Drive train question

[DIESEL/VETTE]

On my 2003 2500 duramax, in front of the rear end between the universal joint is a large round metal piece, around 8 to 10 inches in diameter, what is this for and what does it do?

[DmaxMaverick]

Vibration/harmonic damper. It helps prevent damaging (and possibly annoying) vibration and harmonic frequencies generated by the axle from transmitting through the shaft.

[DIESEL/VETTE]

Thank you.

[More Power]

Road salt and de-icer can affect these dampers by eating away at the cast iron/steel components. Not sure what to do about that, or how extensive a repair it might be to fix it. Anyone replace one of these?

[DmaxMaverick]

Road salt and de-icer can affect these dampers by eating away at the cast iron/steel components. Not sure what to do about that, or how extensive a repair it might be to fix it. Anyone replace one of these?

The damper is part of the pinion yoke (not separable), and a repair would simply be a replacement of the yoke. If the damper fails due to corrosion, the shaft and other nearby components (axle, springs, etc.) should also be suspect. The damper appears, to me, to be the least of the worries in that area. Something serious would likely fail long before it became a factor.

[More Power]

Lil Red's rear driveshaft doesn't have a driveline damper. Doesn't appear to be a negative because of that, at least no negative yet in 10k miles.

I'm sure that some truck owners who see their OE driveshaft damper deteriorate to a point of failure will simply cut it off. I'd bet they wouldn't see much in the way of a negative for quite some time, at least.

PS... Back in the 1990s I re-installed a TH700R4 in the 1982 GMC 6.2L Banks turbocharged pickup I owned at the time. That truck had 3.42 differential gearing. The first thing I noticed after re-installing the TH700R4 was that at low(er) engine rpms and lugging the engine a bit in overdrive, the engine's torque impulses would produce a "ringing" in the rear driveshaft. The TH700R4 was a 4-speed with 0.71 overdrive and locking torque converter. I never did "fix" the ringing problem - just simply dropped out of OD during those times which increased engine speed just enough to stop the ringing.

One cure for the ringing would be to fill the driveshaft tube with a type of foam, which deadened the ringing - the auto industry does this sort of thing for the same reason. With the introduction of the Duramax/Allison, GM apparently chose to incorporate a harmonic damper on the pinion yoke to: reduce/eliminate any ringing and possibly reduce the likelihood that torque impulses might damage the nearby bearings and gears after long-term higher power demand type driving. There could be a power/torque threshold involved because GM didn't do anything like this with the 6.5TD powered trucks and SUVs. Even our 6.5TD Power Project truck, which made significant power, didn't have a driveshaft-related ringing/durability problem. In fact, the U-joints built into the rear 2-piece driveshaft during that truck's build were still going strong with 300K miles on them.

[DmaxMaverick]

As I recall, Lil' Red is running a GM Corporate, 10.5" axle (semi or full, I don't recall). The Allison-equipped trucks (to include the 8.1L) all have the AAM 11.5" axle, and all have the damper, regardless of gearing (3.73 or 4.10). So, the damper is either a manufacturer standard thing, or a requirement of the axle thing. I don't know if damper removal is even possible. The inner part IS the pinion yoke forging. One could cut off the outer ring and remove the rubber, I suppose, but to what end? Mine is over 20 years in service, and doesn't look the worse for wear. It's intact, presumably still functional, and isn't showing any breakdown or separation of the rubber. 6.5L crank dampers should do so well (although I know their service environments are entirely different).

I suspect the dampening effect is intended to prevent harmonics created by the axle from damaging the much more delicate components of the tranny and/or transfer case, rather than the other way round.

[More Power]

Lil Red has a 9-1/2" 14-bolt corporate semi-floating rear axle.

A CA truck doesn't suffer from the effects of road de-icer quite like the northern trucks do. I've seen rear diff yoke dampers online that look like an outer ring failure was imminent, due to rust... Personally, if the outer ring on the diff yoke damper in my 2001 GMC ever deteriorates to a point of coming loose, I'll just remove it with a cut-off wheel. In the meantime, I'll treat the rust to help slow down the decay.