# Need help with trans/diff fluid change



## kegbelly (Mar 23, 2006)

Ok, finally going to change the trans fluid and rear diff fluid in my '06 M6, and I need a couple pointers...

For the trans, I'm going with Royal Purple Synchromax, 4.6 qts. This should be a simple drain&fill operation, correct? 
I have a little pump to fill up the trans w/ new fluid. Anything I need to know beforehand?

For the rear diff, I'm going with Royal Purple Maxgear 75-140, 1.7 qts with no additive required, right? 
I've looked at the diff but the only thing that looks like a drain plug is a BIG plug about halfway up the right side, am I missing something? Or do you have to pull the whole cover off to drain it?

I called Royal Purple this morning, these are the fluids the tech recommended and said they meet or exceed all GM specs so there shouldn't be any warranty issues.

I have done some extensive searches on the forum, read a lot of opinions on various brands but haven't quite found the "how to" I'm looking for. Thanks for the help!


----------



## kegbelly (Mar 23, 2006)

I can only get about 4 qts into the trans using the fill plug on the driver's side, then the fluid starts running out. There's a sensor of some type on the passenger side, can I unscrew this and finish topping it off? A quick reply would sure be appreciated! Thanks.


----------



## Verdoro 68 (Dec 27, 2005)

Remove the reverse switch from the upper front passenger side of the tranny and fill the remaining .8qts there.


----------



## kegbelly (Mar 23, 2006)

Thanks Verdoro, I finally figured it out. I just ran it a few miles up and down the road after the change to RP synchromax, definitely much smoother and slicker shifts. I like it a lot better. Seems a little quieter too, but that might be wishful thinking on my part. 

The differential is on tomorrow's list. One more question on that: The tech at RP said I don't need to add a friction modifier, it's already in the RP Maxgear 75-140. I've read a bunch of posts on the subject, some people add an additive anyhow and some don't... which is it? If it's already in there, adding more would give it too much wouldn't it? Thanks again!


----------



## Verdoro 68 (Dec 27, 2005)

The stuff I put in my diff (Valvoline synthetic 85-140) supposedly had a friction modifier in it too, but I bought some extra Red Line modifier just in case. I'm glad I did because it was pretty noisy with just the straight gear oil. I continued adding friction modifier until the noise stopped. I think I ended up with about 3oz of the 4oz container.


----------



## b_a_betterperson (Feb 16, 2005)

You do not need a friction modifier with RP. If you were about to use Torco or Mobil 1, you'd need to add it. 30MM plug, 1.7qts. Have fun. You get oil all over the place while doing the transmission?


----------



## kegbelly (Mar 23, 2006)

Ok, thanks. Any recommendations on which brand to use, os should I go with what the dealer says?


----------



## kegbelly (Mar 23, 2006)

b_a_betterperson said:


> You do not need a friction modifier with RP. If you were about to use Torco or Mobil 1, you'd need to add it. 30MM plug, 1.7qts. Have fun. You get oil all over the place while doing the transmission?


:willy: Ok, again one person says no, someone else says yes. I'm going to try it without the friction modifier first, and if I think it needs it I can add it later.

I got a little oil on the driveway, but that was mainly what dripped out of the pump hose when taking it in and out of the filler hole and when changing the pump to a new bottle, and some trickled out of the fill hole when it got full. It was a pretty easy and clean job actually, I was surprised.

I ended up not using the reverse plug, I was able to raise the car up enough on the driver's side to get that last .6 quarts in thru the fill plug. I have two floor jacks so I put one at the front and the other at the rear jack point and alternated jacking up the front and rear a little at a time until I got it high enough, and I had jackstands under it for safety in addition to the floor jacks. Took me a little extra time to do that, but next time it will be a 30-minute job.


----------



## b_a_betterperson (Feb 16, 2005)

Go with RP. 

BTW, in your first post, you were asking about potential warranty issues. Dealers can do pretty much whatever they want. The service guys at the dealer I bought my car from freaked out when I mentioned the change, saying it would void the warranty, while another one I went to said that was stupid because the fluids are far better than the factory fill. 

Honestly, if you don't mention anything, I do not think they'll be able to tell the difference between factory and aftermarket fluids as GTOs are so far and few inbetween. Too busy working on Grand Ams -- and it's not like they'll be cracking open transmissions and differentials all day.


----------



## kegbelly (Mar 23, 2006)

b_a_betterperson said:


> Go with RP.
> 
> BTW, in your first post, you were asking about potential warranty issues. Dealers can do pretty much whatever they want. The service guys at the dealer I bought my car from freaked out when I mentioned the change, saying it would void the warranty, while another one I went to said that was stupid because the fluids are far better than the factory fill.
> 
> Honestly, if you don't mention anything, I do not think they'll be able to tell the difference between factory and aftermarket fluids as GTOs are so far and few inbetween. Too busy working on Grand Ams -- and it's not like they'll be cracking open transmissions and differentials all day.


That's kind of what the RP tech told me... he actually said it was illegal for a dealer to analyze your fluids to see exactly what you used. Don't know if that's true or not. I just wanted to make sure whatever I used met the factory specs so in the event I ever did have any problems, I wouldn't be giving them an easy excuse. I know the factory fluid was red, though, and the RP is, uh, purple, so that might tip them off if I ever have any trans problems.


----------



## Verdoro 68 (Dec 27, 2005)

I tried went to buy some GM rear diff oil and additive from a local dealer *cough*MichaelSteadinWalnutCreek,Ca*cough* a few weeks ago - $49/qt for the oil and $30 for the additive! If I didn't know any better I'd say they are trying to get us all to void our warranty 

I ended up going across the street to Napa and getting the same spec in Valvoline synthetic for $10/qt.


----------



## kegbelly (Mar 23, 2006)

That's crazy. I changed the trans fluid and diff oil two years ago in my Firebird. For the diff I got Valvoline Durablend 80W90 from Advance Auto for about $11. I bought the additive from the dealer, but I think it was only about $12. I guess it's gone up since then. :rofl: 

I don't know why dealers jack up the prices to such stupid levels, you'd think they'd figure out they could sell a lot more parts if their prices were competetive. Then again maybe they don't want to sell a lot of parts. For example... the driver's side window motor finally died on my firebird last year, dealer price was around $160. Bought the same identical brand new OEM part at my favorite 'old-style' parts store for $68. I can understand they need to make a profit and they mark up their parts, but that's over 200%.


----------



## kegbelly (Mar 23, 2006)

Good news: Took my GTO to the dealer this morning for its 4000-mile oil change. They sent me a coupon a while back, so I got the whole service for $15.95 and that's with Mobile1 oil. Can't beat that with a stick. Also asked the tech to check for any leaks anywhere while he had the car on the lift, he said it's dry as a bone.

More good news: Just finished changing the rear differential fluid to RP Maxgear 75-140. Easy job, 30 minutes tops. Only spilled a few drops.  

Bad news: It started raining just as I finished up, and I don't want to get my freshly washed and waxed car out in the rain, so I'll probably have to wait till tomorrow to see if I can tell any difference after the rear end fluid change.

Thanks again to everyone for the help and info!


----------



## kegbelly (Mar 23, 2006)

Just a quick update...

I'm really impressed with the Royal Purple fluids. I added the Maxgear 75-140 to the rear end, no friction modifier necessary--smooth and quiet. Not that I was having any rear diff noises before, just wanted a better fluid with better protection. Love the Synchromax in the trans too, shifts are smooth and slick and the trans _does_ seem a little quieter.

I also added a K&N drop-in air filter. Seems like it feels a little more responsive. Just drove the GTO to the Florida coast last night, 356 miles in a little over 5 hours. Averaged 23.5 mpg running 80-90 mph with the car packed pretty well (that's better mpg than my wife's minivan with an anemic v-6). And I still have 400 hp on tap to get around the slower drivers. I swear there were several times I'd look down and find myself doing 100mph+ and never had a clue... it's so smooth. I love this car!


----------



## The_Goat (Mar 10, 2005)

I did the RP changout too when I had my GMM Ripshifter put in. I've noticed a little better mileage but the tranmission is pretty noisy. I'm guessing that's because we left the black rubber seal off (made 4 hard to get into). I'm thinking of putting it back on and cutting out a notch or something. The RP did eliminate the rear end noise I'd had.


----------



## kegbelly (Mar 23, 2006)

I'm still running the stock shifter, I've heard the Ripshifter can be noisy. I'll probably go with the Lou's short stick and leave the rest of the shifter alone.

My mpg went up too, I usually average around 22.5 mpg per tank with about 80-85% interstate travel and the rest city & town driving with an empty car. I think I can get an average of about 24mpg per tank now, considering I got 23.5 and had the car fairly loaded (as far as you can load a GTO with its tiny trunk).

My only real complaint with driving the car over a long distance is the tilt wheel, I _really_ wish it came down about another inch. My arms got kind of tired. The seats are pure pleasure to sit in. I only stopped one time for a quick restroom break and to grab a cold soft drink.


----------



## ELP_JC (Jan 9, 2007)

Have the same complaint about the stupid wheel not lowering enough, so had to learn to grab the wheel at the 3 and 9 o'clock positions to alleviate fatigue on my arms from the 12 o'clock position I've used all my driving life.

As far as the fluid changes, I changed all 3 at 540 miles. Also replaced both tranny and diff with RP (75/140), but my diff didn't like the RP stuff. After reading all threads on the subject over the LS2 site (many), the consensus was the best diff fluid for our cars is Torco RGO 85/140 with 2-oz of type-F (not G) modifier. This was recommended by a very large differential shop which did extensive testing with all other oils. 

I decided to replace the RP with the Torco, even though the Torco is NOT a synthetic fluid, but after not finding ONE bad comment about Torco on our diffs, and many about RP (especially the 75/140 weight), I opted for the change. Tranny feels great, and RP is the overwhelming fluid of choice, so no problems there. At the very least, 85/140 should be used instead of 75, even though that's what it's called for on the manual. Many other cars use the same differential as our cars, so it's not unique in any way. 

My differential started whining noticeably more with the RP (but no chatter, so no more FM was needed), but I was driving without the back seats for a while; nothing could be heard with the seats in place. However, I didn't like that, and that's why I changed it to Torco. Maybe RP 85/140 would have made the same difference as Torco; who knows. But decided to put what the experts on that diff recommended. Hope this helps.
JC


----------



## ELP_JC (Jan 9, 2007)

Few comments. Checked my car today, and first thing it was obvious was no way in hell a pipe can be UNDER the steering rack, so no power steering fluid would ever hit a pipe. Second, both cats are not close enough to the rack to cause any problems IMO, so it's almost obvious those guys had aftermarket headers and (high flow) cats installed. Finally, checked those 2 big bolts/nuts, and no leaks in my car. 
If you don't have headers, disregard my comment about having problems with the steering rack. Hope everybody had a great easter weekend gang. Later.
JC


----------



## WanaGTO (Sep 7, 2008)

The super bump! Didnt wana start a new thread but would appreciate what anyone can tell me about how much rear end fluid you need and how to change it. Im good on the tranny, just need to know everything about the rear end. Thanks!


----------



## GTO JUDGE (May 14, 2005)

WanaGTO said:


> The super bump! Didnt wana start a new thread but would appreciate what anyone can tell me about how much rear end fluid you need and how to change it. Im good on the tranny, just need to know everything about the rear end. Thanks!


Rear End

SAE 75W-140 GL-5 Synthetic Gear
Oil (GM Part No. 89021809). With a
complete drain and refill add 1 oz.
(25 ml) of Limited-Slip Differential
Friction Modifier 7098
(GM Part No. 89021958).

Couldn't find an amount specification. I'm sure someone will know that answer.


----------



## GM4life (Mar 18, 2007)

GTO JUDGE said:


> Rear End
> 
> SAE 75W-140 GL-5 Synthetic Gear
> Oil (GM Part No. 89021809). With a
> ...


4.6 quarts.


----------



## shadrag (Oct 18, 2008)

gm4life said:


> 4.6 quarts.


That's the tranny, the diff takes less than 2qts


----------



## GM4life (Mar 18, 2007)

shadrag said:


> That's the tranny, the diff takes less than 2qts


Oops thanks for that, it was the one above the diff. yes it takes 1.6 quarts to be exact.


----------



## WanaGTO (Sep 7, 2008)

Thanks guys...so how do I go about draining and refilling the rear end? What equipment will I need to do it? I've heard of pumps or what not....I always thought it was the same procedure as changing the oil...one of the few things I actually have done before


----------



## GM4life (Mar 18, 2007)

You dont need any special equipment, for conveance there is a pump that screws on to the quart bottles you can pump the fluid into the diff. The pump you can get at any autoparts stores. Or you can just snip the top portion of the snout and pour/squrt it in like I've allways done. The bottom most bolt on the diff cover is the drain plug, the larger bolt on the passenger side with the LSD tag on it is your fill plug. I would drive the car for about 10 mins before starting to drain your gear oil.









-- Remove the rear axle housing oil level fill plug (1) from the rear axle housing. 
-- Remove the rear axle housing drain plug (4) from the rear axle housing and drain the rear axle housing. 

-- After the rear axle housing has completely drained, install the rear axle housing drain plug (4) into the rear axle housing. Tighten
-- Tighten the rear axle housing oil level filler plug to 27 N·m (20 lb ft).

-- Refill the rear axle housing with approximately 1.0 liter (1.0 qt) of Synthetic Gear Oil 75W-140 GM P/N 89021809. 
-- Using a graduated measuring cup, add 25 ml (1.0 oz) of Limited Slip Differential Friction Modifier GM P/N 89021958 to the rear axle housing. 
-- Fill the rear axle housing with the remaining 0.575 liter (0.644 qt) of Synthetic Gear Oil 75W-140 GM P/N 89021809. The oil level should be even with the bottom of the rear axle housing oil level filler plug hole.(*Fill untill the fluid runs out of the hole) *
-- Install the rear axle housing oil level fill plug (1) with a new gasket and the lubricant tag (2) into the rear axle housing. Tighten(*You don't need new gasket*)
-- Tighten the rear axle housing oil level fill plug to 27 N·m (20 lb ft).

-- Remove the drain pan from under the rear axle housing.


----------



## WanaGTO (Sep 7, 2008)

Thanks...gonna go for it today!


----------



## GTO JUDGE (May 14, 2005)

Make sure you add friction modifier to the rear. If you use Royal Purple, I understand the F.M. is included. If using other gear oil make sure you use the specified F.M. from GM.


----------



## svede1212 (Nov 1, 2005)

GTO JUDGE said:


> Make sure you add friction modifier to the rear. If you use Royal Purple, I understand the F.M. is included. If using other gear oil make sure you use the specified F.M. from GM.


true. one thing to emphasize tho is that the friction modifier you need to use is the *FORD type (Type F)* friction modifier not the GM type (Type G). the G Type is for a posi with clutches and the F Type is for a posi with cones like ours.


----------



## WanaGTO (Sep 7, 2008)

Yes, thanks guys. Going with Mobil 1 for the tranny and Torco RGO 85/140 for the rear. I will add the Type F modifier as well. I've heard of clutch rear diffs and gear rear diffs but never cones before.

Odd


----------



## 06goatm6 (Dec 5, 2008)

I just changed the rear diff fluid and transmission fluid in my car last weekend. The rear end went as planned, drained out the lower hole, filled through the fill plug and somewhere between 1.5 and 2qts fluid started rolling out, no surprise there. But when I did change the trans fluid after draining and filling through the backup lamp switch something didnt make sense. On any trans I have ever worked on you only fill to the level of the fill hole and then your done. I got to thinking where does this extra .6 quarts of fluid come from? Well I called my friend who runs the shop at the local dealer and this is what he told me. "The transmission in the GTO is installed at a steeper angle and requires more fluid for one of the bearings to be properly lubricated. The procedure for filling is to remove the backup lamp switch and fill until it reaches the bottom of the hole." This is per GM database instructions. I also have access to All Data Pro Online through work and it states the same procedure. I poured all 5 quarts of the synchromesh I bought into the trans and it was still short of the back up lamp switch. Who came up with this 4.6qt value? And has anyone filled all the way up to the backup lamp switch level? Will this be too much and blow out any seals? How much fluid does it take to reach this level?
I would like to get this solved once and for all before we all screw up our transmissions due to inadequate lubrication. Mine has 5qts in it right now, but I wont be driving it for a few more months so Im not in a big hurry to find out, but I do need this solved before it gets plates on it.


----------

