Maj.Malfunction

I,m about to buy a new rear gear for my 65 f/b with slightly built 289 and a 4 speed toploader. Also...In the future i do hope to go the t5 route so i,d like to have a fitting ratio. Any suggestions on venders and a good compromise in ratio.Ahh...and another thing..I want posi..of course..Traction lock or detroit locker? This car is a fair weather weekend cruiser and performance and reliability will be key. It,s a 9in...almost forgot ....

mr-mstng

Mr. GT350Clone should be able assist you here.

GT350Clone

For a street car, I'd favor a Traction-Loc. If you do a lot of racing, then go with the locker.

As far as ratio..... There's a lot of variables that can change this - specifically, engine build, use, tire size, and what compromises you're willing to live with...

For the typical "street toy",
With a 4-speed, I'd stick with a 3.50 gears.
With a 3.35 1st gear T-5, 3.50 or 3.25 gears.
With a 2.95 1st gear T-5, 3.70, 3.89, or 3.50 gears.

Your choice could vary as much as .5 from any of the above. Some are willing to live with 3.89's and a 4-speed for stoplight fun. However, others (like me) do a lot of highway driving. I can tell you 3.25's and a 5-speed make for some NICE 2000 rpm / 70 mph long-distance cruising.

Keep in mind your overall first gear ratio as well. That's the tranny's 1st gear * the rear gear. 10:1 makes for a nice "off the line jump". The further you strray from that, 1st gear can become too steep or too tall. Here's a look at some overall 1st gear ratios plus approximate 70 mph rpms with different combo's.

Examples:
CR 4-speed - 2.32 first gear
3.50 = 8.12:1 / 3300 rpm@70
3.89 = 9.02:1 / 3750 rpm@70
4.11 = 9.53:1 / 3900 rpm@70

WR 4-speed - 2.78 1st
3.25 = 9.04:1 / 3100 rpm@70
3.50 = 9.73:1 / 3300 rpm@70
3.89 = 10.8:1 / 3750 rpm@70

3.35 T5
3.25 = 10.88:1 / 2000 rpm@70
3.50 = 11.7:1 / 2200 rpm@70

2.95 T5Z
3.25 = 9.59:1 / 2000 rpm@70
3.50 = 10.33:1 / 2200 rpm@70
3.89 = 11.48:1 / 2450 rpm@70

See why the 5-speed has become such a popular swap? B)

Maj.Malfunction

I ended up finding a WAR cased 3.70 with a open diff for CHEAP.. ..It will get me through the summer and this winter i,ll get a posi unit in it...This will give me a chance to see which way i want to go with ratio.
I never realized how hard(and expensive) these units are to find...I got lucky and found a garage with a couple.