[Daily car maintenance] BMW 5 Series driving in low-speed gear and shifting difficulties_vehicles, vehicles

[Daily car maintenance] BMW 5 Series driving in low-speed gear and shifting difficulties

September 6, 2024

Recently, there are fewer posts, mainly because there are more maintenance vehicles and the maintenance cases are updated more slowly. It may not be reproduced without permission of the original work.
Today’s maintenance is a BMW 5-series factory code F18, equipped with 3.0T (N55) engine, matching eight-gear manual transmission, with a cumulative mileage of about 80,000 kilometers. The rider made an appointment in advance to change the gearbox oil. I have prepared the ZF gearbox oil and the strainer. When the oil pan was removed from the old gearbox, we found that there were residues of friction plates inside the oil pan, which could be clearly felt as the residue of very normal damage. After asking the owner if he had a sudden setback at the start and at low speed.. The rider said yes, and for this reason, considering that he had driven more than 80,000 kilometers, he hoped to change the gearbox oil to see if it could be improved. So I clearly told him that changing the gearbox oil in this situation would not change, because the internal mechanical failure needed to be broken down and repaired. We just sent a BMW X5 the same fault phenomenon, the situation is more serious than this car low-speed shift impact. This kind of failure is a problem in the design of ZF8HP gearbox. How long it can take depends on maintenance and a little bit of good luck.

This is the BMW, and the third series next to it is ready.

The oil released seems to be OK. Coming up.

What we see is the hardware that controls the gear, and the computer (equivalent to software) controls the solenoid valve on the valve body to shift gears.

There are many small impurities precipitated on the oil pan, normally there are some but very few impurities, there will not be so many impurities. This attracted attention at that time, so I asked the riders, and there was a dialogue. But it’s not as serious as the car in the picture below.

This is what is on the transmission screen of the X5. What is circled is that the friction material on the friction plate falls off very obviously, and there are abnormal particles in the oil.

We dismantled the gearbox in about 2 hours and began to decompose it.

Automatic gearbox after disintegration

Compared to see the problem, brown is a problem.

What’s normal is the color.

Let’s press down the piston and check to see if there is something wrong with the piston.

We found that different degrees of burr appeared in the sealing part of the piston, which was abnormal.

Then we found that there are signs of skidding on the steel plate, which means that the pressure is relieving, because the pressure relief causes the grinding inspection plate and the steel plate to slip at high speed and high temperature. Once the material on the high temperature friction plate is very easy to leak, this may have something to do with the way the piston works.

Then we clean the useful parts.

Check every part carefully.

Dry / oil ready for assembly.

Install the last set of friction plates.

Prepare to install the oil pump.

Tighten the gearbox housing screws

Check whether the gap is normal.

Install oil circuit board (valve body)

Install ZF oil pan, only the original ZF oil pan will have new screws. If you don’t have it, consider whether it is authentic or not.

The 8-speed gearbox is best replaced with new gearbox screws.

When the gearbox is assembled, remember to replace the oil seal of the input shaft in case of oil leakage (zf).

After installing the gearbox, add the gearbox oil, and clear the original learning value, go out and run for 10 kilometers to automatically learn the shift logic, especially in the low gear. After the road test failure is basically solved, waiting for the evening off work to try the high-speed gear.

After 30 kilometers of high-speed driving back and forth to switch high-speed gear, there is nothing abnormal. Test again the next day, each gear works normally, the fault is completely eliminated.