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Changing Diff fluid in a 2017 GT 350

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Agreed, my recommendation was to avoid running the pump with cold fluid repeatably.

I err on the side of caution and change Diff/Tranny fluid every 12-15 hours of track time.

I agree with your recommendation, and now that I've changed it twice and it's taken exactly the same amount both times, I'll probably skip running the pump from this point forward.

When you change your diff fluid, do you put the XL3 in as well? My understanding is that Torsens don't actually need it, so why bother, other than that's what Ford puts in it? Sometimes I wonder if Ford puts things like that in because they want to keep life simple for the guy running the lube rack, and not because the gears actually need it.
 
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I talked directly with Torsen regarding adding the friction modifier to the Torsen diff in the Boss. They said it was not necessary and that it was used to quiet down the diff. Not sure if it applies to the GT350 but I wouldn't be surprised if the reason is the same.
 
I agree with your recommendation, and now that I've changed it twice and it's taken exactly the same amount both times, I'll probably skip running the pump from this point forward.

When you change your diff fluid, do you put the XL3 in as well? My understanding is that Torsens don't actually need it, so why bother, other than that's what Ford puts in it? Sometimes I wonder if Ford puts things like that in because they want to keep life simple for the guy running the lube rack, and not because the gears actually need it.

Hello JAJ -

I finally got my cradle back into the car and I am going to fill the diff tonight. Before the cradle was removed I disconected the lower cooler line and let all of the fluid drain. Based on your method of filling the diff, all I need to do is fill the diff untill it is 9mm below the fill hole correct? I do not have access to a scan tool so I will not be running the pump. It seems so simple so I want to make sure I am not missing something.

Thanks for your help!
 
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If you put 56 ounces of new fluid in, as I noted above, and don't run the pump, the oil level will be higher than 9mm below the fill hole because of air trapped in the cooler lines. That's fine. Once the diff gets hot enough to run the pump, it'll flush the air out of the cooler lines and the level will drop to the 9mm mark, right where it's supposed to be.
 
If you put 56 ounces of new fluid in, as I noted above, and don't run the pump, the oil level will be higher than 9mm below the fill hole because of air trapped in the cooler lines. That's fine. Once the diff gets hot enough to run the pump, it'll flush the air out of the cooler lines and the level will drop to the 9mm mark, right where it's supposed to be.
You are the man! Thanks!!
 
I’m finally getting around to this. Any trick to pulling the purple retaining clip on the cooler line to remove? Wasn’t sure what type of fitting that is.
 
25
23
Exp. Type
Autocross
Exp. Level
3-5 Years
Houston
If you put 56 ounces of new fluid in, as I noted above, and don't run the pump, the oil level will be higher than 9mm below the fill hole because of air trapped in the cooler lines. That's fine. Once the diff gets hot enough to run the pump, it'll flush the air out of the cooler lines and the level will drop to the 9mm mark, right where it's supposed to be.
I am really late to the game here, but hopefully this is a simple question with a simple answer. How much higher will the fluid level be?

The simple answer is just add the 56 oz, but what's a good second check to make sure someone does it right?
 
188
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Exp. Type
Time Attack
Exp. Level
10-20 Years
75024
I am really late to the game here, but hopefully this is a simple question with a simple answer. How much higher will the fluid level be?

The simple answer is just add the 56 oz, but what's a good second check to make sure someone does it right?
I just fill until it starts dripping out of the fill port. Probably the right amount, it's such a stinky mess with gear oil to measure and pump it in exactly, fill to top has never caused an issue.
 
25
23
Exp. Type
Autocross
Exp. Level
3-5 Years
Houston
I just fill until it starts dripping out of the fill port. Probably the right amount, it's such a stinky mess with gear oil to measure and pump it in exactly, fill to top has never caused an issue.
I do the same for every other car, but the exact ness of JAJ makes me think I should do it perfect the first go round so that I know what it should look like every other time I do it.

Not to mention I can't get a straight answer on the friction modifier. But one bridge at a time haha
 
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In the V6L
I do the same for every other car, but the exact ness of JAJ makes me think I should do it perfect the first go round so that I know what it should look like every other time I do it.

Not to mention I can't get a straight answer on the friction modifier. But one bridge at a time haha
I got the 9mm level from the factory Shop Manual, so I've used it since 2016 and never had a problem. Some people have complained about leaking seals if they fill it right up to the bottom of the hole, but I've never experienced it myself.

As for friction modifier, Ford says use four ounces of XL-3 friction modifier in each fill when using the Motorcraft 75w85 spec fluid. Again, I've used FM as advised and never had a problem. A lot of people believe it's not necessary, and they might be right, but I just follow the instructions and it all works. If you switch to another brand of diff fluid, it might come with friction modifier in it already, and if it does, you don't need to add more.
 
25
23
Exp. Type
Autocross
Exp. Level
3-5 Years
Houston
I got the 9mm level from the factory Shop Manual, so I've used it since 2016 and never had a problem. Some people have complained about leaking seals if they fill it right up to the bottom of the hole, but I've never experienced it myself.

As for friction modifier, Ford says use four ounces of XL-3 friction modifier in each fill when using the Motorcraft 75w85 spec fluid. Again, I've used FM as advised and never had a problem. A lot of people believe it's not necessary, and they might be right, but I just follow the instructions and it all works. If you switch to another brand of diff fluid, it might come with friction modifier in it already, and if it does, you don't need to add more.
Thanks for the response. I wasn't sure I'd get one on such an old thread.

My plan is to take basically a paper clip and bend it such that 9 mm hangs down, and use that for a secondary check after I add 56 oz. That will get me dead nuts on, then, validate I'm 9mm below the fill hole after cycling the diff pump either through forscan or going for a ride. After that, I can streamline the process.

Thanks again. When I did this on my previous cars it was simply fill to the hole, done. This one would likely be fine with the same process, but I like this car a lot more than the others haha
 
1,246
1,243
In the V6L
Thanks for the response. I wasn't sure I'd get one on such an old thread.

My plan is to take basically a paper clip and bend it such that 9 mm hangs down, and use that for a secondary check after I add 56 oz. That will get me dead nuts on, then, validate I'm 9mm below the fill hole after cycling the diff pump either through forscan or going for a ride. After that, I can streamline the process.

Thanks again. When I did this on my previous cars it was simply fill to the hole, done. This one would likely be fine with the same process, but I like this car a lot more than the others haha
You're welcome - I'm happy to help.
 

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