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Gonna swap the rear ends from a 97 sport (3.27 ls) with the one in my 94 LX (3.08 open).

The replacement pumpkin has 137k on it so I was gonna drain and refill it with Mobil 1 75/90 LS gear oil. How many bottles is it gonna take? Do I need to add additional friction modifier if using the the LS oil.

Also is there a gasket for the cover?

Any trick to pulling the driveshafts out of the pumpkin? Or putting them back in?
 

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PostWhore, The AFDB is on a lil tight.
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THe only trick I know of I using a 12mm gear wrench and a light blow hammer. I pop the cover cover off the get all the old oil out.

I cant answer your question of if you should use the ford friction mod. Just use mtorcraft gear oil and add the FM if you have any doubt.

People go with and without gaskets. I have one and it doesnt leak and I used gray rtv to seal it back up after the break in.
 

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Gonna swap the rear ends from a 97 sport (3.27 ls) with the one in my 94 LX (3.08 open).

The replacement pumpkin has 137k on it so I was gonna drain and refill it with Mobil 1 75/90 LS gear oil. How many bottles is it gonna take? Do I need to add additional friction modifier if using the the LS oil.

Also is there a gasket for the cover?

Any trick to pulling the driveshafts out of the pumpkin? Or putting them back in?
It will take about 1 1/2 quarts of differential oil. Mobil 1 LS Gear lube already has modifiers so you do not need to add any additional friction modifier.

Yes, you need a standard Ford 8.8" differential gasket (some people don't use them, but you should).

I've never removed 'Bird half-shafts, but I've done plenty of front-wheel drives and I just pop the shafts out with a crow bar.
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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I used black RTV to re-seal. Took about 1.75 quarts of fluid.
 

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Discussion Starter #5
Ok.....thanks. Hopefully no surprises tomorrow doing the swap.
 

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WOT Junkie and avid corn burner
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When the 3.73 TL rear was put in my car, it took 2 qts of oil and a container of the Ford friction modifier. For oil, I used Royal Purple 75W-140. When I replaced the oil in my old rear end, I just used ultra black rtv as the cover gasket. Laid down 3 rows of it and let it set for an hour before refilling.
 

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+1 For RTV. I have always used this in the past with good results.
 

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+1 For RTV. I have always used this in the past with good results.
I always use RTV on the differential cover. As a matter of fact so did Ford!
 

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WOT Junkie and avid corn burner
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I always use RTV on the differential cover. As a matter of fact so did Ford!
Yup. Even the Ford shop manual tells the technicians to do the same thing.
 

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When the 3.73 TL rear was put in my car, it took 2 qts of oil and a container of the Ford friction modifier. For oil, I used Royal Purple 75W-140. When I replaced the oil in my old rear end, I just used ultra black rtv as the cover gasket. Laid down 3 rows of it and let it set for an hour before refilling.
75w140 is a bit thick. I run the factory spec 80w90 or 75w90 even here in Las Vegas. Friction modifier is required on any ford trac-lok differential, if there is friction modifier added to the product contact the hotline on their bottle to confirm that it is enough for a ford limited slip differential. I know of a few that call for the factory additive on top of their own additive package mixed into the oil.

As far as gasket or no gasket If your using the factory cover RTV only. If your using an aftermarket cover like the LPW unit then I'd use the gasket only. I wouldn't use both, but I have seen and heard of people doing so.
 

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WOT Junkie and avid corn burner
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75w140 is a bit thick. I run the factory spec 80w90 or 75w90 even here in Las Vegas. Friction modifier is required on any ford trac-lok differential, if there is friction modifier added to the product contact the hotline on their bottle to confirm that it is enough for a ford limited slip differential. I know of a few that call for the factory additive on top of their own additive package mixed into the oil.
I just did as RobertP recommended. :zdunno:
 

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I know at the shop we always use RTV because that's what the boss tells us to do. Like y'all said, most every rear end I see come in there was sealed with RTV. The fluid is so thick, it's not likely to leak.

As for the Mobil 1 LS fluid - that's totally synthetic which is great to use and it includes all modifiers for the trac-lok. It's also much thinner than standard 75-90, 75-140, or whatever other conventional y'all use, which is why - again - if it was MY vehicle and I was running total synthetic, I'd use a gasket.
 

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I ran Valvoline full synthetic with my original ford trac-lok limited slip differential without issue.

I was told NOT to run the full synthetic with the carbon clutches and stiffer s-spring in my rebuilt unit by my local builder and the ford fluid hotline. Currently I use 80w90 conventional with the ford friction modifier.

Contrary to what many think the modifier doesn't make the clutch type engage it actually makes it slip to avoid chattering and damage.

I was told that with the setup I'm using I would risk excessive slipping even with straight synthetic with no modifiers. Hence fully synthetic with a friction modifier would only be worse.

As far as synthetic being thinner theoretically it shouldn't be any thinner hence why the weight is the same, however it does typically flow faster than or looser then conventional. Which is one of the reasons why it is a better lubricant, on top of the fact that it resists thermal breakdown, varnishing, and foaming better.
 

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I ran Valvoline full synthetic with my original ford trac-lok limited slip differential without issue.

I was told NOT to run the full synthetic with the carbon clutches and stiffer s-spring in my rebuilt unit by my local builder and the ford fluid hotline. Currently I use 80w90 conventional with the ford friction modifier.

Contrary to what many think the modifier doesn't make the clutch type engage it actually makes it slip to avoid chattering and damage.

I was told that with the setup I'm using I would risk excessive slipping even with straight synthetic with no modifiers. Hence fully synthetic with a friction modifier would only be worse.

As far as synthetic being thinner theoretically it shouldn't be any thinner hence why the weight is the same, however it does typically flow faster than or looser then conventional. Which is one of the reasons why it is a better lubricant, on top of the fact that it resists thermal breakdown, varnishing, and foaming better.
Synthetic oil is WAY thinner at all grades. Go pour out a bottle of 75-90 conventional versus a 75-90 fully synthetic if you don't believe it. Viscosity (weight) numbers (for the most part) refer to the oil's resistance to allowing contact of two metal surfaces (of which synthetic is FAR superior; this property changes with temperature. Point being, it's not how "thick" the oil is (not totally, anyways).

Good reading about it here:
http://www.synthetic-oil-tech.com/Gear Lube White Paper.pdf

Oh, and most synthetics do not require frictions modifiers added AT ALL. And yes, the modifier added to conventional is to allow slip for chatter control, not make it grab as you stated.

As for not running synthetic with carbon clutches, I have no idea - haven't had enough experience with them. If that's what you were told by some experts and it works for you, then go for it!
 
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