too much limited slip additive?

[mobilaltima]

99 F250 in my sig, changed the rear gear oil back when it had 223k miles last year, it now has 231k with no problems. its the 10.5 Sterling, 3.73 limited slip. I used Amsoil Severe Gear 75W140 and 8 oz of Ford XL-3 LS additive. I've had no chatter from the rear end. I was reading earlier that if too much additive is used it can render the LS useless and act like an open diff, and it could also shorten the life of the gear oil. I'm not really knowledgeable on rear ends whether open or limited slip, so how would I know if the LS is working properly? Also the heaviest weight this truck tows is a 21 foot Carolina skiff with a 200 four stroke Yamaha. Using Severe Gear Amsoil, would it be ok to change it out every 100k miles or should I do it every 50k? Thanks

 

[saginawmale50]

How much LS fluid should be in there? Change it every year if youre worried about it, but it will probably outlast the truck.

 

[bdcardinal]

How does it feel when you do figure 8's in a parking lot?

 

[Colt45ws]

Extra LS additive will reduce the ability of the clutches to grab and hold, making it act more like a open differential. If it has 231k I would suspect the LS clutches + preload spring are probably due to be replaced anyway. They have to slip everytime you go around a turn. So I know you can test it by jacking one wheel, trans in park and parking brake off, put a torque wrench on a lug and seeing how much torque it takes to begin turning the wheel. I have a value of 20ftlbs minimum but thats for a smaller axle, not sure on the larger one like you have. Amsoil Severe gear should be good for 100k.

 

[Oro_O]

Originally Posted By: bdcardinal

How does it feel when you do figure 8's in a parking lot?

And that is the quick, simple, reliable test.

 

[xtell]

Originally Posted By: Colt45ws

Extra LS additive will reduce the ability of the clutches to grab and hold, making it act more like a open differential. If it has 231k I would suspect the LS clutches + preload spring are probably due to be replaced anyway. They have to slip everytime you go around a turn. So I know you can test it by jacking one wheel, trans in park and parking brake off, put a torque wrench on a lug and seeing how much torque it takes to begin turning the wheel. I have a value of 20ftlbs minimum but thats for a smaller axle, not sure on the larger one like you have. Amsoil Severe gear should be good for 100k.

Question: If the oil says "supplemental friction modifier not required", like Valvoline Synpower 75W-90, will that be good enough to prevent any issues OR should you just get oil without LS friction modifier and add the approved supplement to it? Reason I'm asking is I just got a used Ford Truck with a Dana M80 limited slip differential and it is supposed to use Ford M2C-192A additive. The Synpower label states that additional M2C-192A is not required.

 

[demarpaint]

Originally Posted By: xtell

Originally Posted By: Colt45ws

Extra LS additive will reduce the ability of the clutches to grab and hold, making it act more like a open differential. If it has 231k I would suspect the LS clutches + preload spring are probably due to be replaced anyway. They have to slip everytime you go around a turn. So I know you can test it by jacking one wheel, trans in park and parking brake off, put a torque wrench on a lug and seeing how much torque it takes to begin turning the wheel. I have a value of 20ftlbs minimum but thats for a smaller axle, not sure on the larger one like you have. Amsoil Severe gear should be good for 100k.

Question: If the oil says "supplemental friction modifier not required", like Valvoline Synpower 75W-90, will that be good enough to prevent any issues OR should you just get oil without LS friction modifier and add the approved supplement to it? Reason I'm asking is I just got a used Ford Truck with a Dana M80 limited slip differential and it is supposed to use Ford M2C-192A additive. The Synpower label states that additional M2C-192A is not required.

You should be good to go. Operative word, should. Try the figure 8 test, if you notice anything out of the ordinary add the LS additive, and try it again. I remember an old Ford work van I had many years ago, had a little chatter turning corners with one of the gear oils that stated "no friction modifier required" a bottle of Ford's LS additive solved the problem real quick.

 

[Colt45ws]

Originally Posted By: demarpaint

Originally Posted By: xtell

Originally Posted By: Colt45ws

Extra LS additive will reduce the ability of the clutches to grab and hold, making it act more like a open differential. If it has 231k I would suspect the LS clutches + preload spring are probably due to be replaced anyway. They have to slip everytime you go around a turn. So I know you can test it by jacking one wheel, trans in park and parking brake off, put a torque wrench on a lug and seeing how much torque it takes to begin turning the wheel. I have a value of 20ftlbs minimum but thats for a smaller axle, not sure on the larger one like you have. Amsoil Severe gear should be good for 100k.

Question: If the oil says "supplemental friction modifier not required", like Valvoline Synpower 75W-90, will that be good enough to prevent any issues OR should you just get oil without LS friction modifier and add the approved supplement to it? Reason I'm asking is I just got a used Ford Truck with a Dana M80 limited slip differential and it is supposed to use Ford M2C-192A additive. The Synpower label states that additional M2C-192A is not required.

You should be good to go. Operative word, should. Try the figure 8 test, if you notice anything out of the ordinary add the LS additive, and try it again. I remember an old Ford work van I had many years ago, had a little chatter turning corners with one of the gear oils that stated "no friction modifier required" a bottle of Ford's LS additive solved the problem real quick.

Yes, I'd try without any first. Ive personally used Synpower, Severe Gear, and Schaeffers XP fluids in diffs with no additive and never heard a peep even with fresh tight clutches. If you do need some, I'd add maybe half a bottle to start and drive 50-100 miles to mix it in and see how it does then. There is additive in it, you just might have an edge case where it isnt enough and just a bit more will quiet it.

 

[mobilaltima]

what exactly would it sound like if the LS is acting up due to not enough or no additive? I ask this cause my truck is an early 99, these years have a loud rattle from the torque converter. While it works just fine, at idle or low speeds the rattle is all I hear. Just want to know what I need to listen for.

 

[xtell]

demarpaint & Colt45ws, Thank you for the advise. I'll try the Valvoline Synpower 75w-90. I'll fill the differential but leave enough room for the Ford limited slip additive - drive the truck to get the rear end warmed up and then do some figure "8"s in a flat parking lot. If I hear anything. I'll add 8oz. of the Ford M2C-192A additive - drive it a bit, and then recheck. I'll have 8 more ounces of the additive left over in case it needs a little more. Are the Ford manufactured limited slip differentials real touchy about LS additive amounts? I just don't want to over-add a supplemental friction modifier to the point that it may compromise the proper operation of the unit.

 

[mobilaltima]

I spoke to one of the guys who own Custom Differential in Bloomsdale, Missouri today. Theyre a pretty reputable builder of custom diffs and the like. I told him I was running Amsoil gear oil and he said for me to add two bottles of additive regardless if the fluid has any in it already from the manufacturer, with no worries. He said it would take alot of additive to start giving problems. He also said depending on the build and if a larger capacity diff cover is used when he builds axles, he'll add 3 bottles of friction modifier sometimes.

 

[xtell]

well, that's good to know. I guess adding the whole bottle 16oz of friction modifier and being done with it will be the way to go.

 

[mobilaltima]

I use two 4 oz bottles of Fords XL-3 additive

 

[2strokeNorthstar]

I use none in my Ford 9.75. Synpower 75w140 works fine. Don't add it if you don't need to. You give up the limited slip. Hit the gas on a dirt road and see if you leave 2 marks or 1.

 

[Colt45ws]

Originally Posted By: 2strokeNorthstar

I use none in my Ford 9.75. Synpower 75w140 works fine. Don't add it if you don't need to. You give up the limited slip. Hit the gas on a dirt road and see if you leave 2 marks or 1.

Agree. These stock type LSDs already have a pretty pathetic bias ratio to keep people from losing control and wrapping their vehicle around a tree. You might get as high as 1.5:1 on fresh clutches. (Ratio is torque avaliable at non-slipping tire:torque used to spin the loose tire. So if it takes 50ftlbs torque to break traction on one tire, with 1.5:1 ratio up to 75ftlbs would be available at the other tire. If you need more than that to move your rig, the clutches will slip and you will go no where.) Adding more FM than needed just reduces said bias ratio. The diff shop just adds a bunch because they dont want any come backs for grinding or noises, so they dump more than necessary and is frankly kinda sleazy. I would go so far as to not give them my business if they told me that, but thats just my opinion. If I paid $300-400 + install for a good after market LSD with a high bias ratio, say like 2.5:1, and they dumped a bunch of FM in it, ruining it; I would be incensed to say the least. I already have to fight sometimes with this stock LSD to get more traction because its taking so little torque to get one tire spinning there isnt enough at the other tire to get the car moving. If the bias ratio was any worse you might as well call it an open diff than happens to be able to make 2 skid marks on dry pavement because thats all it would be good for.