Service Bulletin 2500/3500 Front Diffs

[DA BIG ONE]

MP, I see sometime ago you mention in another post on differentials that GM sent out a bulletin to dealers up north to use only synthetic lube in 2500/3500 series front differentials because dyno lube causes seals to leak in cold weather.

Question 1:
Does synthetic expand more when hot, or?

Question 2:
I see owners manual states that the fill level for the front diff is 1/2" below filler port cold, and right at the bottom of filler port hot, does this apply to synthetic too, or?

[More Power]

Originally posted by DA BIG ONE:
MP, I see sometime ago you mention in another post on differentials that GM sent out a bulletin to dealers up north to use only synthetic lube in 2500/3500 series front differentials because dyno lube causes seals to leak in cold weather.

Question 1:
Does synthetic expand more when hot, or?

Question 2:
I see owners manual states that the fill level for the front diff is 1/2" below filler port cold, and right at the bottom of filler port hot, does this apply to synthetic too, or? That TSB refers to the 2001+ 2500HD/3500. The front diffs used on these 4WD trucks were originally filled with dyno lube. Seems a few individual trucks that ran for long periods of time, some at highway speeds in 4WD, and in really cold weather would result in damage to the diff carrier and pinion bearings. The dyno lube became more viscous in cold temperatures, and would "plate-out" on the inside of the housing, causing the bearings to run without adequate lubrication. Synthetic solves that problem.

The TSB went on to say that the original vent tube (plastic) wasn't compatible with synthetic, and would need to be changed when switching to synthetic.

As far as I know a "leak" wasn't a problem. Always follow your owner's manual for fill levels and such. regardless of whether you use dyno or synthetic.

Jim

[DA BIG ONE]

Originally posted by More Power:
</font><blockquote>quote:</font><hr />Originally posted by DA BIG ONE:
MP, I see sometime ago you mention in another post on differentials that GM sent out a bulletin to dealers up north to use only synthetic lube in 2500/3500 series front differentials because dyno lube causes seals to leak in cold weather.

Question 1:
Does synthetic expand more when hot, or?

Question 2:
I see owners manual states that the fill level for the front diff is 1/2" below filler port cold, and right at the bottom of filler port hot, does this apply to synthetic too, or? That TSB refers to the 2001+ 2500HD/3500. The front diffs used on these 4WD trucks were originally filled with dyno lube. Seems a few individual trucks that ran for long periods of time, some at highway speeds in 4WD, and in really cold weather would result in damage to the diff carrier and pinion bearings. The dyno lube became more viscous in cold temperatures, and would "plate-out" on the inside of the housing, causing the bearings to run without adequate lubrication. Synthetic solves that problem.

The TSB went on to say that the original vent tube (plastic) wasn't compatible with synthetic, and would need to be changed when switching to synthetic.

As far as I know a "leak" wasn't a problem. Always follow your owner's manual for fill levels and such. regardless of whether you use dyno or synthetic.

Jim </font>[/QUOTE]Jim, As always thank you for your response.
DBO