Differential Fluid Additive
Thread Starter
Pro
Joined: Feb 2021
Posts: 729
Likes: 317
From: Ashevile, NC
Differential Fluid Additive
About to change my diff fluid ('05) and I've read about using only the A/C Delco 88862624 fluid, however I've also seen guys say to use 4 oz. of an additive. What is the additive and what does it do? Thanks!!
Drifting
Joined: Apr 2016
Posts: 1,286
Likes: 611
From: DFW Texas
I believe GM updated the Diff fluid formula following the model year of your car and it has the additive included, so you do not want to add additional friction modifier to this one. (See the * under the viscosity rating on the bottle.) Also you may want to review Dano523 response in this thread for information. Check your rear axle nuts also, as they may be loose.
https://www.corvetteforum.com/forums...iguration.html
Cheers
GD
https://www.corvetteforum.com/forums...iguration.html
Cheers
GD
Racer
Joined: Sep 2002
Posts: 278
Likes: 14
From: Las Vegas, Nv
St. Jude Donor '14-'15
Important:DO NOT add any limited-slip additive (friction modifier). With this new fluid (Dexron LS Gear Oil 75W-90) it is no longer required to add friction modifier. If friction modifier is added, it will cause the fluid to lose some of it's friction reducing properties as well as reducing seal life.
Drifting
Joined: Sep 2014
Posts: 1,924
Likes: 392
From: Atlanta - - - - - Save the manuals
I have an 05 Z51 and I've changed the diff fluid. DON'T add friction modifier and ONLY use the correct ACDelco fluid. (If you don't you'll find out why I changed my fluid twice. )
Race Director
Joined: Dec 2013
Posts: 12,502
Likes: 3,629
Where you see the guys adding slip additive, it to lower the 100ftlbs of break away value for tight autocross tracks, where it allow them to come out of the corners harder before the diff does a full lock up on the way out (so they can drive the car like it's a Miata). The downfall, this allows the clutch packs to slip at a lower torque value, so instead of the clutch packs only lasting 20K when the car is used for such with out the added slip fluid, clutch pads end up wearing out in less than 10K from the extra slipping isntead.
As for road car, normal street driven only, the LSD clutch packs normally last 100K with just the stock OEM fluid alone.
Burning Brakes
Joined: Dec 2018
Posts: 893
Likes: 540
From: Ivanho,Illinois
2025 C6 of the Year Finalist - Modified
I changed the rear differential and trans fluid last year. For the rear differential I used 3qts of RedLine ShockProof Gear oil. No additional additives required.
Race Director
Joined: Dec 2013
Posts: 12,502
Likes: 3,629
Go do a hard burn out with drag slicks, and make sure that the LDS is locking up, not getting a one wheel only peg leg burn out. Only, make sure that the fluid is thin enough that it will allow clutch dust to wash from the disc packs, and that you don't end up with a lot of pack chatter from the fluid too thick.
Trust me, even a lot of strip guys have gone to what they thought was a better diff lube, only to find it it did not only lower the clutch lock up break away values on disc packs still in good condition, but in road course conditions where your working the clutch packs hard, and the fluid not flushing the built up dust out of the packs, and went back to the oem GM diff fluid.
Hell, have seen the same trick with M6 trans, only to find that the after market fluid does not play well with the syncro discs, to cause excess problems for the same reason. Hence fluid too thick/too slick, and as the syncro disc pad it trying to lock the gear to the same speed at its engagement gear, it not speed matching instead.
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Racer
Joined: Dec 2020
Posts: 355
Likes: 200
From: North TX
Dammit!
OK, officially feeling like I've been duped, or that I'm an idiot...either fits, and only one offends me.🤣
Went to a local dealership in Frisco, TX for new diff lube, and the old guy behind the desk sold me the 88900401 diff lube and additive instead of the newer p/n that has the additive mixed in. I drained and filled the diff yesterday and did my 8-10 figure 8s this morning in a local HS parking lot (with one of Frisco's finest boys in blue looking on...probably wondering if I was drunk at 7am!). Everything seems fine, and previous clunking was gone, but now I see this post.
I don't track my car (too chickenshit to break something, I guess)...should I buy the 88862624 and repeat the beating, or will I be fine with what I've done?
Went to a local dealership in Frisco, TX for new diff lube, and the old guy behind the desk sold me the 88900401 diff lube and additive instead of the newer p/n that has the additive mixed in. I drained and filled the diff yesterday and did my 8-10 figure 8s this morning in a local HS parking lot (with one of Frisco's finest boys in blue looking on...probably wondering if I was drunk at 7am!). Everything seems fine, and previous clunking was gone, but now I see this post.
I don't track my car (too chickenshit to break something, I guess)...should I buy the 88862624 and repeat the beating, or will I be fine with what I've done?
Drifting
Joined: Apr 2016
Posts: 1,286
Likes: 611
From: DFW Texas
I cannot find that part number that is recommended for a C6 diff, even with adding the modifier. You might call the parts dept. @ Classic Chevy in Grapevine and discuss what you were sold and if it is acceptable for your 07 C6. They are a high-volume Corvette dealership and you should get an acceptable answer from them. Otherwise, take the safe route & put in the proper diff fluid. (which is what I would do). Sorry you were mistreated by your local dealer.
GD
GD
Racer
Joined: Apr 2006
Posts: 435
Likes: 69
From: Houston Texas
OK, officially feeling like I've been duped, or that I'm an idiot...either fits, and only one offends me.🤣
Went to a local dealership in Frisco, TX for new diff lube, and the old guy behind the desk sold me the 88900401 diff lube and additive instead of the newer p/n that has the additive mixed in. I drained and filled the diff yesterday and did my 8-10 figure 8s this morning in a local HS parking lot (with one of Frisco's finest boys in blue looking on...probably wondering if I was drunk at 7am!). Everything seems fine, and previous clunking was gone, but now I see this post.
I don't track my car (too chickenshit to break something, I guess)...should I buy the 88862624 and repeat the beating, or will I be fine with what I've done?
Went to a local dealership in Frisco, TX for new diff lube, and the old guy behind the desk sold me the 88900401 diff lube and additive instead of the newer p/n that has the additive mixed in. I drained and filled the diff yesterday and did my 8-10 figure 8s this morning in a local HS parking lot (with one of Frisco's finest boys in blue looking on...probably wondering if I was drunk at 7am!). Everything seems fine, and previous clunking was gone, but now I see this post.
I don't track my car (too chickenshit to break something, I guess)...should I buy the 88862624 and repeat the beating, or will I be fine with what I've done?
Race Director
Joined: Dec 2013
Posts: 12,502
Likes: 3,629
Up and down the rabbit hole we go again, since if the fluid its too slick, peg leg burns out with the break away torque of the LSD clutch too low, and if the fluid it too thick, then LSD chatter from the packs not flushing crud out instead.
Hence is the whole reason that GM went to the 88862624 replacement fluid in the first place.
Racer
Joined: Dec 2020
Posts: 355
Likes: 200
From: North TX
I get it, Dano. I'm going to take the one bottle I have left, along with what's left of my pride, back to the damned dealer that sold it to me in the first place and get the right stuff. It's really too easy to drain and refill to not do it the right way with the right goo. Just pisses me off that I have to come to a web forum (no offense to anyone here...*most* of what I've read here has been very informative, and it's part of my morning routine along with eggs, toast, and coffee) to get the information that those who SELL the cars can't give me.
Thanks for your input!
Thanks for your input!
Race Director
Joined: Dec 2013
Posts: 12,502
Likes: 3,629
Would take the receipt, and what you have left of unused lube back to the dealer, and have them give you the correct lube for the C6 at no cost instead (so your not paying for a second time, for the correct diff lube from them).
Hence the 88862624 has been the correct lube for the C6 since 2006, and even the 2005 cars that the different lube had to be changed out to 88862624 to keep the diff's from making chatter noise (clutch packs not flushing themselves out correctly from the OEM fluid before 2006 begin too thick), was done at the dealers as part of a TSB for free.
Hence the 88862624 has been the correct lube for the C6 since 2006, and even the 2005 cars that the different lube had to be changed out to 88862624 to keep the diff's from making chatter noise (clutch packs not flushing themselves out correctly from the OEM fluid before 2006 begin too thick), was done at the dealers as part of a TSB for free.
6th Gear
Joined: Apr 2019
Posts: 6
Likes: 1
From: Columbus, OH
Has anyone used Mobil 1 Synthetic Gear Lube LS? https://www.summitracing.com/parts/m...+5ba2890b95770
Race Director
Joined: Dec 2013
Posts: 12,502
Likes: 3,629
Again, use the correct fluid, since even GM take two tries to get the fluid correct so it was not too thick or slick to cause chatter or lessened clutch lock up torque values.
Hence was an TBS to replace the diff fluid in the 2005 and 2006 models with the 4034, since the fluid used for these was too thick, and was not flushing the dust out of the LDS clutch packs/was causing chatter problems.
Hence was an TBS to replace the diff fluid in the 2005 and 2006 models with the 4034, since the fluid used for these was too thick, and was not flushing the dust out of the LDS clutch packs/was causing chatter problems.
Melting Slicks
Joined: Dec 2017
Posts: 2,008
Likes: 916
From: Baie-D'Urfe, Quebec
2023 Corvette of the Year Finalist - Unmodified
2022 C6 of the Year Winner - Unmodified
So I've used both the GM A/C Delco 88862624 (with friction modifier included) as well as Amsoil Severe Gear 75w90 (with the separate Amsoil slip-lock additive).
Honestly, no discernible difference to me for street or track use.
But, I do flush it out every 600 or so 'track' miles....
When I bought my car in 2018, it had only 6k miles on it, presumably still with the original factory fill from 2008 in it. It had been serviced annually at a GM dealer (only average 600 miles/yr), but I guess they only changed engine oil, based on the condition of the diff oil when i drained it out.
The car did seem to have a slight diff chatter when making slow parking lot type turns and the fluid was pretty dark and smelled bad.
That condition disappeared with the Amsoil, as well as a subsequent AC Delco fill with the newer, improved elixir.
I only used the Amsoil because I was ordering from them anyway...and when draining, both look about the same condition, but of course that's kinda vague because I go to different tracks, temperatures, conditions etc.
Honestly, no discernible difference to me for street or track use.
But, I do flush it out every 600 or so 'track' miles....
When I bought my car in 2018, it had only 6k miles on it, presumably still with the original factory fill from 2008 in it. It had been serviced annually at a GM dealer (only average 600 miles/yr), but I guess they only changed engine oil, based on the condition of the diff oil when i drained it out.
The car did seem to have a slight diff chatter when making slow parking lot type turns and the fluid was pretty dark and smelled bad.
That condition disappeared with the Amsoil, as well as a subsequent AC Delco fill with the newer, improved elixir.
I only used the Amsoil because I was ordering from them anyway...and when draining, both look about the same condition, but of course that's kinda vague because I go to different tracks, temperatures, conditions etc.