Pinion seal leak

[ScottD]

I have a pretty stock 85 C10 short box and I noticed my differential pinion seal is leaking.  I'm getting a small puddle on the floor, so it appears to be more then a little seeping. I replaced the lube 3 years ago shortly after buying the truck, so this is the first sign of any leaking. I've never done any serious differential work, so I'm a bit leery of taking this on myself.  How big of a job is this? Is it better suited for an expert?  What other work would you recommend that I consider doing at the same time?  Lastly, the truck has a 2.73 ratio and I've debated changing that to something a bit shorter.  And, if its already apart is this the time to do it.  Its a fairly stock (rebuilt) 350 and drives great on the highway, so how much performance difference would I notice if I changed to a 3.42.  What RPM impact does that have at highway speeds? If I'm not out racing or doing burn outs, should I leave it.  I'm open to opinions, as I know most die hard performance guys would never recommend a 2.73.  And advice or opinions are always welcome.  thanks in advance

[VileZambonie]

Changing the pinion seal is relatively easy and doesn't offer up one of those, while you're in there you might as well opportunities when it comes to changing the final drive ratio. Unfortunately that is a bit more involved and better suited for the experts if you do not have the tools and knowledge.

If you are considering changing ratio's and want opinions you should list more details about your truck, what engine, trans, tire size etc.

Changing the pinion seal basically chock the wheels, witness mark and remove the driveshaft from the companion flange, witness mark and index the nut, shaft and flange, remove the nut, remove the yoke (companion flange) and remove the seal. Make sure it is clean and apply a small amount of liquid Teflon to the splines. Reinstall in reverse of removal and top off the fluid.

[ScottD]

Thanks for taking the time to respond.  It sounds like the pinion seal can be replaced without disassembling the differential, which I'm glad to hear that. Motor is a rebuilt 350 that was put in prior to me buying the truck.  I'm told its rated at 200 hp and 300 ft-lb torque.  Tires are P275 60R 15 and the transmission appears to be a stock T350.  On a side note, if you accelerate at modest to medium level the truck performs great.  Has a great deal of passing power.  However, if you stump on it, the tranny doesn't want to shift out of first unless you let off the gas a bit.  Its been 25 years since I drove my last 350\T350 so I don't recall that nuance.  I digress from the axle ratio question. Seems like 2.73 was an 80's thing for gas mileage over power, so I'm just trying to decide if changing to a 3.08, 3.42, 3.73 would be beneficial or ruin a good cruiser.  I would assume that a 3.73 with a 3 speed tranny would not be that enjoyable to drive at 70 mph.

[roundhouse]

If you're happy with the performance I wouldn't change the axle ratio


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