Leaking rear axle seal


I have a 2000 3500 gmc van. I have replaced the rear axle seal too many times to count and it always fails. I have replaced bearings and seals and verified the rear vent tube is working. The axle does not appear to be damaged in any way. It should be noted that I do carry lots of weight all the time… Any ideas on what is causing the leak???

Which axle seal, driver’s side, passenger side, rear? Is this a live axle or floating axle? A live axle includes the mounting flange for the tire and supports the load. A floating axle bolts to the hub assembly, and does not support the load. A floating axle has the load supported by the hub assembly.

If it is a live axle, you may have a bent axle. If the van was overloaded at any point, the axle may have bent, and this is why the seal is failing. You’ll probably need a replacement axle to fix this.

If a floating axle, then the housing may be bent. You may need to replace the whole axle. Just swapping the guts to a new housing will cost more to properly shim the gears to be worth that.

I would not hesitate to use a salvaged part to fix this.

Thanks for your help. The seal which is leaking is the passenger side rear. There is a 100 gallon h20 tank located on that side of the van which is filled 99% of the time. The van has a full floating axleshaft ( the type which does not require the differential cover and c-locks to be removed to remove axles.) Are you suggesting that the entire differential axle/housing be replaced??? or just the axle on that side?? The passenger side is the only seal which leaks…

It may be the water tank has caused the outer axle shaft housing to bent under that kind of strain. I don’t know if just the housing can be replaced. The housing holds the load, and something on that side is bent, causing the seal to abnormally wear. You may have to have someone with tools and experience check the axle and housing for proper alignment. A driveshaft specialty shop normally can tell you.

Approximately 830 lbs of water is putting a strain on that axle.

Do you think it makes sense to try and replace the axle shaft and the outer housing with a junkyard part? or buy original GM?

yes it is lots of weight all the time!! This is a carpet cleaning truck. These trucks are manufactured to work within the gvw and capacities of a 3500 series gmc and they have been apparently made this way for many many years. It seems I just got unlucky…

i would suggest that although the truck innards, vaccuum, pumps, hoses reels, tools etc etc etc. are made to weigh in UNDER the 3500 lb capacity, having over 800 lbs in ONE area is too concentrated a weight in one area.

the 4119lbs (as rated by the specs for the truck) is (i think) supposed to be evenly distributed. not necessarily all over, but not just on one side. but then thinking about it, almost 25% of the carrying capacity is in that water tank. how much does everything weigh?

it sounds like you do have a bent axle. most likiely aggravated by the heft over the right side.

by any chance do you sort of pile the equipment in the back, in the right corner too?

certainly the majority of the weight I carry is the fresh water tank which is directly over that axle. That is 100 gallons of clean water all the time! The balance of the weight is under 500 lbs. There is also a dirty water tank on the other side (100 gallons also). When 1 tank empties 90% of that is captured and pushed to the other side …

Would u suggest replacing both the axle and the housing which the axle bolts to? The housing is where all the bearings are and the seal is pressed into the back.

are you trying to do this yourself?

as bustedknuckles says: a dirvetrain rebuilding shop would remove the guess work out of this, and they coudl trouble shoot it, and repair it quick. i realize you want to save $$, but like you said, you’ve replaced this how many times? how much is YOUR time worth?

you seem to be asking for definitive advice, but that is hard to do, without seeing it. and a trip to a shop could give you the professional advice you need.

I hate to tell you guys this but on a full floating axle setup the axle doesn’t support any weight. Why do you think you can pull the axle with out having to pull the wheel.

I will agree that there could be a problem with the axle but it doesn’t support weight.


Am I missing something here? Then what path does the truck weight take from the chassis to the road if not through the bearing and ultimately through the axle to the wheel?

One afterthought. Are you sure that a burr on the axle shaft didn’t make a small tear in the axle seal surface when sliding in the axle?

No. The axle shaft does not carry any weigt, the axle does, as that is the whole point of it.

On a full floating axle system the axle SHAFT does not support the weight of the vehicle. The weight of the vehicle is carried by the tires, hub, hub bearings, axle housing.

There are 3 types of rear axles, semi-floating-ball bearing, semi-floating-roller bearing, full floating. The full floating axle is the only one that doesn’t support vehicle weight. It is used in heavy duty applications because it takes the vehicle weight off the axles and reduces the chance of a bearing and seal failure.

There are 2 seals in this system. One on the back side of the drum and one under the axle flange. If the fluid is leaking on the back side of the drum then either the axle hub sealing surface is damaged or the seal is damaged. The axle shaft itself has no sealing surface on it.

Now maybe this van doesn’t have a full floating axle system.

ANDY… does the rear wheel have a hub sticking thru it with about 6 bolts on the end of it? If it does then it is a full floater. The axle can be removed by taking out the 6 bolts without having to take the wheel and drum off.

o.k. let me hopefully clear some things up. I am looking at a Haynes repair manual which describes the system my van has as a “full floating system”. This is a system which allows you to remove the axle shaft without removing the differential cover to remove c-clips … You can pull the axle shaft by removing the bolts on the hub. I think there are 6 or 7 of them. Yes you could actually remove the axle without removing the tire. The axle shaft does not appear to have any burrs or any damage to it. I am wondering if it is bent which is making the seal fail prematurely.

So where does the leak occur. Is it on the outside of the wheel where the axle shaft bolts up to the hum with the 6 or 7 bolts? Is it on the inside of the hub where the hub rides on the axle housing? Is the oil leaking onto the brake linings, onto the brake backing plate, onto the inside wheel and tire, or onto the outside wheel and tire? I am assuming that this is a dualie setup.

I also would like to know where is the fluid is leaking from? If it is leaking on the backing plate then the problem is the rear seal and sealing surface on the axle hub.

It is not a dualie. Single rear wheel. The gear oil leaks on the inside of the hub onto the brake linings and eventually will soak the backing plate and eventually will end up on the garage floor if you let it.

A close inspection of the axle housing hub is needed, that is where the seal rides. Look to see if there is a groove in it or any burrs.