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Discussion Starter · #1 ·
I recently bought a used 94 2500 Suburban 4x4 with a 6.5 (236k). After getting it home I took it by my mechanic for a once over. He said that the rear end was low in gear oil and he added some. After getting it back I took it to have some new tires put on (previous owner had put 4-ply’s on it). We found that the axel seal on the right rear was leaking some (not too bad) but I also noticed that there was gear oil all over the left shock and corner of the fuel tank. We figured that this was from the differential vent. Now my mechanic says that it could have been over filled some or that I could have a bearing going out or some other cause of overheating in the rear end causing the oil to expand and come out of the vent. He says that next time I drive it hard I should feel and see if one particular area of the rear end is hotter than the rest that it might tell which bearing is going out.
Questions:

1.)Any one else have a different idea – or does this sound accurate?
2.)What about replacing the bearings? I’m going to have to pull the right axle anyway, should I just go ahead and replace all the bearings while I have it torn down? Or is there a good way to figure out just what needs replacing.
3.)Related but not exactly – according to the previous owner this truck has a 4.10 rear end. Is there anyway to verify this (the info sticker on the door jam is non-legible)? Maybe a VIN look-up?
3b.) I’ve read that the 2500’s came with two choices in the rear end: 3.73 or 4.10. If this is true, does anyone have any idea how much increased MPG one might get by going up from the 4.10 to the 3.73? Also, I guess if you change the rear diff. you also have to change the front diff as well – right?

Thanks!
 

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Since you don't list the mileage we can only assume being a 94 its most likely has some miles on it. Since you already have one side apart I would change both axle bearing and put in new seals just for a peace of mind. Clean up the entire rear and watch for any new leaks. I don't know about the MPG difference but you need the ratios to be the same.
 

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1) Vent is probably plugged and blew the seals out.
2) You have to tear it down for the seals, might as well replace bearin's while your in there.
3) Look in the glove box for RPO codes. If you can read them look up the codes in the 6.5 reference section to see what axle you have.
3b) Not sure
 

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Discussion Starter · #4 ·
I understand how a plugged vent would blow seals (in this case only the left one is leaking - and not really that bad - although I will still replace it), but not how (if it's plugged) I would have oil all over the shock and fuel tank on the side of the truck right next to the vent outlet??

Yes the truck has a few miles on it (236k).

Sounds like I should just tear the rear end apart, replace both seals and bearings all around. Isn't there a bearing toward the front of the diff where the drive-shaft attaches?

Also, appears that the consensus is that a gear swap would probably not amount to much fuel savings. I just wanted to decide that before I tore the rear end apart - seemed like it might be a good time to do it.
 
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