Rear End

[mobilevet]

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!

[Robyn]

Hello.
Does this truck have the semi floating axles or the true full floating setup.
The full floating axle will have a ring of bolts holding the axle shaft in the hub (Right behind the hub cap)

The oil could have gotten onto the brake shoes and been thrown out the drum and on the shock and fuel tank.
That would take a lot of leaking.

The shocks can leak and puke oil too.

If your in the thing drop the cover and clean out the old oil and generally look things over good. Replace the seals on both sides while its apart and look the bearings over well. Be sure to squirt enough oil in the bearings to lube it well until fresh oil screws out from the axle center section to fill the bearing cavity up (Full floater)
If yours has the semi float setup it will have C lock axles like the 1/2 ton rigs do.

I have seen these either way.
The gear ratio must be swapped on both ends and the cost is prohibitive to do this unless the gears are shot.
The gain in mileage is so minimal that you would be hard pressed to pay for the gears and such. The difference between 3.73 and 4.10 is very little.
The gear sets are spendy enough and the work to swap is however not hard but can be costly unless you can do it yourself.

The front ones are a real PITA to do, been there done that :(

Hope this helps

Robyn

[xtrempickup]

the coding for which rear ratio is on the sheet in the glove box. if its a 6 lug, most likely a semi floating, if its an 8 lug then might have a gov loc full floating rear. the gears are fine for stock size tires, but if you want to run large tires, a better ratio is needed to compensate if you want to save fuel. i'm running the stock gear with 35s and i bet i could save a little going back to the stock tires and rims

[mobilevet]

This truck is the 8 lug. They pulled both brake drums when replacing the tires to check the brakes. That's how we noticed the leaky seal on the left rear. The right rear was dry. The vent from the rear end comes out the left side of the diff, but then runs back over the diff and is attached just in front of the RIGHT shock. All the oil was on the right shock and right front corner of the fuel tank and smelled like rear end oil (also didn't feel hot - don't know if that matters). Because of this I don't think it is a seal leaking (the right seal was dry). Unless shock oil smells like gear oil then I doubt it's the shocks - and I doubt a shock would hold as much oil as was coming out - and the shocks are relatively new.

I'm running 265's.

Sounds like the consensus is that swapping gears would be to little or no advantage - good to know.

Someone mentioned a pugged vent - but unless it got UNPLUGGED I don't see how it would have resulted in oil everywhere?????

[xtrempickup]

sounds like you need the rear axle and related seals replaced. I have a 95 6.5L with a the 6 lug semi floating which sucks. I can say that the 35s have no real problems beng turned on the stock 3.73s i would guess on the highway the idle would be down in OD considering if the gearing was 4.10s or better

[6.5 Detroit Diesel]

Still don't know if this is a Full Floater or a Semi-Floater
Like Robyn said, the way to tell is to look at the hub. If there is a smaller circle of bolts on the end of the axle then you have the Full Floater which is by far one of the strongest ever put out. If there is just the 8 studs and no inner bolts then you have the Semi-Floater rearend, which is not as strong or easy to change out.
The full floater is really strong and will handle almost any tire size.

[mobilevet]

I'm pretty sure there are bolts on the end of the hub, so my guess is it's a full-floater (I'll look to be sure tomorrow).

xtrem: can you explain why I need to replace the axles themselves - along with the seals?? Why not just replace the bearings?? Or are you talking about the "rear axle seals"??

We can forget the gear ratio question - that's solved, there will be no gear swap.

Now I just want to figure out why the gear oil came out the vent. If it's bearings I want to replace them at the same time I replace the seal(s).

I'm going to drive it some tomorrow so I'll check to see if there is any more leakage.

Thanks

[DmaxMaverick]

If you have a semi floater, the bearings and seals are in direct contact with the axle shaft. A full floater has the bearings and seals between the hub and spindle, and the axles "float" through the axle tube to the side gears, only secured at the outer end by the 8 flange bolts, which are sealed with a flat flange gasket. The FF axle will have a large cylindrical part sticking out through the wheel (like the front end of a 4x4 with solid front axle, only with 8 bolt heads visible), while a SF is nearly flush with the wheel. You can remove the axle from the rear end of a FF and the wheel and hub will still be attached to the axle tube (but the lube will run out). A SF axle has the studs/wheels attached directly to the axle flange, and the axle is held in place by retainers inside the diff.

When your vent gets lube vapor built up in it (and it will), it needs a continuous downhill path back to the diff. If you have a loop or dip (or trap, like your kitchen sink), it will collect the lube and block the venting. Eventually, the heat buildup will overpressure the seals with no effective vent, and it can also blow the lube out the vent tube. This can also happen if it's been overfilled. If you have a lot of lube blown out of the end of the vent tube, you very likely have an overfill situation. The axle seals are not designed for any significant pressure above what it sees from gravity. Even if you don't blow a seal when it gets hot, driving through deep water after it's hot will cause them to suck in water. That causes a different failure all it's own. The vent needs to work both ways, all the time.

[mobilevet]

Dmax - thanks for your comments. Based on what you said, I am sure that the rear in is a full-floater. And, based on your description, it sounds like I can do all the work (replace bearings and seals) without cracking open the diff. - that sound right? As you can probably tell this is my first 3/4 ton. I've had several smaller 4x4 (Toyota, Jeep). The toyotas had manual locking hubs, which I packed periodically as routine maintenance. It sounds like working on these back hubs will be similar (i.e. bearings located out at the hubs, etc).

Also your explanation of the vent situation seems to correlate better with an over-fill +/- vent clogged - maybe the vent was clogged (leading to the left oil seal failure) and then the overfill just made it apparent, because there was no vent leak prior to the service job.

That makes me wonder if I even need to bother replacing the bearings, but with the high miles, I guess I might as well do them and the seals all at once.

Is the vent tube just a straight run, or does it have any check valves or such that should be taken into consideration when cleaning/un-clogging? Best way to remove the vent, flush with solvent, and blow out with an air compressor?

Thanks

[mr. monte]

the vent tube should have a check valve on the end of the tube

with the miles you say it has, I would at least pull apart the hub/wheel bearings for inspection

[DmaxMaverick]

No check valves. The cap at the end is a filter, of sorts, to minimize water and contaminant entry. A check valve would be as bad as a plugged vent.

You can change the bearings and seals on a FF without even removing a lug nut, if you had a mind to. I don't suggest it, but you could.

Once the axle is removed (those 8 outside bolts), the inside of the hub is very much like your previous Toyota front hub. Lock nut, hub nut (or a nut with locker), then the hub and bearings will slide off the spindle.

Even with a lot of miles, your bearings may not need replacement. As long as they are good and haven't been abused, they will be work hardened and seated, which is better than a replacement. They are worth looking at before tossing. Usually, by the time the bearings are shot, the spindle and races need a real close look, too. The bearings are not "sacrificial". Unless something has happened to indicate a bearing failure, they should be good for the life of the spindle. Never install a new bearing on an old race (I've done it, but out of necessity).

Here's some off the cuff advice......
Check the hub for play of any kind, before you loosen anything. If it's snug and turns quiet and smooth (be sure to back off the brakes if needed), read on.....
If you do in fact have a blocked vent, with lube blown out the end and a seal, don't replace the seal just yet. Clear the vent and do a thorough service on the diff (careful attention to the fluid level and vent routing). Many times, the seals are replaced unnecessarily, just because a leak is found. If the leak is due to the blocked vent, odds are the seal is fine, and was just sounding off to the diff. pressure. Give it a try if you can spare the trial time. If you watch it closely for a period, there's no safety or equipment risk. It may be worth it. Parts are expensive, and your time is valuable.

[Robyn]

Replace the little vent unit that should be in the end of the little hose and has been mentioned make sure the hose does not have a loop or other low spots that cant drain back.
The little vent is cheap.

Drain the entire differential by removing the cover and dropping all the oil in a sutable drain pan (Clean) and this way you can also scrape out the old oil and completely clean the gearbox. This will allow you to see what the gears look like and to check for any excess wear and or other issues.
Look at the color of the oil, it should be a dark green to light brown color.
If it is black to dark gray then look for metal in it.

If the color is good go ahead and replace the seals in the hubs and check the bearings too.
Look at the rollers as well as the races for brinelling, pitting or shellout.

Wash the parts is a suitable solvent and blow dry. you can then look the bearings over. A good bearing will show only a slight color change where it rides in the race.
Drop the bearings in the clean/dry races and turn by hand with a little pressure, they should turn smooooooooooooooooth.

Reinstall the bearings with some 9ow (85w-140) gear lube and then install the seals and replace the assembly.

Now you will need a special socket to get these little creatures apart and back together.
The torque on these bearings is important and be sure to reinstall the locking setup as it came off as this keeps the bearings from coming loose and the wheel coming off.

Run the retaining nut down to good and snug, spin the assembly to seat the parts then back the nut off slightly until its just loose. Now snug it back up until its just snug (NOT TIGHT BUT SNUG) These bearings run under a light preload.
Once you are there you can install the locking mechanism. If your locking device will not line up you can go slightly tighter on the inner nut.
Alway go tighter and never looser on a drive axle bearing.

Once the setup is all locked the assembly should turn with relative ease.

Its important to keep the torque correct on this type of bearing.
The is an actual inch pound spec to turn these but I have done so many over the years that my finger do the calibrating.

Zero slack and just light preload will do fine.

***** very Important*****

Look over the bearing locking device carefully when you take it apart and be sure toy get the setup back exactly as it should be.

There are several different setups used such as. dual nuts with a locking washer with a tab and sometimes there are little clips and other goodies to keep the nuts locked.
Varies with year.model and who made the axle.
The little nuts will require a special socket that you can get at almost any parts house (Napa is usually a good one)

I think I have about 2 drawers in my rollaway full of this sort of stuff for all the different axles I have done over the years.

Good luck and keep us posted.

Robyn

[DA BIG ONE]

Sounds like overfilled differential, pressure buildup an slinging of lube will drench areas you mentioned.

Another thought;
If diff is getting real hot consider pinion mount might be installed improperly w/oil way being blocked which will +heat+pressure+blowout of lube wherever it can find a way out. Looking at pinion mount (when out of differential) you will see an opening (oil path) at top of mount that matches to the top of differential (oil way) as it is installed. Diff lube is slung up by ring gear and into that oil way to lube the pinion bearings then drains back into diff to start trip again.

[mobilevet]

Thanks for all the good information. I did take it for a spin yesterday and before going took some degreaser to the area to clean it so I'd know if it was still slinging - it was. Upon returning I also go down and gave it a good "palpation". The diff was warm but not overly hot. The axle channels were cool to the touch and the hubs were not hot either (feeling from the back side since they have plastic covers over the wheel side). I hope to get to work on the vent here pretty soon.

thanks again

[MTTwister]

Which I think Mine is, based on the descriptions herein. Does the brake Drum come off the axle, so I don't have to pull the axle shaft? the right side drum is "moist" looking, so I believe I need to check and replace brake shoes, and up grade to the larger NAPA rear brake 'servo' unit. Would really like this to be an easier drum removal job.

BTW - has anyone ever been able to get one of those brake spring pliers to work? If so, link to instructions would be really appreciated :) ... Thanks.

[DmaxMaverick]

You don not have to remove the axle to get the drum off. The drum may be seized onto the axle flange (time, corrosion, etc), but it is not integrated. You will have to remove the axle if a seal (or bearing) needs replacement. The procedure is very different from the full floater.

Don't know about the brake spring tool. Never use one. I've always made due w/out (wear eye protection). A brake adjustment tool is worth its weight in gold, although you can make the adjustments w/out it (PITA).