Using Synthetic Fluid in Rearend

[97whitez71]

I had new pinion bearings and seals, and all other bearings replaced on my '97 K1500 about a month ago. Basically, had the rear end rebuilt. It's a 14 bolt with the G80. The mechanic said instead of putting regular gear oil and the additive in, they filled it up with synthetic fluid. Every since then the diff. cover, pinion seal and filler plug leaks. The only thing I can think of that would cause this is the synthetic fluid. I know you are not supposed to put synthetic in an older engine, but what about an older rear end? Also, now at about 55- 60 mph, I can feel a vibration that wasn't there before. Any thoughts? Thanks.

[95Sierra2500]

If they rebuilt the entire rearend and used all new seals, then it shouldn't be leaking. Sounds to me like they did a s**tty job sealing it back up. As for the filler plug, try tightening it down just a little bit.

[Mr. Smith]

I had new pinion bearings and seals, and all other bearings replaced on my '97 K1500 about a month ago.  Basically, had the rear end rebuilt.  It's a 14 bolt with the G80.  The mechanic said instead of putting regular gear oil and the additive in, they filled it up with synthetic fluid.  Every since then the diff. cover, pinion seal and filler plug leaks.  The only thing I can think of that would cause this is the synthetic fluid.  I know you are not supposed to put synthetic in an older engine, but what about an older rear end?  Also, now at about 55- 60 mph, I can feel a vibration that wasn't there before.  Any thoughts?  Thanks.

 

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It isn't the synthetic. I bet the pinion yoke has a grove wore in it by the seal.

[z85violator]

check and tighten all bolts, they tend tp loosen after a couple days.