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Discussion Starter · #1 ·
Hey there, I have a manual 2011 mustang gt with 3.31's currently installed and 6000 miles on the car. I recently purchased ford racing 3.73 gears which included the pinion, pinion nut, gear, shims, and crush ring. Do I need anything else like bearings or seals. Also I plan on putting 75W140 royal purple and I was wondering if I need to add ford friction modifier, and if so, how much do I need to add? Thanks for your help.
 

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If you use the RP, you shouldn't need additional friction modifier.
 

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I think the friction modifier is for the LSD and is required.
 

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Royal Purple manufactures both motor and gear. Most have had good results with it. It, as Amsoil , has been credited for making gears engage smoother. The above has made many Harley's shift like butter when prior they shifted very clunky. Many, who have Vette's, have had their noisy diffs quieted by Amsoil gear oil and I would imagine that RP would do the same. This is not a "better then that" post but just an opinion from seeing what has worked. Whether it will do the same in the 5.0 is unknown, however I don't think there is anything special about the Ford 5.0 diff....
 

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Royal Purple manufactures both motor and gear. Most have had good results with it. It, as Amsoil , has been credited for making gears engage smoother. The above has made many Harley's shift like butter when prior they shifted very clunky. Many, who have Vette's, have had their noisy diffs quieted by Amsoil gear oil and I would imagine that RP would do the same. This is not a "better then that" post but just an opinion from seeing what has worked. Whether it will do the same in the 5.0 is unknown, however I don't think there is anything special about the Ford 5.0 diff....
Yea, it works well in both the diff and tranny in my 93 Cobra. Not sure about my 11 but I am going to change the tranny oil soon on that one tool. Will provide feedback when I know more.
 

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Discussion Starter · #9 ·
Thanks for all the answers. I was just curious if I needed anything else when changing the rear end gears? I have the pinion, gear, pinion nut, crush ring, and shims. Thanks for the help. Also, when looking online for the royal purple for the differential, I noticed that they sell 3 bottles of royal purple 75w140 and a small bottle of the ford friction modifier as a kit. If the rp alread has it in it I don't understand why that comes with it? Will it hurt to add the friction modifier also. Thanks!
 

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Be sure you take a great big whiff of the friction modifier. That is the worst smelling stuff ever.
 

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Installation Progess

Have you had any luck with the gear installation yet? Was thinking about doing the same thing. I'm runnin 3.31's as well, as was considering going to the 3.73's. I do a fair bit of driving, and was a little worried about losing mpg's. Of course, we didn't buy these things for the mileage...:rollgrin:
 

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Have you had any luck with the gear installation yet? Was thinking about doing the same thing. I'm runnin 3.31's as well, as was considering going to the 3.73's. I do a fair bit of driving, and was a little worried about losing mpg's. Of course, we didn't buy these things for the mileage...:rollgrin:
Do it man! I lost 1 mpg overall compared to the mushy 3.31's. I found highway mpg to be the same unless you're cruising over 90 all of the time. It's the city/traffic driving that knocks it down a little.
3.73's are much more fun overall. It's not too much gear at all. I would have thrown 4.10's in there but my dealer was acting weird about it.
Do it and don't look back :yup:
 

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Discussion Starter · #14 ·
I haven't got to get the gears installed yet, I have 3.31's in it now but I have the 3.73's waiting to be installed. I'm just deciding on if I should attempt to install them myself or to have someone install them for me.
 

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I haven't got to get the gears installed yet, I have 3.31's in it now but I have the 3.73's waiting to be installed. I'm just deciding on if I should attempt to install them myself or to have someone install them for me.

If you don't have experience with installing rear gears then I would advise you to take it to a qualified shop. It isn't something that's easy to get right if you don't have the proper tools and experience.
 

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id put some friction modifier in it again on rop of the royal purple or redline. wont do any harm. just half a bottle or so if your nervous. too much will cause slip, but you'd have to really overdo it. the stuffs not that sensitive and you'll have more peace of mind.
 
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