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Discussion Starter #1
I recently changed my rear diff fluid. I've got a F-350 DRW with a 4.10 rear end. The manual stated 75W-140 for 10.50 rear axle and 75W-90 for Dana 80 rear axle. I've got Dana stamped right on the cover but I am wondering if I made a mistake.

Any and all help would be appreciated, I don't want any repair bills!!

Thanks,
Coop
 

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On DRW you put 75W-90
 

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Discussion Starter #3
Regardless of the diff being a 3.73 or 4.10???
I thought the 3.73 is a 10.50 rear and a Ford while the 4.10 is a Dana. Like I said I have Dana stamped on the rear diff, but I just wanted to make sure. The 10.50 calls for 75W-140. Is that a 3.73??

Thanks,
Coop
 

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The differance is in whether it is a SRW or a DRW, the ratio has nothing to do with it.
 

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I use good quality gear oil and DONT ADD any additive untill you drive the truck a bit. If the rear end starts to chatter [should occur right away] then you need to add the limited slip additive. I use the stuff from Chrysler becasue all Dodges use Dana limited slips and the stuff works good. If you add too much additive you can render your limited slip inoperative due to excessive clutch slippage.
 

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OK, SMOKESKULL. I think you'll feel bad if the poor advice you give Cooperdog takes out his clutch packs in his rear end, or even worse takes out his rear end. COOPERDDOG, you NEED to use synthetic rear differential lubricant. IF, you do in fact have a Dana 80 rear differential, you will need two bottles of friction modifier to protect your diff and it's components. If you need help on lubricant types, or Ford part #'s, let me know.
 

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Sorry, forgot to add, the friction modifier is for limited slip rear ends. Oh and also, Coop, your Torqueshift is actually a 6spd.
 

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I wont feel bad for the advise I give, becasue its good advise. Like I said adding FRICTION MODIFIER to gear oil that already contains it is not only a waste of $ but it can and will render your limited slip inoperative. I have personally experienced this first hand after purchasing the super expensive full synthetic gear oil from Ford parts and having them insist I add 3 bottles of F/M rtoo. Within a week of SERVICING the rear diff the right rear dually would spin on take-off on anything other than dry pavement. Take my word for it that adding too much F/M will render the L/S inoperative! Most high quality gear oils already contain the F/M right out of the bottle! No B/S
 

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Discussion Starter #9
So just to be clear....75W-90 for my DRW.
 

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I thoght it was supposed to be the 85W140 for the Dana and 75W90 for the Corporate rear end!
 

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Dana 80 is 75W-90, and 75W140 for the Ford. There is also a Dana S110 and an S135. The S110 uses 75W-140, and the S135 uses 80W-90 (standard package) or 75W-140-(tow package). I'm not sure if the S110 and S135 are for 1 ton applications or not, so you'll need to find out exactly what your truck has. Also, if your rear end is still the original, you can call your dealer's parts dept. They can tell you what diff. you have by your VIN #.
 

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Discussion Starter #12
Good deal. I will call now. I appreciate the feed back.
 

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From what I can tell the manual is wrong. On a Dana website thay definatly call for the 75W140 for towing applications. Also the Dana 44 and 60 axles require 75W-140 synthetic also, but I dont know why unless your doing some sever 4x4ing. When I purchased the replacement synthetic gear oil from Ford I was sold the 75W140 for my Dana 80DRW.
 

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Discussion Starter #14
Well I called two different dealerships and they said they could not tell what rear end I had by my Vin#. I got the feeling they could really couldn't care less. One guy told me to just follow the manual, but couldn't tell me anything about what rear end I acually had. I had no idea this wasn't just a simple task.

My alternator just died so I guess I'll have to get the info straight from the techs. Thanks for the help.

Coop
 

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[ QUOTE ]
Well I called two different dealerships and they said they could not tell what rear end I had by my Vin#.

[/ QUOTE ]


They're right. You can't tell which rear end is in a vehicle by interpreting the VIN. However, the dealer can use the VIN to access the Ford database for your truck, and that database includes everything Ford knows about your truck - including the rear end type and gear ratio. However, most Ford dealers will charge you one hour labor rate to access the Ford database through the OASIS computer system.

If you have a '99-up DRW, then you have a Dana 80 rear end with either a standard 3.73 gear ratio without limited slip (LS), or an optional 4.10 gear ratio with LS.

All '99-up SRWs come with a Ford/Visteon "Sterling" rear end with a 10.5" ring gear and 3.73 ratio. Open axle was std, and LS was optional.

Your Owner's Guide probably says to use 75W90 synthetic in your Dana rear end. But Ford recently told all their dealers to change that to 75W140 synthetic.

So the current gear oil for your Dana 80 rear end is 75W140 synthetic.
 

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Discussion Starter #16
That clears it up, and does make some sense. I just couldn't see putting 75W-90 in a DRW. I really appreciate your input and time Smokey.


Thanks,
Coop
 

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Like Smokey said... the dealer (well, a wise dealer, anyway) can access HVBOM and tell you more about your truck than you care to know...

FWIW, Ford is discontinuing 75W90 and switching everything to (I can never remember) 75W140.... Price difference is minimal... the 75W140 performs better. If you are looking at a fluid spec change, stepping up is always a better choice than stepping down....

This ain't rocket science, ladies....
 

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[ QUOTE ]
FWIW, Ford is discontinuing 75W90 and switching everything to (I can never remember) 75W140....

[/ QUOTE ] I suspect that you are referring to its use in rear axles. I find it unlikely that 75W90 would be "discontinued" across the board. There will still be some applications in cars and most front differentials of trucks where it would be better suited. Especially in cold locations. I will continue to use it in front axles.
 

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well I'm doing this now and I am pulling my hair out !! I am about to refill the diff tomorrow I'm waiting for the gasket maker to cure. A good friend also diesel mechanic says 75 90, called a dealer they said 75 90 but when I went to another Ford dealer closer to home they sold me 75 140 and 4oz modifier. so which do I use?? 2006 f350 dually dana 80. on my door sticker it says 4N which I found to be dana 80 410 gear limited slip. thank you for any advise!!
 
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