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too much limited slip additive? #4584923
11/25/17 09:09 PM
11/25/17 09:09 PM
Joined: Feb 2011
Posts: 1,260
Golden Meadow, LA
mobilaltima Offline OP
mobilaltima  Offline OP
Joined: Feb 2011
Posts: 1,260
Golden Meadow, LA
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


2006 2500 Dodge 5.9 Cummins Mobil Delvac 15W40, Fleetguard Stratapore 90k miles
Early '99 F250 ECLB 7.3 Stroker, 223k miles
Re: too much limited slip additive? [Re: mobilaltima] #4584926
11/25/17 09:12 PM
11/25/17 09:12 PM
Joined: Dec 2006
Posts: 75
saginaw michigan
saginawmale50 Offline
saginawmale50  Offline
Joined: Dec 2006
Posts: 75
saginaw michigan
How much LS fluid should be in there? Change it every year if youre worried about it, but it will probably outlast the truck.

Re: too much limited slip additive? [Re: mobilaltima] #4584935
11/25/17 09:20 PM
11/25/17 09:20 PM
Joined: Jun 2005
Posts: 11,612
Santa Barbara, CA
bdcardinal Offline
bdcardinal  Offline
Joined: Jun 2005
Posts: 11,612
Santa Barbara, CA
How does it feel when you do figure 8's in a parking lot?


2014 Ford Mustang GT Track Pack
1995 Ford Mustang GT

Ford/Mazda Parts Counter
NRA Benefactor Member
Opinions expressed are my own.
Re: too much limited slip additive? [Re: mobilaltima] #4584943
11/25/17 09:26 PM
11/25/17 09:26 PM
Joined: Aug 2006
Posts: 9,883
Central Washington
Colt45ws Offline
Colt45ws  Offline
Joined: Aug 2006
Posts: 9,883
Central Washington
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.

Last edited by Colt45ws; 11/25/17 09:27 PM.

-Colton
2002 Ford Crown Vic PI 207k, Ex-Kootenai County, ID Unit #42
Down for engine swap
2003 Ford Crown Vic PI 75k
Castrol EDGE HM 5W30, Fram XG2
Re: too much limited slip additive? [Re: bdcardinal] #4585080
11/26/17 12:15 AM
11/26/17 12:15 AM
Joined: Sep 2014
Posts: 1,486
Seattle-ish, WA
Oro_O Offline
Oro_O  Offline
Joined: Sep 2014
Posts: 1,486
Seattle-ish, WA
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.

Re: too much limited slip additive? [Re: Colt45ws] #4585111
11/26/17 02:28 AM
11/26/17 02:28 AM
Joined: Dec 2006
Posts: 551
ohio
xtell Offline
xtell  Offline
Joined: Dec 2006
Posts: 551
ohio
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.

Re: too much limited slip additive? [Re: xtell] #4585164
11/26/17 05:37 AM
11/26/17 05:37 AM
Joined: Jul 2005
Posts: 30,972
NY
demarpaint Offline
demarpaint  Offline
Joined: Jul 2005
Posts: 30,972
NY
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.


God Bless Our Troops

Re: too much limited slip additive? [Re: demarpaint] #4586048
11/26/17 07:34 PM
11/26/17 07:34 PM
Joined: Aug 2006
Posts: 9,883
Central Washington
Colt45ws Offline
Colt45ws  Offline
Joined: Aug 2006
Posts: 9,883
Central Washington
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.


-Colton
2002 Ford Crown Vic PI 207k, Ex-Kootenai County, ID Unit #42
Down for engine swap
2003 Ford Crown Vic PI 75k
Castrol EDGE HM 5W30, Fram XG2
Re: too much limited slip additive? [Re: mobilaltima] #4586111
11/26/17 08:42 PM
11/26/17 08:42 PM
Joined: Feb 2011
Posts: 1,260
Golden Meadow, LA
mobilaltima Offline OP
mobilaltima  Offline OP
Joined: Feb 2011
Posts: 1,260
Golden Meadow, LA
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.


2006 2500 Dodge 5.9 Cummins Mobil Delvac 15W40, Fleetguard Stratapore 90k miles
Early '99 F250 ECLB 7.3 Stroker, 223k miles
Re: too much limited slip additive? [Re: demarpaint] #4586145
11/26/17 09:16 PM
11/26/17 09:16 PM
Joined: Dec 2006
Posts: 551
ohio
xtell Offline
xtell  Offline
Joined: Dec 2006
Posts: 551
ohio
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.

Re: too much limited slip additive? [Re: mobilaltima] #4586920
11/27/17 07:07 PM
11/27/17 07:07 PM
Joined: Feb 2011
Posts: 1,260
Golden Meadow, LA
mobilaltima Offline OP
mobilaltima  Offline OP
Joined: Feb 2011
Posts: 1,260
Golden Meadow, LA
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.


2006 2500 Dodge 5.9 Cummins Mobil Delvac 15W40, Fleetguard Stratapore 90k miles
Early '99 F250 ECLB 7.3 Stroker, 223k miles
Re: too much limited slip additive? [Re: mobilaltima] #4587069
11/27/17 09:48 PM
11/27/17 09:48 PM
Joined: Dec 2006
Posts: 551
ohio
xtell Offline
xtell  Offline
Joined: Dec 2006
Posts: 551
ohio
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.

Re: too much limited slip additive? [Re: mobilaltima] #4587090
11/27/17 10:12 PM
11/27/17 10:12 PM
Joined: Feb 2011
Posts: 1,260
Golden Meadow, LA
mobilaltima Offline OP
mobilaltima  Offline OP
Joined: Feb 2011
Posts: 1,260
Golden Meadow, LA
I use two 4 oz bottles of Fords XL-3 additive


2006 2500 Dodge 5.9 Cummins Mobil Delvac 15W40, Fleetguard Stratapore 90k miles
Early '99 F250 ECLB 7.3 Stroker, 223k miles
Re: too much limited slip additive? [Re: mobilaltima] #4587101
11/27/17 10:30 PM
11/27/17 10:30 PM
Joined: Jul 2017
Posts: 363
PR CA, USA
2strokeNorthstar Offline
2strokeNorthstar  Offline
Joined: Jul 2017
Posts: 363
PR CA, USA
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.

Re: too much limited slip additive? [Re: 2strokeNorthstar] #4587118
11/27/17 11:05 PM
11/27/17 11:05 PM
Joined: Aug 2006
Posts: 9,883
Central Washington
Colt45ws Offline
Colt45ws  Offline
Joined: Aug 2006
Posts: 9,883
Central Washington
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.


-Colton
2002 Ford Crown Vic PI 207k, Ex-Kootenai County, ID Unit #42
Down for engine swap
2003 Ford Crown Vic PI 75k
Castrol EDGE HM 5W30, Fram XG2

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