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  #1  
Old 04-30-2019, 08:48 PM
bradleyheathhays bradleyheathhays is offline
 
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300k mile old diff fluid

I have a '11 Crown Vic with 300k miles on it and my rear diff fluid looks like this...



Been watching some utube vids on how to change this fluid out but after a visit to the local Advance store I've got some questions. Up til now, forums on the net have led me to believe that all former police cars (which is what mine is) need 75w-140 fluid with friction modifier, but after giving them my VIN at Advance the computer comes back with a fluid suggestion of 80w-90.

Here's the diff tag...



I believe that shows a 3 (L or 1)? 27 which indicates a 3.27 gear ratio, and then an 88 after, which indicates the 8.8 axle. Not sure what that SYN means, unless it means synchronous?

This car is driven VERY sparingly, long distances at 60-65mph but never hard, and operates in a climate that can get up to 95F in the summer.

When the rear is jacked up and one rear wheel is spun, the other moves in the opposite direction.

So my first question is... what weight fluid should I use? Also, I need confirmation if I should use a friction modifier.

Next is how to go about changing the oil out. I'm being lazy here and after watching a vid on how you can extract 80% of the diff fluid out the fill hole by using a flexible hose I'm thinking about just doing it that way. But if you guys think it's necessary to get all that old fluid out I'll take plate off and do it the regular way.

And lastly, if I take the plate off, should I spray all the gears down with brake cleaner to get all the old fluid out, or just let it drain for a while and call it good?

Last edited by bradleyheathhays; 04-30-2019 at 09:31 PM.
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Old 04-30-2019, 08:52 PM
bradleyheathhays bradleyheathhays is offline
 
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Sorry, that large picture makes things hard to read. Not sure how to change that.
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Old 05-01-2019, 04:46 AM
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If the opposite wheel turns in the opposite direction, that indicates an open differential.(No limited slip) The axle housing has a date code of 10J08, which indicates a date of October 8, 2010.
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Old 05-02-2019, 09:28 PM
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I found a spec sheet that said 75W-140 for the police version of the car.

As for cleaning it out, I would spray it out with brake cleaner considering how dirty it looks.

If you have concerns about getting all of the cleaner out, maybe do a flush. Spray/clean it out with brake cleaner, let dry for a while, refill with oil, circulate the oil by turning the wheels or driving it a short distance, drain again and refill for good.
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Old 05-02-2019, 10:24 PM
bradleyheathhays bradleyheathhays is offline
 
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Thanks for the advice yall. Couple wrap up questions...

What advantage is there to using the more expensive Mobil 1 synthetic as opposed to a cheaper Valvoline full syn... $20 a bottle vs. $13, times 3.

Also, I've been given advice to replace the clutches and 'steels?' in the diff as mine are probably worn out. What advantage in performance would I gain by doing this and is it expensive/ worth it?
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Old 05-03-2019, 03:46 AM
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Originally Posted by Jasperrc View Post
I found a spec sheet that said 75W-140 for the police version of the car.

As for cleaning it out, I would spray it out with brake cleaner considering how dirty it looks.

If you have concerns about getting all of the cleaner out, maybe do a flush. Spray/clean it out with brake cleaner, let dry for a while, refill with oil, circulate the oil by turning the wheels or driving it a short distance, drain again and refill for good.


thats how ive always cleaned them out... also how we did it in the dealership... that and parts washer solvent... biggest thing is getting it cleaned out when your done before adding the new fluid back in.. nice thing with the BPC is it dries quickly so long as its not in a big puddle...
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Old 05-04-2019, 08:57 PM
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Based on the fact that it currently acts like an open diff, I'd agree that the clutch pack is worn out and needs to be replaced.

That being said, if you aren't driving it hard and open diff behavior is fine with you it may not be worth the expense to replace although I'm seeing clutch pack kits available for around $50 which doesn't seem too bad to me.

I've never replaced one myself so I don't know how involved a job it is but I'm sure Sparky or someone else may be able to give you insight there.
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Old 05-05-2019, 05:04 AM
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Originally Posted by Jasperrc View Post
Based on the fact that it currently acts like an open diff, I'd agree that the clutch pack is worn out and needs to be replaced.

That being said, if you aren't driving it hard and open diff behavior is fine with you it may not be worth the expense to replace although I'm seeing clutch pack kits available for around $50 which doesn't seem too bad to me.

I've never replaced one myself so I don't know how involved a job it is but I'm sure Sparky or someone else may be able to give you insight there.
its about like rebuilding an automatic... alternating steel and friction disks... youll want to soak the plates in diff fluid before installing them just as you would the automatic disks.. keep record of how many and what shims are on the outside of the diff so you dont have to get the diff back in alignment with the pinion gear... when your taking it apart also keep count of how many steels and friction disks are on each side... some aftermarket kits come with extras since theyre designed for multiple vehicles and dont want to get too many in there...
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