2003 Audi A4 Avant 1.8T MT

A new problem arose this week. This has happened 4 times so far...

When in fourth gear, while i'm lightly accelerating, I hear a sudden Thunk, Thud, Jolt, Buck, Clunk, or Bump while i'm driving. It's certainly in the driveline because I get a sudden lack of acceleration and then everything returns to normal. I don't get any lights on the instrument cluster.

So far, this has only happened in 4th gear (perhaps coincidence?). Also, I was not accelerating particularly hard. Actually, it was quite light all four times.

To add, I seem to have a faulty crank position sensor because my car stalls and the battery light comes on. When I try to restart, the engine cranks for a long time until it finally catches with the EPC light on and sometimes the Check Engine light comes on too. I ordered the part and it's coming next week.

Secondly, I still have this very annoying groan coming from the drive-line that I described in another post... https://www.audiforums.com/forum/sho...d.php?t=137539

Do you think any of these two issues are related?

Needless to say, as much as I love my car, I think I made a big mistake buying it.

Thanks in advance for your help.

 

Maybe is oil related, or a bearing. Difficult to diagnose. Have you checked anything or changed anything on the driveline?

 

6 month and 12,000 miles ago, a 3 bearings were changed on the output of the torsen to address the groaning (obviously didn't work). Also, the fluid was changed in the transmission and the rear diff.

 

when the thunk happens is like the transmission dissengages?

 

That's what I was thinking originally, but I was wondering if it might be the engine cutting out because of the faulty cam shaft position sensor / engine speed sensor.

 

Could be, but I don't think so. Maybe what you have is two different problems. Maybe is a transmission problem, I cannot confirm this but your synchro on 4th gear might be showing signs of wear, or maybe you're just low on brake fluid for your master cylinder, worth checking.

 

Dan, thanks for your input.

From what I understand, the purpose of the synchro is to get the collar gear, which is fixed to the rotation of the wheels, to synchronize in RPM with the gear that the collar gear is being shifted into. So, it doesn't seem like the synchros. However, I'm not a mechanic, so I might be missing something.

The thud happened in 3rd gear yesterday.

Do you think I might have an issue with the U-Joint in the drive shaft? Perhaps that might also be the cause of the groaning I hear? Does anyone know the symptoms of a wearing U-joint in the drive shaft?

 

I'm not sure if there's a U joint down there, but there has to be something holding the drivetrain in place thus the groaning could be caused by that item failing. Check your brake fluid for giggles; then check your axles, shake them a bit to see if you get something that bad. It could also be your snub mount (tranny mount) worn out.

 

After I changed the engine speed / crank position sensor, the problem went away. Perhaps it's a coincidence, but I doubt it.

Either way, I'm happy the problem is gone!

 

Good deal, at least you got it fixed, this goes to my little amount of knowledge when someone comes with the same problem.