Diff Fluid Change.

[WilliamBos]

Hi All,

 

My Apologies if this is in the wrong forum. Pleas feel free to relocate it if it is.

 

Looking to change the rear diff fluid in an 04 GMC 1500 CC (G80) and was wondering what torque spec the diff cover bolts go on at?

 

Also, and special gasket and sealer that I should use? Gonna use Amsoil 75w90 synthetic.

 

Thank you.

 

Will

[alwcurlz]

Hi All,

 

My Apologies if this is in the wrong forum. Pleas feel free to relocate it if it is.

 

Looking to change the rear diff fluid in an 04 GMC 1500 CC (G80) and was wondering what torque spec the diff cover bolts go on at?

 

Also, and special gasket and sealer that I should use? Gonna use Amsoil 75w90 synthetic.

 

Thank you.

 

Will

 

You're in the right place.

 

It will be the same as mine. I just got a paper gasket from the auto parts store and used "form a gasket" non-hardening sealant. I put the sealant on the cover and on the differential and put the paper gasket back on. I've never had leaks doing it that way. I torqued the bolts down to 100in lbs. I put Mobil 1 gear oil in. Empty, you'll need to put in exactly 2 3/4 qts. It's supposed to be at a level of 10mm below the fill hole but, who can see that? Hope this helps!

[WilliamBos]

It sure does, Thank You!! Another question, when I do the front diff, there is a drain and fill plug, where do I find them?? I know I will need a pump to put it back in.

 

 

You're in the right place.

 

It will be the same as mine. I just got a paper gasket from the auto parts store and used "form a gasket" non-hardening sealant. I put the sealant on the cover and on the differential and put the paper gasket back on. I've never had leaks doing it that way. I torqued the bolts down to 100in lbs. I put Mobil 1 gear oil in. Empty, you'll need to put in exactly 2 3/4 qts. It's supposed to be at a level of 10mm below the fill hole but, who can see that? Hope this helps!

[alwcurlz]

It sure does, Thank You!! Another question, when I do the front diff, there is a drain and fill plug, where do I find them?? I know I will need a pump to put it back in.

 

There is a drain plug smaller black painted at the bottom of the unit and a larger un-painted fill plug in the same area a bit higher. You'll need to remove your skid/brush plate to access this area.

 

Here is a picture of what your front diff looks like. This one is upside down in the pic.

 

 

Good luck!

[Matt_]

Just a few more points:

 

1) I highly recommend the use of a gasket on the rear diff (combined with some gasket maker is fine). Depending on which synthetic fluid you're running and the type of gasket maker (RTV) you can have leaking issues, even with the "special" rtv. Gaskets are around $8 from the dealer and a worthwhile investment IMO.

 

2) Because of some of the points above, I do not recommend synthetic fluid in the front diff. Put some quality 80w-90 in the front and you'll be set. (GM issued a service bulletin a while back due to leaks resulting from RTV gasket maker and Synthetic fluid)

 

 

Edit:

Here's a great thread discussing the use of gaskets: http://www.gm-trucks.com/forums/index.php?...2589&hl=rtv

I say it's a great thread because, if i remember correctly, two of the people who said i was full of %&$* ended up either having their rear diff leak, or found that their RTV was in such bad shape they're surprised it wasn't leaking. Someone also found the TSB and posted it (i didnt even realize there was a TSB until someone found it, i just knew that RTV + Synthetic = Bad)

[alwcurlz]

Just a few more points:

 

1) I highly recommend the use of a gasket on the rear diff (combined with some gasket maker is fine). Depending on which synthetic fluid you're running and the type of gasket maker (RTV) you can have leaking issues, even with the "special" rtv. Gaskets are around $8 from the dealer and a worthwhile investment IMO.

 

2) Because of some of the points above, I do not recommend synthetic fluid in the front diff. Put some quality 80w-90 in the front and you'll be set. (GM issued a service bulletin a while back due to leaks resulting from RTV gasket maker and Synthetic fluid)

 

 

Edit:

Here's a great thread discussing the use of gaskets: http://www.gm-trucks.com/forums/index.php?...2589&hl=rtv

I say it's a great thread because, if i remember correctly, two of the people who said i was full of %&$* ended up either having their rear diff leak, or found that their RTV was in such bad shape they're surprised it wasn't leaking. Someone also found the TSB and posted it (i didnt even realize there was a TSB until someone found it, i just knew that RTV + Synthetic = Bad)

 

Yup, I've never been a fan of silicone for sealants and have always, always had to fix leaks. On the oils used, yes, the front diff does not need or benefit from a synthetic fluid. Although another point I forgot to mention is the rear end fluid should be synthetic because it is required for our limited slip posi traction rear ends.

[WilliamBos]

Thanks so much guys. I am going to run Amsoil 75w90 synthetic in the rear, and no gasket. Can I use hi-tack to hold it on the cover? 9the red spray from Permatex?)

 

And what do you guys recommend for fluid in the front??

[alwcurlz]

Thanks so much guys. I am going to run Amsoil 75w90 synthetic in the rear, and what do you guy recommend for the front??

 

Just a standard 80/90 gear oil will work. Also check the outside seals and input shaft seal. If it's making a mess on your skid plate it would be a good idea to either check the fluid levels frequently or get the seals replaced. I had to have the inside and outside bearings replaced on mine because the previous owner didn't check the leaky front diff fluid levels and it had been too low and the bearings were shot. My truck would make a growling noise up front all the time. Cost over $700 to fix. The seals aren't too difficult to replace or that expensive so it could be something to consider as preventative maintenance. The seal that most often leaks is the passenger side, the black extension tube. GM has a new designed seal for that issue if you do get new seals or put them in yourself. I couldn't find a number online or from a dealer for that particular seal but, I think whatever is available probably IS the new design.

[WilliamBos]

Thanks so much guys. I am going to run Amsoil 75w90 synthetic in the rear, and what do you guy recommend for the front??

 

Just a standard 80/90 gear oil will work. Also check the outside seals and input shaft seal. If it's making a mess on your skid plate it would be a good idea to either check the fluid levels frequently or get the seals replaced. I had to have the inside and outside bearings replaced on mine because the previous owner didn't check the leaky front diff fluid levels and it had been too low and the bearings were shot. My truck would make a growling noise up front all the time. Cost over $700 to fix. The seals aren't too difficult to replace or that expensive so it could be something to consider as preventative maintenance. The seal that most often leaks is the passenger side, the black extension tube. GM has a new designed seal for that issue if you do get new seals or put them in yourself. I couldn't find a number online or from a dealer for that particular seal but, I think whatever is available probably IS the new design.

 

 

 

Our right front seal is leaking, how hard is it to change? Does the diff need to come out of the truck?

 

How much does the front hold??

[alwcurlz]

Thanks so much guys. I am going to run Amsoil 75w90 synthetic in the rear, and what do you guy recommend for the front??

 

Just a standard 80/90 gear oil will work. Also check the outside seals and input shaft seal. If it's making a mess on your skid plate it would be a good idea to either check the fluid levels frequently or get the seals replaced. I had to have the inside and outside bearings replaced on mine because the previous owner didn't check the leaky front diff fluid levels and it had been too low and the bearings were shot. My truck would make a growling noise up front all the time. Cost over $700 to fix. The seals aren't too difficult to replace or that expensive so it could be something to consider as preventative maintenance. The seal that most often leaks is the passenger side, the black extension tube. GM has a new designed seal for that issue if you do get new seals or put them in yourself. I couldn't find a number online or from a dealer for that particular seal but, I think whatever is available probably IS the new design.

 

 

 

Our right front seal is leaking, how hard is it to change? Does the diff need to come out of the truck?

 

How much does the front hold??

 

 

The diff won't have to come out to replace the external tube seal. My repair book, a Chilton's manual explains how to remove only the output axle shaft tube. You should go get a repair manual, either the Chilton's or Haynes book. It's an extensive process that needs close attention so take care in your plans to remove and replace that seal!

[WilliamBos]

So have the Chilton manuals improved lately?? I will have to stop and get one then. I was going to get the Helms, but that will have to wait.

[alwcurlz]

So have the Chilton manuals improved lately?? I will have to stop and get one then. I was going to get the Helms, but that will have to wait.

 

Well, the Chilton's manual didn't go into enough detail for me to figure out how to repair the rest of the unit unfortunately so I had to get it taken care of because of circumstances of my own mistake.

[Mossyoakglock]

When you add the 80w-90 to the front, are there any additives that you need to put in the fluid?

[WilliamBos]

When you add the 80w-90 to the front, are there any additives that you need to put in the fluid?

 

From what I was told - No!! But I hope others chime in on this.

[alwcurlz]

When you add the 80w-90 to the front, are there any additives that you need to put in the fluid?

 

Front differentials won't need any additives, just regular 80/90W

 

For Rear Limited Slip Differentials, you need put either full synthetic which will cover what you need. If you use a non-synthetic oil, you'll need to add an additive. This is for the G80 differentials.