Installing 3.73 gears
09-25-2018, 03:31 PM
#2
Gentleman's Relish
Join Date: Feb 2005
Location: AZ
Posts: 13,090
Never done one myself and it's not something I would. Special tools and if you do it wrong, you'll get whinning. I'd rather pay a shop to do it. If they screw up, they have to fix it. The quote I got for labor to install a kit I was going to buy from American Muscle that included fresh bearings, seals, and oil was about $500 from a drive line shop that worked on performance and bracket cars. Probably about $50-75 more than the average shop.
09-25-2018, 03:31 PM
#3
3rd Gear Member
Join Date: Aug 2015
Location: SE Michigan
Posts: 939
Not terribly hard... with the right tools. You will need access to a shop press in order to swap the bearings over to the new pinion, and a beam-style lb-in torque wrench to set the pinion bearing preload. Cost depends on how much you can do yourself, and how far you want to go while it's all open. Besides the gears themselves, you're already looking at a gasket/gasket-maker to put it back together, and new gear oil (+friction modifier). Unless it has low miles, this would be a great time to install new bearings & seals too. You may also want to consider putting fresh clutch-packs in the carrier. Your call.
The ring & pinion gears can be changed without replacing any other hard parts. You'll just have to be very careful removing the inner bearing from the old pinion gear. And if you are asking about reusing the old carrier, the answer is yes. The ring gear bolts right to it.
May I ask why you're interested in 3.73 gears if you're not sure what ratio you already have?
The ring & pinion gears can be changed without replacing any other hard parts. You'll just have to be very careful removing the inner bearing from the old pinion gear. And if you are asking about reusing the old carrier, the answer is yes. The ring gear bolts right to it.
May I ask why you're interested in 3.73 gears if you're not sure what ratio you already have?
09-25-2018, 05:02 PM
#5
3rd Gear Member
Join Date: Aug 2015
Location: SE Michigan
Posts: 939
Technically correct (the best kind of correct! 
). According to Ford's officially preferred terminology here, the ring gear bolts to the "differential case". Not to be confused with the exterior casing, known as the "axle housing". (BTW Ford doesn't call the overall assembly a "live axle". This axle type is referred to as an "integral carrier".) And there are actually three pinion gears- the "differential pinion" gears inside the differential case, and the "drive pinion" that connects to the driveshaft via the pinion flange "rear axle universal joint flange".
). According to Ford's officially preferred terminology here, the ring gear bolts to the "differential case". Not to be confused with the exterior casing, known as the "axle housing". (BTW Ford doesn't call the overall assembly a "live axle". This axle type is referred to as an "integral carrier".) And there are actually three pinion gears- the "differential pinion" gears inside the differential case, and the "drive pinion" that connects to the driveshaft via the Last edited by Urambo Tauro; 09-25-2018 at 05:06 PM.
09-25-2018, 05:29 PM
#6
Thread Starter
Join Date: Sep 2018
Location: Florida
Posts: 35
Not terribly hard... with the right tools. You will need access to a shop press in order to swap the bearings over to the new pinion, and a beam-style lb-in torque wrench to set the pinion bearing preload. Cost depends on how much you can do yourself, and how far you want to go while it's all open. Besides the gears themselves, you're already looking at a gasket/gasket-maker to put it back together, and new gear oil (+friction modifier). Unless it has low miles, this would be a great time to install new bearings & seals too. You may also want to consider putting fresh clutch-packs in the carrier. Your call.
The ring & pinion gears can be changed without replacing any other hard parts. You'll just have to be very careful removing the inner bearing from the old pinion gear. And if you are asking about reusing the old carrier, the answer is yes. The ring gear bolts right to it.
May I ask why you're interested in 3.73 gears if you're not sure what ratio you already have?
The ring & pinion gears can be changed without replacing any other hard parts. You'll just have to be very careful removing the inner bearing from the old pinion gear. And if you are asking about reusing the old carrier, the answer is yes. The ring gear bolts right to it.
May I ask why you're interested in 3.73 gears if you're not sure what ratio you already have?
09-25-2018, 06:24 PM
#7
Banned
Join Date: Jan 2018
Location: Pennsylvania
Posts: 2,327
That's less than a half rotation of the driveshaft difference at +.46 rotation. You will
notice the RPMs are higher at 70, which should be around 2100/2200, that's where my '08
is at 70.
I went from a 2.87 to 3.64 in my Charger, that was a huge difference... I was at 3700 RPM
at cruising...
Don't forget the Tuner, to change the gear ratio.
Out in the Net:
For manual transmission, the 3.73 gear set is the go to set. Depending on what you’re after, a 3.55
set can also do the job for street/daily Mustangs. Automatic Mustangs; 4.10s, because they typically
have lower gears, and with the converter, you need a little more differential gear to get up and running.
The 4.10 makes up for the lower first gear of the transmission, and the slip of the converter.
The 3.73 for a 5/6 speed manual offers great performance around town and off the line.
Forced induction, maybe run between a 3.08 and a 3.27, you have enough engine power from the
start.
notice the RPMs are higher at 70, which should be around 2100/2200, that's where my '08
is at 70.
I went from a 2.87 to 3.64 in my Charger, that was a huge difference... I was at 3700 RPM
at cruising...
Don't forget the Tuner, to change the gear ratio.
Out in the Net:
For manual transmission, the 3.73 gear set is the go to set. Depending on what you’re after, a 3.55
set can also do the job for street/daily Mustangs. Automatic Mustangs; 4.10s, because they typically
have lower gears, and with the converter, you need a little more differential gear to get up and running.
The 4.10 makes up for the lower first gear of the transmission, and the slip of the converter.
The 3.73 for a 5/6 speed manual offers great performance around town and off the line.
Forced induction, maybe run between a 3.08 and a 3.27, you have enough engine power from the
start.
09-25-2018, 07:03 PM
#8
Thread Starter
Join Date: Sep 2018
Location: Florida
Posts: 35
That's less than a half rotation of the driveshaft difference at +.46 rotation. You will
notice the RPMs are higher at 70, which should be around 2100/2200, that's where my '08
is at 70.
I went from a 2.87 to 3.64 in my Charger, that was a huge difference... I was at 3700 RPM
at cruising...
Don't forget the Tuner, to change the gear ratio.
Out in the Net:
For manual transmission, the 3.73 gear set is the go to set. Depending on what you’re after, a 3.55
set can also do the job for street/daily Mustangs. Automatic Mustangs; 4.10s, because they typically
have lower gears, and with the converter, you need a little more differential gear to get up and running.
The 4.10 makes up for the lower first gear of the transmission, and the slip of the converter.
The 3.73 for a 5/6 speed manual offers great performance around town and off the line.
Forced induction, maybe run between a 3.08 and a 3.27, you have enough engine power from the
start.
notice the RPMs are higher at 70, which should be around 2100/2200, that's where my '08
is at 70.
I went from a 2.87 to 3.64 in my Charger, that was a huge difference... I was at 3700 RPM
at cruising...
Don't forget the Tuner, to change the gear ratio.
Out in the Net:
For manual transmission, the 3.73 gear set is the go to set. Depending on what you’re after, a 3.55
set can also do the job for street/daily Mustangs. Automatic Mustangs; 4.10s, because they typically
have lower gears, and with the converter, you need a little more differential gear to get up and running.
The 4.10 makes up for the lower first gear of the transmission, and the slip of the converter.
The 3.73 for a 5/6 speed manual offers great performance around town and off the line.
Forced induction, maybe run between a 3.08 and a 3.27, you have enough engine power from the
start.
09-26-2018, 04:19 AM
#9
Banned
Join Date: Jan 2018
Location: Pennsylvania
Posts: 2,327
You can modify the stock tune, and not write a canned tune from the tuner. You can
get the InTunes for as low as $100, not married. There are some available on FaceBook,
there was an SCT x4, with one unlock left for $120. I got my InTune1000 from Facebook
Marketplace for $100 shipped.
SO, you modify the stock tune by changing the gear ratio, then write it. So, you may as well
install a performance tune. I get better MPG with the 93 Octane Tune, but the fuel isn't
cheap. Still the same as buying goof octane boost + 87 gas, so, I run 91 to 93 depending
on how many miles I a, going to run it that day.
