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Discussion Starter #1 (Edited)
So I have had my 16 Challenger Scat for 3 1/2 years now and just rolled 20k miles. (Purchased new 8 miles) I also have at least 50 Drag Races under my belt. I have had rear end whine for most of the time I have had it. It has not bothered me because most of the Hot Rods I have owned in the past have had gear whine. So I would consider it normal. However, after reading about all the rear end changes Mopar has done....I decided to change the Diff Fluid to see if it would change anything.

I selected Max Gear Royal Purple 75W140 for a couple of reasons. I have used it in the past in manual gear boxes and the results have always been spectacular. MUCH smoother and shifting is 50% + easier and quieter. Pretty slick stuff by my personal experience. I decided to use 75W140 because I want the best gear protection...period. Factory's tend to use lighter fluids in everything to maximize gas mileage.

I have the Per4mance Diff Brace.....and I had to partially remove it because it blocks the fill hole. That blows.....but the brace is awesome and worth the wrench time.

Also....the Diff plugs are Allan heads.....not Torx . I see some people recommending a T50 bit but this is not correct. The T50 DOES fit snugly in the Diff Plug.....but the correct tool is a 5/16" Allan bit. Neither were very tight fortunately. Going back take care to not over tighten. The housing is Aluminum so go to "snug" and bump just a touch.

I purchased the bottle pump from Advance Auto for 10 bucks and it worked FLAWLESSLY! Well worth it. Also a tip from decades of wrenching: When the diff fluid is drained.....spray "brake clean" in the fill hole to flush out any remaining oil and particles. Then I use my air hose blower in the top fill hole to completely blow out any remaining fluid or particles. If you have compressed air this really cleans out the housing.

My RESULTS: My fluid looked fairly clean watching it drain from the Diff. But in the pan...it is dark. Taking the pan in the Sun.....and sloshing the fluid around.....there was zero metal particles and no smell of burn. It felt slick to the touch. At this point I was not expecting much of an improvement.

I went on a 15 mile drive with a mix of city and country driving with a stop for groceries. Speeds ranged from idle to 90 mph. Radio was OFF the entire time. The rear Diff noise was fairly loud before. The first few miles it did not change too much. But then it started to get much quieter. By the end of my drive ALL the noise is completely gone!

I have an aggressive Trans Tune and the shifts are fast and firm. Every shift you feel and hear a slight metallic "clunk" or "tink". Again...normal to me compared to past Hot Rods. Now...all the clunk and tink are gone. Also...you cannot "feel" the shift either. It now just shifts lightning fast.....silently. You can now tell there is a "cushion" in the gear set. Cruising the gear whine is gone. It was similar to exhaust drone. Different speeds produce different pitches. Now GONE.

This tells me the Factory fill is not the best fluid available for our heavy and powerful Hot Rods. This was time and money well spent....and once again the RP did it's magic on gears. It only takes about 1 1/2 quarts so it needs to count!

I would HIGHLY recommend changing your Diff fluid because of the aforementioned results. If you wait too long you may have to have yours replaced. Warranty or not.....I would rather protect what came from the Factory.

At the end of my test ride...I did a couple of mild launches and the 315's spin evenly and smoothly. The Anti Slip additive comes in the fluid and works perfectly.

And no...I have NOTHING to do with RP.....so please do not go down that road. Just my personal experience with the stuff. I only use RP for my gears. An easy job and well worth the effort:)
 

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Thanks very much for taking the time to write this. It is appreciated.
 

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Solidman,

The wannabe scientist in me applauds you! Great write-up about your experience with the new fluid and great advice on how to change the fluid. What you've described in amazing in terms of the now absent differential whine, and the smoother no more "clunk" shifts. Are you talking 8 speed auto, or 6 speed manual transmission in your 2016 SP?

Interesting comment about lighter OEM differential fluid to obtain higher gas mileage. It might also be cost related.

Best,

Finface
 

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I would HIGHLY recommend changing your Diff fluid because of the aforementioned results. If you wait too long you may have to have yours replaced. Warranty or not.....I would rather protect what came from the Factory.
And here I felt bad having let the diff fluid change go to a bit over 2,000 miles (normally I change at about 500).
That could be a blessing in disguise if Royal Purple is as good as you say it is. I was going to use Amsoil, which I've had good luck with.
 

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Discussion Starter #5
Thanks very much for taking the time to write this. It is appreciated.
You are most welcome Mike and I really appreciate your great comment:) I hope it helps....Gene:)
 

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Discussion Starter #6
Solidman,

The wannabe scientist in me applauds you! Great write-up about your experience with the new fluid and great advice on how to change the fluid. What you've described in amazing in terms of the now absent differential whine, and the smoother no more "clunk" shifts. Are you talking 8 speed auto, or 6 speed manual transmission in your 2016 SP?

Interesting comment about lighter OEM differential fluid to obtain higher gas mileage. It might also be cost related.

Best,

Finface
Thank you so much Finface:) I really appreciate the very kind words and I hope it helps! I do have the A8 transmission. Yes...the shifting was an unexpected surprise. It is so smooth now that I checked to see if it was in Sport mode...and it was. I thought it was in granny mode! Pretty cool to have lightning fast shifts but be smooth as glass:)
 

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Discussion Starter #7
And here I felt bad having let the diff fluid change go to a bit over 2,000 miles (normally I change at about 500).
That could be a blessing in disguise if Royal Purple is as good as you say it is. I was going to use Amsoil, which I've had good luck with.
2,ooo miles? Shame on you! lol Did u go back with Mopar stuff? I used Amzoil gear lube in my 2007 Can-Am 650 4 wheeler at first fluid change. Second fluid change I used RP and it was a major difference in the shifter lever effort and gear noise. I used RP when I bought my Can-Am 1000 Renegade and it was an amazing difference as well in it. Definitely a major improvement.

I have used it in several auto gearboxes through the years and it is amazing stuff. I wasn't sure the first few miles....but as it permeated the gears and bearings it performed another miracle in my Scat:) I will only use this stuff for my gears....Gene.
 

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I run Schaeffer's in all my diffs, like the moly in and it does quiet the noise down...……….


Their engine oil helped my 2013 Hemi big time in noise and MPG form Valvoline...………..


Just not a Purple fan,,,,,,,,,,,,if it works for U cool.
 

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Discussion Starter #9
I run Schaeffer's in all my diffs, like the moly in and it does quiet the noise down...……….


Their engine oil helped my 2013 Hemi big time in noise and MPG form Valvoline...………..


Just not a Purple fan,,,,,,,,,,,,if it works for U cool.
Schaeffer's and RP have a lot in common. They both have a lot of Moly and are built for racing. The only bad thing about Moly in an engine is it can accelerate piston bore wear. The moly can actually become an abrasive with the piston speed and heat. Lot's of published material on this. Racers don't usually care because they replace engines when needed. And Moly helps seal the rings and can increase power. For us poor folks that own our cars (make payments) we need em to last a LONG time! lol For gears however........Moly is just what the doctor ordered:)
 

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Well if moly is bad for engines, why does ALL German cars prefer it...…………


Seen moly in the shop test and it stops start up wear cold dead.

look up the million mile ford engine on u tube, engine was perfect inside...………………..
 

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2,ooo miles? Shame on you! lol Did u go back with Mopar stuff? I used Amzoil gear lube in my 2007 Can-Am 650 4 wheeler at first fluid change. Second fluid change I used RP and it was a major difference in the shifter lever effort and gear noise.
Umm, no. Much worse than that. At a bit over 2,000 miles I haven't changed it yet, with anything. That's very unlike me, so I can only make a lame excuse by saying that I'm falling behind on maintenance because of having too many vehicles.

Anyway, thanks for reminding me. I'll put something new in there. Royal purple? I dunno. I have the Amsoil, so it's tempting to use it.
 

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Discussion Starter #12
Umm, no. Much worse than that. At a bit over 2,000 miles I haven't changed it yet, with anything. That's very unlike me, so I can only make a lame excuse by saying that I'm falling behind on maintenance because of having too many vehicles.

Anyway, thanks for reminding me. I'll put something new in there. Royal purple? I dunno. I have the Amsoil, so it's tempting to use it.
Well...you beat me by 18,000 miles! I need to be beaten with a stick! lol You do not have to use RP for sure....however....I would definitely use something with Moly in it. It is magic in gear sets. I can personally attest to the results of RP in gears....
 
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Discussion Starter #14
Well if moly is bad for engines, why does ALL German cars prefer it...…………


Seen moly in the shop test and it stops start up wear cold dead.

look up the million mile ford engine on u tube, engine was perfect inside...………………..
Interesting....I'll have to check that out. The data I have seen was many years ago. Products always evolve and get better in most cases. If memory serves....the suspension was an issue....and since Moly is a solid....it tended to accumulate in pockets. High levels would then become abrasive. I called Blackstone Labs (oil analysis) a few minutes ago....and spoke with a young buck Tech. I asked him if they noticed any problems with Moly now days. He said the only problem he has heard of is Moly clogging the pick-up tube in the oil pump.....starving the engine. He said this was due to high levels. He was not sure if it was an accumulation over time or the owner just added too much.

I remember similar problems with Teflon additives back in the early 80's. I used to use "Slick 50" when it was 50 bucks a can back then! I noticed a big improvement in my Honda 900 and was a believer. However....some people experienced catastrophic results. (higher mileage engines not well maintained) and Slick 50 was sued. They lowered the Teflon content by a mile and the product was never the same. I guess with all things....use as directed and keep one eye open.....Gene.
 

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Discussion Starter #15
If you have limited slip, don't forget to buy a bottle of friction modifier.
Good advice. However...most premium lubes come with it already added. You have to check the label for sure. As I stated....if you use RP it comes with it already added and it works perfectly in my Scat.
 

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If you have limited slip, don't forget to buy a bottle of friction modifier.
I wouldn't forget. But I would deliberately leave it out.
Then, if the clutches start showing signs of binding, I'd add just enough to make them operate smoothly again.

So far I've never had a limited slip that "worked too well", including ones that I set up to be very tight. Making one less effective on purpose seems counter intuitive to me.
 

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Good advice. However...most premium lubes come with it already added. You have to check the label for sure. As I stated....if you use RP it comes with it already added and it works perfectly in my Scat.
I used to think that way too but discovered these LSD diffs like FM.
https://www.challengertalk.com/forums/8373721-post2.html

I am running RP which says it has FM but it does not have enough...I had to add a bottle of FM from Mopar.
 

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In use half a tube of transx even when it’s already added. Swapped these rears three times already from 3.09 to 3.70 and back again and again ...change the oil every time.


Sent from my iPhone using Tapatalk
 

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I change differential oil at each oil change, easy access to drain/fill plugs on my '12 R/T, using AmsOil 75W-90 Severe Service gear lube with friction modifier for the posi unit. Cheap insurance and keeps it lubed well with only a normal gear whine, if at all, after 118K miles on the car.
Oil thread? Use what works best for you!
 
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