Diff juice

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blert

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Which diff juice for a 3.73 non-limited?
Manual says 75w-90 syn but I have seen a few posts on the net saying Ford now recommends 75w-140.
I happen to three bottles of Mobil1 75w-90LS syn sitting in my garage. Ok to use?

No hauling/towing. Not much heavy lifting.
 

swshawaii

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After reading the Ford TSB I had the same question for my 2005 with a 3:73 open differential. No towing or heavy use for me either. Never had whine and don't believe the MPG savings would be that significant with lighter gear lube. Still chose to use Amsoil Severe Gear 75W-90. After 30,000 miles no regrets and the only thing I hear is tire and wind noise at highway speeds. IMO, use the 75W-90 Mobil 1 you already have with added friction modifier even though you have an open diffy. Mobil 1 says it's compatible for open axles and many other open axle owners use it.

Note Amsoil lists 75W-90 and 75W-110, not 75W-140 in their fitment guide for Gen 1 Tracs.
 

EddieS'04

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When I rebuilt my open gear with a Richmond Gear mechanical slip. I used Redline Syn Heavy Shockproof. I run the same in my Harley Trans. I'm satisfied so far. Specs below.

Heavy ShockProof®​

Film thickness greater than an SAE 75W250, yet low fluid friction like 75W90
 
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kmartin

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After reading the Ford TSB I had the same question for my 2005 with a 3:73 open differential. No towing or heavy use for me either. Never had whine and don't believe the MPG savings would be that significant with lighter gear lube. Still chose to use Amsoil Severe Gear 75W-90. After 30,000 miles no regrets and the only thing I hear is tire and wind noise at highway speeds. IMO, use the 75W-90 Mobil 1 you already have with added friction modifier even though you have an open diffy. Mobil 1 says it's compatible for open axles and many other open axle owners use it.

Note Amsoil lists 75W-90 and 75W-110, not 75W-140 in their fitment guide for Gen 1 Tracs.
I just read the TSB. Looks like the Sport Tracs are not listed, but yet, some of them have the same axle. I assume it is the ring and pinion bearing that made the noice. At 112,000 miles in my 04 sport trac, I had my differential make a noice, but it was a carrier bearing. But mine is a 4.10 rear. I had them replace all the bearings while they were at it as well as upgrade to a limited slip differential. Would of this TSB been addressing the same situation I had? I rarely haul heavy and don't tow with it.
 

EddieS'04

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If you use the Mobil 1, that says with friction modifier. You need to get a bottle of Ford friction modifier.
I changed the diff fluid in my 'Stang, 373 with LS. The mobil 1 friction modifier. Did not do the job. I still had to get a bottle of ford"s modifier. m2.jpg
 

Phil Frady

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I just read the TSB. Looks like the Sport Tracs are not listed, but yet, some of them have the same axle. I assume it is the ring and pinion bearing that made the noice. At 112,000 miles in my 04 sport trac, I had my differential make a noice, but it was a carrier bearing. But mine is a 4.10 rear. I had them replace all the bearings while they were at it as well as upgrade to a limited slip differential. Would of this TSB been addressing the same situation I had? I rarely haul heavy and don't tow w
Did you order yours with an open carrier? All ST w/4.10 came with LS. It was actually part of the “package” that included fog lights, running boards, and the 5 spoke wheels. Yours may have been like mine and worn out.
 

EddieS'04

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Not all 4:10 ratio came with LS. mine didn't'. That is why I went with the Richmond gear mechanical. It replaces all the spider gears. Without disturbing the ring and pinion lash.
The LS clutches do wear out. I added an extra clutch plate to my 'Stang. Both wheels would bite immediately no lag time,.
 

kmartin

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Did you order yours with an open carrier? All ST w/4.10 came with LS. It was actually part of the “package” that included fog lights, running boards, and the 5 spoke wheels. Yours may have been like mine and worn out.
Mine came with a marriage. Wife bought it brand new off the lot. Eddie is right, not all 4.10 are LS. She bought the XLT Premium which I saw the 4.10 was standard for them, that is probably why it was open. I have the old carrier in my garage to show it was indeed open. I put a Yukon DuraGrip in, because it was reasonably priced. So far, I can tell a difference in just normal driving. I started out using 80w90 for break in. Just trying to figure, should I go 75w90 or 75w140 to replace that?
 

DILLARD000

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This 2001 ExST has factory 4.10 Diffs, LimitedSlip Rear, Open Front.
Have always used 75w140~FullSyn+Modifier in Rear & 75w90~FullSyn in Front without issue.
240kMiles now, though I drive like a ChurchLady.
4WD gets most use winter plowing & 50Mile runs to town if roads are too snowy\icy for the car.
 

swshawaii

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Attn OP- Apologies for hijacking/derailing this thread. Just wanted to share this and will delete if requested.
I wish I still had it. I built it strong enough for a power adder. The buyer totaled it 4 months later.
Recently I was behind a black, but identical MB AMG C63S hot rod being driven by a young and very inexperienced driver that was 100% throttle and sideways after every stop. Worse yet, the roads were wet. He got on it in a sweeping curve and saw the car get sideways and hit the median guardrail head on. Air bag blew and I drove by flipping him the bird after I saw him get out of the vehicle. Know I failed to render aid but was very angry and there were many other witnesses close by. I'm certain the car was totaled, and hope he learned his lesson. Insurance company knows the EDR (black box) doesn't lie.

 

EddieS'04

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the EDR (black box) doesn't lie.
Your right. Most people don't know about the black box. Not sure of the year they became normal.
I have always been a hotroder. I learned at an early age about the car and my own limits. Nothing serious just enough to realize the bad potential.
I have a PDF file all about the box I can post if anyone interested?
 

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