I have a posi rear end stamped SB. Not positive of the actual year but it's after 69' bc it's not the axle with sealed bearings...my gears are 2.78 as of right now but heard that gear ratios were limited for this rear....could anybody confirm what gear ratuo options I have for this? I want some thing lower but I'm not taking it to the strip either it's a street car. Thanks

 

Uh, does it have a 12 bolt cover or a 10 bolt cover?

I am guessing it's an O-Type 12 bolt since you said 2.78 ratio, and a 1970 version since it does not have sealed bearings, but that is just me guessing in a vacuum of information.

The O-Type 12 bolt has a very limited number of ratios, either aftermarket or factory. Currently the aftermarket ratios available from Richmond Gear are 3.42, 3.90, and 4.10 and these fit the 2.93-3.23 carrier only. Monzaz was making ring gear spacers for the 2.56-2.78 carrier but you would need to check with him to see if they are still available.

 

Yes it is the Type O 12 bolt. I should have stated that. I will contact him and see. Thanks I appreciate it

 

Only the 3.42 and 3.90 gears are available new. There is a modified Ford 8.8 posi available that is good quality that works with these gears. I too have a 2.78 open I need to replace. The gears and posi cost around $900, not cheap. The 3.42 is the max I would consider with a 3spd trans.

 

Yea this is a completely rebuilt rear end with less than 500 miles on it...all I want to change are the gears.

 

Sell the rear end you have and put the rear end under it that you want. Your current carrier is only good for 2.56 and 2.78 gears. Put a 71-72 8.5" under it with the ratio you desire.

 

The 8.8 Ford carrier is only redrilled for the Type O gears it is such a ripe off that they are so expensive.

 

Is that all that is done to them? No other machine work?

 

Richmond is showing the 4.10 gears on their web catalog. I remember a while back the 4.10s weren't listed but they are now.

 

And those work on the factory 3.08/3.23 carrier and on the Ford 8.8.

 

Yep, just trying to clarify that there may be THREE options for gears instead of two. Wow, what a selection, huh?

 

Strange, I went to their website, only seen the 3.42 and 3.90 gears. Hopefully the 4.10 gears exist again.

 

The 2.78 posi rear axle would make a great cruising gear ratio. What engine is in your car? Most 455 equipped cars have plenty of torque in combination with the 2.78 axle ratio to still light up the tires while retaining efficient highway travel. Even a 4-bbl, dual exhaust equipped 350 is still sprite with 2.78 gears, if you are not looking to go racing with the car.

 

3.42, 3.90, and 4.10 are listed.
https://www.richmondgear.com/wp-cont...n1.pdf#page=32

 

With a 3 SPD non lock up auto, I agree. Unless you drive mostly in the city, even the 3.42's get old fast. Cruising around with a reasonable height 205/75R14 tire at 26.6", I still ran 2300+ rpm at 60 mph and more like 2500 rpm at the speed I wanted to drive. With 3.42's that jumps to 2800+ rpm at 60 mph and 3000 rpm at speeds you want to drive. With the 2004R and lock up, it drops nearly 1000 rpm. I will be running at 1500 rpm at 60 mph till I get the 3.42 gears in.

 

Multiple sights show the 4.10's on back order, hopefully with them now in their catalog, they are being reproduced again. I also found these but look at the price! https://www.google.ca/url?sa=t&sourc...G1WfQ0s1JTpalw

 

That's nuts!

 

It's a 350 rocket bored out 68 over with aluminum forged flat tops from Mark EFI, Edelbrock Performer RPM Intake with a 750 Quick Fuel carb and No.5 heads with 1.99 intake valve and very small cam from Comp cams. Almost stock cam. 350TH with a shift kit from B&M. Just wanted a lil more getty up and go. Drives good on open highway with the 2.78, I agree.