Diff Friction Modifier: When is it really needed?

Status
Not open for further replies.
C

chucky2

Joined
Apr 17, 2003
Messages
398
Location
Chicagoland, IL USA
Friction Modifier: When is it really needed?


My dad has a rumble coming from the read end of his 2000 Ford Expedition Eddie Bauer w/ 5.4L, A4WD, and air leveling suspension.

The owners guide says this:

"Your vehicle’s rear axle is filled with a synthetic rear axle lubricant and is considered lubricated for life. These lubricants are not to be checked or changed unless a leak is suspected, service is required or the axle has been submerged in water. The axle lubricant should be changed any time the axle has been submerged in water. Add 118 ml (4 oz.) of Additive Friction Modifier C8AZ-19B546-A or equivalent meeting Ford specification EST-M2C118–A for complete refill of Traction-Lok axles."

Now, on Amsoil's site, it lists two type of rear diffs for that engine, one takes the modifier, the other doesn't. For the diff that doesn't take the modifier, obviously don't add any. For the one that takes the modifier, Amsoil doesn't say either way to add it...but that they make note of it seems to suggest it should be added. On the 75W-140 Severe Gear page, it does have this little blurb, "AMSOIL SEVERE GEAR® is compatible with most limited slip differentials. If limited slip differential chatter occurs, add AMSOIL Slip-Lock™ friction modifier additive." So that seems to suggest not adding it unless there's a problem.

Royal Purple and Redline say they don't need it.

Not sure about Mobil-1.

Really, I'd like to use either Specialty Forumlations (which I don't think is back in business yet), Redline, or Amsoil.

I know which viscosity I need, I know how much I need to order, what I don't know is just whether I need this FM...and that's k1lling me because I'm thinking the rumble he's getting is from the FM not having been added - or added in too small of an amount, or, maybe just degrading over time - so I want to make sure I get this FM thing straightend out before I change it.

Anyone have thoughts on this???

Chuck
 
So this is happening before you have done anything to the oil? I just want to confirm. If it is something that just started happening, the diff might be torn up - or it could be something completely different.

If you changed the oil and you are hearing rumbling or chattering (however you want to describe it) when you are making turns, then you need the additive in there.

Some oils say that they MIGHT not need a friction modifier, but it depends on the differential. I'd add it in small doses until it goes away.
 
Last edited:
Yeah, sorry about that Laminar Lou, I should have been more clear about that:

When starting from a stop or a very slow speed, many times the rear diff will groan and sort of rumble. I found after searching online that someone had fixed this by changing the rear diff fluid, seems that the clutch's in the diff were what was causing the problem.

So, I don't want to go get some lube, change it out, and then have it still happen because I didn't add the FM.

From what I've read, when you need the FM, you're supposed to add it first after putting the diff cover back on, that way it gets all in. Then you add the normal diff lube until it's filled. Else, you end up either overfilling and/or not getting the correct amount of FM in there.

That's why I want to get it straight first if I really need the FM or not...

Chuck
 
Thanks for the clarification, I can only say that I added the FM a day later than the oil and it worked almost immediately. I too had the same dilemma as you, so that is what I did. If you just add it all it once, you run the risk of making the "limited slip" portion of your limited slip differential inactive (or less effective).

I am not totally sure about having to have it in there before you put the cover on to "get it all in".

That was a Toyota limited slip, and the Ford may have some requirement that I don't know about. All I can offer is that adding it later worked fine in the Tundra.
 
Yes that's correct - The Severe Gear line of Amsoil diff lubes have a light amount of FM blended in. Some diffs need more in application. The Long Life line does not have the FM, and always requires the secondary FM additive.

I hope this clarifies it a bit.
 
Laminar Lou- Cool man, thanks for the info! I think that's what I'll do then. Maybe I'll intentionally underfill the diff by a bit, that way if it needs some, I can add and not overfill the diff.

Pablo- Sounds like I may be placing another order with you real soon. How's the Severe Gear line working out?

Chuck
 
i work at a ford dealer in the parts dept. just letting you know we had a expedition, close to the same year come in last week with teh exact same complaint. the tech took the cover off and one of the carrier bearings was taking itself apart. it needed a whole rebuild.
 
That's troubling you say that bdcardinal, because my dad (who's got 35 years in with Ford, most at Ford's Chicago Assembly Plant as a Millwright, so he does a lot of PM's on equipment), is betting it's a bearing.

I was really hoping the fluid fixed the problem before we had to either have someone tear into it, or tear into it ourselves.

Fluid is easy...I hope I'm right and he's wrong...
smile.gif


Chuck
 
Severe Gear is an awesome line-up. Not one complaint, huge step forward in formulated gear oils.

I'm glad Mr. Cardinal stepped up. I was going to mention that maybe this is a “non-fixable” with fluid noise. Sometimes FM do indeed quiet LS noises, but if it’s a bearing and the noise has started, there isn’t a miracle lube that will “rework” the problem.
 
bdcardinal- Thanks man, that's great! I'll have to bookmark that site for sure!

Pablo- Yeah, I totally realize this my not be able to be fixed with a lube change. It more than likely is mechanical, but before we spend some serious ching on that fix, I'd like to try a cheap fix first. If it doesn't work then I'll drain the Severe Gear out of there, put in some cheap fluid, and he can take it in to get fixed. I'll put the Severe Gear back in after it's clear they fixed the problem.

Who knows though, we may end up trying to fix it if the price is too high...one Stealership was talking $1000 for their guess on the problem...just crazy...

Chuck
 
bdcardinal- Thanks man, that's great! I'll have to bookmark that site for sure!

Pablo- Yeah, I totally realize this my not be able to be fixed with a lube change. It more than likely is mechanical, but before we spend some serious ching on that fix, I'd like to try a cheap fix first. If it doesn't work then I'll drain the Severe Gear out of there, put in some cheap fluid, and he can take it in to get fixed. I'll put the Severe Gear back in after it's clear they fixed the problem.

Who knows though, we may end up trying to fix it if the price is too high...one Stealership was talking $1000 for their guess on the problem...just crazy...

Chuck
 
Quote:

I'll put the Severe Gear back in after it's clear they fixed the problem.


Click to expand...

Not a good idea. If there is a bearing problem, the oil most likely will full of wear metals, which will not be good for your re-build.

Use fresh oil only.
 
Tempest- Shoot man, that's a good point, didn't think of that. You really think it'd be that contaminated in 150 miles to not be able to be used again? We ought to know if the problem has fixed itself really in a day of driving...I just say three because if we have to tune the FM, it may take longer.

Jim Allen- If we decide to tackle the job ourselves, I'll be ordering your book. We'll need all the help we can get...
smile.gif


Chuck
 
Chuck, the only time I've ever seen friction modifiers needed in an automotive diff, is for those diffs with a clutch pack style limited slip mechanism. There are other types of limited slip (cam lock, etc..) that do not require a tube of FM.

Joel
 
just so everyone knows, almost every Expedition came with a Ford Traction-Loc differential which is a clutch type LSD. some had open rear ends. if you look at the tag that is bolted onto the diff cover there will be a bunch of numbers. one will be a set that gives the gear ratio, usually 3 55, 3 73. if there is a L in there then it is a Trac-Loc.
 
JTK- Yep, I think his has a clutch style as bdcardinal explains below. My Ford Ranger FX4 Level II has a Torsen that works extremely well, and the good thing about those is that their operation could care less about FM, it's all mechanical.

bdcardinal- Thanks again for the info! This is a 4WD Eddie Bauer from 2000, so I really don't think it'd have an open rear...which means it must have the Traction-Loc.

Chuck
 
Status
Not open for further replies.

Similar threads

O
What gasket for 2014 f150 2wd Differential.
Replies
6
Views
296
tcp71
C
Mercury Grand Marquis LS 1998
Replies
17
Views
1K
CARLOS DE LA CRUZ
EMOTO
2017 JKUR (Wrangler Rubicon) Locking Diff Fluids?
Replies
1
Views
259
Rand
S
75W-90 Synthetic WITHOUT Limited Slip Additive - Mobil Delvac?
2
Replies
26
Views
2K
Spddm0n
T
Friction modifier for eBay Eaton posi
Replies
12
Views
1K
theraymondguy
Back
Top