2006 Silverado Rear Differential Cover Leak

[mikear]

Hey guys, new here so please bear with me. I have a 2006 Silverado Z71 with a G80 rear differential. I bought the truck new and she just rolled over to 239k.

 

Anyhow, I was changing front and rear differential fluids two weekends ago because it was time. Now I have an issue.

 

Try #1 - I drained the rear diff and replaced the gasket. I torqued the cover down to 30 ft/lbs using a star pattern and filled it to 5/8” below the fill hole. I messed it up this time because I had rolled the top of the gasket over and didn’t realize it until later that day.

 

Try #2 - After I noticed it was leaking I picked up a new gasket and drained it again. I used a small amount of Permatex aviation gasket maker to hold the gasket in place, being very careful to line everything up. Reassembled everything, went for a short drive, and re-torqued. All looked ok so I took about a 150 mile round trip. I noticed a small drip forming at the bottom of the cover when I had parked in the driveway. Cleaned it up real well with B12, rechecked torque, and drove it a little more. Same thing. At this point I questioned my use of the gasket maker in tandem with a gasket.

 

Try #3 - So yesterday I changed the oil and gasket again, this time without gasket maker. Torqued it back down, took it for a spin to warm it up, then re-torqued. Everything seemed good so I went fishing, pulling the boat around 30 miles round trip. Last night when I got home I noticed there was once again a droplet forming at the bottom of the cover at the gasket. Checked torque, all was good. Cleaned it up again with B12 and today, same thing.

 

What gives? Could my factory differential cover be slightly warped causing a poor seal? Could rolling the gasket the first time and torquing it down have caused this warp since it would have been an uneven sealing surface? I never had a leak prior to changing the fluid.

 

This is getting expensive at $13/qt of Mobil 1 75W90.

 

Thanks in advance,

Mike

[txab]

Always check the over flange for flatness while off. you may need to flatten distorted areas. Pay attention around bolt holes. Are you using a good quality gasket?

 

Or just go straight gasket maker goo

[steve76t]

cleaning is the #1 issue with sealing up differentials.  Make sure your mounting surfaces are 100% clear of old gasket material & sealers.  #2, lightly sand the surfaces of both the housing and the cover to make sure they are smooth and clean.  Also try to remove as much gasket material from the holes.  #3 use a high quality gasket or gasket maker RTV.  RTV can be tricky as you really need to have a even bead all the way around.  Any differences in thickness in one area will likely allow it to leak eventually.  That's why I don't use RTV anymore.  Instead I use LubeLocker gaskets on my Jeep's axles.  They're a little more expensive, about $20 each, but they super easy, provide a leak free seal AND they're reusable.  I've had them on my Jeep for a couple years now, had to remove & reinstall a couple times, beat on the axles lots of times while out rock crawlin' and they're still completely leak free. 

[mikear]

I used Fel-Pro gaskets. Not real sure how to accurately check flatness in my garage though. And if it was not flat, then get out the hammer?

I did clean the surfaces of gasket very well, including hitting them with steel wool. I don’t mind paying for a better gasket. Honestly, I’ve never heard of lube locker before. Are these gaskets thicker to fill a void that my cover apparently has?

Thanks guys

[muddkatt]

To check for a distortion in the cover you can lay it on something that is truly flat such as a piece of glass, counter top, etc and while holding light pressure on it, try to slide a .010 feeler gauge between the cover and the surface it is laying on. Another way would be to hold it against the differential without a gasket and use the feeler gauge.

 

If it has a high/low spot, get out the hammer and adjust it to true flat.

[PTXer]

     Could "torquing" the rear end cause the pan to leak?  Last week, my rear end wheel hopped pulling away from an intersection and that night the pan started leaking.  Up to that point had been a perfect leak free truck since I bought it in September.

[muddkatt]

6 minutes ago, PTXer said:

     Could "torquing" the rear end cause the pan to leak?  Last week, my rear end wheel hopped pulling away from an intersection and that night the pan started leaking. 

No, unless the housing is cracked or something internal lets go and pushes on the cover. Either way, the leak would be the least of the problems.

[txab]

On 3/13/2018 at 7:51 AM, muddkatt said:

To check for a distortion in the cover you can lay it on something that is truly flat such as a piece of glass, counter top, etc and while holding light pressure on it, try to slide a .010 feeler gauge between the cover and the surface it is laying on. Another way would be to hold it against the differential without a gasket and use the feeler gauge.

 

If it has a high/low spot, get out the hammer and adjust it to true flat.

Where you want pay attention to primarily is around the bolt holes. If someone overtorqued them then they could be mushroomed somewhat and need to be flattened out. See the attached picture. Note my crude drawing in the pan.

Just use a good straight edge like a framing square or steel ruler

 

 

[mikear]

Where you want pay attention to primarily is around the bolt holes. If someone overtorqued them then they could be mushroomed somewhat and need to be flattened out. See the attached picture. Note my crude drawing in the pan. [emoji4]
Just use a good straight edge like a framing square or steel ruler
 
 

Thank you for the information. It makes perfect sense. However, the factory differential cover isn’t flat on the gasket sealing surface due to some indentations between the bolt holes. It may not be easy to straighten out. Would it just be easier to replace the cover? My fear is that if I mess with it and it leaks, I’ll be changing the oil for a 5th time instead of 4th.

[diyer2]

Buy a new cover then.

 

[txab]

Yep would be easy to replace the cover, if you on't feel comfortable straightening cover. Cost is $20 - $30

[AlljackedupZ71]

Lube locker gasket.... these things are bad to the bone. Ive used them with damaged covers ect... no leaks.

 

https://www.lubelocker.com/product/llr-g850/

 

 

[mikear]

Any recommendation on differential covers? I hear a lot of guys talking about mag hytec, but I’m not looking to spend that kind of money. Just seems like a machined gasket surface would seal better than these factory covers. I will definitely be grabbing a lube locker gasket.

[sdeeter19555]

PML can be had in a raw finish that is usually a little more reasonable.

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