rear end gears

[goertz]

The '73 454 I am buying has 3.70 gears in the rear. Some time ago, I assume in the 70's, the tranny was replaced with a Doug Nash 5 speed, which is a non-overdrive trans back then. I assume the lower gears are pretty steep, and 5th is 1-1. I'll probably keep this trans in the car, but was thinking with the steep tranny gears, that a 3.08 in the rear would be more suitable to modern freeway driving without blowing up the engine. It currently runs about 3300 at 65 mph.

my question is.....is it usually cheaper to take the car to a rear end shop, and have them swap the ring and pinion to a 3.08, or just buy a complete unit and pop it in all ready to go, and if this is the way, how much do they usually run?

 

[KANE]

The '73 454 I am buying has 3.70 gears in the rear. Some time ago, I assume in the 70's, the tranny was replaced with a Doug Nash 5 speed, which is a non-overdrive trans back then. I assume the lower gears are pretty steep, and 5th is 1-1. I'll probably keep this trans in the car, but was thinking with the steep tranny gears, that a 3.08 in the rear would be more suitable to modern freeway driving without blowing up the engine. It currently runs about 3300 at 65 mph.

I'd replace the tranny unless you think the rear end needs it (like grinding noises). I'd go with a ROD or even a T56. I'm sure your engine's torque can handle the wider spread between gear ratios. Then, you'd get the benefits of the OD

 

[GTR1999]

Depends on what you want to do. If you have a good shop there they'll probabaly charge about $600-$800 to change the gears and do a general overhaul-maybe. Buying a rebuilt one you get pretty much the same thing for equal or same amount.
When I build these I blueprint them but that cost even more-$1,200 range but you get unit that's has more parts and time in it that you'll get anywhere else unless you do the job yourself.
I would go the rear end overhaul route myself since the tranny is in and aligned. Those 5 & 6 speeds are nice but did you see the cost of a Keisler kit? Very nice but about 3x the cost of a blueprinted rear end!
A rebuilt Muncie or ST-!0 run about $900 and still leave you with 1:1 4th gear.
If you PM your email I'll send you some information to help make your decision.

 

[norms72]

You may find a few members more than willing to trade their 3.08 for your 3.70.

 

[goertz]

well the tranny is in really nice shape, and a trans swap is way more expensive to get the same results. a 1:1 5th gear with a 3.08 out back, gives you approx the same effect as an OD trans with 3.53 or 3.70 in the rear. Back in the 70's before OD technology was widely used, they went the opposite of what we do today, instead of adding an extra high end gear, they added an extra low end gear, and ran higher rear end gears.

 

[74bigblock]

3.08 should work fine for you. My '74 454 w/ stock 3 speed Auto with a 3:08 runs 65 MPH @ apx 2700 RPM. I recommend you send your diff in to VTech or any shop you trust.. have it rebuilt with a 3.08, and never have to touch it again.