Thoughts guys...4.09:1 gears or the FRPP Power kit for my 2020 Mustang GT PP1 manual

[Rpinaiii]

^^ what post # is it? I tried going through your posts but you are pretty active.

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[Sivi70980]

Called both Ford Performance and U.S. Gear and asked for their recommendations for breaking in the new gears. FPP said leave the car on jack stands and run it for 10 minutes, then let it cool back to room temperature. USG said if it's not tracked, leave it on jack stands and run it in 1st and reverse for 3 minutes, then take it down and drive conservatively for 10 miles, then park it until the diff is completely cool. Something about running it unloaded on jack stands and that complete cool-down must be important.

Here ya go

 

[Sivi70980]

Actually the entire thread is a good read...

https://www.mustang6g.com/forums/threads/how-are-people-liking-4-09-gears-in-the-mt82.111146/

 

[Rpinaiii]

Got it thanks. I read about the cool down part In between drives too when I researched. The shop also recommended adding motocraft limited slip additive, 4 oz when I change out the gear oil.

 

[Rpinaiii]

Just quick update. I have 190 miles more for break-in then change diff fluid. So far all I can say is WOW. I havent really got on it yet. But will soon. But it feels really good. I thought switching to 4.09 will be too short in gear but I am just fine with the shifting and the mustang feels like it just wants to break loose. Especially the first 3 gears. Like its saying give it to me baby dont be skeeerd. Lol. Now I am using 6th gear on the highways at 80 mph I am at 2400 rpm so not bad at all. There is a whole bunch of room for 4.09s. I cant wait to do an all out rolling pull from 2nd. Gonna be nuts. Also, the exhaust note sounds better or louder seems like, but I think its because I move up in rpm so much quicker.

 

[Rpinaiii]

I saw in owners manual the rear axle takes 3.2 pints (pt) it shows for 2018 Mustang GT. Am I reading that correctly? About to buy the oil online and I think by next weekend I'll change it out.

 

[Dave2013M3]

I saw in owners manual the rear axle takes 3.2 pints (pt) it shows for 2018 Mustang GT. Am I reading that correctly? About to buy the oil online and I think by next weekend I'll change it out.

Is it required to replace the fluid? Didn't have to do it with factory fill. I remember with BMW M3s you had to take the car the first 1200 miles in for an oil change and they did change out the diff fluid.

 

[Rpinaiii]

I am changing the diff fluid since I am in break in process for new 4.09 gears.

 

[Dave2013M3]

I am changing the diff fluid since I am in break in process for new 4.09 gears.

I guess thats what I am asking, is a break in process necessary for the new gears? We didn't have to change the OEM fluid out with the initial gears.

 

[Rpinaiii]

I see what you are saying but I think its precautionary more than anything.

 

[Superspirit]

Just quick update. I have 190 miles more for break-in then change diff fluid. So far all I can say is WOW. I havent really got on it yet. But will soon. But it feels really good. I thought switching to 4.09 will be too short in gear but I am just fine with the shifting and the mustang feels like it just wants to break loose. Especially the first 3 gears. Like its saying give it to me baby dont be skeeerd. Lol. Now I am using 6th gear on the highways at 80 mph I am at 2400 rpm so not bad at all. There is a whole bunch of room for 4.09s. I cant wait to do an all out rolling pull from 2nd. Gonna be nuts. Also, the exhaust note sounds better or louder seems like, but I think its because I move up in rpm so much quicker.

You have that report ready yet?

 

[Rpinaiii]

^^ yes, just changed fluids last weekend after break in. I dont drive mustang every day so it takes me a while to get familiar usually. I started to really get on it though. I want to do some 0-60 pulls and get a time, but need to find a decent place to do it. But for sure the acceleration improved big time. Driving is pretty interesting now. Everyday type driving is not bad at all. I dont have any interesting racing stories YET, but will soon lol. It pulls down low really good. Right now I am trying to get familiar with shift gears, rpms, and speed. It seems like I am about even in 2nd gear at 40 mph about 4,000 rpms, 50 - 5,000, 60 - 6,000 but that is just a quick glance. I dont have digital dash. Whole lot of room to do pulls, down shifting to 2nd gear. I'll be driving it this weekend for sure! I enjoy the change so much I am considering changing rear gears on my 2019 Corvette. It's a manual too and has 3.42 gears right now with 7 shift gears, 3 are overdrive. Where as the mustang had 2 overdrive gears. I read 3.90 rear for the Corvette manual is perfect just like the 4.09s for mustang! The price for the rear gear change was worth it. I think even if mustang was stock, without the ford performance power kit, it would have made a huge difference as well. I notice with the mustang I reach 60 mph way faster than before.

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