2005 Tahoe Rear Diff Fluid Change Help

[jfab1165]

I changed the gasket and refilled with Amsoil 75/90 syn gear oil. I put about 3 and 1/4 quarts and it did not leak out and I can not feel the fluid when I test for the level. It still may be 1 inch or so below the fill hole. Should I keep adding fliud. I only test drove it and it seemed OK.

[tnord]

it will work, but i'd keep putting it in until it spills out.

 

less fluid capacity ---> less heat sink ----> higher temps ----> accelerated wear ----> increased risk of failure.

[C & A s Dad]

I changed the gasket and refilled with Amsoil 75/90 syn gear oil. I put about 3 and 1/4 quarts and it did not leak out and I can not feel the fluid when I test for the level. It still may be 1 inch or so below the fill hole. Should I keep adding fliud. I only test drove it and it seemed OK.

 

 

You can fill it until it comes out of the hole but you run the risk of causing seal leaks at the wheels. GM recommends the gear oil be apprx 5/8" below the fill hole. This would mean you could possibly touch it with your finger but I use a cable tie bent on the end to make it into a "dip stick".

 

As Travis said, you want all that is supposed to be in there as it helps control heat but you do not want it overfilled.

[tnord]

wait a second....how does oil in a diff cause seal leaks at the wheels?

 

these things have big hollow axles that carry oil out to the wheel bearings or something?

[C & A s Dad]

Yes,

 

The oil in the diff flows in the axle tubes right out to the wheels. If it is overfilled, there is more oil present in the axle tubes creating a higher risk of leaks at the wheel seals.

 

I am not sure all vehicles specify 5/8" below the fill hole but I know GM does on our trucks.

[tnord]

why would that cause a seal failure though? i can see how more fluid creates slightly increased pressure in the system, but i have a hard time accepting that the marginal difference in pressure resulting from an extra half a quart of oil directly causes the seal failure. if there is an oil leak (and this is a very strange system to me) the seal has either already failed, or it was horribly engineered to begin with.

[C & A s Dad]

I am certainly no engineer and not sure the following answer will explain this correctly.

 

If the proper amt of gear oil would be 1/4"(just using this as an example) deep in the axle tubes and the bottom lip of the seal where it rides on the axle, rests 1/2" from the bottom of the tube this would mean gear oil would only be getting to the seal from splash. If the gear oil was 1" deep in the axle tubes, the gear oil would be above the seal line at all times. Now with heat, splash, horizontal axle movement, etc, there is a greater chance of the gear oil getting between the seal and the axle causing a leak.

 

Again, I did not engineer the system and am sure my explanation could be flawed. However, I researched this before I changed my gear oil and differential cover and discovered that the recommended fluid fill is approx 5/8" below the fill hole.

 

I also noticed the fill hole in my PMC alum cover is apprx 5/8" below the OE fill hole in the diff housing. For this reason, I can fill mine to the gear oil runs out of the hole in the cover and it leaves the level about 5/8" below the OE hole in the diff housing itself.