Part 1: Do-It-Yourself 3.73 Gear Swap How-To

One of the first hot rod tricks a hot street car gets is a set of gears.  If your ‘Stang’s 8.8 inch rearend came from Ford with a set of 3.08’s or even worse, 2.73’s, the car was pretty much a DOG!  A set of 3.73’s, 3.90’s or even 4.10’s really wakes ’em up.  Don’t throw away those 2.73’s though, you may wanna go for a run down the Salt.  haha

Here is “Calera Kid” himself doing a burnout at the now defunct L.A.C.R. drag strip.  This was taken at the “Hang Over Nationals” in 2002.  Anyone ever hit the Hang Overs at Palmdale?

Mustang 5.0, SN95, drag strip, LACR, burnout

“Sally” has run a best time of 12.85 seconds at 106mph at Famoso with 4.10’s.  Eventually the plan is to replace the stock ported E7 heads for the GT40P heads and the stock cam with a higher lift unit.  For now, a set of Ford Racing 3.73 ratio Ring and Pinion from might allow the low revving stock head/cam “five oh” motor to utilize the good torque with a set of 3.73’s.

If you’re a “do it yourself” hot rodder, here’s the step by step instructions for the swap.  Part 1 will focus on the removal of the 3.90’s currently in the car.  Also, we’ll point out some of the home-brewed rear suspension tricks.

3.73's, mustang, gear swap how-to

First, get your car up on jackstands and remove the rear wheels.  Then remove  the two rear brake caliper bolts (13mm) on each side.  You can see at one point the stock calipers were painted red.  Also, note the stock catback.  Honestly, the Ford Small Block with the stock catback and mufflers when combined with a nice offroad x or h pipe is one of THE best sounding engines on the planet.

3.73's, caliper bracket, Mustang, gear swap, muscle car

To finish removing the calipers, remove the two 15mm bolts for the caliper mounting bracket.  Note the Lakewood 50/50 rear drag shocks.  Yep, this SN95 Mustang ran 12’s with basically the stock suspension front and rear.  The front struts are stock, just unbolted from the top to allow more travel (yikes!).

mustang 5.0, sn95, anti-lock brake sensor, muscle car, drag racing, LACR

Here’s the hall-effects sensor for the anti-lock braking system.  This needs to be removed.

3.73, Mustang gear swap, ring and pinion, drag racing, muscle car

To remove the sensor, simply remove the small bolt on the opposite side.

Next, you’ll want to drain the diff oil and remove the rear cover.  Sorry no pics of that step.

3.73's, Mustang sn95, muscle car, how-to, hot rod

With the rear cover off you can see the ring gear.  Remove the spider gear shaft, its a 5/16″ socket.  In this picture you can see a hint of the Eaton posi (with carbon fiber clutches) unit that has over 100,000 miles on it.  This was one of the most important parts we installed that allowed “Sally” to use the 8″ slicks and achieve a best short time (that’s the first 60ft for the drag noobies) of 1.72 seconds.

3.73's, eaton posi, lsd, Mustang,

Push the axle in so that the C-clip can be removed.

3.73's, Mustang, how-to, DIY, drag racing, muscle car

Here is a view of the C-clip removed.

3.73's, Mustang, Muscle Car, drag strip, DIY, SN95, 8.8 rear

Now pry the diff and ring gear reward (out the back of the housing) and save the left and right shims.  Identify the shims as left and right, you’ll need them later and will want to keep left and right separate.

3.73's, Mustang, SN95, driveshaft, drag racing

Hold the driveshaft flange and remove the pinion nut.  Dig this homemade tool utilizing a long pipe welded to a piece of steel sheet with holes drilled.  “Big B” the breaker bar is also a necessity.

3.73's, Mustang, SN95, drag racing, 8.8" rearend, Posi, Ford Racing

Now you can tap the flange off and push the pinion out of the rearend.

3.73's, Mustang, SN95, drag racing, Ford Racing

Pull the pinion gear out of the rearend case.  Dig the ARP studs for added strength.  Also, note here the pinion spacer shim pack that was purchased separately.  This is not a crush sleeve type, which is what the Ford Racing gear set came with.  The spacer shim pack is much easier to work with compared to the crush sleeve type.

3.73's, Mustang, Ford Racing, ring and pinion, 8.8" rear end, posi diff

The pinion gear assembly with its spacer shim pack for bearing preload.

3.73's, Mustang, 8.8" rear end, drag racing, Ford Racing

Now, you can remove the 10 bolts from the ring gear and then tap the ring gear off.

It is very highly recommended that you use a gear set with the shim and spacer setup.  The crush sleeve is a big pain to get the bearing pre-load just right.  The Ford Racing gear set from is a quality piece.

Stay tuned for Part 2 where we’ll show you the detailed instructions and pictures for installing the new 3.73 ring and pinion in the Mustangs 8.8″ rearend.

For those who’ve done their own gear changes, let us know what helpful hints you may have for removal and installation.

Hechtspeed, Mustangs, SN95, S197, hot rod parts

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