About to jump into a gear swap to 3.73. Ive heard many great things about Ford 9" with 3.73s. Its a weekend car so its gona be seein alot a red light to red light travel. I was curious about your thoughts about the pros and cons of Ford 9" installs and availability. If this is a good poption that is somewhat affordable compared to the alternative then where are the best places to find Ford 9" with the 3.73 gears already installed. Junk yards?

Ford 9" with 3.73s already installed

vs

OE GM rear end after purchasing and installing 3.73s

Help me disect the money involved here because Im a dummy when it comes to Rear Ends so a shop will be doing all the installing...

 

A properly setup full 9" rear will run you FIVE TIMES the cost of a good-condition 10-bolt with 3.73s. If you aren't going to be doing any hard-core track driving the 10-bolt will be plenty. You aren't putting down a tremendous amount of power either beings that you are bolt-on only and an automatic.

Keep in mind that when you change rear gears you will also need PCM programming to adjust your speedometer so that the shift points remain accurate.

 

Yea just doing light to light pedal stomping isn't enough to warrant a rear swap. Hell my 10 bolt 6 speed bolton car has survived many nitto 555r lauches with a spec IV clutch at its still kicking. With you A4 I would just buy the gears and call it a day.

 

My car is not a race car and it might see the strip once every couple years. I made the decision to go with a 9" because I am making nearly 400RWHP and my car is 3800# plust it has a M6 with a grippy clutch.

I just wanted the piece of mind that I was not going to blow the 10 bolt w/ 4.10's up if I banged on it simply driving the way I like to drive it. I pulled my good 10 bolt w/4.10s and girdle and cleaned it well then painted it black. It looked brand and I sold it for $450 IIRC and I put that money toward the fabbed 9".

Did I really need the 9"? Probably not. If I had an auto tranny, I would have kept the 10 bolt and rolled the dice.

 

You could always split the difference and get a 12 bolt

 

Cost is roughly the same IIRC. The 9" has significant advantages over the 12 bolt. Its stronger and far easier to set up the gears.

 

true, but its also heavier, and robs a little more rwhp

 

I did some research on the 10 bolt, 12 bolt, and 9" awhile back and both the 12 bolt and 9" were quite a bit heavier than the 10 bolt, got some estimates from the Moser technician -- appx 60 pounds for the 12 bolt and 75 pounds for the 9". You can reduce the 9" weight with an aluminum carrier and fabbed housing to close to the 10 bolt for a bit on the hot side of $4K...so I still have a 10 bolt (modded with welded tubes, a girdle, high strength bolts, etc.)

 

Any dead-weight and RWHP loss of a 9" can easily be offset with a spool. They are incredibly light and the reduce rotating mass can easily transfer more RWHP.

Then again, that's the track-only part of me speaking.

 

And how many gear changes have you done, in your 9"??

I also have a 3800lb. vert. with a T56 M6. Put 3.73's in the stock diff. Been to the track and driven for years, no problems.

 

Awsome Fellas.... I was curious what to expect as far as cost for a 3.73 install - parts and labor? Since Im lost when it comes to rear ends. The rar end will be in the car when the install is necessary. What do you guys think would be a fair price for a good name set of gears installed correctly by a honest mechanic?

 

I weighed my Strange 12-bolt when it came off the shipping pallet (fully assembled with lube), and then compared it to my stock 10-bolt in the identical configuration (no brakes) and the weight difference was nowhere near 60#. I think is was no more than 15# max. Maybe the Moser weighs a lot more than the Strange because of the larger axle tubes, but I doubt its that much heavier.

Another alternative is the Strange (Dana) S60, stronger than either the 9-inch or the 12-bolt, lowest mechanical losses of all, and weighs 25# more than the Strange 12-bolt.

As far as the 9-inch being stronger than the 12-bolt, the difference is insignificant in "base" configuration. There are a lot more (expensive) high strength options for the 9-inch. But up to 750/800HP the 12-bolt is more than adequate, unless you have an M6, a killer clutch, super sticky tires, and make 10 passes every weekend, with 6K clutch dumps.

The 9-inch has the worst mechanical efficiency (10% loss, vs 7% for the 12-bolt and 5% for the Dana), has a dropped (0.75") pinion shaft centerline compared to the 10-bolt or 12-bolt, and has the pinion shaft offset to one side, off the centerline of the chassis. Very tough on the driveshaft, and usually requires the BFH mod to the tunnel to prevent the torque arm from banging into it. And, the cumbersome 9-inch torque arm bracket complicates the drop-out gear swaps.... it took us about 2 hours to make the switch at the track on a buddy's 97 SS. 9-inch was the right choice for him... because the car was making 1,350HP at the flywheel, and he could afford all the light weight options.

 

The guy at Moser I spoke to on the phone did not weigh them as opposed to guesstimating over the phone, so not sure how accurate the weight differences are. It is great to know that the strange 12 bolt is only 15 pounds more as I was concerned about losing cornering performance due to increased weight over the 10 bolt. Effective immediately, I am dumping the clutch at every green light so Santa gets me a strange 12 bolt for Christmas!

 

let me know If that works I personally bake him some cookies, and milk the cow