Fart sound

[ropinfool2]

I was driving up a pretty steep mountain road this weekend, whenever the transmission shifted into OD (about 50mph) I would get a loud fart sound under the hood on the passenger side. I've heard this sound before but never as loud as this. And it happened about 4 times, I then pulled the transmission out of OD. Any ideas? Thanks. John

 

[Mactruck]

Sounds like Turbo bark.

 

[CLAYTON]

Did it happen when you let off the pedal or when it shifted? When I'm going up a long hill or up in the mountains if I have my foot on the go pedal and then let off I'll get that turbo bark but I have never had it when it has down shifted or in overdrive

 

[bighammer]

WHo was sitting next to you?

 

[JRG]

Is this common?



I hear a sound under the same conditions, low RPM, and let off the diesel real fast, BUT the sound seems to come from the transmission or the transfer. Dealer said the couldn't hear it(no supprise) but did document it for waranty.



JRG

 

[RAMINSPEED]

Sounds like torque converter lockup. With maybe a little turbo burp for good measure.

 

[ropinfool2]

It happened when the transmission shifted into OD. What is turbo bark? My wife was sitting next to me but she wouldn't claim it! No smell anyway, knew it wasn't her. Is this normal? Thanks. John

 

[SKelly]

Does it happen as the truck shifts into OD at around 50 mph? Mine will "bark" at that speed as it drops into OD but not all the time. I am not convinced it is the transmission. It seems more to resonate from the exhaust. I had the dealer look at it but they could not duplicate the problem. I have found that if I put my foot into it at 45 and force the OD shift to around 60 mph it does not make this noise.

 

[Steve M]

If it's a metallic sounding fart, look at your transmission dipstick tube. It's too close to the a/c line next to it. When the motor leans that way under torque load, the dipstick tube will vibrate against the a/c line. I pushed mine over and it stayed far enough away that it doesn't do it any more. I can't say the same for myself though.

 

[Dean Upson]

Fireman had that bark and it was his exhaust mod. I think he has it fixed. Send him a pm.



Dean

 

[rbattelle]

Originally posted by ropinfool2

It happened when the transmission shifted into OD. What is turbo bark? My wife was sitting next to me but she wouldn't claim it! No smell anyway, knew it wasn't her. Is this normal? Thanks. John

Turbo bark occurs when there is a sudden loss of power to the turbine, but still plenty of pressure on the compressor (from the intake manifold). Basically, it's a sudden loss of speed of the compressor accompanied by reverse flow. It might also be called compressor stall. It's really not a good thing. If it's mild, it probably won't hurt anything. If it's too severe, you could snap the turbo shaft.



I don't want any of that to panic anyone. It seems the 48re's do this quite a bit when they snap into overdrive under heavy throttle (or heavy towing). I would assume Dodge and Cummins are aware of the condition and consider it minor enough not to warrant any safety features.

 

[JWerkheiser]

Hey guys, thanks for all the excuses. I'm keeping a printout of this thread to hand to my wife after our visits to Taco Bell and Cracker Barrell.