does anybody sell the full rear axle for 67' mustang fastback? im talking 9" rear end w/ housing, axles, disk brakes. also if i go with the 9" rear end there are different numbers, 3.00, 3.5, 3.55 etc the gears, what do these numbers mean to me?

 

try currie enterprises, and the numbers represent gear ratios

 

yeah i know they are gear ratios. but the higher the gear ratio the better or what? im still new with all this rear end talk.

 

depends on what tranny your using most of us on here love 3.55 or 3.73 for a highway gear a 4.11 up is more drag racing will make you take off really fast but youll lose topend speed.currie is nice a little pricey but well worth it to me.if you want a cheaper one try http://www.perogie.com/Rears.htm

 

At best, "better" is a compromise that you have to make for yourself and the way you expect to use the car.

What those numbers represent is the gear reduction in the axle, in terms of ring gear tooth count divided by pinion tooth count. More usefully, this is driveshaft rpm compared to axle rpm. The larger this number, the greater the 'leverage' your engine has to get you moving. But it also means that for any given road speed you'll need to be running the engine at relatively higher rpms.

Larger numbers = better acceleration, though not as much better as a straight comparison of the ratios might suggest. In my opinion, anything above 3.55's in a daily-driver or weekend trip car is a candidate for use with an overdrive tranny of some sort (T5, AOD, etc.), and 3.55 itself is borderline at best.

Smaller numbers = better mpg (usually), more relaxed cruising, and potentially a higher top speed. 3.00 and below is not a particularly good match with most manual transmissions, though.

As you can see, there is some matching of axle to transmission going on, and that can get quite a bit more involved if you have any particular requirements (the need to be able to do 60+ mph in 2nd gearfor auto-X comes to mind as one example).


Norm

 

for a daily driver, that is probably used 50% on freeway and 50% on streets, with a driver who has a heavy right foot, which gear ratio would be good?

 

what tranny do you have

 

You could get a late 70's Lincoln Versailles 9" rear end and axle assembly with disk brakes from the bone pile. The gear ratios represent how fast or how slow the engine will turn the rear tires. A 2.80:1 ratio will turn the tires slower meaning it will take less RPM from the engine for one revolution than a 3.80:1 etc. So, the larger the number, the faster the car will move from a standstill, but get worse gas mileage on the freeway.

 

3.73's to no more than 4.1 with a T5, Tremec (any), or AOD. Anything deeper (larger numerical ratio) on street tires and you'll start having a hard time putting full WOT power down in two gears instead of just first. On reasonable street tires, anyway.

Something in the 3.0 - 3.25 range with a 4-speed (Toploader, T10) if you're willing to downshift more frequently and use the lower gears to cruise in if road speed warrants it. 3.5 if you're not (and aren't bothered by having to run up around 3000 rpm at 60 mph)

Slightly taller than for the 4-speedwith a C4 or other automatic with a direct drive top gear, especially if you're running a slightly "looser" torque converter than OE.

Dragstrip or other competition may require something different (usually shorter) for best results.

Norm

 

I think this could be clarified a little.

A differential ratio with a lower number (higher geared) will turn the tires at a higher RPM, given the same engine RPM, than a higher number (lower geared).

In general:
The larger the number, the quicker the car will accelerate from a standstill. Also, the larger number will reduce the car's top speed and increase engine RPMs for a given vehicle speed.