Knocking sound

[bterry123]

Using the screwdriver to ear test to try and determine where a new knocking sound is coming from, I discovered that the knock is possibly coming from inside the transmission case. The noise is audible at idle and gets louder when shifted into gear, forward or reverse. I have checked the air compressor and the sound coming from it is the same for any transmission selection, so I have eliminated it and could find no soot around exhaust manifold, so I don't think I have a cracked manifold. The sound reminds me of a loose lifter or rod noise in a gasoline engine. My coach has the Cummins 400 ISL with the 3000MH Allison. The tranny was converted to Transynd when the coach had 4000 miles on it. I recently performed the 4 year transmission service and replaced with new Transynd and the level shows to be ok according to the gear selector checking method. Anyone have any ideas? Thanks in advance

Bill Terry
2004 MADP

[TXiceman]

You might check the bolts that bolt the torque converter to the flywheel. If they are loose, you can get an intermittent knocking sound that can be hard to track down.

Ken

[rmmpe]

Suggestion:
Considering some of the early ISL engines had a wrist pin/recall issue, I suggest you make sure the sound is coming from the transmission and not the engine (your comment about checking the manifold leads me to believe you may not be absolutely certain).

[EngineerMike]

According to Cummins, the wrist pin failure (2006 era engine builds, so ~06-07 coaches) evidence themselves in the first 10,000 miles or never at all. At least that's what they say...

[rmmpe]

Good thought, Mike.

I didn't know what years were affected. But, the statement "The sound reminds me of a loose lifter or rod noise in a gasoline engine" hints at wrist-pin slap.

While a wrist-pin issue is certainly not a simple fix, I'd still be aware of it.

I've had a few of those type problems; one (1) was in 1964 when a spun rod bearing put me on the side of the NY Thruway between Syracuse and Albany at 0200. The biggest problem with that was I had to be back in New London because my Boat was departing for the Med at 0800 that morning (joy of joys).
Fortunately, it was a Corvair and I was able to drain the oil into a gas can, drop the pan and rod cap and use the tongue of my shoe to make a temprorary bearing. It actually worked pretty well and I got there in time (just).

Another one was in 1966 when I found myself just west of the Soo in Ontario on a very early Sunday morning with a failed alternator. The only place open was a gas station attended by a fella that spoke only French. But, using the carbon post from an old distributor cap I kept, a file and an old Bernz-o-matic torch, I "Got 'er done" and made it to home (that fix lasted almost a year).

Been driving for 50 years and the "War-stories" are myriad (adapt, overcome and improvise).

While I wouldn't attempt a major fix for a Cummins, I'd sure like to know what it turned out to be. But the OP hasn't been back.