Changing differential fluid, tranny fluid, and transfer case

fallvitals · Post by **fallvitals** » Wed Mar 04, 2009 2:16 am

Hey, I just got a used 2003 S-10 crew cab ZR5, 55K miles. I replaced the air filter in it today, And here shortly I want to replace the fluid in the differential in the front and rear. So, whats a good fluid to use? I see the sticky above, it says, SAE 80W-90 GL-5 Gear Lubricant. But I am wanting to use synthetic. I don't know much about it, I have heard rave stories, and horror stories about synthetic. Enlighten me. Plus, does the diff have a drain and fill plug? or do I have to take off the diff cover?

From what I understand, you drain the diff, then fill it till new fluid starts to leak from the fill hole? Right?

And as for the tranny. I saw a few threads on here about it being very hard to remove the tranny pan without damaging the selonoids or other things.. I would have to pay $150ish to have a place do a full fluid swap (ot sure if that includes the filter, I usre hope so), but it would be much cheaper for me to do it, and replace the filter, but I would only change like 1/2 of the ATF fluid. And again, this is something I havent done before, the sticky says: DEXRON®-III Automatic Transmission Fluid. Is that synthetic?

And change the fluid in the transfer case. Any tips or sugestions on any of these maintenance tasks?

I also am gonna pull one or two spark plugs to see how they are wearing and gap. Hopefully fine, I dont wanna have to mess with those! lol.

Any other things I should look at, change, on this newly acquired truck?

thanks guys.

04crewvt · Post by **04crewvt** » Wed Mar 04, 2009 5:29 am

Add changing the fuel filter to your list, cheap and easy to do it can keep your fuel pump from working itself to death if it starts to get plugged up, every 15K it needs to be done. Please use the search function, there are a lot of threads on each item you just brought up on how to change and what to use in each component. We try to keep all info in the same threads so it is easier to find later so go ahead and post in a thread that may have been started before.

Post by **HenryJ** » Wed Mar 04, 2009 5:50 am

There is a very good thread on oils that explains the additive package that causes problems with the metallic compounds in the clutch media. Avoid those if you have a G80 rear. Synth for the trans is a no-no too, in my book.
There is no drain plug for the rear. Check out what others have done to add a beefier cover. Lots of them have a drain plug.

If you do the filter change yourself, pay the extra to have all the fluid exchanged. Well worth the investment.

green02crew · Post by **green02crew** » Wed Mar 04, 2009 8:35 am

While you are under there, read the thread on the transfer case vacuum switch. And also read about the plastic distributor for when you will eventually be changing the cap and rotor. Two good things to look for and remember on these trucks.

fallvitals · Post by **fallvitals** » Wed Mar 04, 2009 8:56 am

ill try to search function again. i have been around net forums long enough to know the importance of the search

I did infact search, I just couldn't find exactly what I was looking for,,, maybe I didnt use the right terms.

Yes fuel filter, forgot to add that to the list.

Ill read up on the vacuum switch and distruibtor cap too. thanks.

EDIT- Since I have this thread going, and honestly cant locate the answer via search, what about synthetics, like Royal Purple, in the diffs?

killian96ss · Post by **killian96ss** » Wed Mar 04, 2009 11:29 am

Gear Oil - Redline 75W/90NS or Royal Purple 75W/90 (both are synthetic and work very good with the G80).

Transmission Fluid - GM Dexron IV (this is the new synthetic Dexron used in the newer GM vehicles and works well with all GM automatic transmissions). I'm running the synthetic Dexron IV in all my GM vehicles right now and so far all 3 transmissions are performing great.

Transmission Filter - GM (most of the other brands out there are not made as well as the GM filter). If you do this yourself or have someone do it for you make sure the seal is also replaced or you can damage your transmission from air being sucked into the pump.

Transfer Case Fluid - Dexron III, Dexron IV (synthetic), or Royal Purple Synchromax (synthetic).

Spark Plugs - AC/Delco Professional Platinum (aka double platinum), or Autolite XP.

Spark Plug Wires - MSD Super Conductor, or Taylor Thundervolt.

Coil - Accel (the Accel coil has the highest voltage available for our trucks).

Cap & Rotor - Accel (probably the most expensive, but also the best quality available).

Fuel Filter - AC/Delco (do not use Fram as they are know to have internal failures).

Steve

fallvitals · Post by **fallvitals** » Wed Mar 04, 2009 6:58 pm

killian, great commentary on the posted sticky. Im gonna save that to my computer for future referance.

i think its a sticky here too, or somewhere on this site, but a page tells you how many quarts it takes to fill the tranny, diff, transfer case, etc. I thought the diff would be like 4 or 5 quarts, and if I recall right I think its only like 1.7 quarts? Little bit cheaper on fluid then I was expecting

Post by **HenryJ** » Wed Mar 04, 2009 7:24 pm

GM Fluid and Lubricant Recommendations

fallvitals · Post by **fallvitals** » Wed Mar 04, 2009 7:34 pm

green02crew wrote:While you are under there, read the thread on the transfer case vacuum switch. And also read about the plastic distributor for when you will eventually be changing the cap and rotor. Two good things to look for and remember on these trucks.

I looked at that vacuum switch thread tonight

I just got this truck two days ago, 55K miles... ill get uner it tommorow and se if its the dreaded green or blue strip switch. Thats an insane little problem

Jongo88 · Post by **Jongo88** » Thu Mar 05, 2009 3:53 am

Just change it. You won't be able to see it. You don't want it to leak.

fallvitals · Post by **fallvitals** » Thu Mar 05, 2009 12:13 pm

well all the fluids are gonna be put off for another day. I spent $75 today in some effin wire ($11) crimps ($12, I know we have tons, but can't find em! Thought i was getting jacked on the price but they were the same atanother store

) And the new Vaccum Switch, $48 with tax from the dealer! i told em it was $26 on their gm parts website, they said they couldnt do that. SoAfter seeing they have a high shipping cost, and a long wait to ship, I just "splurged" and got the damned switch. I couldn't find it in the transfer case for the life of me, then finally spotted it. Doesn't look as bad as i thought,, but doesn't look fun.

ALSO! i read on here with the S-10 crew cabs, changing the tranny filter is a bitch cuase of the cross member in the way and getting it out right?

Well, While i was under there, I dont see what the problem is? The cross member just slightly blocks some screws, which it still should be an issue un bolting them. Looks liek the pan on my s-10 drops straight down, its an 03, did they change that from earlier models? Or am i missing something? Ill take a picture later if needed.

Post by **HenryJ** » Thu Mar 05, 2009 12:49 pm

fallvitals wrote: i read on here with the S-10 crew cabs, changing the tranny filter is a bitch cuase of the cross member in the way and getting it out right?

Nope. Easy but not straight down. Use finesse

fallvitals · Post by **fallvitals** » Thu Mar 05, 2009 7:09 pm

well no, not striaght down, I might have to cant the pan itself 3/4" to get it out... but, they had to change things on the 03.. cuase theres no way I would have any issues with hitting valve bodys, and selonoids removing the pan on my tranny that I have read about here from other users... I didnt take a picture, but i will. I would do it tommorow when I do the Vaccum switch, but im going trout fishing in the mountains instead! but I work 10pm-2am... so no sleep for me tonight or tommorow before work!

fallvitals · Post by **fallvitals** » Sat Mar 07, 2009 11:18 am

Alrighty, got the new vaccum switch in. I tried it from the side, and wwasnt' going any where... I moved around and saw I could tackle it a hell of a lot easier from the front facing back. I dont have any deep well 3/4" drives, so had to use a wrench and it worked perfectly. Once I firgured out to go from the front it wasnt 10 minutes, tops. My old vaccum switch, and the harness goinginto it looked leak free.

Jongo88 · Post by **Jongo88** » Sat Mar 07, 2009 12:08 pm

Did it have the green stripe???

fallvitals · Post by **fallvitals** » Sat Mar 07, 2009 1:40 pm

Jongo8 wrote:Did it have the green stripe???

That was the first thing I looked for once I got it off. And i didn't have any paint on it. I guess it just wore off.

So i started on my sub install. And broke a spring in the drivers seat leaning against it

New thread for that....

fallvitals · Post by **fallvitals** » Fri Mar 13, 2009 6:44 pm

alright, few questions.

Im gonna get some Red Line LightWeight ShockProof Gear Oil for my f/r diffs. Apperantly no one around here sells it, so im gonna have to order it from summit, or someplace. Along with a tranny cooler kit.

When i go to fill the diff,,, whats the best way? im not sure where the fill hole is, this is something I have never done, is there a special pump you can use to pump oil from the bottle into the diff? or can it pour right in?

I dont wanna spill it. Im paying $40 for 4 quarts of redline o_0 ZERO WASTE!

And a few years ago, for some reason, I bought two bottles of Valvoline HIgh Milage ATF Decron III. Would that be fine for the transfer case? Its a 03, with 55K miles. I dont see a problem , but wanted to ask first.

Post by **HenryJ** » Fri Mar 13, 2009 7:05 pm

Do you plan to offroad your truck? What about water crossings? Did you relocate the vent tube yet?
I change the differentials after a trip with a water crossing.

Read as much as you can about the synthetics before you make that investment. That can get costly in a hurry.

I am against the use of friction inhibiting compounds in the Eaton G80 locked rear differential.

If you see street duty and don't NEED the G80 to lock then the reduced friction may gain you some mileage and pay off in the long run.
Check out the last link in the synthetics thread. That is a good article and opens your eyes to some options when choosing lubricants.

Personally I would rather not extend service intervals. It gives me a chance to judge the condition of the component. Using synthetics that can be expensive and I am not sure the cost would out weight the benefits.

That will be for you alone to decide. Each case will be different. What works for one may not be the best for all.

Check with the racers at your local track. Someone will be a Redline dealer and make a better deal than elsewhere, maybe?
I used to sell a little when I was racing full time and had a Redline sponsor. I have been out of it for a few years now and the distributor I went through died, so no help here. I get it from a local drag racer now, since I don't need the large quantities any more.
It is great stuff. I just might not make financial sense for a daily driver.

F9K9 · Post by **F9K9** » Fri Mar 13, 2009 9:58 pm

HenryJ wrote:.....Read as much as you can about the synthetics before you make that investment. That can get costly in a hurry......Personally I would rather not extend service intervals. It gives me a chance to judge the condition of the component. Using synthetics that can be expensive and I am not sure the cost would out weight the benefits.

That will be for you alone to decide. Each case will be different. What works for one may not be the best for all........................

I have to go a tad further in advising you not to buy into the hype of big names! Grape smelling BS and other colors doesn't impress me. Some purple colored and pyramid promoted products cannot tell you that they meet and exceed industry standards.

I am stepping on a huge bunch of toes but, do your research on the industry's requirements, and research who actually makes which products. Wallyworld's products and prices just might have you running to you your local "A" supplier demanding his head.

fallvitals · Post by **fallvitals** » Sat Mar 14, 2009 1:26 am

the link in the thread you gave me, i will read tommorow when im not so tired.

Well... the whole idea of using Red Line stuff was from the searching I did here. Read nothing but praises and saw were some guys gained a few MPG, plus I do want to put good stuff into this truck.

f9k9, what brands do you have in mind that would work just fine?

My truck is prodominantly a street truck. If I do take it offroad it would probably be some old logging roads, perhaps a few creek crossings, but I doubt they would reach the diff. for things I have in mind. I do wanna offroad, but dont have places too, nor do i wanna put the work into my truck to take it "extreme" places.

I see what your saying about financial sense for a daily driver. What really got me intresting in Red Line, liek I already mentioned, is the fact some people said they got a little better MPG with it. But no, I don't plan on extending maintence times.

well, im gonna read that link in the morning, to tired now, lol. But now im kinda lost again... red all kinds of great stuff about redlien on this forum, seems to be highly recommended, but you all are saying it might now make financial sense? Can you recommend me another gear lube(s) to look at?

But still, how do you fill the diff and not spill all the lube?

DLP · Post by **DLP** » Sat Mar 14, 2009 4:09 am

The easiest way I found to fill the the pig with lube. Is to use the nipple supplied with the bottle and add a 3" or 4" piece of clear tube to the end. Pulling the tire off the same side as the filler hole lets you reach in there pretty good. If it's cold out, I put the 2 bottles of gear lube in the kitchen sink floating in HOT watter for awhile first. Makes it a lot runnier (sp) Do it before you break the seal on the bottle. Saves a marrage!

Post by **HenryJ** » Sat Mar 14, 2009 7:16 am

I think if you look all those repeat posts praising the synthetic are from one poster. Don't take repetition or one forum as a judge of what works. Use several different views and make up your own mind.
Many things are done in the name of better mileage. Don't count on it. A 1% gain takes a long time to break even and if the service interval is not extended you get deeper in the hole. If you get a benefit from better performance then at least you get something.

I would much rather see you spend the money on a good support cover with a drain. This will make your next service easier. It will stiffen our flexy rear case. A notch can be filed to improve side bearing oiling and may get a little better cooling.

In the search for better mileage I would let it breathe. Do the exhaust first.
Take the time to read about what others have done to "improve mileage and performance." Air pressure in your tires and a regular maintenance dose of injector cleaner are the very best.

Investing in high dollar lubricants is way down at the bottom of the "to do" list, IMO. Don't get me wrong, I run decent stuff. Not the recycled generic, but not the big name "synthetic" either.

F9K9 · Post by **F9K9** » Sat Mar 14, 2009 7:51 am

fallvitals wrote:..............f9k9, what brands do you have in mind that would work just fine?..........

I wouldn't be afraid of Super Tech. Check out the back of the bottle and make sure that it meets are exceeds the required specs.

fallvitals · Post by **fallvitals** » Sat Mar 14, 2009 9:48 am

Alrighty, ill see what the local places have in the way of valvoline and such...

also, I have a couple bottles laying around of Valvoline High Milage ATF Decron III. Would it be fine for the transfer case? Probably a stupid question I only ask becuase it says "high milage" and wonder if it mioght have additives or something that wouldnt be good for it?

Post by **HenryJ** » Sat Mar 14, 2009 10:09 am

If I had it, I would use it. I might choose something else next time. High mileage may contain additive to swell the seals. Dextron III is the specified lubrication. It meets that.

fallvitals · Post by **fallvitals** » Sat Mar 14, 2009 11:01 am

alrighty, thanks.

last question (I hope, for my sake and this forums sake, lol), diff covers.

I searches Summit, and all the covers I am seeing are $120-$170ish

Nor do I know the size I need, (if it matters I have a 03, with 3.73 gears, ZR5). Advance gives me a gasket that is 7.5", and Summit gives me a gasket thats 7.625". My buddy who had an 2000 s-10 ZR2 bought diff cover's for his through the dealer he wasnt sure of the size, so bought em both. went to take the other back, and they wouldnt take it cause he took it out of the plastic

But he said its been laying around since, he would let me see if it fits when I replace the fluid. Which, thats too good to be true, but would be awesome if it does fit.

So im asking, is what im seeing the going price for diff covers? also, im assuming whatever diff cover fits the rear, fits the front? and how hard is it to change the front diff fluid? (curious because of the natural 'tightness' of the front end)

Post by **HenryJ** » Sat Mar 14, 2009 11:41 am

7.5 and 7.625 use the same cover and gaskets, however all gaskets are not the same. Read up on the oil hole that can be missing.
The front is not the same and does not have a cover.

fallvitals · Post by **fallvitals** » Sat Mar 14, 2009 12:23 pm

ahhhh. Well I dont think my buddys diff cover will fit then. He said it was a 7" or 7.25 or soemthing... but were still gonna try it.

Ill do a search on the different gaskets.

alright, well,,, since the front doesnt have a cover.... how do you drain it and all that???

Sorry for all the dumb questions... this is just something I have never done, nor have I watched any one do.

Post by **HenryJ** » Sat Mar 14, 2009 1:40 pm

The information is all just a search away

barch97 · Post by **barch97** » Thu Apr 08, 2010 8:19 am

killian96ss wrote:Gear Oil - Redline 75W/90NS or Royal Purple 75W/90 (both are synthetic and work very good with the G80).

$19.99 / quart @ Autozone

HenryJ wrote:Capacities - Approximate Fluid

Application - Specification

Axles
Front Axle = 1.27 quarts
Rear Axle-7.625 = 1.8 quarts
Rear Axle-8.6 = 2.0 quarts

So, like $40 worth of gear oil? And, I've been wasting time trying to save a few bucks on a cover? Is there any reason not to use Mobil1 Synthetic Gear Lubricant LS 75W-90 for $10.89 instead? I guess if I'm only going to change it every 8 years, I oughta splurge a little, huh?

gocntry · Post by **gocntry** » Thu Apr 08, 2010 8:40 am

barch97 wrote:Is there any reason not to use Mobil1 Synthetic Gear Lubricant LS 75W-90 for $10.89 instead? I guess if I'm only going to change it every 8 years, I oughta splurge a little, huh?

That's What I Used In My Crew And It Worked Well, Even When The Rear End Was Full Of Water With The Mobil 1

I Also Run That In The Front & Rear Differential In My Tahoe.

Post by **HenryJ** » Thu Apr 08, 2010 9:00 am

barch97 wrote:...Is there any reason not to use Mobil1 Synthetic Gear Lubricant LS 75W-90 for $10.89 instead?

Do you have a G80 Eaton Govloc?
If you do you need to make sure it meets the GL5 specifications, does not contain friction modifier for limited slip differentials and does not have additives that may damage the Eaton Govlocs clutch plates.

gocntry · Post by **gocntry** » Thu Apr 08, 2010 10:46 am

I Had / Have A G80 In Both Truck Here Is The Data Sheet On The Mobil 1 Data Sheet Mobil 1 Gear Oil 75W90

killian96ss · Post by **killian96ss** » Thu Apr 08, 2010 8:15 pm

Mobil 1 gear oil is a good choice and it work will work with the gov-lock.

Steve

border man · Post by **border man** » Thu Apr 08, 2010 10:10 pm

Thats the fluid (mobil 1 75/90) I use in my Harley's tranny. Make for smoother shifts and quiet operation.

barch97 · Post by **barch97** » Fri Apr 09, 2010 4:23 am

Sweet... thanks for all the helpful input, fellas. Y'all just saved me $20. Looks like I'll be drinkin' fancy imported beer while I knock this job out tomorrow.

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Changing differential fluid, tranny fluid, and transfer case

Changing differential fluid, tranny fluid, and transfer case

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