How are people liking 4.09 gears in the MT82?

[Mikepol2]

Quick cost summary:

Ford Dealer #1 said they wouldn't do it, call a speed shop.

Dealer #2 said drop off the car, gears, and install kit, and they'd do the whole thing for $1,200.

Dealer #3 said if I bring them the diff, gears, and install kit, they'd put the gears in the diff for $560.

Local speed shop #1 said $100/hr and "about 8-10 hours" to do the whole thing but wouldn't give a firm price.

Speed shop #2 said $225 if I bring the diff, gears and kit, but reviews on him were mixed online.

Guy who ended up doing it is a buddy of a co-worker who is a car guy and recommended him, he did it for $225. I trust him because he was referred by a friend but also because his wife works in a Ford service dept and could get spec information if needed. Also I could tell from talking to him about it that he had done gear installs before (just not on S550 Mustangs). I just picked it up about an hour ago. He said the factory shims were perfect and the gear alignment pattern was as good as he's ever seen, the Ford Performance gears seemed to be very well made. He struggled a bit with the crush sleeve because it was out of the car but other than that said it went well.

Hope to start installing it back into the car in a few days, just ordered a Steeda H-pipe because I wanted to try a different sound from my X-pipe while the exhaust was out of the car. Also have to replace the rear brake pads because half of one of the pads had broken off and just fell out of the caliper when I took the caliper off. H-pipe, pads, and gear oil due to arrive Friday.

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[Sammy123]

Nice,

Seeing the same cost issue here as well. $287 for the part but $850 install (minimum). Doesn't seem like a good bang for buck mod unless you can do it yourself or know a friend.

 

[Mikepol2]

Nice,

Seeing the same cost issue here as well. $287 for the part but $850 install (minimum). Doesn't seem like a good bang for buck mod unless you can do it yourself or know a friend.

The guy who did mine said that about 2/3 of the dealer labor cost is removing and reinstalling the diff (and now having removed the diff I totally believe it).

Also I got the gears for $175 and the install kit for $38, both on Ebay after a lot of patient searching.

 

[Mikepol2]

Diff bolted in, driveshaft attached, half shafts in, brakes back on. At a stop for now till the new H-pipe comes in tomorrow and then I can finally bolt up the exhaust and try out the 4.09's.

Lining up the diff with the floor jack and wood platform was pretty tough, the front bushings have a slot in them and you have to line it up perfectly and lift straight up to fit the diff in.

There was blue Loctite on the 4 diff bolts when they came out which seems useless, blue is good for about 110 ft-lbs and the diff bolts get torqued to 130. The shop manual doesn't call for adding thread locker at reinstallation.

Don't use a Sharpie to match-mark the pinion flange to the driveshaft. Somewhere along the line it got wiped off the flange so hopefully I guessed right on the orientation, although I don't understand why the instructions recommend match marking in the first place.

A $10 hand pump is a must for adding the gear oil.

Putting the knuckle back on was a PIA, you have to put in the 21mm bolt last. If you put it in before the two 18mm bolts closer to the front of the car, you can't start the threads into the holes.

Had to switch mental gears at that point for the brake reinstall...when I wash the car (all my vehicles for years, really) I spray water down into the calipers to wash out all the brake dust. With this car though, I noticed that the next day the car was always "stuck" and you had to give it some gas until hearing a "crack" before the car would move. Turns out it was the crappy semi-metallic OEM rear pads rusting onto the disc. Installed Powerstop Z23 carbon fiber / ceramic pads, wow the Powerstops seem really well made and have a lot more friction surface area than the OEM pads. Also the rear caliper pistons are the screw-in type, not the compress-with-a-C-clamp type.

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.

I'll be posting the 3.73's and the remaining parts from the install kit for sale soon, but not counting selling those parts, my total cost for the 4.09 install was $611. That includes the gears and install kit (great price new on Ebay), my buddy installing them into the diff, 2 quarts of Red Line 75W85, a 32mm socket, used BMR jacking rails, 2 new axle nuts, and blue 242 Loctite.

So here I sit...probably one more update in a day or two.

 

[Mikepol2]

All done. 10 minute run yesterday on jack stands went fine, although there was a loud clank the first time I put it into reverse, I basically dropped the clutch and there was no weight on the wheels. Let it sit overnight, then took it out today for a 15 mile test drive. Not a drop of fluid on the garage floor after sitting overnight. No hard acceleration yet, still breaking them in. NOTICEABLE improvement in acceleration, especially 2500-4000 rpm in 3rd gear. Ran it at speeds up to 75 mph, no vibration, whining, or roaring - smooth as butter. Very driveable and shiftable. If I'm careful with the clutch, there's no clank putting it into reverse, maybe it just sounds louder because the gears are a steeper angle or something.

At 2000 rpm in 3rd gear with the 3.73's I was going 31 mph, now with the 4.09's it reads 28 mph, which lines right up with the predicted calculated speeds. It adjusted to the new gears automatically like other people have posted.

So it's still early but as of now, to quote Gene Hackman in Hoosiers: I regret nothing.

Side note: If you lined up two of my car next to each other, one with the X-pipe and one with the H-pipe, I'd never be able to tell them apart.

 

[BmacIL]

All done. 10 minute run yesterday on jack stands went fine, although there was a loud clank the first time I put it into reverse, I basically dropped the clutch and there was no weight on the wheels. Let it sit overnight, then took it out today for a 15 mile test drive. Not a drop of fluid on the garage floor after sitting overnight. No hard acceleration yet, still breaking them in. NOTICEABLE improvement in acceleration, especially 2500-4000 rpm in 3rd gear. Ran it at speeds up to 75 mph, no vibration, whining, or roaring - smooth as butter. Very driveable and shiftable. If I'm careful with the clutch, there's no clank putting it into reverse, maybe it just sounds louder because the gears are a steeper angle or something.

At 2000 rpm in 3rd gear with the 3.73's I was going 32 mph, now with the 4.09's it reads 29 mph. It adjusted to the new gears automatically like other people have posted.

So it's still early but as of now, to quote Gene Hackman in Hoosiers: I regret nothing.

Side note: If you lined up two of my car next to each other, one with the X-pipe and one with the H-pipe, I'd never be able to tell them apart.

Nice! That ratio is really necessary for the 2018+ MT82. I just installed a 3.73 diff in my 2015 (had 3.31) and it's exactly how it should be. I've driven several PP cars but when it's your own it's always different. The 4.09 in the D4 is pretty similar to 3.73 in the 2015-2017.

I'm probably going to actually get better fuel economy with these gears in my commute because I can use 6th more often without it being so sluggish.

 

[Mikepol2]

First daily commute to work today and the gears were fine. The highest speed limit I encounter is 45 mph so there's really no difference in driveability, other than shifting into 6th in a few places where usually I'd stay in 5th with the 3.73's. As other people have mentioned, 1st gear isn't very useful, other than starting on hills - on level spots I'm starting out in 2nd more often now. The only other ratio I've seen advertised is 4.56's, and I'd never go that route now, having felt what the 4.09's are like. I think Ford Performance did a good job picking a ratio to offer.

A co-worker who is a car guy and former GM test engineer wanted to take it for a ride so I let him drive it at lunchtime, and he was blown away with how fast it is for a dime-a-dozen Mustang. Ha!

 

[DuRsT]

I've been researching this very mod for my '19 GT PP1 M6.

Very interested to hear how it goes, I've been shopping around for a decent installation price but out here there doesn't seem to be any 'friends of friends' that I can call on.

 

[Mikepol2]

Well if you're near Pittsburgh I could see if my guy would be willing to install them for you, if you bring him the diff and the gears...

 

[DuRsT]

Well if you're near Pittsburgh I could see if my guy would be willing to install them for you, if you bring him the diff and the gears...

Man I REALLY appreciate that but you're about 950 miles away from me.

 

[Mikepol2]

Aaah bummer, well good luck, I get the feeling that hanging around car shows is a good way to find gear guys...especially the more classic 70's cars, those guys all seem to either have done their own or know "a guy"...

 

[DekiDoo]

Well I just made up my mind for 4.09s. Thanks for the thread and the updates.

 

[Mikepol2]

Unless most of your driving is over 75 mph, I would be shocked if you don't love it!

 

[ash9785]

Yukon Gear says they will produce 4.30s if they can get 100 orders. Who's in?

 

[Mikepol2]

Oh sure, now they're thinking about it...I asked them and US Gear a few months ago about 4.30's and they both said forget it LOL!

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