Differential fluid change and the addition of friction modifier

[lochnessmonster]

Hey guys,

So, as I stated in an earlier thread, I decided to change my differential fluid last Friday while I was changing my transmission fluid. Being the Viper noob that I am, I thought all I had to do was fill the diff back up with my Pennzoil 75W-140 and call it a day just like all of the other cars I've owned. Um, nope.

I was driving the car yesterday and at slow speeds with the wheel at or near lock, I could hear a terrible grinding/groaning sound coming from the car, which I could actually feel. After a little research, I realized that I should have added the friction modifier (4oz bottle) to the diff fluid when I made the change. So, I went to Napa, bought a $10.00 bottle, jacked the car back up last night (arrrggggg), used my wife's measuring cup from the kitchen to meter out 4oz of diff fluid (she didn't seem to like that) and added the modifier.

Much to my amazement, the sound is completely gone!!!!! So, for any noobs like me who are going to change out your diff fluid, if the fluid you are putting in doesn't already have the friction modifier in it, it is an absolute must. You really won't like the sound you hear from your diff if you don't.

[Steve-Indy]

Glad it worked out...but a search here first could have saved time. Also, since the Viper World is made up of lots of nice, knowledgeable folks, never hesitate to call someone before trying a new procedure. "ready, aim, shoot" is much preferred over "ready, shoot, aim" !!

[FrgMstr]

I always double up on the friction modifier. Never an issue since I started doing that.

[Steve-Indy]

Doubling the friction modifier in a Gen IV stock diff is reportedly associated with possible issues per some experienced techs.

[XSnake]

The mobil 1 stuff has the friction modifier in it already which is nice

[lochnessmonster]

In my noob defence, why doesn't the owner's manual state that the friction modifier needs to be added if it isn't in the fluid you are adding? I read the manual. It said 1.4-1.5 liters/quarts of 75W-140 but no mention at all of the friction modifier. It would have been nice to know. As far as I am concerned, the manual should have made the necessity of this additive VERY clear, since it has an obvious detrimental effect on the diff clutches.

[ViperPete]

How many miles/long is diff fluid good for in these cars?

[Steve M]

How many miles/long is diff fluid good for in these cars?

Assuming the differentials are the same Gen 4 vs. 5, my car was 3 years old with about 9,500 miles on it when I bought it, and it needed changed (the front tires would skitter across my driveway making a sharp turn when cold). I don't put many miles on my car, so I'll change it probably every 2 years or so. If I tracked my car, I would change it probably after every 1-2 events...these things don't hold much fluid at all, so it doesn't take much to cook it.

[ViperPete]

I don't understand how you would have a front wheel problem with the rear diff.

[SRT BILL]

Monster was the Pennzoil 75w-140 synthetic oil?? Also have you changed the trans oil and if so what did you use.

[Steve-Indy]

Lochnessmonster, sorry about my post's tone.

From page 324 of my printed 2014 Viper Owners Manual:

Rear Axle..."We recommend you use Castrol SAF-XJ/SAE 75W-140 Synthetic Gear and Axle Lubricant...1.5 Quarts ( 1.4 Liters )

[lochnessmonster]

No worries. And I agree, that's what it says, but shouldn't it say "........which contains a friction modifier that is essential to the normal operation of your rear differential," (I'm assuming it does???) so guys like me, who don't have access to Castrol SAF-XJ/SAE 75W-140 (my NAPA doesn't stock it and it's the only parts store in our little town), are better informed? That way we don't make the mistake of thinking Pennzoil 75W-140 is just as good?

For example, Ralph Gilles has indicated that Shell developed Pennzoil Ultra Platinum synthetic along with the development of the Gen V motor, and it is what is "recommended" in all SRT engines, yet I hear people on this, and other forums, using everything from Royal Purple to Mobil 1 0W-40. No big deal right? Well, in this case, it wasn't a "huge deal" because I figured it out pretty quick, but if there is something in the Pennzoil Ultra Platinum that is absolutely essential to the operation of the Gen V engine, then it's something people need to know. Similarly, if there is something in the Gastrol gear oil, such as a friction modifier, that is essential to the proper operation of the differential, that would be good to know, rather than having a manual "recommend" it. I'm sure I'm not the only one that looks at something like that and goes, "Yeah, I wonder how much Castrol paid SRT to promote it's product?"

I can say this, if you do a search for "loud grinding sound at low speed with sharp turns" you'll see there are a lot of people who have experienced this problem. Was it because they didn't have the friction modifier in their diff fluid? In fact, I read several posts where the techs at a well known Texas based dealership told customers that it was a normal noise....hmmmm.

For reference, here is the best article/write up I found on the subject: https://www.vipermagazine.com/viper-...ation-service/

[lochnessmonster]

Yep SRT Bill it was a full synthetic, but it clearly didn't have the friction modifier in it. I put Royal Purple Max ATF in the transmission.

- - - Updated - - -

I don't understand how you would have a front wheel problem with the rear diff.

I didn't realize the problem was coming from the rear diff. I associated it with the front end, because every time I would turn the wheels sharply, the noise would occur.

[lochnessmonster]

How many miles/long is diff fluid good for in these cars?

As I recall the change out on the diff fluid was supposed to occur at 36,000 km (22,500 miles) as per the manual. I just did it because I was down there anyway, and it's cheap insurance.

[lochnessmonster]

The mobil 1 stuff has the friction modifier in it already which is nice

Good to know.

[FrgMstr]

Doubling the friction modifier in a Gen IV stock diff is reportedly associated with possible issues per some experienced techs.

Viper Tech is the one that suggested this. Had issues at 13K miles. Been doing it since, now at 36K miles and never an issue.

[Steve-Indy]

Thanks, FrgMstr... I was never able to track the definition of "issues".

Lochnessmonster...Here is a quote from the 2014 Viper Service Manual CD found under the section on differential installation..."6.Remove rear axle fill plug (1) and fill rear axle with 0.07 L (2.3 oz.) of Mopar® Limited Slip Additive and 1.36 L (43.7 oz.) Mopar® Synthetic SAE 75W-140 Gear and Axle Lubricant."

Now, will someone in the "know and in the flow" PLEASE help sort this for all of us !!

[kirkinsb]

I always double up on the friction modifier. Never an issue since I started doing that.

Same thing happened to me when I had 3.55 gears put in. The shop was not aware of the friction modifier requirement. My diff started barking and howling at me on slow tight turns too!!!

The diff sure does sound horrible without the modifier. Scared the heck out of me! Like FrgMstr......I doubled up on the friction modifier and my diff is happy again. Yep, seems Viper diffs simply cannot live without the stuff!

[lochnessmonster]

Wow, nice work Steve-Indy! Now that's an excellent description of how the differential fluid change should happen. I wish they had put that in the 2013 owner's manual In any event, that certainly clears up the issue of whether or not the friction modifier should be added, which was a reoccurring question/theme I came across in my research. It also emphasises why the "service manual" is far superior to an "owner's manual."

I'm still amazed at what a difference the addition of that little bottle made. To be honest, I had very little faith in it's effectiveness, and was fairly certain I would be looking at wheel bearings etc. I'm not kidding, the sound was brutal. Right after I put the friction modifier in, I took the car for a drive (10-15 min at highway speed), then pulled over to a weigh station that had lots of room for some figure 8's and the sound was completely gone. This additive is amazing.

BTW - The additive I used was ACDelco since, again, my Napa store didn't have any Mopar product, and I wasn't going to drive another mile without trying to fix this problem.

[Steve M]

I don't understand how you would have a front wheel problem with the rear diff.

If the clutches in the differential aren't working properly (i.e. slipping appropriately), the problem will manifest every time you try to turn the steering wheel, especially when trying to make sharp turns. I had actually noted the same thing on a Grand Sport Corvette I drove at Spring Mountain...when I looked into it, the differential fluid came up as the most likely suspect. As soon as it was changed, the problem went away entirely.

[lochnessmonster]

Yeah, I was looking for wheel rubbing marks etc., but none were evident, and the wheels/tires are stock and hadn't been making the noise before. I thought back to the diff fluid change I had done last Friday, and thought, "Hmmm....is that the culprit?". So I took the car to a dirt lot, and did some figure 8's, sure enough, when the diff "didn't have to work" due to the slippage on the dirt, the sound went away, but you could tell when the wheels had traction, the sound was there. I then took the car to a paved lot and the sound was there all the time. It was at that point I realized it is definitely a rear differential issue, and the only logical explanation was it was fluid related, since I had just changed it a couple days ago. That's when I started looking into this problem, and settled on the most obvious and inexpensive solution.

I'd hate to think how many other Viper owners (and otherwise) have suffered with this issue when the solution is a $10.00 bottle of magic potion. As kirkinsb indicated, not everyone is aware that it is essential to the proper operation of this differential. My S2000 diff doesn't need it, Subie diffs don't need it, FJ doesn't need it, Viper........likes its friction modifier. To be honest, I had never heard of such a thing until yesterday. A good learning experience.......

[ViperPete]

Based on what you guys are saying, yes it makes sense. I appreciate the info, if I ever have sounds like that- I know where to look!

[lochnessmonster]

Based on what you guys are saying, yes it makes sense. I appreciate the info, if I ever have sounds like that- I know where to look!

Cheers. I'm hoping my screw up saves some people a lot of headache

[Steve M]

Based on what you guys are saying, yes it makes sense. I appreciate the info, if I ever have sounds like that- I know where to look!

If the tire skittering thing happens, you'll know it...there's no mistaking what's going on. Basically, it feels like the car binds up and then releases over and over again (because it is).

[FrgMstr]

Thanks, FrgMstr... I was never able to track the definition of "issues".

The diff was "grinding" with fresh fluid and the appropriate amount of friction modifier added per the manual. We doubled up on the friction modifier since then and it has never been an issue again.