2.75:1 rear axle with limited slip?

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While strolling through my 1972 facts book, I recognized that there was an option for a 2.75:1 rear axle with limited slip (axle code K). Never heard of it before! I don't want to change the axle ratio but limited slip diff sounds interesting.

What type/system of limited slip was it?

Is it possible to upgrade a standard 2.75:1 to limited slip?

Any sources for the parts?

Thank you in advance.

Cheers Frank

 
It is the clutch-type, also called posi-traction. Yes, you can upgrade. You can get everything from the clutch-type, to gear-type Eaton Truetrac, to Detroit Locker. My preference, for long life, low maintenance, and driveability would be the Eaton Truetrac. They are available from most automotive vendors.

 
I installed a Eaton TrueTrac with 3.50 gears in my 73 351C 2v with a C6 and it is like having an open rear until to get on it. Since you will be replacing the ring and pinion too, you might want to consider a modest gear ratio change to 3.00. You will also need to change your speedo driven gear. You will need to swap the ring gear bolts to the longer posi bolts ( D8OZ4216A ) as the open rear bolt are too short, but wherever you buy the truetrac from should be able to help set you up with everything.

 
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I installed a Eaton TrueTrac with 3.50 gears in my 73 351C 2v with a C6 and it is like having an open rear until to get on it. Since you will be replacing the ring and pinion too, you might want to consider a modest gear ratio change to 3.00. You will also need to change your speedo driven gear. You will need to swap the ring gear bolts to the longer posi bolts ( D8OZ4216A ) as the open rear bolt are too short, but wherever you buy the truetrac from should be able to help set you up with everything.
Rich

I'm really happy with my 2.75:1 ratio. As you might know, we are allowed to go a little bit faster on our motorways. :whistling:

Even 3000 revs at 75 mph are really relaxing when you know having another 1000 to 1250 revs up in your sleeve. :D

Sometimes when the streets are wet and I push the pedal, only the right rear wheel gets all the power and the car swerves. This I am planning to eleminate with a limited slip. Until now, I have been told, that limited slip is just possible with 3.00:1 ratio or up. So I wondered about the facts book's writings.

Cheers

Frank

 
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Oooh!

1- Also for 73?

2- Can a 351C 2V with 2.75 Truetrac make stripes?
Answer to question # 2

Yes... go fairly fast in reverse, without braking shift to drive, as it shifts to drive FLOOR IT. AKA reverse roll back

It will either leave two marks, or make a loud noise when something in the drive train breaks :D

 
While strolling through my 1972 facts book, I recognized that there was an option for a 2.75:1 rear axle with limited slip (axle code K). Never heard of it before! I don't want to change the axle ratio but limited slip diff sounds interesting.

What type/system of limited slip was it?

Is it possible to upgrade a standard 2.75:1 to limited slip?

Any sources for the parts?

Thank you in advance.

Cheers Frank
I ordered my original 72 mach new with posi 2.75, and yes 351 2v and 3 sp stick will mark its territory...

 
I do not know how many of you have ever driven a Traction - Loc , Limited Slip or Detroit Locker car but it can be a handful if you have some power. You see the drift cars and they all have them so they can bring the rear around easy. In some types of autocross you can actually do better without the Traction Loc or Posi.

Say you are pulling out of a parking lot into the road and stand on it. If you do not follow up with steering wheel corrections you can just spin around in the road, lol. If you do get one go to a parking lot and learn how to drive it before going crazy with it.

The Detroit locker is noisy have on in my 72 CJ vert. Even rolling in garage you can hear the clicking which is normal.

BTW radial tires will make you loose control much faster than belted when you have a posi rear and spinning. When they break loose they are gone. The old bias tires were much more forgiving. When I did autocross I tried Dunlap, BFG radials and of course the Goodyear polyglass bias came on the car. The best tire I found in the day was a Gillette brand tire and bias not radial. I averaged about 2,000 miles on a set of tires. I also broke 3, 9" rears in my Mach 1 with stock engine and were all replaced under warranty. They put the wrong rear in the car from factory and finally changed to correct and did not break again.

 
Good points, David. Especially with a Detroit Locker, it goes from an open differential to a spool in a split second, and can result in extreme understeer when turning on a slick road, or numerous donuts in traffic. On ice covered and packed snow covered roads with both back wheels spinning the rear end follows the slope of the road and often off the road. Even given the idiosyncrasies of a locking rear end I prefer them to an open differential.

 
Oooh!

1- Also for 73?

2- Can a 351C 2V with 2.75 Truetrac make stripes?
Answer to question # 2

Yes... go fairly fast in reverse, without braking shift to drive, as it shifts to drive FLOOR IT. AKA reverse roll back

It will either leave two marks, or make a loud noise when something in the drive train breaks :D
You mind if I do not follow your advice?  :chin:

Seriously, I have people say yes and people that say no so I still don't know :huh: 

I have a C6 btw, no stick.

 
I installed a Eaton TrueTrac with 3.50 gears in my 73 351C 2v with a C6 and it is like having an open rear until to get on it. Since you will be replacing the ring and pinion too, you might want to consider a modest gear ratio change to 3.00. You will also need to change your speedo driven gear. You will need to swap the ring gear bolts to the longer posi bolts ( D8OZ4216A ) as the open rear bolt are too short, but wherever you buy the truetrac from should be able to help set you up with everything.
Rich

I'm really happy with my 2.75:1 ratio. As you might know, we are allowed to go a little bit faster on our motorways. :whistling:

Even 3000 revs at 75 mph are really relaxing when you know having another 1000 to 1250 revs up in your sleeve. :D

Sometimes when the streets are wet and I push the pedal, only the right rear wheel gets all the power and the car swerves. This I am planning to eleminate with a limited slip. Until now, I have been told, that limited slip is just possible with 3.00:1 ratio or up. So I wondered about the facts book's writings.

Cheers

Frank
Hey Frank,

That is a really nice cruising gear. I've been on the Autobahn with my Uncle driving, when I was visiting family what a ride that was. I wish we had a road like that here.

Good luck with the swap,

Rich

 
Not making stripes is better than making stripes. If you are burning rubber you are not moving forward as fast as you could.

I know Mike bit it's fun I guess :) I'd like to keep 2.75 because of milage but it would be fun if I was able to do a burn out with it as well :)

 
To have the best of both, you need a transmission with overdrive. I have 3.73 gears, a lot of fun around town, but unrealistic on the highway. I finally started working on mine to install a 4R70W in place of my C6 (which needs a new shift lever seal), lower first gear plus overdrive.

 
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