Question 8 1/4 rear end

[Steve Agrella]

I have a 74 Duster with 81/4 rear end is there a way to tell what gears are in there without pulling the cover.

 

[halifaxhops]

Sometimes there is a tag on the bolts if not jack it up on jackstands under both sides of the axel in neutral and count how many turns of the driveshaft it takes to turn the tire one full revolution.

 

[diymirage]

sure
drop the engine in neutral, jack the rear end up, and lock on rear wheel up
then mark your driveshaft and turn the other rear wheel
count how many turns of the shaft to get a full rotation on the wheel

 

[JBurch]

One approximation if it is a sure-grip rear is to jack car up get both wheels off the ground, put car in neutral, rotate wheel one turn, count number of turns of drive shaft.....approx 3 1/4 turns would be 3.23, approx 3 1/2 would be 3.55, OR look for a tag under a cover bolt, OR measure tire diameter, tachometer reading, MPH and do some math

 

[Steve Agrella]

Thanks for the replies

 

[Steve Agrella]

Will this rear handle 450hp

 

[AJ/FormS]

Another method for lazy people like me is ;
If you have a tach, an accurate speedO,and a manual trans, it's real easy. Just run it up to 50mph in top gear and record the rpm. Then a little math will spit it out.
With an auto you might have TC slip to deal with, and that will throw the math off. So it's best to finish at an rpm higher than the stall speed. So then you would probably use Second gear. The trick is now you have to know your second gear ratio.
In both cases accuracy will be improved by knowing the tire roll-out, or circumference.