AFN Gearbox Problems: Power Loss & Troubleshooting

Hey everyone, it's me again.
It's possible that a faulty transmission could prevent the engine from delivering its full power. During gear changes, there's always a feeling that the car is being slowed down, as if a brake is dragging. However, the brakes are working properly; there's nothing actually dragging. Because my car (CYP) has some issues, I suspect, and my workshop, which handles the major repairs, suggested that this could be caused by a defective transmission, such as worn bearings. I can completely rule out any defect in the engine; I've already gone through everything in Ulf's test, and everything checks out.

What do you think about it?

Greetings.
Reuselkopp.

Nun ja wenn du das so beschreibst. WIe lässt sich das Auto denn im Leerlauf rollen? Das ist ja "ausgekuppelt. WIe sieht es mit der Temperatur des Getriebes aus? Wenn es da zu erhöter Reibung durch Verschleiß kommen sollte, muss es sich durch hohe Temperatur bemerkbar machen. Wie sieht denn der Getriebeölstand aus. Und like oil.

I can't quite picture the whole thing...

Hi,
Okay, so I was driving on the highway, going downhill, and I accidentally depressed the clutch and let the car roll. I could feel that braking effect again. I can't say anything about the transmission itself. What's noticeable is that this braking effect is strongest when the car is really warm (after about 30 km of driving). I can't tell you anything about the transmission fluid level except that it was changed about 4 weeks ago during the clutch replacement. The old fluid was a very dark, almost black color, and it smelled like it was completely burnt. My mechanic, Fuzzi, said he'd never seen fluid like that before. He's the one who diagnosed "transmission damage." This is also reflected in the very jerky shifting of the first two gears.

Used transmission oil always smells a bit strange. It's odd that your problem appeared after the clutch replacement. Something might have gone wrong during the process. Could it be that the clutch is slipping?

Hi,
"No, this problem has been going on for a while. Could this sluggish behavior also be caused by excessive crankcase pressure? Or could the brakes be dragging during driving if there's something wrong with the crankcase ventilation system?"

You can rule out the brakes by stopping, getting out, and checking the brake temperatures. It's best to let the vehicle roll freely for this. If the effect is observed when the wheels are free-rolling or when rolling in neutral, then there is primarily no frictional connection between the wheels and the motor, so you can also rule that out. Try checking the KWG pressure.

reuselkopp wrote:

Once, while driving on the highway and going downhill, I accidentally pressed the clutch and let the car roll.

I could feel that braking effect again. Then, try letting the car roll in neutral gear to see if it behaves differently.

Whether I let it roll in a decoupled state or in neutral, there's not a huge difference. Usually, when you roll downhill and decouple, the car should accelerate quickly, but in my case, it maintains its speed or only accelerates slowly. It's particularly noticeable when braking while going uphill and then shifting gears. You decouple, and you really feel how unusually hard the car brakes, and then, after engaging the clutch, it slowly starts moving again. I've also checked the brakes at different temperatures, but I didn't notice anything unusual. The rear drum brakes were cold, and the front ones were slightly warm, but the temperature was the same on both sides. I can't check the KWG pressure because I don't have anything suitable for testing. I was thinking of removing the pressure valve and blowing it out to see if anything is blocked. At what pressure does the valve open?

I can really only imagine that such strong resistance is coming from the brakes. Could you put the car on a lift and really check everything for free movement, all the wheels, the brakes? When turning a front wheel, observe and listen to see if anything is coming from the direction of the transmission. Maybe try rolling down a hill in neutral with the engine off (careful with the brakes/steering) and listen. A dragging brake should be audible with the window open. How does the car track straight? Does it pull to one side? Is the alignment/camber correct?

Otherwise, I'm out of ideas... I'm having trouble imagining how this could be the problem with the transmission, because the two defective ones I've seen and heard so far had obvious defects, and the shifting resistance in some gears was insurmountable.

Okay.
Okay, I'll check the brakes again. But I have another question about that. How easily should the front wheels spin? Is there a rule of thumb for that? I mean, at least so many revolutions of free spinning before they come to a stop. I can't imagine that they should spin as freely as the ones on the rear axle.

Well, I don't know a specific formula for that. Just turn them, and they should rotate without requiring any force. Whether they lag behind by half a revolution or two revolutions depends on the amount of force applied .

reuselkopp wrote:

How easily should the front wheels be able to rotate? Is there a rule of thumb for that? I mean, at least so many revolutions should be possible before they come to a stop. I can't imagine that they would rotate as freely as the ones on the rear axle.

That's right, because on the rear axle, you don't have a differential, no drive shafts, etc.
"Rule of thumb: As long as the rims aren't noticeably hot after 10 km of driving with only a few braking maneuvers, the brakes are working properly, and your problem lies elsewhere."

After a longer drive, at a moderate speed of around 30 km (taking the braking effect into account), I would carefully feel the entire transmission to check for any warm or hot spots.

You turn the wheel with one hand, and it should turn effortlessly. With disc brakes, you need to know that the pads are always in contact, so the wheel never spins freely and won't even rotate on its own. It always requires some effort. Drum brakes, on the other hand, are much looser, and you can easily feel the difference. The problem with drum brakes is that if they are too tight, the wheels spin freely with cold brakes. However, if you drive a few kilometers, they heat up, and they become increasingly difficult to turn and get hotter and hotter!

Just do the test easily: when your car is warm, drive it home, put a jack under it, and try to turn each wheel one by one. You'll then be able to tell exactly whether they turn easily or not.

Based on how you're describing it, the car needs to be braked properly. If it's a brake issue, you need to figure out what's causing it.