Question Regarding Diff Fluid Change..

I was planning on changing my rear diff oil to RP. However is there some sort of additive I have to use? or can I use the RP 75/90 fluid on its own? Did a search and wasn't quite clear on that, Thanks.


FYI: this is for a 05 4x4 Tahoe.

i am curious about this as well... i want to swap to RP all the way around

RP = Royal Purple?

BOSS

yeah, I ended up just doing the rear diff for now with Royal Purple; dam thing took 3.5 qts! Didn't expect it to be that much. Truck seems to be a bit smoother, but it could all just be in my head; I also did an oil change at the same time; so maybe a combo of the two. Planning on doing the Transmission soon too, switching it to RP probably. Just need to work out the issue with the 4 wheel drive not working.

I'm going to be doing this within the next couple of weeks?

Side question: Did the differential fluid stink? I changed it in my old mustang and got it all over my clothes. I ended up having to throw the clothes away because the smell was all over me.

yeah the old stuff smelled bad. Not sure if the previous owner even bothered to change the fluid.

Gear fluid in general smells like crap. However comparing it to supercharger oil it smells like roses. S/C oil stinks so bad it will stain your skin with the foulest smell for days.


Just a FYI-RP diff fluid will also help keep the temps down. Most failures are due to excessive heat over time.

guys on denalitrucks swear by schaefers over rp in their diffs.

can anyone walk me through a diff fluid change? Do you have to remove the cover or is there an easier way?

I'm surre if I had bothered to search here or GMFS a little I could come up with something but it just now crossed my mind.

A little off topic but has anyone gone with a bigger dif cover like a TA? I know a lot of the 4 wheeling guys do it for looks, but the TA cover holds more fluid and is supposed to be stronger. I think there about $140 and they look sharp.

http://cgi.ebay.com/ebaymotors/TA-A...TruckQ5fPartsQ5fAccessoriesQQsalenotsupported

^ that's very interesting. Anyone have experience with those? will it clear the sway bar?

anyone have a write up or want to do a write up on how to change the Diff. Fluid?

tybardy said:

anyone have a write up or want to do a write up on how to change the Diff. Fluid?

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I plan on changing mine out in 2 weeks (have a trip to Ohio next week). When I do I will take pictures and do a write up on it.

dec322 said:

I plan on changing mine out in 2 weeks (have a trip to Ohio next week). When I do I will take pictures and do a write up on it.

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good deal!

Just finished this process...

The way I did this was the only way I've done it in the past on other vehicles. I wish there was a bottom plug to make the drain process easier,but unlike some vehicles, there is not. Mine is an '03 so it may be different on other models. I have the yukon SLT, NOT THE DENALI, so the process may be different for that model.

It was pretty simple, I placed an oil catch under the diff, cracked the cover bolts, let it drain completely.

Once drained, I cleaned up the area of all the oil and tightened down all the bolts. Now, just from habit, I followed a criss cross pattern and tightened them down in a stepped pattern.

Once tightened back up, I used a 3/8" ratchet, located and removed the plug. It sits on the front passenger side of the diff, look towards the driveshaft from the rear. It's pretty hard to miss.

Now, I know it's not "the best" in some peoples opinion, but it was readily available, so I went with Mobil 1 synthetic 75/90. I initially bought only 2 quarts, after reading a post on here regarding the required amount.

I put in the 2 quarts, replaced the plug and took it for a test drive. It had a "smell" to it when I got home, so I did more research and found that others had used closer to 3.5 qts.

I added a full 2 more qts, total was 4 quarts to fill it up. I found that it was easiest to use some old clear fishing tank tubing...it was clean and unused! I cut the tubing and placed over the cut nipple on the bottle. Worked great for me, filled her all the way up I believe.

A side note, make sure you are on a flat surface! I started on a slight incline with the nose down...thought she was full, then turned it around and finished filling.

Aany questions or help, let me know.

i thought rear 10 bolt diffs only took 2 1/4 quarts of synthetic? that's how much is in my silverado and tahoe rears. 1/2 inch from the bottom of the fill hole.

yeah take the extra few minutes and remove cover and clean, don't just drain and fill.

also i guess gm doesn't even recommend the separate additive anymore (gm bulletin), they want you to use a fluid that already has it in the fluid. that's why i put royal purple in my silverado.

YNOT said:

i thought rear 10 bolt diffs only took 2 1/4 quarts of synthetic? that's how much is in my silverado and tahoe rears. 1/2 inch from the bottom of the fill hole.

yeah take the extra few minutes and remove cover and clean, don't just drain and fill.

also i guess gm doesn't even recommend the separate additive anymore (gm bulletin), they want you to use a fluid that already has it in the fluid. that's why i put royal purple in my silverado.

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i too thought it was 2.25 to 2.5 qts for the rear diffs. I was tld the way to find the level was to use a small finger or an allen wrench and that the level of fluid should be about 1/2 inch below the fill plug.

OKLAGMCRUISER said:

i too thought it was 2.25 to 2.5 qts for the rear diffs. I was tld the way to find the level was to use a small finger or an allen wrench and that the level of fluid should be about 1/2 inch below the fill plug.

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once and a while you hear about guys adding 3 to 4 quarts to there rear diff. i don't even know how thats possible.

yep jammed my pinky finger in the fill hole whiling doing both my silverado and tahoe. both ended up using 2.25 quarts or so each, of course then you have to put a few ounces on the floor. lol

1.75qt front
2.25qt rear

My $.02. It's pretty much how Jasper described it. I would recommend taking your diff cover off and cleaning it with carb and brake cleaner. At least do it to take a look at your magnet, make sure no large metal chunks, and clean it off. You have the option of using a gasket, RTV, or both. Really it's just what you like. I just use RTV. Make sure you get the high temp black stuff and don't put too much on. When replacing make sure you torque bolts on appropriately. I'm pretty sure it's 15 ft/lbs. It's not much. Trust me they're very easy to torque off and a ***** to get out. More the number of bolts rather than the torque holding it on. Most people that have diffs that leak over torque. I used a $2.99 (Harbor Freight Tools) pump with clear tubing that screws on the oil bottle. Hell of a lot easier than tipping it in. Really works the best for the transfer case. My 05 took Exactly 3 quarts and was 5/8 of an inch below the fill hole (owner's manual recommendation). I used an allen wrench to check it. A 3/8" ratchet torque wrench fits perfectly in the filler plug, but I forget what the torque is on it. I'll have to look it up.

You don't need limited slip additive. Oh by the way if you're towing a lot you can use 75w140 instead of 75w90. Are you going to change out your front diff fluid at the same time? If you 4 wheel a lot consider doing your transfer case as well. Hope that helps.

i was under the impression that 99+ had synthetic fluid in the diffs, as well, can anyone else confirm/deny this impression?

Pat