Rear differential
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From: MN
Rear differential
I got a new to me truck. It's a 2004 F150 Lariat 4x4 with the 5.4L. It's got a whine that I believe is coming from the rear differential. I'm going to change the fluid to see if that helps any. My axle code is 26 which I believe is 3.73 non-limited slip. My owners manual says to use 75w-90 but I've seen a lot of posts on here that say to use 75w-140. Which is right or better? Also, is my rear differential the 9.75"? Thanks.
Logistics Pro
Joined: Jul 2004
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From: Middleville, MI
75w-140 is due to the limited slip. (EDIT: as to not spew bad info, it offers more protection on the high temperature end, and clutch limited slips generate extra heat. unless you're towing heavy and/or really beating on it i wouldn't bother with the 140 weight especially in an open diff.)
can you describe your whine? is it only under load/go away when off the throttle?
can you describe your whine? is it only under load/go away when off the throttle?
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So, I should stick with 75w-90 then in a non-limited slip? Yes, the whine is only under load starting at about 40mph and will stop when I let off the throttle. That's probably the rear differential right?
Logistics Pro
Joined: Jul 2004
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From: Middleville, MI
edited my post above.
i have a driveline whine with the exact same symptoms. i've only owned the truck since november, and one of the first things i did last fall was change the rear diff fluid (went with 75w-140, 3.73 LS rear end), and if anything it has gotten louder. i've done a little reading and it sounds like it's not uncommon on these trucks. curious to see what other answers you get.
i have a driveline whine with the exact same symptoms. i've only owned the truck since november, and one of the first things i did last fall was change the rear diff fluid (went with 75w-140, 3.73 LS rear end), and if anything it has gotten louder. i've done a little reading and it sounds like it's not uncommon on these trucks. curious to see what other answers you get.
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From: MN
Thanks Brandon. I think a differential whine is usually a symptom of it's initial setup but I figured a fluid change wouldn't hurt. I hope someone else chimes in on whether it's best to use 75w-90 or 75w-140 in a non-limited slip diff.
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I didn't think about the cold weather. That's a good point. I probably should just stay with the 75w-90. The all terrain tires do make some noise but the whining noise will stop when I let off the throttle.
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Fleet Mechanic
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That pretty well points to the rear alright. I guess it depends on how loud it gets and how much it bothers you. I noticed today I have a very slight whine on my truck with only 19,500 miles, and it does the same - stops when you let off the gas. I had a Jeep Cherokee that did that for the whole 90,000 miles I had it. Sometimes I think we're listening too hard for noises. 
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Interesting thread right here: Ford 9.75" 75w90 | ATF, Differential, Trans, Brakes, P/S | Bob Is The Oil Guy
Logistics Pro
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From: Middleville, MI
this holds truth in my case; i paid more than i wanted to for my truck, so everything working less than optimal gives me anxiety haha.
that said, and back to the subject, i wonder about the pinion bearing.
that said, and back to the subject, i wonder about the pinion bearing.
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After Tim's post, I did a little more research. See the links below:
2004 F150 Rear Diff fluid [Archive] - FSB Forums
Help with correct differential fluid selection... - Page 2 - F150online Forums
Ford is saying to change the 75w-90 recommendation to 75w-140. It seems that they're usually talking about the limited slip rear but one of the Ford notes makes it sound like all vehicles should use 75w-140 now instead of the 75w-90. They even say to change the tag on the rear diff. They don't really make a distinction about climate so I think I'm going to go with full synthetic 75w-140. It probably won't stop the whine but at least it will be fresh fluid and have what Ford now recommends.
2004 F150 Rear Diff fluid [Archive] - FSB Forums
Help with correct differential fluid selection... - Page 2 - F150online Forums
Ford is saying to change the 75w-90 recommendation to 75w-140. It seems that they're usually talking about the limited slip rear but one of the Ford notes makes it sound like all vehicles should use 75w-140 now instead of the 75w-90. They even say to change the tag on the rear diff. They don't really make a distinction about climate so I think I'm going to go with full synthetic 75w-140. It probably won't stop the whine but at least it will be fresh fluid and have what Ford now recommends.
Hotshot
Joined: Jul 2005
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on your noise, I had a 2001 with the 9.75 axle and 3.55 gears. Changed the lube every 50K miles... still had the pinion bearing go out about 200K miles... I bought a kit and did the ring gear bearings also to make it like new........... used original clutch (LS) and gears.
Cross-Country
Joined: Oct 2002
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From: North Dakota
2004 F150 rearend whine
Same story on mine. 103500 miles or so currently. Been whining since I bought it four years ago @ 72000 miles. Just under load. Coasting it gets quiet. Changed the fluid etc. No difference. Had a mechanic tell me 20,000 miles ago the rearend was shot. He might have been wrong? 3.73 with LS. Gonna run it, see what happens.
3.73 with LS. Gonna run it, see what happens.
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From: MN
I crawled under mine the other day and saw the new tag on it saying to use only 75w-140 indicating to me that it has already been in for service at some point and had the new recommendation fluid put in. I think I'm going to leave it alone for now.
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