eh gear hunting

Post by sanships »

M535i 4hp22eh was replaced using the old and a used transmission parts fused together by the PO before it was sold to me without getting the car running long enough due to the pandemic and lockdowns in the past year. The valve body was overhauled but no specific record on what parts were changed. The car was passed around at least 3x in the last 6-8 yrs not really running due to the bad transmission. Fluids and filters has been recently changed. So maintenance records are not that complete due to different mechanics worked on it through those years.

Pre purchase quick impression was that the engine was ok. Transmission sharp thump going from drive to reverse and from park to drive. Other than that the transmission seemed to shift normally. We only got to about 50kph due to car being unregistered for public open roads.

All suspension and driveline/differential bushings and mounts have been checked and seemed to be in ok shape. It drove straight and stopped well.

Second drive 2 weeks ago was accompanied with overheating problems but initially the transmission was quite fuzzy in choosing gears in sport mode. There was still shift shock going from park to drive but seemed less than the first time. Economy mode made things worse. It kept going up and down the gears constantly. Although the shifts felt not as bad. So I shifted it to 321 where the transmission was very responsive on each gear selected. But when the engine overheated, there were times the shifts became very rapid in sport mode with partial throttle. Like 2 shifts/seconds going 2nd to 3rd and down again in traffic. Then it will hold the gears again for a bit and start again after a minute. So I just kept it mostly in 321 and shifted manually. Got up to 70kph and ride was good.

Third drive was 4 days ago and although it got hot, it didn’t overheat. The engine started hesitating at partial throttle(see other post). Felt like fuel starvation. The transmission pulled strongly in sport mode. Got up to 100kph and it felt solid. The gear hunting was not as apparent(maybe because of the engine hesitation). The mechanic says that by driving the car more, it might get better over time. He also suggested that the tcu might need to be replaced.

I’m trying to keep the transmission original while I’m getting other issues resolved before I decide if I should keep the car and upgrade to a manual. A manual swap would probably be a major expense that I would be upside down on it if I sold it. Although I wouldn’t mind keeping it and doing a partial restoration and get it back to mostly original condition. The body seems solid enough. Suspension and driveline looks good and rattles seems at a minimum.

Questions
1. What are the signs that the tcu needs to be replaced?

2. With the transmission pulling well and shifting well enough when it’s not “hunting”, other than kinda sharp shift shock when going from drive to reverse and reverse to drive.(although the shift shock felt less as we drove it). Does it mean that the transmission might be ok or should I just start looking for parts for a manual swap?

3. Does using 321 mode constantly hurt the transmission? Thinking of just having kids use the car around town might get the problems resolved by itself. So we can trace down other problems with the engine and electrical issues.

I’m still reading through my newly acquired Bentley manual and have to show the testing and adjustment procedures needed to troubleshoot it to the mechanic. They don’t own a Bentley manual since there’s only 3 e24’s and 1 other e28’s but not the 535’s. They mostly work on e36’s and newer cars. But I’ve seen a couple of e21’s. So whatever I learn here will surely be passed to them or the next mechanics to fix the problems. I have read through other forums but this forum has the best information from what I have seen.

Thanks
sanships
Posts: 20
Joined: Jun 09, 2021 11:36 PM
Location: Cebu Philippines

Re: 4hp22eh gear hunting

Post by sanships »

Read somewhere that the transmission mode selector switch should always return to E when restarting the car. My selector doesn’t do that. What should I check? Does this affect the transmission performance? Does it hurt the transmission when left to 321 mode all the time while we use the car trying to troubleshoot the other problems?
sanships
Posts: 20
Joined: Jun 09, 2021 11:36 PM
Location: Cebu Philippines

Re: 4hp22eh gear hunting

Post by sanships »

Solved the problem, it was connected to the tps which when cleaned and adjusted properly functioned well and had direct link to the transmission control unit. Thanks to all for the help in the other topics I had.
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