Exhaust Brake Issue

[john_harris]

Returning from trip, I noticed a relative high pitched squeal after lifting off accelerator. As I was traveling mountainous areas of VA and WV, I routinely keep exhaust brake engaged. Noise was intermittent, but seemed to be associated with exhaust brake and deceleration although it also seemed to be present a few times while accelerating. I disengaged it for a while as road conditions permitted and it mostly went away, but not entirely.

After returning home, I tried to replicate condition while driving to local Cummins service center but could not get it to "squeal" for them, even on a test drive.

Anyone out there experienced similar issue? Not really sure it is exhaust brake. Could it be belts, exhaust leak, turbo, other?

[wolfe10]

John,

Not sure how an exhaust brake could cause a squeal. Yes, if you have an exhaust leak upstream of the brake, it would cause a noise, but probably more of a "hissing" sound as the back pressure escapes. And an exhaust leak would show itself on a diesel by the deposit of black soot around the leak. The turbo should not be working-- with exhaust back pressure from exhaust brake, it would be spinning very little.

Wonder if it was RPM related-- engaging the exhaust brake normally raises engine RPM. So, a belt, bearing in A/C compressor, alternator or water pump may make more noise at higher RPM and, with less noise from the engine itself (throttle closed) may be more apparent.

You might try playing around with the "down arrow" on the Allison and see if it is RPM related.

[huffypuff]

I believe some exhaust brake have an orifice on its plate that may cause more than a hiss out the tailpipe under extreme condition. I sometimes hear something similar when I get a heavy downshift with the exhaust brake on.

[john_harris]

Certainly not a hiss but Brett may be on to something with increased RPM creating strain on belt, AC compressor, or water pump. Will continue to investigate and let you know.