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Q10377 - HOWTO: Differential, Manual Transmission & Engine Oil changes

Differential, Manual Transmission & Engine Oil changes

The Fluids

Castrol Syntec 0w-30 motor oil (aka German Castrol or GC)
K&N Oil Filter, HP-1008  HP-1007

Torco RGO gear oil, 85w140
Torco Type F Limited Slip additive

Royal Purple Synchromax transmission fluid

Here is the hand pump. I purchased it from Advance Auto Parts for a couple bucks. The tube for it was actually longer, but I cut it in half so I can get to the hard to reach places easier, and it's also easier to pump when you have half the hose.


Last year I suffered from the dreaded "whine" some of our diffs can make. So the dealer replaced the entire rear end, which you can read about here. Some people say you should do a 500 mile break in with the new diff, some don't. I decided to play it safe and break it in. After the 500 miles was up I wanted to swap out the stock fluid for something a little tougher.

Here is a pic of the drain and fill holes:

It takes a 30mm wrench to get the fill plug off, and a 15mm to get the drain plug off.

I drained the stock gear oil. It was a thick, gray-ish color. I could also see some metal flakes mixed in with the fluid. It wasn't alot, but enough that you could see it pass by. Oh, and like alot of people have said on here... this fluid STINKS! Once the fluid was drained, put the drain plug back in (duh).

Next, I used the hand pump and squeezed about half a bottle of gear oil in. After that, I measured 2oz of friction modifier and poured it into the half full Torco bottle. I did this so it would be easier to get the fricion modifier mixed in with the gear oil.

After adding the friction modifier, I opened up the other bottle of gear oil and added it to the half full bottle w/ the friction modifier. I did this because with a hand pump, it was a MAJOR pain in the ass to try and squeeze out the last half of a bottle. Either that or it was just me.

You can tell when you have enough fluid in the diff because the oil will start to come out of the fill hole. Once that happens, just put the fill plug back in, and you're done with the rear differential.


Next I decided to up my tranny fluid from stock to Royal Purple. After reading alot on here, it seems the RP Synchromax was the way to go. So I figured since I was changing out the gear oil and the engine oil, why not change the tranny oil while I was at it?

Here is a pic of the drain plug. It's located on the rear passenger side of the transmission. I used a small rachet (with no socket) for this. Be careful, this fluid like to spew out... so just be prepared.

Once all the fluid is drained and you replace the drain plug, you have a few choices on where you want to fill from. You can remove the back-up light switch on the passenger side of the transmission, you can remove your shifter (from inside you car), or you can use the fill plug, which is located on the drivers side of the transmission. I decided to use this fill plug, which is pictured here:

Filling the transmission was alot like filling the diff. I used the hand pump, and squeezed in the tranny fluid, half a bottle at a time, until tranny fluid started coming out of the fill hole. Once this happens, just put the fill plug back in. Keep in mind if you use this fill hole like I did, you'll only get approx. 3.8 quarts of tranny fluid into the transmission. The owner's manual calls for 4.6 quarts. So how do you get the remaining 0.8 quarts into the transmission then?

Right here...

On the upper front passenger side of the transmission you'll see this. It is the reverse sensor switch. This is what tells your reverse lights to come on when you shift your GTO into reverse.

Disconnect the wiring harness from the sensor, then get a 7/8" wrench. I tried using a socket, but the deepwell socket was too tall, and a regular size socket is too small. Using the wrench, take the sensor out of the transmission. This may take several minutes if you're using the wrench, so be prepared for alot of 1/4 turns until it comes out.

Once you have the reverse sensor switch out, start to fill your transmission until the fluid starts to come out of the reverse sensor hole. put the reverse sensor switch back in, reconnect your wiring harness and you're done!

NOTE: You can start to fill your transmission straight from the reverse sensor hole and completly avoid using the Fill Hole on the driver's side. I only did the Fill Hole on the driver's side because I found out about using the reverse sensor hole after the fact (ALWAYS refer to your owner's manual before changing fluids and you can avoid this). (Thanks Fox Mulder, why2kmax and Cyclone Chris)


Everybody should know how to do this. I don't have many pics of this because the battery on my camera was dying, so use your imagination.

Just remove the four bolts holding the skid plate (13mm). Once removed, you'll see your oil pan and oil filter. On the passenger side of the oil pain is your drain plug. Use a 13mm wrench (thanks Kanding) to get it off. Once the oil is drained, replace the drain plug. Next, remove your oil filter. I use K&N oil filters, so I can use a 1" wrench to get the filter off.

Next, get your new oil filter ready. I like to fill my oil filter up with oil before putting it back on. It's a little easier on the car during that first start up. I also take a little bit of oil on my index finger, and lubricate the seal on the oil filter before screwing it back on.

Once you have the oil filter on, go ahead and put your skid plate back on. I took this opportunity to replace my stock skid plate with a fancy new one that I fabbed out of a spare stocker I bought in the For Sale section. The thread about my fancy new skid plate is found here.

Here is a pic of my new skid plate on the car. Sorry it's so dark...

With everything under the car in order, go ahead and pop your hood and fill your car up with your oil of choice.


- Buy extra fluids. If you're using a hand pump like I did, having an extra bottle of tranny/gear oil makes things a little easier. With the hand pump, I could only get about half a bottle into the car before I couldn't squeeze any more out. I would then open up another bottle and squeeze about half of it out until I couldn't squeeze any more. Then I would pour one half full bottle into the other half full bottle and repeat the process until my fluids were topped off. It was a long process because I didn't have gravity working with me (couldn't get the bottle in a good position for that). Hard to do? No. Just took a while.

- Bring something good to measure your friction modifier. I had to eyeball about 2oz of friction modifier. It would be nice if you could measure right out of the bottle, but you can't. Next time I have to change out the diff fluid, I'm going to buy one of those plastic syringes (the kind that you would use for children's medicine).

- Invest in magnetic drain plugs. I forgot to do this, but next time I change out the engine oil, I'm going to replace my drain plug with a magnetic one. This is purely optional, but you'd be surpised what that little magnet at the end of the drain plug can pick up. I suppose you could also do the same thing with the differential's drain plug. Having a magnet in there could catch any metal shavings before they get grinded between gears.

- Always remove the fill plugs before you remove the drain plugs! Not because you have to, but it's alot better remove the fill plugs first, just incase you find out you don't have the right tools, or can't remove the drain plugs. Nothing is worse than draining your fluids in your diff or tranny and finding out you can't get the fill plug off! (thanks 2k6 GTO)

- Check you tires for strut rub.Whether you're on jacks or on a lift, while you're under the car you might as well check your front tires for strut rub. What is strut rub? This topic has been extensively covered on this forum, so a quick search for "Strut Rub" will bring up plenty of helpful info.

Anyway, I hope this tutorial will be helpful to some of the newbies out there who want to do their own maintenance on their vehicles. I'm no pro by any stretch of the imagination, so if there are better methods out there, please feel free to post them up here.

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Approved Comments...
Missing torque specs. Approved: 5/27/2007
It would be great to have the magnetic drain plug part numbers added to this article. Ive already installed the magnetic drain plug on my engine (GM# 11518377), I was wondering if anyone knows if a magnetic drain plug for the transmission and rear axle is available from GM or parts store etc that could be added to this article ? Approved: 5/15/2007
Thank you for posting the pictures I have no idea about cars but I have cofidence that I will be able to change my own oil. Approved: 4/30/2007
Thank you for posting the pictures I have no idea about cars but I have cofidence that I will be able to change my own oil. Approved: 4/30/2007
This was great for explain how to change the oil, ive never dealt with a Ls2 engine before, and i just got my new GTO 05, Its defiantly my prize so this was a great explanation, and i feel comfortable doing it and i know the best oil to us with it!!! great article. Approved: 4/10/2007
perfect to the "T" Approved: 4/9/2007
Great article, jack placement is an issue. The brace to the left/right of the bottom of the radiator has been suggested by those who do not have a lift or ramps. Approved: 4/8/2007
very well written and illustrated. Approved: 4/4/2007
some trucks dont have drain plugs on diffs and the ha nd pump would take forever Approved: 4/1/2007
Been there, done that. Had to search all over to get this amount of collected information and its with pictures too! Thanks for putting it all together in one spot! Approved: 3/1/2007
Created on 3/1/2007.
Last Modified on 10/28/2008.
Last Modified by Chris Butigieg.
Suggested by Grave (
Skill Level: Beginner.
Article has been viewed 65619 times.
Rated 8 out of 10 based on 158 votes.
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