Limited Slip diff (changing fluid)
Thread Starter
Heel & Toe
Joined: Feb 2005
Posts: 21
Likes: 0
Limited Slip diff (changing fluid)
Hello,
Needed some advice in changing out the limited slip diff oil in rear end. Just bought a 1991 L98 six speed. Car has 93K on it possibly higher mileage as the odometer may have been messed with. Does this need changing in the first place and if so is this a bear to do and what weight oil shoud I use. I read 75 w 90 is this correct. The book I read said this is not easy to do and chev. really designed this never to need changing. Sounds funny to me.
I also want to change the trans fluid as well for my six speed. I read in a book that 5w 50 (Synthetic) was ok to use. Any help would be appreciated here. I'm new at this but eager to learn. Car is a blast to drive. Thanks in advance
Jack
Needed some advice in changing out the limited slip diff oil in rear end. Just bought a 1991 L98 six speed. Car has 93K on it possibly higher mileage as the odometer may have been messed with. Does this need changing in the first place and if so is this a bear to do and what weight oil shoud I use. I read 75 w 90 is this correct. The book I read said this is not easy to do and chev. really designed this never to need changing. Sounds funny to me.
I also want to change the trans fluid as well for my six speed. I read in a book that 5w 50 (Synthetic) was ok to use. Any help would be appreciated here. I'm new at this but eager to learn. Car is a blast to drive. Thanks in advance
Jack
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
that is pretty much correct - I don't think they specify a changing schedule.
However, it isn't hard. You need a small hand pump, like the Mighty-Mite, that is available from PepBoys for about $15.00.
Get a bottle of the lube (75-90) and TWO bottles of diff additive from your local GM dealer.
There is a bolt on the side of the housing. It has a tag hanging on it, if I remember rightly. The pump will then suck the old stuff out.
Use the pump to then pump in the 2 bottles of additive and then the oil.
All done.
However, it isn't hard. You need a small hand pump, like the Mighty-Mite, that is available from PepBoys for about $15.00.
Get a bottle of the lube (75-90) and TWO bottles of diff additive from your local GM dealer.
There is a bolt on the side of the housing. It has a tag hanging on it, if I remember rightly. The pump will then suck the old stuff out.
Use the pump to then pump in the 2 bottles of additive and then the oil.
All done.
Race Director
Joined: Jun 2004
Posts: 13,953
Likes: 706
From: WI
It was very easy to change the diff. fluid for my car. You don't even need to jack it up, though there is more room if you do. You either need a big Torx to fit inside the drain plug, or use a pipe wrench to go around the plug. A channel locks might go big enough. Looking under your back liscense plate toward the front of your car, you'll see the round pumpkin diff. On the right (pass side) there is a drain plug. FYI you can sick a hose in there and siphon it yourself. Suck the fluid till it starts to drain then put the end in a pan. It will gravity siphon. Then put the hose on the end of your 75 w 90 diff lube bottle and squeeze it in.
I used 75 w 90 Valoline something, that I got at Walmart. I think it was five bucks. It specifically states in the label to NOT add more diff additive. There was mentioned a Moroso climbing gear lube that I was tempted to order, that doesn't require more additive either.
At 90K miles on my car the oil that came out was pretty grey. I'd have liked to change it sooner.
If you get a hand pump, go with a self primeing pump.
I used 75 w 90 Valoline something, that I got at Walmart. I think it was five bucks. It specifically states in the label to NOT add more diff additive. There was mentioned a Moroso climbing gear lube that I was tempted to order, that doesn't require more additive either.
At 90K miles on my car the oil that came out was pretty grey. I'd have liked to change it sooner.
If you get a hand pump, go with a self primeing pump.
Melting Slicks
Joined: Oct 2000
Posts: 2,491
Likes: 1
From: prescott AZ
I suggest Mobil 1 synthetic gear oil for the diff and 4oz of the GM additive as even Mobil 1 recommends it with the synthetic. Jeeps that are ordered with the towing package come with synthetic in the diff so that tells you it is for HD use.
Make sure you drive the car 15 or 20 miles to get all the particles into suspension so they can be drained out.
Make sure you drive the car 15 or 20 miles to get all the particles into suspension so they can be drained out.
Elite Torch Red Member
Joined: Sep 1999
Posts: 57,805
Likes: 23
From: Exit 89 GSP,Lakewood,NJ The Land Of Mojo
Cental/South NJ Events Coordinator
CI 1-2-3-4-5-6-7-8-9-10-11-12 Vet
CI-II Burnout & Drag Champ
St. Jude Donor '03-'04-'05-'06-'07
Originally Posted by bogus
eh... it is done so infrequently, why create another leak point?
Race Director
Joined: Dec 2002
Posts: 13,348
Likes: 233
From: SCMR Rat Pack'r Charter Member..Great Bend KS
There is no drain plug on the differential.
There is no replacement schedule published by GM.
Tribal knowledge says change every 30K or so.
Suck and refill through the fill plug.
Use the GM recommended lube and LSD additive.
ZF has a drain plug.
All plugs on ZF and Dana are 17mm hex (Allen wrench).
They can ALL be a bear to break loose without destroying the drive hole, since they are aluminum and tend to stick in place.
Use the GM recommended fill or the Castrol/BMW motor oil that the ZFDoc likes so much.
It's not difficult if you have the requisite 17mm Allen socket and a big 1/2" drive breaker bar.
Good luck!
Larry
code5coupe
There is no replacement schedule published by GM.
Tribal knowledge says change every 30K or so.
Suck and refill through the fill plug.
Use the GM recommended lube and LSD additive.
ZF has a drain plug.
All plugs on ZF and Dana are 17mm hex (Allen wrench).
They can ALL be a bear to break loose without destroying the drive hole, since they are aluminum and tend to stick in place.
Use the GM recommended fill or the Castrol/BMW motor oil that the ZFDoc likes so much.
It's not difficult if you have the requisite 17mm Allen socket and a big 1/2" drive breaker bar.
Good luck!
Larry
code5coupe
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
Race Director
Joined: Feb 2003
Posts: 16,475
Likes: 270
From: Kingman AZ
Cruise-In VII Veteran
Cruise-In VIII
St. Jude Donor '06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16
In Gordon Killebrew's class for C4s he recommends TWO bottles of GM positraction fluid and then fill with Mobil 1 synthetic.
Melting Slicks
Joined: Apr 2004
Posts: 2,771
Likes: 138
From: cyberspace NY
you think sucking the fluid removes the particles way down on the bottom ???????????????
There is a kit with a plug specifally designed for the C4 . you drill and tap the case, then plug it. everything drains out like a normal rear.
There is a kit with a plug specifally designed for the C4 . you drill and tap the case, then plug it. everything drains out like a normal rear.
Le Mans Master
Joined: Sep 2003
Posts: 5,874
Likes: 0
From: Littleton CO
Originally Posted by rocco16
All plugs on ZF and Dana are 17mm hex (Allen wrench).
They can ALL be a bear to break loose without destroying the drive hole, since they are aluminum and tend to stick in place.
They can ALL be a bear to break loose without destroying the drive hole, since they are aluminum and tend to stick in place.
Good news is that it came out easy.
Drifting
Joined: Nov 2000
Posts: 1,428
Likes: 1
From: Jacksonville FL
Originally Posted by ed petrucci
i was thinking about putting LUCAS gear oil. that make great products for oil treaments, injector cleaner, tran treatment, power steering, gear oil too. GREAT stuff.
http://www.bobistheoilguy.com/images/lucas/lucas.htm
Premium Supporting Vendor
Joined: Aug 2001
Posts: 5,364
Likes: 38
From: King George VA
Originally Posted by jbransdorf
I also want to change the trans fluid as well for my six speed. I read in a book that 5w 50 (Synthetic) was ok to use. Any help would be appreciated here. I'm new at this but eager to learn. Car is a blast to drive. Thanks in advance
Jack
Jack
AMSOIL just came out with a new tranny fluid specifically designed for this type of application.
AMSOIL Synthetic Synchromesh Transmission Fluid (5w30)
The advantage of using a fluid like this vice a motor oil, is that as a tranny fluid, this fluid can use higher levels of anti-wear additives than is allowed for a motor oil which meets API standards.
AMSOIL also sells an excellent 75w90 which I use in my Z06 on the track:
AMSOIL Severe Gear Extreme Pressure Synthetic 75w90
You may find this handy if you do your own changes:
AMSOIL Hand Pump
Enjoy the car!
Request a Free AMSOIL Catalog
AMSOIL Ordering Information
AMSOIL Preferred Customer Program
__________________
C66 Racing #66 NASA ST2, SCCA T2
AMSOIL Dealer (Forum Vendor)
AMSOIL Preferred Customer Program (Members buy at Wholesale - a savings of about 25%)
C66 Racing #66 NASA ST2, SCCA T2
AMSOIL Dealer (Forum Vendor)
AMSOIL Preferred Customer Program (Members buy at Wholesale - a savings of about 25%)
Race Director
Joined: Dec 2002
Posts: 13,348
Likes: 233
From: SCMR Rat Pack'r Charter Member..Great Bend KS
Originally Posted by jrp
I can say with certainty that the fill plug on my D44 is 3/8 inch hex. ...it came out easy.
Sounds like a PO put in a different plug.
Larry
code5coupe
Instructor
Joined: Apr 2005
Posts: 173
Likes: 0
PS... about the amsoil MTF, is the ZF spec one of these?
AMSOIL Synthetic Synchromesh Transmission Fluid (MTF) replaces GM part # 12345349, 12345577, 12377916 and 1052931 as well as Chrysler part # 4874464 and 4874465. It meets GM specifications 9985648, 9986105 and 9985535 and Chrysler MS-9224 and MS-9417.
AMSOIL Synthetic Synchromesh Transmission Fluid (MTF) replaces GM part # 12345349, 12345577, 12377916 and 1052931 as well as Chrysler part # 4874464 and 4874465. It meets GM specifications 9985648, 9986105 and 9985535 and Chrysler MS-9224 and MS-9417.
Le Mans Master
Joined: Sep 2003
Posts: 5,874
Likes: 0
From: Littleton CO
Originally Posted by rocco16
I'l bet it's steel, too, right?
Sounds like a PO put in a different plug.
Larry
code5coupe
Sounds like a PO put in a different plug.
Larry
code5coupe
Last edited by jrp; Jun 13, 2005 at 01:17 AM.
Premium Supporting Vendor
Joined: Aug 2001
Posts: 5,364
Likes: 38
From: King George VA
Originally Posted by OdinsRage
PS... about the amsoil MTF, is the ZF spec one of these?
AMSOIL Synthetic Synchromesh Transmission Fluid (MTF) replaces GM part # 12345349, 12345577, 12377916 and 1052931 as well as Chrysler part # 4874464 and 4874465. It meets GM specifications 9985648, 9986105 and 9985535 and Chrysler MS-9224 and MS-9417.
AMSOIL Synthetic Synchromesh Transmission Fluid (MTF) replaces GM part # 12345349, 12345577, 12377916 and 1052931 as well as Chrysler part # 4874464 and 4874465. It meets GM specifications 9985648, 9986105 and 9985535 and Chrysler MS-9224 and MS-9417.