Limited slip diffs and synthetic lube

[AggieJustin]

A question for you guys running synthetic lube in your limited slip rear diffs...



How much friction modifier (if any) did you add when you put in the synthetic? And how well does your diff work now?



I switched over to Valvoline 75W-90 full synthetic over the weekend but didn't add any modifier to the rear diff. I did quite a few tight turns in a paved parking lot and didn't detect any chatter or binding from the rear wheels. I also didn't see any tire marks where it looked like one wheel might have been trying to spin. On loose ground, both wheels spin immediately when I push the go pedal judging by the tire marks.



It worked pretty well on the rain-slicked streets this morning. The only thing I could notice is some grabbing when hitting the accelerator while turning a corner, but that was there before to some degree.



TIA,



Justin

 

[Chipstien]

None here!

I used Amsoil in the rear with no modifier because Amsoil adds friction modifier to their gear lube. Seems that this topic varies with each case. Some run Amsoil and still need the modifier to stop the chatter. Wasn't the case for me.

 

[DCMille290]

I spoke with the service manager at a dealship in Cottonwood AZ last weekend. All of the SW area techs were at a meeting with DC engineers regarding the Dana's in the 2500/3500 TD's.

Their recomendation was to use synthetic oil instead of standard gear lube and that there was no need for the modifier. The reason was a lower operating temp, longer service. They had determined a 30 degree drop in operating temp vs standard oil.

Changing over this week. Will see what happens with the trailer on.





DC Miller

aka Marbleman

 

[klenger]

Amsoil 75-140 with no modifier and it works fine.

 

[RustyJC]

I'm running Royal Purple 85W-140 synthetic. It has friction modifier built in, and I don't have any LSD chatter running it straight out of the bottle with no Mopar friction modifier.



Rusty

 

[Cliffman]

couldn't hurt

I'm running the Amsoil also and threw in the friction lube just for safe keeping.

 

[LSMITH]

I am running Mobil 1 75-90 in the rear diff and put in a LOT of modifier. The quality of the modifier used is a big factor in how much you will need, the stuff you get at the parts house will not stop the chatter in my LSD regardless of what oil it is used with. The Mopar modifier works well. My LSD is EXTREMELY tight, without a big dose of modifier it acts like a spool. The tightness of the LSD seems to vary quite a bit from truck to truck.

 

[redeye]

Just hit 18,000 on the odometer . Diesel Dynamics used eight quarts of Redline synthetic to fill the newly installed Dyna 80 Mag-Tech cover.

Redline also has a fully synthetic diesel motor oil that meets all of the manufacture specs.

 

[DEZLPWR]

I used Mobil1 75w-90....

No friction modifer. I must have a "loose" LSD!

 

[Mpoland]

Modifier

I'm running Amsoil 75-140... and I had to add modifier to mine.

 

[chuck3]

I,m using amsoil in mine, did not need any at first but after a couple of months it started grabing on left turns. Figure 8's did not help at all. Bought a bottle of the dodge stuff, either 4 or 6 oz bottle, no problems since.

chuck.

 

[AggieJustin]

Thanks....

Thanks for all the responses guys. I guess I'll just keep my eye on it to make sure it doesn't develop any chatter. Who knows what it might do to me after sitting around all week while I'm up here in the Great White North (Calgary).



Also, I noticed in another thread that someone mentioned the front diff comes from the factory with synthetic 75-140. Is this true?? I thought both diffs came with dino 75-90 and you only needed to step up to 140 for heavier/more frequent towing.



JM

 

[BarryG]

I am sure I saw the same info in the service manual about the front diff coming stock with synthetic. It definitely looked different than the rear when I replaced them. If I recall the rear looked like normal dino and the front was a clear/greyish color. Thought it might be contaminated with water but there was no seperation and for the life of me couldn't remember any weather bad enough to get water in it and I know I didn't do any water crossings over 6 inches deep. I know what I put in so we shall see if it has a "funky" look to it when I replace it again in a couple months or as soon as the new maghytec front cover is out whichever comes first. If so then I guess I will be looking for a bad seal somewhere.

 

[gatoram]

Just changed mine in the Dana 80 this Monday. Went to Amsoil 75w-140 with no modifier. No chatter, no problem. About 48,000 miles with maybe 10% of that towing 8000+# trailers and the factory dope looked good... ... ... Checked the front axle and it also looked clean. It's on the schedule next week.



Tom

 

[gmorrison]

The Mobil 1 75W-90 already contains the limited slip additive in the appropriate treat rate when purchased in quarts. The 5 gallons pails/drums of Mobilgear SHC 75W-90 does not contain the addtive, however. Regarding the use of heavier gear oils in the rear end: every tractor/trailer you pass on the highway is running synthetic 75W-90 gear oil. The normal warranty for rear ends is 100,000 miles but by switching to synthetic within 3,000 miles (Eaton/Rockwell), the warranty is then extended to 770,000 miles. No additional cost, just proof of switch. A no brainer.

However, running a thicker gear oil (like a 140W) robs power, fuel economy and creates heat. Not needed, not recommended. .

George Morrison, STLE CLS

 

[RustyJC]

Originally posted by gmorrison

However, running a thicker gear oil (like a 140W) robs power, fuel economy and creates heat. Not needed, not recommended. .

George Morrison, STLE CLS

George,



Actually, 75W-140 synthetic is specifically recommended in the Dodge owner's manual for heavy towing applications.



Rusty

 

[gmorrison]

I realize the recommendation and temper it with reality. Again, *every* tractor trailer on the highway is running synthetic 75W-90 and the rear ends are pulling 80,000 pounds! There are no highway recommndations for a 140 weight for over the road tractor use due to the previously mentioned shortcomings. i. e. the synthetic 75W-90 load carrying capababilities are incredibly high.



I run into the "if two asperins are good, four must be better" syndrome quite a lot. i. e. end users running 15W-50 engine oils when the engine manufacturer calls for a 10W-30. I also see many end users running the 140 weight on the basis "it will be better" (the manufacturer recommends it) even tho the vehicle never sees heavy loading, pulling tree stumps, etc. when in fact the use of 140W is detrimental to the life of the rear end, fuel mileage, etc.

George Morrison, STLE CLS