Cpriester123

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

Fun71

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.

Cpriester123

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

olds 307 and 403

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.

Cpriester123

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

oldsmobiledave

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.

lemoldsnut

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

oldsmobiledave

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

Fun71

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.

oldsmobiledave

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

Fun71

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

olds 307 and 403

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

anthonyP

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.

Fun71

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

olds 307 and 403

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.

olds 307 and 403

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

Fun71

That's nuts!

Cpriester123

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.