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#1885687 - 05/09/10 09:05 PM Ford Limited Slip Problem
IndyFan Offline


Registered: 06/16/05
Posts: 360
Loc: Danville, Indiana
I've got a 2001 F150 4wd Supercrew with a 3.55 limited slip. I had the diff oil changed last week. I've just noticed, after a long day of highway driving, that it is making a grinding noise and vibration when accelerating from a stop into a turn. It won't do it if accelerating straight ahead, and the truck feels fine when up to speed. If I accelerate with very light throttle and only a light turn, it won't do it.

I'm thinking that the mechanic did not put friction modifier in with the diff lube, and I'm hearing and feeling the clutches in the limited slip grinding. Does this sound like a possibility, or is there potentially another, larger problem going on? I'm taking it to a Ford dealer early in the morning and will have them help assess it. I'm either going to have them open it up, inspect it, and refill with diff oil and friction modifier, or I might just have them suck out some lube and top it back off with the modifier.

Ideas and suggestions are welcome. I'll be towing a VERY heavy boat for about 650 miles over the next two days, as I return home, so this thing has me a little nervous.
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#1885691 - 05/09/10 09:10 PM Re: Ford Limited Slip Problem [Re: IndyFan]
Colt45ws Offline


Registered: 08/15/06
Posts: 7640
Loc: Central Washington
Lack of FM is a possibility. Do you know what kind of gear oil was installed?
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#1885692 - 05/09/10 09:11 PM Re: Ford Limited Slip Problem [Re: IndyFan]
demarpaint Offline


Registered: 07/03/05
Posts: 22214
Loc: NY
Check the the level of the gear oil and add the limited slip additive. Odds are the guy didn't put it in or used a fluid that says good with any differentials, no additives needed.

My 3.55 Ford Limited Slip Differential isn't happy unless the additive is in it, the so called gear oils that say no limited slip add needed didn't cut the mustard.
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#1885693 - 05/09/10 09:12 PM Re: Ford Limited Slip Problem [Re: Colt45ws]
Nick R Offline


Registered: 07/14/09
Posts: 10877
Loc: NEO
No friction modifier. If you don't get it done soon it's going to be destroyed and the clutch pack will need to be replaced. (about $800 if I recall correctly) it is a fairly common problem on the early 200X Expeditions with the Limited slip and never getting the gear oil changed.
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#1885701 - 05/09/10 09:21 PM Re: Ford Limited Slip Problem [Re: Colt45ws]
IndyFan Offline


Registered: 06/16/05
Posts: 360
Loc: Danville, Indiana
Originally Posted By: Colt45ws
Lack of FM is a possibility. Do you know what kind of gear oil was installed?


Unfortunately, I don't. It is my mother-in-law's truck and I gave her a list of things needing done to it, including changing the rear diff fluid. At the time, I didn't realize it had a limited slip, so I didn't get picky about the gear oil. I'm going to go ahead and have it done over, using synthetic gear oil with the additive. I'm almost sure they used a 75w90, and I'm going to go with a heavier oil, since I'm using it to tow this heavy (nearly 7,000lbs) boat.

What gear oil does Ford specify for towing with this setup? Also, does Ford have their own friction modifier or additive for this diff that will do a good job of quieting it down? If so, what do they call it.

Thanks for all the help!
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#1885712 - 05/09/10 09:38 PM Re: Ford Limited Slip Problem [Re: IndyFan]
demarpaint Offline


Registered: 07/03/05
Posts: 22214
Loc: NY
Not sure on what Ford specs for towing but they do make their own Limited Slip additive. Go to any Ford dealer and ask for it. The last time I changed my gear oil I used Mobil 1 gear oil, and the Ford additive. IIRC the Mobil 1 gear oil said no FM was needed, a ride around the block proved that wrong. The addition of the Ford additive fixed everything.
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#1885713 - 05/09/10 09:39 PM Re: Ford Limited Slip Problem [Re: IndyFan]
cronk Offline


Registered: 01/06/09
Posts: 748
Loc: Watertown, New York
I would get any good 75w140 synthetic gear lube, and go to your Ford dealership parts counter and ask for a bottle of friction modifier for a limited slip diff, they should know what you are talking about.
Even if the gear oil says it has the friction modifier in it, the Fords seem to be picky. Always add the Ford additive!
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#1885735 - 05/09/10 09:59 PM Re: Ford Limited Slip Problem [Re: cronk]
IndyFan Offline


Registered: 06/16/05
Posts: 360
Loc: Danville, Indiana
Thanks for the tips.

The local dealer is going to have to do it, because I'm 500 miles from my garage. I'm going to have them use whatever synthetic 75w140 they've got along with the Ford additive, and I'm going to watch them do it. Hopefully, that will do the trick. Thanks again, everyone for the tips and help. I always get great advice and feedback here on BITOG!
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#1885737 - 05/09/10 10:04 PM Re: Ford Limited Slip Problem [Re: IndyFan]
HWEaton Offline


Registered: 12/18/09
Posts: 396
Loc: Wyoming
That Ford takes a 75W-140 and you NEED that FM in there. Like now.

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#1885765 - 05/09/10 10:35 PM Re: Ford Limited Slip Problem [Re: HWEaton]
Colt45ws Offline


Registered: 08/15/06
Posts: 7640
Loc: Central Washington
Originally Posted By: HWEaton
That Ford takes a 75W-140 and you NEED that FM in there. Like now.

+2^10
_________________________
-Colton
2004 Ford Crown Vic LX, 82k "Tank"
2002 Ford Crown Vic PI, 165k "Highwayman" (Ex-Kootenai County, ID Unit #42)

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#1885791 - 05/09/10 11:12 PM Re: Ford Limited Slip Problem [Re: Colt45ws]
SuperDave456 Offline


Registered: 10/29/08
Posts: 2283
Loc: Dallas, Texas
My 1998 Ford F150 had a little steel tab on one of the bolts that says "75w140". And it also says it is "Full Synthetic 75w140 is required" in the manual. It also says that it is a lifetime fill unless it gets submerged, but I wanted to change out the fluid when I got mine.

I changed mine out last year, not that difficult, and put in Amsoil products. Even their Slip Lock just to make sure.
It runs great.

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#1885826 - 05/10/10 12:05 AM Re: Ford Limited Slip Problem [Re: SuperDave456]
bdcardinal Offline


Registered: 06/03/05
Posts: 6970
Loc: Santa Barbara, CA
XY-75W140-QL is the part number for the Ford gear oil and XL-3 is the part number for the friction modifier.
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#1885852 - 05/10/10 12:47 AM Re: Ford Limited Slip Problem [Re: bdcardinal]
OVERKILL Online   content


Registered: 04/28/08
Posts: 27867
Loc: Ontario, Canada
Definitely a lack of FM that caused the clutch chatter. My parent's Expy does it, even with a single bottle added. Probably needs another.

The clutches chattering won't break them. But it is definitely annoying! Common to NOT put it in for "tighter" T-Lok in Mustang-land.
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#1886069 - 05/10/10 09:30 AM Re: Ford Limited Slip Problem [Re: OVERKILL]
mechtech2 Offline


Registered: 09/05/06
Posts: 19479
Loc: Chicago Area
First, make sure the proper viscosity lube is in there.
If this is OK, then you need the additive.
Some fluid may need to be removed first.

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