Hi, everyone. I'm new here, but I just acquired a '71 SS that is now a Yenko Deuce clone. Engine is not original so I'm doing a resto mod. I'll put in a Bill Mitchell/World 427 sb. Car has a M20 muncie. I want to replace the rear end with a stronger unit, and I'm looking for opinions. Should I get a 12 bolt or a 9" unit?

12 bolt or Dana 60. The 9" robs power do to the pinion gear location. Personally I've been puttin over 900 horse on the bottle through a glide and an 8.5 10 bolt for several years. Good axles and yokes are key here as is also the right driveshaft. If you're gonna go 12 bolt or Dana 60 get 35 spline axles....you'll never break it.

The Moser 12 bolt is stronger than a stock 12 bolt. The casting is stronger and the axle tubes are also stronger. These can handle a lot of power and should be good enough for your application. You can go with the 33 spline axles and an Eaton posi, or Truetrac. If you need more information or prices send me an email. I'll help all that I can.

12 Bolt all the way. I have one in front of a 582 and it has held up for 5 years. Besides Don Yenko was a Chevy guy, he never installed a Furd any thing in his cars even thought the only Ford part in an aftermarket 9" rear is the axle bearings.

12 bolt with a 31 spline axle is stronger than the stock 9 inch. You can upgrade on the street with 33 splines in an Eaton Posi or if it is a trailer queen a 35 spline spool. A Dana 60 is a 12 bolt on steroids. Same axle in design made by the same company just bigger and stronger (and a tad heavier because of that extra metal). GM bought all of their rear ends after 1963 from Dana/Spicer.

Big Dave

I'd vote 12-bolt as well, less power lost through the rearend and usually cheaper. One advantage the 9" has is gear swapping. If you want 2 ratios, set-up two chunks and about 30-40 minutes andn some gear lube to swap them.

Derek

Only thing faster than changing the gear ratios with a Salisbury style rear end (removable center chunk) is that of a quick change. Another plus for the quick change is you also get that sought after annoying gear noise (cam gear drive, or a M-22 Rock Crusher, or a roots style blower sound).

Big Dave

I think a 12 bolt gear change can be as fast as a 9 inch if you have everything set up right to begin with. If you set the pinion depth and backlash on 2 gear sets then all you have to do is keep up with the shims and drop one set out and stick the other set in and set the pinion bearing preload. If you use a solid pinion spacer then you don't even have to do that. I don't see quick gear changes as an advantage in the 9 inch. There is a lot more money involved in setting up 2 complete chunks for the 9 inch, and I think I could change gears in a 12 bolt just about as quick.

How many of you guys with 9" actually change your gears out to go racing??? That is a totally moot point. The actual power loss compared to 12 bolt is really not worth even mentioning either. Only in drag race application when 1000's and 10,000's of a sec are critical. Which usually for use is bracket racing anyway. So it really comes down to choice and resale. I think the vehicle will have much more resale with a 12 Bolt chevy rear. Keep you investment intacted and always ready for resale when you need it. Plus ypu will have the respect of your Chevy perrs...lol. 12 bolt does have a larger pinion shaft at 1.625 compared to ford 1.313 BUT the ford does have the 5 bearing for the head pinion support too.

My Vote goes to the Chevy 12 bolt also. Just belongs under the car and you will have as much strength hands down...(AS LONG AS BOTH ARE BIULT CORRECT OF COURSE!!) :thumbsup:

Good luck on your choice and remember it is your car and you must be happy driving your choice. Jim

What gearing are you going with?

I think a 12 bolt gear change can be as fast as a 9 inch if you have everything set up right to begin with. If you set the pinion depth and backlash on 2 gear sets then all you have to do is keep up with the shims and drop one set out and stick the other set in and set the pinion bearing preload. If you use a solid pinion spacer then you don't even have to do that. I don't see quick gear changes as an advantage in the 9 inch. There is a lot more money involved in setting up 2 complete chunks for the 9 inch, and I think I could change gears in a 12 bolt just about as quick.

Freddie you are the man! It takes me one to two days to get one right! (I don't have that much time left, as I'm getting pretty old).

Big Dave

What I mean by changing the gears quickly is this. You set up 2 complete differentials for the Ford. This takes some time, but when they are done then all you have to do is swap the complete assembly. You have a lot of money invested in this because you had to buy 2 of everything.

Now set up a set of gears in the 12 bolt using a solid pinion spacer. When you have them set up correctly you can remove them and set them aside with all of the shims marked for the correct location. Then set up your other set of gears. Now all you have to do is remove one set and put the other set in with the shims that you used to set it up. In about the same amount of time it takes to swap the complete assembly in the 9 inch you can switch a set of 12 bolt gears. Just put all of the shims in the correct location and tighten everything up. Fill it with oil and you are ready to go. You have spent much less money on this because you can use the same differential for both sets of gears and all you had to was spend the extra money on one more set of gears and shims.

How many of you guys with 9" actually change your gears out to go racing??? That is a totally moot point. The actual power loss compared to 12 bolt is really not worth even mentioning either. Only in drag race application when 1000's and 10,000's of a sec are critical. Which usually for use is bracket racing anyway. So it really comes down to choice and resale. I think the vehicle will have much more resale with a 12 Bolt chevy rear. Keep you investment intacted and always ready for resale when you need it. Plus ypu will have the respect of your Chevy perrs...lol. 12 bolt does have a larger pinion shaft at 1.625 compared to ford 1.313 BUT the ford does have the 5 bearing for the head pinion support too.

My Vote goes to the Chevy 12 bolt also. Just belongs under the car and you will have as much strength hands down...(AS LONG AS BOTH ARE BIULT CORRECT OF COURSE!!) :thumbsup:

Good luck on your choice and remember it is your car and you must be happy driving your choice. Jim

What gearing are you going with?

Thanks everyone for the input. I was leaning toward a Moser 12 bolt for all the reasons stated. I only considered the 9" because it seems lots of resto-mods are using them. Monzaz, I'm also leaning towards 4.10 gearing because I will be adding a Tremec TKO also. I owned a '69 SS 396 in high school. It had 4.11 gears and it screamed!

An over drive transmission allows you to have steep gears and enjoy them too!

The reason the Furd nine inch is under so many rides is because GM stopped selling them in 1972. It wasn't until Moser and Currie started to recast the high nickel pumpkins again, a few years ago, that one had any choice. Given a choice of only a 10 bolt or a 9" there is no question, but a 9" and a 12 bolt choice is a different question. Once again I say Furd because the only Ford part in today’s 9" rears are the axle bearings, everything else is an aftermarket part. A stock Chevy 12 bolt is stronger than any nine inch made by Ford found under an old Merc or Lincoln. It is only the aftermarket pieces designed to fix the weak pinion bearing support out of high nickel that approach the strength of the formerly unobtainable 12 bolt.

The parasitic loss of the 9" is designed into the gear. By mounting the pinion low on the ring it meshes with more contact surface area. That extra contact patch is responsible for more friction so that there is about a 3% penalty to use that design (3% off whatever flywheel horsepower you have). It is that extra contact patch that keeps from ripping the teeth off of the ring gear that accounts for the strength of the nine inch rear (and the added pinion bearing to hold the front of the pinion in place).

Of course there are no C-clips to worry about with a Furd 9". I do not know what the engineers at GM where smoking the day they dreamed that up that solution to cutting production costs; but it caused them to over look the axle bearing race as well, so that a C-clip equipped 12 bolt axle rides on the bearing rollers instead of sitting inside a replaceable race.


Big Dave