75w-140 or 85w-140 hot climate

[Miker]

I took my car to a hot rod shop today and got a recommendation for rear diff oil.
They said because where we live (it's going to be 104 here tomorrow) a thicker oil will quiet down the gear lash being amplified with an aluminum drive shaft. They recommended any 85w-140 and a bottle of the Ford friction modifier.
Now that I am home and doing some reading I am seeing the 75w-140 is synthetic and the 85w-140 is dino. The diff oil in it probably has about 50K on it now and was done at a Ford dealership in 2012 so it's probably the 75w-140.
I'm sure these guys know their business but has anyone here tried or heard of this? It never gets close to freezing here.

 

[GriffX]

I know somebody who changed to 85w140 in his Truetrac diff to dampen the specific clicking noise of it and it worked.

 

[Miker]

That's exactly what I am trying to do. Thank you for posting that.

 

[Pentalab]

I took my car to a hot rod shop today and got a recommendation for rear diff oil.
They said because where we live (it's going to be 104 here tomorrow) a thicker oil will quiet down the gear lash being amplified with an aluminum drive shaft. They recommended any 85w-140 and a bottle of the Ford friction modifier.
Now that I am home and doing some reading I am seeing the 75w-140 is synthetic and the 85w-140 is dino. The diff oil in it probably has about 50K on it now and was done at a Ford dealership in 2012 so it's probably the 75w-140.
I'm sure these guys know their business but has anyone here tried or heard of this? It never gets close to freezing here.

You can get either in synthetic or dino.

I installed the Eaton tru-trac LSD into my 2010 GT, and Eaton sez NOT TO USE SYNTHETIC, nor friction modifiers. What I used was 75-140...dino oil. It's sold by Lucas and several others.
The oem style LSD's require synthetic gear oil, plus friction modifiers. OEM gear oil was 75W-140.

 

[86GT351]

Forgetting the viscosity numbers. Thicker oil will generally help with noise reduction. Always add Friction Modifier.

 

[07 Boss]

Forgetting the viscosity numbers. Thicker oil will generally help with noise reduction. Always add Friction Modifier.

No, you should never add friction modifier to a helical gear differential.

Both of those gear oils will have the same viscosity when up to temp. The difference is one will be a little thicker when cold, but once operating temps are achieved they will be the same thickness.

 

[Miker]

You can get either in synthetic or dino.

I installed the Eaton tru-trac LSD into my 2010 GT, and Eaton sez NOT TO USE SYNTHETIC, nor friction modifiers. What I used was 75-140...dino oil. It's sold by Lucas and several others.
The oem style LSD's require synthetic gear oil, plus friction modifiers. OEM gear oil was 75W-140.

Required as in recommended? I know Ford recommended 75w-140 synthetic but dino will work just fine in the stock LSD as far as I understand.

Forgetting the viscosity numbers. Thicker oil will generally help with noise reduction. Always add Friction Modifier.

The hot rod guys specifically said only use the Ford friction modifier.

 

[Pentalab]

Stock LSD's require 75W-140 full synthetic AND friction modifier.

The Eaton Tru-trac LSD operates on friction, hence plane jane 75W-140 DINO oil used....and NO friction modifiers.

 

[Miker]

I am actually pretty excited to try this. The noisy drive train has always baffled me. What is weird is sometimes it would be perfect with no noise. I am thinking that could have been the diff clutch packs intermittently working correctly. I am going to run the 85w-140 Lucas dino and 1 bottle of the Ford X3 FM. I have read that some recommend 2 bottles of the X3? My understanding is that it takes slightly more than 2 qts and 1 bottle of the X3. Should I use 1 or 2 of the X3? If I used 2 it would seem that 2 qts of the Lucas would be enough.
So now I have to source the gasket and parts. I will clean both surfaces. Do I install the gasket dry or should I use some sealer too?
Also is it OK to spray the gears down with brake clean if they look to need it?

 

[JC SSP]

I always thought the friction modifier was specifically used for “clutch style” locking differentials like the stock ones.

I have an Auburn Pro in my little 87’ coupe which is spring activated. I still put in a small bottle of friction modifier. I don’t think it will hurt anything in there…

I use 75W-140 royal purple synthetic but might try the thicker one when I do my next drain and fill.

 

[GlassTop09]

So now I have to source the gasket and parts. I will clean both surfaces. Do I install the gasket dry or should I use some sealer too?

Get this gasket & don't look back:

https://www.amazon.com/Differential-Cover-Gasket-Rubber-Coated/dp/B07Z8X85G1/ref=sr_1_3?crid=3O50AY8AX6RCV&dib=eyJ2IjoiMSJ9.dcD1yV6090cqnzow5S63JPntxGvcFhZRJylljAVJUjecEN1WAYgs1ukIHsXc5XSCcP-BdnXTJ6hbxd55

These Lube Locker F880 gaskets install dry & can be reused several times w\o issue.
Tq to 15-20 ft lbs is all you'll need.

If you already don't have 1, I'd also recommend picking up a FR M-4033-KA 8.8" "Track Pack" Finned Diff Cover to keep your gear oil as cool as you can..........this will also go a long way into maintaining the gear oil's hot viscosity over time by further lessening the issue of oil overheating causing breakdown, regardless of whether it's synthetic or GL-5 dino (if going dino oil, GL-5 spec is what you want to get..........IMHO, Lucas HP 85W-140 GL-5 dino oil is the king daddy product of all the 85W-140 GL-5 products out there).

If you do get this cover, it comes w\ a 1/4" NPT plug so pull your axle vent out of the PS axle tube, install this plug in the axle tube & move the axle vent to the top of this finned cover (has an internal baffled 1\4" NPT axle vent port) & kiss any potential future hot axle oil puke out goodbye. Also makes future rear axle oil changeouts much easier as this cover has a drain & fill plug in it (these 2 plug locations are also where a GT500 rear diff cooler's lines will mount if desired in future).

My 2 cents added...................

Hope this helps.

 

[GriffX]

The Motorcraft 75w140 has no friction modifier in it, therefore the additive, I assume. For me it was very hard to get an oil from different brands without limited slip additive already included to use in my Truetrac. I used a paper gasket with no silicon or hylomar or else and re-used it 3 times with no problem.
I have the finned Ford cover from the 2013+ and there the lower plug is not enough to open for fluid change. There is a lower "sump" in the housing right below the ring gear which in my case was full of metal slime. No fun to get it out with towels.

 

[Miker]

Are there any clearance issues wit this cover? FRM-4033-KA

 

[GlassTop09]

Are there any clearance issues wit this cover? FRM-4033-KA

Tis why I'll only recommend this specific finned diff cover...........this is a genuine Ford SVT designed\built part & will clear all Ford designed PHB's--including the OEM units--thus will clear most aftermarket PHB's as most are built to fit this S197 chassis design specs.

As long as the rear axle LCA hole centers are at OEM S197 LCA center distances (so the rear axle isn't pushed further rearward.......something that gets overlooked IMHO.......especially when adjustable LCA's are used but also when using fixed LCA's as well......I know this 1st hand as some aftermarket LCA's do get past QA\QC checks that have longer center distances than OEM S197 spec), you should have no issues w\ clearance using this FR M-4033-KA cover.

Hope this helps.

 

[GriffX]

Are there any clearance issues wit this cover? FRM-4033-KA

No, the only difference I saw between the Ford Performance and the regular was that there were no bolts included, it needs longer ones. But, it was way cheaper. I payed below 100$. And I moved the axle vent to the top of it.

PS: Looks like the price has become ridiculous.....

 

[Miker]

No, the only difference I saw between the Ford Performance and the regular was that there were no bolts included, it needs longer ones. But, it was way cheaper. I payed below 100$. And I moved the axle vent to the top of it.

PS: Looks like the price has become ridiculous.....

$185 at LMR and it comes with the hardware but no gasket. They have a lube locker gasket for $27

 

[Miker]

Forgetting the viscosity numbers. Thicker oil will generally help with noise reduction. Always add Friction Modifier.

Get this gasket & don't look back:

https://www.amazon.com/Differential-Cover-Gasket-Rubber-Coated/dp/B07Z8X85G1/ref=sr_1_3?crid=3O50AY8AX6RCV&dib=eyJ2IjoiMSJ9.dcD1yV6090cqnzow5S63JPntxGvcFhZRJylljAVJUjecEN1WAYgs1ukIHsXc5XSCcP-BdnXTJ6hbxd55

These Lube Locker F880 gaskets install dry & can be reused several times w\o issue.
Tq to 15-20 ft lbs is all you'll need.

If you already don't have 1, I'd also recommend picking up a FR M-4033-KA 8.8" "Track Pack" Finned Diff Cover to keep your gear oil as cool as you can..........this will also go a long way into maintaining the gear oil's hot viscosity over time by further lessening the issue of oil overheating causing breakdown, regardless of whether it's synthetic or GL-5 dino (if going dino oil, GL-5 spec is what you want to get..........IMHO, Lucas HP 85W-140 GL-5 dino oil is the king daddy product of all the 85W-140 GL-5 products out there).

If you do get this cover, it comes w\ a 1/4" NPT plug so pull your axle vent out of the PS axle tube, install this plug in the axle tube & move the axle vent to the top of this finned cover (has an internal baffled 1\4" NPT axle vent port) & kiss any potential future hot axle oil puke out goodbye. Also makes future rear axle oil changeouts much easier as this cover has a drain & fill plug in it (these 2 plug locations are also where a GT500 rear diff cooler's lines will mount if desired in future).

My 2 cents added...................

Hope this helps.

So I am ordering the M-4033-KA 8.8" "Track Pack" Finned Diff Cover. Going with the 85w-140 dino Lucas. Should I add 1 or 2 bottles of the X3 Ford friction modifier?

 

[JC SSP]

Some lubes come with friction modifier already included.

 

[Miker]

Some lubes come with friction modifier already included.

Thanks for that. I checked the Lucas sight and it does say,
"Our formulation contains an embedded friction modifier for use in standard or limited slip differentials."
Now I need someone with more experience to say if I even need the ford X3 FM or not.

 

[07 Boss]

Stock LSD's require 75W-140 full synthetic AND friction modifier.

The Eaton Tru-trac LSD operates on friction, hence plane jane 75W-140 DINO oil used....and NO friction modifiers.

Its the other way around. The Eaton TrueTrac is a helical gear differential, not friction clutch, so you don't use friction modifier. Friction modifier is needed for clutch style limited slip differentials like our stock traction loc. Friction modifier is used in friction clutch type differentials to help smooth out the operation and prevent chattering while turning tightly.

I use full synthetic and extra friction modifier for my Auburn Pro. I use full Dino oil with no friction modifier for my trutrac.

If you want to run a thicker oil then look at the second number. There is really no difference between 75w-140 and 85w-140 when at operating temp. If you want to use a thicker oil look for like 75w-90 gear oil. It will remain thicker after it heats up than the 75w-140.

Miker, do you have a true trac or the stock traction lok?