What is that noise??, tranny? Options

[jr91472]

Ok, I have been listening to this sound for a couple a hundred miles and am stumped.

Best described as a roaring sound coming from the back, but does not occur at all speeds or driving conditions. Specifically, only when in either 4th and 5th and only at lower rpms (say between 2800 and 3200).

Additionally, I only hear it when holding at a constant speed. I.E. if I accelerate through that rpm range - no roar. Only occurs if I let off power, then re-apply power but only to maintain a constant speed. Consequently it only seems to occur while "cruising" in 4th and 5th (at the stated rpm range).

My first fear was tranny bearings, but wouldn't I hear it at all speeds?

CV joints?

please help, so far my only solution is to either downsift or turn on the radio (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

[ClayPerrine]

Backlash 101.

Every gear in a 914 transmission other than reverse are "helical cut" gears. The teeth are not straight but spiraled. This will make the gears run quieter. But only when properly meshed. The disadvantage to them is that the driving gear will "climb" or "decend" the driven gear if there is too much backlash. That means that the gear is allowed to move in and out on it's rotational axis. This changes the relationship between the drive and driven gear. That makes noise. The drive gear will ascend the driven gear under power, and decend the driven gear when coasting.

What you are probably hearing is a gear lash problem. It may be due to the bearing running loose when the nut backed out on you.

It should not be fatal, but we need to listen to it next Sat.