I've had my step-father's 01 Sierra ECLB equipped with the 8.1 and Allison for a few weeks, and I just noticed an 'odd' sound, seemingly from the transmission today. I was sitting at a drive through, and I didn't really 'notice it' until I put the truck in neutral and it went away. The best way I can describe the sound is imagine a belt sander and you have a block of wood against it. While in D, stopped with foot on brake, it's there, shift to neutral, gone, back to drive and it's back. Totally repeatable. The only thing I can think of off the top of my head that might be able to cause it under those conditions would be torque converter - everything else in the transmission should be fully locked up for forward motion in first, with only the torque converter slipping.
Slight back story on it, it currently has 60k-ish on it, and a handful of years ago, the transmission was allegedly replaced with a new or reman unit because allegedly, it was slipping on take off (It was probably at 50k-ish at the time). I'm not sure that I've ever heard of an Allison with such low miles behind a powerplant as 'weak' as a stock 8.1L slipping any of the first three or so gears - as far as I know, USUALLY, 5th is the first gear to go, and if I'm not mistaken even with how 'dumb' the 01 OS was, it would still recognize slip and limp, which as far as I know, it never did. And nobody consulted me at the time. Personally, I suspect it was the carrier bearing/bushing for the two piece driveshaft causing the shuddering that was interpreted as slipping, and the dealer raked him over the coals.
That being said, Mike, do you or anyone else have any thoughts on this? Any other info I can get to help?
Slight back story on it, it currently has 60k-ish on it, and a handful of years ago, the transmission was allegedly replaced with a new or reman unit because allegedly, it was slipping on take off (It was probably at 50k-ish at the time). I'm not sure that I've ever heard of an Allison with such low miles behind a powerplant as 'weak' as a stock 8.1L slipping any of the first three or so gears - as far as I know, USUALLY, 5th is the first gear to go, and if I'm not mistaken even with how 'dumb' the 01 OS was, it would still recognize slip and limp, which as far as I know, it never did. And nobody consulted me at the time. Personally, I suspect it was the carrier bearing/bushing for the two piece driveshaft causing the shuddering that was interpreted as slipping, and the dealer raked him over the coals.
That being said, Mike, do you or anyone else have any thoughts on this? Any other info I can get to help?
