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How to Change your Rear Diff Fluid


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#1 techboy

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Posted 24 June 2017 - 09:42 PM

I'm putting this post here for now in the VM b/c I'm assuming it'll get moved to the FAQ, maybe :o .   Most of us are aware of the Starquest Forums being lost and along with it the SOS manuals.  So, I've kinda made up in mind anytime I do a job from here on out I'm going to do my best to create a "how-to" tutorial to go along with it and try to recreate some of that info here.  There's a TON of great info on this site as we all know, but if you do some searching some of the old threads are missing pics and whatnot so I'm hoping to just enhance some of the information already out there, at least until I become old and all my pics are missing.  I've got two other how-to's in the works already and a 4th one in mind.

Here goes ...
1988 Starion ESi-R ... crushed by a tree 10/31/11 - back from the dead 8/2016
1988 Conquest TSi ... current driver - sold to Bigjoe 6/2016
1987 Conquest Flatty ... F/S thread - sold 8/2014
1987 Conquest TSi ... parts car - sold to Coldscrip 12/2011
1999 Eclipse 4G63 ... heavily modified.
Feeback Thread | Motor rebuild thread | Restoration thread

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#2 techboy

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Posted 24 June 2017 - 10:33 PM

Your car is about 30 years old now and most likely has had a handful of owners.  If you're anything like me, you have very little history to go on, esp. as it relates to basic maintenance.  So, if you haven't, maybe it's time to change the fluid in your rear diff.  If you changed your own oil before, it's not too much harder than that, just a little bit more difficult b/c you don't have an easy access fill in your trunk like you would your engine oil in the engine bay.  Let's get started:

First, if you don't have access to a lift you need to jack up the rear of your car nice and high.  It's going to probably end up being a bit of a messy (and smelly) job, so you might want to throw down some cardboard if you have any, esp. if you care at all about your garage floor.

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My metrics only go up to a 22mm and that wasn't big enough, so I had find a standard that fit the drain and fill plug.  A 15/16 seemed to be the perfect fit.

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Now let's find the drain and fill.  The drain is smack right on the bottom of the diff here:

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The fill is up a bit further on the drivers side of the car here:

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Because I was curious about whether or not my diff was even filled to proper level, I decided to crack the fill plug first.  To my surprise, it actually was as I got a little bit of seepage once I cracked the bolt.

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Now that I knew that, it was time to throw a pan under and drain the old fluid.

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While the fluid was draining I thought it was a good time to clean up the two plugs a bit.  The one with the magnet on the left is your drain plug and will probably have some heavy gunk on the magnet, you can go ahead and clean that up.  The one on the right is the fill plug.  I ran both of the them on the wire wheel to clean them up.  Be careful of the copper crush washers found on both of the plugs.  I cleaned both the washers up real good with some brake clean.  If you have a store of copper washers laying around and have some that fit, using new ones probably isn't a bad idea.  I didn't realize they were copper until I had the plugs out and didn't have the time luxury to buy new ones, so I reused the originals.  Don't try that will coolant lines or fuel though, usually doesn't work. :wacko:

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Once all the fluid has drained out you can put your drain plug back in with your 15/16th and get ready to go back the other way.  First thing I did was find one of the smaller funnels I had and rigged up about a 6 inch feed tube with some extra hose I had laying around in the garage.  I also cut myself a small piece of a wire tie .. more on that in a minute.

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There's not a ton of room under the car to refill your diff easily, but it can be done.  I wedged my funnel up under the car like so, and used the wire tie to hold the funnel to the brake line right near the rear splitter.

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Here's another look at it from a slightly different angle, looking a bit more toward the drivers side rear tire.  You can see there's a pretty good amount of room in the area in the red to get your hand up in there an pour.  If I were to do it again, I might try taking the drivers side rear tire off and use a longer hose on my funnel ... might be easier ... not sure.

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At this point I stole a small plastic container from the kitchen, about the size of a baby food jar to use to pour the fluid into the funnel since I determined there was no way I was gonna get a whole diff fluid bottle in there.  I'm not gonna discuss in this thread what oil to use, what's good, and what's not.  If you're looking at this I'm assuming you've already done that homework and probably have already purchased whatever it is you're using.  If not, there's lots of good threads you can read up using the search button.  The FSM calls for a 80W-90, I can tell you that much.

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Depending on what threads you read and what oil you choose to go with, you might need/want to purchase an LSD additive as well.

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Almost done.  It took me a little bit, but I just kept filling the little cup and pouring it in slowly.  You need about 1.3 quarts so you won't quite use 1/2 the 2nd bottle.  Just keep filling till it starts coming out the fill hole.

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Put your fill plug back in and tighten it down snug.  You can also sneak one last look at your drain plug too while you're under there.  Make sure you don't see any weeping now that you've got fluid back in the diff, esp if you reused the copper crush washer.  

One last thing, I took a can of brake cleaner and sprayed the whole diff down and cleaned it up real good so I could keep an eye out for any future weeping or leaks.  If all goes well, it should look something like this when your done.  

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Clean up, put your car back down on the ground and go for a test drive.  :D
1988 Starion ESi-R ... crushed by a tree 10/31/11 - back from the dead 8/2016
1988 Conquest TSi ... current driver - sold to Bigjoe 6/2016
1987 Conquest Flatty ... F/S thread - sold 8/2014
1987 Conquest TSi ... parts car - sold to Coldscrip 12/2011
1999 Eclipse 4G63 ... heavily modified.
Feeback Thread | Motor rebuild thread | Restoration thread

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#3 Zoggy87

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Posted 24 June 2017 - 10:49 PM

Thank you for posting a sticky oriented step by. I really really wish everyone would do like you and make it to where we have one for virtually every thing with our cars.

#4 viper1355

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Posted 25 June 2017 - 01:47 AM

Out of curiosity, is there any reason you didn't use a screw on bottle pump like this one: https://www.harborfr...ump-61746.html ? I would imagine that would be easier and quicker.

Edited by viper1355, 25 June 2017 - 01:48 AM.


#5 importwarrior

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Posted 25 June 2017 - 07:35 AM

Can I copy this in to the FAQ?

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#6 tsi_tom

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Posted 25 June 2017 - 09:58 AM

View Postviper1355, on 25 June 2017 - 01:47 AM, said:

Out of curiosity, is there any reason you didn't use a screw on bottle pump like this one: https://www.harborfr...ump-61746.html ? I would imagine that would be easier and quicker.

Those are ok if you don't put them in all the way.  I over filled my transmission with one of those and when I pulled out the insert 90W went everywhere.
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#7 techboy

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Posted 25 June 2017 - 10:16 AM

View Postviper1355, on 25 June 2017 - 01:47 AM, said:

Out of curiosity, is there any reason you didn't use a screw on bottle pump like this one: https://www.harborfr...ump-61746.html ? I would imagine that would be easier and quicker.
I talked to a mechanic friend about one of those before I did the job and he said they don't work "that great" so I figured why spend the money.  But, it certainly is another method.

View Postimportwarrior, on 25 June 2017 - 07:35 AM, said:

Can I copy this in to the FAQ?
Absolutely.  Thanks IW.
1988 Starion ESi-R ... crushed by a tree 10/31/11 - back from the dead 8/2016
1988 Conquest TSi ... current driver - sold to Bigjoe 6/2016
1987 Conquest Flatty ... F/S thread - sold 8/2014
1987 Conquest TSi ... parts car - sold to Coldscrip 12/2011
1999 Eclipse 4G63 ... heavily modified.
Feeback Thread | Motor rebuild thread | Restoration thread

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#8 Zoggy87

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Posted 25 June 2017 - 05:43 PM

View Posttechboy, on 25 June 2017 - 10:16 AM, said:


I talked to a mechanic friend about one of those before I did the job and he said they don't work "that great" so I figured why spend the money.  But, it certainly is another method.


Absolutely.  Thanks IW.

I'm sure different brands perform different ways, but the cheap one from oriellys that's $10 works near flawless for me, and it's WAY more convenient than fighting the bottle.

#9 89fijiquest

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Posted 19 December 2018 - 10:09 PM

From reading all the great posts on the diff and trans fluid experience, it sounds like there are several right answers.  I ended up changing 89 diff and manual trans using 2 quarts of Mitsubishi DiaQueen GL5 LSD Gear Oil (MZ320345) and the 3 quart cocktail of redline MTL and MT-90 that seems to be popular with the evo community. All bought from maperformance.com.  I also chose the pump method over funnel.  The pump I used was a little less than $5 and in stock at the local Walmart:  https://www.walmart....e-Pump/16351021

The fluid that came out looked pretty good so I'm not expecting any drastic difference. Just did it for piece of mind since I didn't know if/when the previous owner did any of that type of maintenance. Thanks to all contributors for the great info !!

#10 tsi_tom

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Posted 19 December 2018 - 10:43 PM

How much was that Diaqueen?
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#11 ucw458

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Posted 20 December 2018 - 02:20 AM

You don't really need limited slip additive.  That's for fiber clutches.  SQs have metal clutches.  I don't use it in mine.



You missed something that gets overlooked till it breaks.  Changing the fluid is fine but you forgot the Torque Tube coupler.  The front part of the diff held on by 4 bolts is the Torque Tube.  It has a splined coupling that connects to the diff.  Over time the grease washes away and the splines rust and grind away.  That TT needs to be removed and greased when you change the diff fluid.
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#12 Hoosierquest

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Posted 20 December 2018 - 06:27 AM

Just an FYI. I re use nearly all my copper gasket washers. Unless they have been majorly deformed you can usually just hit them with a propane torch and it will pull out any mild defects.
Been doing it for years.
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#13 TexasQuest

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Posted 20 December 2018 - 07:34 PM

View Postucw458, on 20 December 2018 - 02:20 AM, said:





You missed something that gets overlooked till it breaks.  Changing the fluid is fine but you forgot the Torque Tube coupler.  The front part of the diff held on by 4 bolts is the Torque Tube.  It has a splined coupling that connects to the diff.  Over time the grease washes away and the splines rust and grind away.  That TT needs to be removed and greased when you change the diff fluid.
Is there a how to on properly greasing the torque tube? I'm pretty sure my car needs it done.
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Zoom clutch, Fidanza flywheel, Stedebani shifter, KSport coilovers, ST swaybars, abs delete, a/c delete, cruise delete, JVE, BSEK, TEP steel brake lines, LSP braided cooler lines, CX Racing radiator,  MK1 silicone hoses, MK1 pullies, *DM hard pipes & intercooler,14G turbo, ported exh. manifold, MAF Translator, 3.5" GM maf, Turbo XS RFL bov, *DM 3" exhaust, Cusco front strut bar, TEP rear strut bar, Enkei 92's, HKS turbo timer, AEM wideband, AEM boost gauge, AEM oil pressure gauge, SPA fuel regulator, Hallman boost controller
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View PostJohnnyWadd, on 04 March 2010 - 10:01 PM, said:

my shaft was big i dont know what your talking about.

<SOS> http://sosmanuals.minagera.org/
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#14 ucw458

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Posted 20 December 2018 - 08:56 PM

View PostTexasQuest, on 20 December 2018 - 07:34 PM, said:

Is there a how to on properly greasing the torque tube? I'm pretty sure my car needs it done.

Not that I know of but it's really simple.  Just smear grease on the splines and add some inside the cup side as a resivour.  The hard part is getting the TT off.
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#15 techboy

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Posted 21 December 2018 - 12:46 PM

View PostTexasQuest, on 20 December 2018 - 07:34 PM, said:

Is there a how to on properly greasing the torque tube? I'm pretty sure my car needs it done.

I'll put this on my list of How-to's for the future.  I'm planning on next winter dropping the entire rear subframe and redoing the whole thing.  I should be able to do a little write-up then.  Unfortunately, that's about a year away.
1988 Starion ESi-R ... crushed by a tree 10/31/11 - back from the dead 8/2016
1988 Conquest TSi ... current driver - sold to Bigjoe 6/2016
1987 Conquest Flatty ... F/S thread - sold 8/2014
1987 Conquest TSi ... parts car - sold to Coldscrip 12/2011
1999 Eclipse 4G63 ... heavily modified.
Feeback Thread | Motor rebuild thread | Restoration thread

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#16 Contsis

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Posted 21 December 2018 - 03:45 PM

I'd love to drop the rear sub on mine and replace all warn parts including the struts.
Might have to wait for your write up.

Edited by Contsis, 21 December 2018 - 03:45 PM.


#17 BuGG

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Posted 21 December 2018 - 06:05 PM

View Posttechboy, on 21 December 2018 - 12:46 PM, said:

I'll put this on my list of How-to's for the future.  I'm planning on next winter dropping the entire rear subframe and redoing the whole thing.  I should be able to do a little write-up then.  Unfortunately, that's about a year away.

View PostContsis, on 21 December 2018 - 03:45 PM, said:

I'd love to drop the rear sub on mine and replace all warn parts including the struts.
Might have to wait for your write up.

Its not a fun job burning out and cleaning those old rubber bushings.

Edited by BuGG, 21 December 2018 - 06:10 PM.

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#18 techboy

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Posted 21 December 2018 - 11:08 PM

I'm rebuidling a new subframe right now for my Eclipse, not the most fun, but not terrible.
1988 Starion ESi-R ... crushed by a tree 10/31/11 - back from the dead 8/2016
1988 Conquest TSi ... current driver - sold to Bigjoe 6/2016
1987 Conquest Flatty ... F/S thread - sold 8/2014
1987 Conquest TSi ... parts car - sold to Coldscrip 12/2011
1999 Eclipse 4G63 ... heavily modified.
Feeback Thread | Motor rebuild thread | Restoration thread

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#19 psu_Crash

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Posted 23 December 2018 - 11:40 PM

View Postucw458, on 20 December 2018 - 08:56 PM, said:



Not that I know of but it's really simple.  Just smear grease on the splines and add some inside the cup side as a resivour.  The hard part is getting the TT off.

Make sure to clean all the old grease out too. I use brake cleaner and a small wire brush. You probably won't get it 100% spotless, just do what you can
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#20 Turbo Cary

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Posted 24 December 2018 - 09:33 AM

They make a hose adapter which twists on/off and connects to 95 percent of bottles like oil, gear oil etc. It has been one of the best things I have ever purchased. 5 to 10 dollars and less of a mess!

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