Differential fluid change

matthewr87

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Hello! Does anyone have the official ford procedure for changing the differential fluid? I am going to need to do this soon and was hoping to find guidance on the subject. I've seen a couple of Youtube videos but wanted to cross-reference with the official method. Thank you.





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FYI, Page 52 of owner's supplement says diff fluid need only be changed every 150,000 miles.
 
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matthewr87

matthewr87

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FYI, Page 52 of owner's supplement says diff fluid need only be changed every 150,000 miles.
For regular use yes. For tracking not so much; I'd rather put some fresh fluid in for next season.
 

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For regular use yes. For tracking not so much; I'd rather put some fresh fluid in for next season.
I have it, and it's pretty straightforward. You drain it by removing the locking ring (take note of how it's oriented so you can put it back the same way) from the lower cooler line, pulling the fitting apart (it comes straight out) and letting it drain. Once it's drained, you reinstall the lower cooler line and put the clip back in. You refill it with 52 ounces of 75w85 and a 4 ounce bottle of XL3 additive through the fill port, then run the cooler pump for 30 seconds or so and check the level. It should be 9mm (3/8") below the bottom of the fill port.

The first change will come out looking pretty bad - black, sparkly and smelly. After a few annual changes, it's a lot more pleasant.

You can run the pump with Forscan or another OBD service tool like IDS. The PID you're looking for is "R_DIFF_PUMP".
 

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matthewr87

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I have it, and it's pretty straightforward. You drain it by removing the locking ring (take note of how it's oriented so you can put it back the same way) from the lower cooler line, pulling the fitting apart (it comes straight out) and letting it drain. Once it's drained, you reinstall the lower cooler line and put the clip back in. You refill it with 52 ounces of 75w85 and a 4 ounce bottle of XL3 additive through the fill port, then run the cooler pump for 30 seconds or so and check the level. It should be 9mm (3/8") below the bottom of the fill port.

The first change will come out looking pretty bad - black, sparkly and smelly. After a few annual changes, it's a lot more pleasant.

You can run the pump with Forscan or another OBD service tool like IDS. The PID you're looking for is "R_DIFF_PUMP".
Thanks for the info! If I do not run the pump my understanding is that I will have leftover old fluid in the system, correct?
 

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Thanks for the info! If I do not run the pump my understanding is that I will have leftover old fluid in the system, correct?
No, the pump run is to make sure there's no air in the cooler lines and cooler itself. That ensures that the level you measure at 9mm is actually correct, and it won't drop after the pump starts when the diff gets hot.

You'll have old fluid in the system - the stuff still in the cooler, pump and lines that doesn't drain out when you unplug the lower fitting. You have to change it twice if you want that out of there. It's not worth it.
 

foolwithtools

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Hello! Does anyone have the official ford procedure for changing the differential fluid? I am going to need to do this soon and was hoping to find guidance on the subject. I've seen a couple of Youtube videos but wanted to cross-reference with the official method. Thank you.
Here's a copy of the procedure from the 2020 service manual. It hasn't been updated since 2015 so it should apply to all GT350s
 

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Tomster

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The key here is replace the exact amount of fluid that you took out (assuming it was filled from the factory). Just like JAJ said, it always (and should be) 56 oz. If you fill it to the fill hole, a high G turn will spew fluid out of the vent all over your strut. If the diff has been serviced before, most likely the tech just filled it to the fill hole, and that is overfilled.

Another note, you don't have to run the pump. Eventually the fluid temp will run the pump anyway (at the track) and that will take care of any air in the line. Besides the fluid will be hot and less viscous. It is not recommended to run the pump with cold fluid.

If you insist on running the pump (i do when fluid is warm), use the Forscan procedure in my post above.
 

Buckwampum

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And before you drain the oil, check and make sure you can remove the fill plug FIRST. Not so much of an issue on new cars but my history with antique muscle cars had me merrily draining the diff fluid first and then discovering that the fill plug was cross threaded........
 
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matthewr87

matthewr87

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Here's a copy of the procedure from the 2020 service manual. It hasn't been updated since 2015 so it should apply to all GT350s
Thank you very much!
 
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matthewr87

matthewr87

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The key here is replace the exact amount of fluid that you took out (assuming it was filled from the factory). Just like JAJ said, it always (and should be) 56 oz. If you fill it to the fill hole, a high G turn will spew fluid out of the vent all over your strut. If the diff has been serviced before, most likely the tech just filled it to the fill hole, and that is overfilled.

Another note, you don't have to run the pump. Eventually the fluid temp will run the pump anyway (at the track) and that will take care of any air in the line. Besides the fluid will be hot and less viscous. It is not recommended to run the pump with cold fluid.

If you insist on running the pump (i do when fluid is warm), use the Forscan procedure in my post above.
Okay thanks. I'll use a graduated cylinder to measure the volume I remove.
 

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