Advice on C7 differential fluid change

[rfh928]

Hi...I have a 2019 M7 with non electronic LSD, that I would like my indie garage to, amongst other services, change the rear differential fluid. Running into a bit of a roadblock with the GM recommended fluid (below) that contains an LSD additive (Canadian part # is the same with a '5' as the last digit). Even amongst GM dealers, it is apparently difficult to find, and the one dealer who offered to order it would only do so if I bought a whole case of 12x 1L bottles.

Couple of questions for anyone who has had experience with this...any sources for this fluid in the GTA? Also...although my owners manual has some fluid capacities listed, the differential is not one of them. Checking online, it seems that it takes about 3L of fluid...is this correct?

Thanks in advance...Robert

 

[Afterimage]

The diff takes around 3L, u can't really overfill it as it would simply spew out of the fill hole if u add too much.

I've changed mine 3 times already and plan to do 1 more in the 9500kms or so of driving since getting my ZR new in 2019.

Phone around, a Toronto dealer will have it in stock. Making u order 12 of them is simply BS IMO.

 

[rfh928]

The diff takes around 3L, u can't really overfill it as it would simply spew out of the fill hole if u add too much.

I've changed mine 3 times already and plan to do 1 more in the 9500kms or so of driving since getting my ZR new in 2019.

Phone around, a Toronto dealer will have it in stock. Making u order 12 of them is simply BS IMO.

Thanks for the information, really appreciate it. That's a good idea...I'll get on the phone and check until I find a dealer that has them or is willing to order 3 of them. I wonder if it was because it was my mechanic who tried to source it out for me...that they would only sell them a case. Just curious since you've done several diff fluid changes...where did you get your fluid from? Thanks again!

 

[Afterimage]

I got mine from Humberview since its close to where I live. I haven't checked lately but they should have it in stock.

Ask for Johnny in parts he'll hook u up.

 

[Late Life Crisis]

I used synthetic gear oil in my diff, got from Cdn Tire, their Motomaster brand is repackaged Shell. I have the base Stingray no eLSDso the friction modifier in the GM fluid isn’t required for the non-electronic LSD. I also had my mech change over the MT7 fluid, I used Royal Purple manual trans fluid (marketed for MT’s using Auto Trans oil like the C7 MT. Also Cdn Tire had that on the shelf. Made a real difference in shifting, much smoother and quieter than with the OEM fluid.

Send me a PM if questions.

LLC

 

[rfh928]

I got mine from Humberview since its close to where I live. I haven't checked lately but they should have it in stock.

Ask for Johnny in parts he'll hook u up.

Thanks...I live on the Scarborough/Pickering border so will try dealers out east first, but appreciate the referral...I'll touch base with Johnny though if I can't come up with any out here.

 

[rfh928]

I used synthetic gear oil in my diff, got from Cdn Tire, their Motomaster brand is repackaged Shell. I have the base Stingray no eLSDso the friction modifier in the GM fluid isn’t required for the non-electronic LSD. I also had my mech change over the MT7 fluid, I used Royal Purple manual trans fluid (marketed for MT’s using Auto Trans oil like the C7 MT. Also Cdn Tire had that on the shelf. Made a real difference in shifting, much smoother and quieter than with the OEM fluid.

Send me a PM if questions.

LLC

Thanks for this information also, very interesting. Are you sure about the additive not being required? In my previous C3 and C5 they had a non electronic LSD also, and back then I was advised to use both the gear oil and a separate LSD additive, similar to the one now incorporated into the Delco oil. I've heard good things about the Royal Purple MT fluid...not getting that changed yet but will consider it when the time comes. Thanks again!

 

[OL Yeller]

I replaced my gear oil in my C5 (assuming the C7 is similar set up) with the Royal Purple 75W90, great product...very easy to change, all you need is a pump similar to the one pictured here. drain the old and fill till it runs back out of the fill hole.

 

[19C7GS]

Why is everyone replacing their diff fluid so often? Is there a memo I missed? Manual says every 72,000km.

Or is it because of tracking?

 

[rfh928]

I replaced my gear oil in my C5 (assuming the C7 is similar set up) with the Royal Purple 75W90, great product...very easy to change, all you need is a pump similar to the one pictured here. drain the old and fill till it runs back out of the fill hole.

Thanks for this information. I haven't done my own auto maintenance in many years, but have an honest & reasonably priced local indie garage that does all of our servicing for us.

 

[rfh928]

Why is everyone replacing their diff fluid so often? Is there a memo I missed? Manual says every 72,000km.

Or is it because of tracking?

My 2019 manual says the same. I've had it for 3 years, just out of the base warranty, and have 11,000 kms on it. I may never get to 72K's...so figured I would do the first diff change now, and then every 5 years thereafter. I don't track the car, but it's my daily driver for the 8-9 non-winter months.

 

[YFCvii]

Did mine at 5 years with a good Corvette friend who has the “know how” and the tools. Looking at the fluid that we drained and checking the plug for anomalies is reason for why I will do this every 5 years now.
Nothing like the aroma of rear diff fluid





Pictures are 1000 words on threads like this …
Wish more would post their photos.

 

[Afterimage]

That gunk will always be there whether you change it every year or every 5 years or longer you'll just have more of it on the factory mag plug if you wait longer to change it.

People change it often especially when you get the car new is due to the fact the factory for the most part didn't fill the rear diff with the right amount of fluid at the factory and most of that "gunk" is from break in of the rear end gears and stuff in the diff. Some people with "new" C7 purchased have measured diff fluid drained out as only around 2.5L or a bit more but below the 3L that usually drains out. The "new" fluid that is drained out from an initial drain and fill is also very black and yucky looking even just after putting 1000kms on the car.

My car was this case. I drained it out after putting 1k on the car back in 2020 and only 2.5L came out and very dark looking and added 3L in before it started coming out the fill hole. The next year drained all 3L out the fluid looked better but still not the new gold looking oil. Spring 2022 drained it out again much better looking fluid and as stated earlier will do 1 more next year then I should be good to go a few years before changing it.

If you track the car manual says to drain and refill after each event.

Did you see this post I did last year sometime???

When you change your rear axle fluid..............

When you remove the drain and fill plugs for the rear axle there is a round rubber looking flat washer. It turns out that this washer is not available separately from the dealer. It is only available if you purchase the complete drain or fill plug (they are the same part regardless of where they...

canadiancorvetteforums.com

 

[rfh928]

That gunk will always be there whether you change it every year or every 5 years or longer you'll just have more of it on the factory mag plug if you wait longer to change it.

People change it often especially when you get the car new is due to the fact the factory for the most part didn't fill the rear diff with the right amount of fluid at the factory and most of that "gunk" is from break in of the rear end gears and stuff in the diff. Some people with "new" C7 when purchased have measured diff fluid drained out as only around 2.5L or a bit more but below the 3L that usually drains out. The "new" fluid that is drained out from a initial drain and fill is also very black and yucky looking even just after putting 1000kms on the car.

My car was this case. I drained it out after putting 1k on the car back in 2020 and only 2.5L came out and very dark looking and added 3L in before it started coming out the fill hole. The next year drained all 3L out the fluid looked better but still not the new gold looking oil. Spring 2022 drained it out again much better looking fluid and as stated earlier will do 1 more next year then I should be good to go a few years before changing it.

If you track the car manual says to drain and refill after each event.

Did you see this post I did last year sometime???

When you change your rear axle fluid..............

When you remove the drain and fill plugs for the rear axle there is a round rubber looking flat washer. It turns out that this washer is not available separately from the dealer. It is only available if you purchase the complete drain or fill plug (they are the same part regardless of where they...

canadiancorvetteforums.com

Thanks for this additional information as well as your detailed former post on this topic. That was my thinking to change it way before the 72,000 kms suggested by GM as I figured there might be some gunk from initial use in there...which you've shown is definitely the case.

 

[rfh928]

Just wanted to post an update...I made a couple of calls this morning and found that Cowan GM in Bowmanville had 10 bottles of the diff fluid in stock. As my son lives out there, he can pick it up for me and I'll book an appointment for my garage to install it. Thanks again to everyone who passed along their very helpful advice!

 

[Afterimage]

Make sure your tech pull the drain plug and let it drain till a bare drip comes out.

Most shops even if u feel they do a great job will pull the drain plug and pop it back in when there's a slow steady drip.

I like to let it drip till anything barely comes out, being I work on it myself in the garage I can leave it to drain ALA I want, in a shop probably not possible but get them to drain as much out as possible. If u have multiple stuff being done drain first and let it keep draining while they work on the other jobs.

 

[rfh928]

Make sure your tech pull the drain plug and let it drain till a bare drip comes out.

Most shops even if u feel they do a great job will pull the drain plug and pop it back in when there's a slow steady drip.

I like to let it drip till anything barely comes out, being I work on it myself in the garage I can leave it to drain ALA I want, in a shop probably not possible but get them to drain as much out as possible. If u have multiple stuff being done drain first and let it keep draining while they work on the other jobs.

Good point...yes I am going to have the brake & clutch fluid changed at the same time, so will pass along your suggestion to let the diff drain as long as possible. Thanks!

 

[YFCvii]

If one is still under the GM Factory Powertrain warranty and/or have an extended warranty, you might consider that “your shop” be a “gm corvette dealership” as any related warranty claim may require proof of “certified” tech service and parts/supplies source receipts. I am past 5 years now - so it no longer matters. JMO

I lost two cylinders with a GM truck at 4yrs & 10months and proof of service/maintenance absolutely saved my a$$. Food for thought.

 

[rfh928]

If one is still under the GM Factory Powertrain warranty and/or have an extended warranty, you might consider that “your shop” be a “gm corvette dealership” as any related warranty claim may require proof of “certified” tech service and parts/supplies source receipts. I am past 5 years now - so it no longer matters. JMO

I lost two cylinders with a GM truck at 4yrs & 10months and proof of service/maintenance absolutely saved my a$$. Food for thought.

Yes I'm just past the 3 year base warranty, but still have close to 2 years on the powertrain warranty. I am still using my local GM dealer for oil changes because of this. I guess the differential is under the powertrain warranty...so if a licensed mechanic uses the GM recommended fluid would they be able to deny coverage in case of any issues? Thanks for your comments.

 

[YFCvii]

Yes I'm just past the 3 year base warranty, but still have close to 2 years on the powertrain warranty. I am still using my local GM dealer for oil changes because of this. I guess the differential is under the powertrain warranty...so if a licensed mechanic uses the GM recommended fluid would they be able to deny coverage in case of any issues? Thanks for your comments.

Exactly how I see it too (likely many
others same) … it played
a huge factor with a major warranty
event for me.
Happy you sourced your supplies