4.11 (original torque tube rear end) to 3.07 (what the original poster mentioned he had) = 25% reduction. If he uses a 3 speed or a 4 speed with that 3.07 rear, he will have a 25% reduction the moment he shifts into 3rd or 4th.
I've posted this at least 10 times, but here are some more wasted electrons on the matter of the T5:
Original transmission ratios (and more importantly overall ratios) GM designed into your 1952 3100:
1st was 2.94 x 4.11 = 12.08
2nd was 1.68 x 4.11 = 6.90
3rd was 1.00 x 4.11 = 4.11
T5 ratios (assuming you get the proper ones)
1st is 4.03 x 3.07 = 12.37 this means you'll be shifting out of first around 17 mph
2nd is 2.37 x 3.07 = 7.27 you'll be shifting out of second around 30 mph
3rd us 1.49 x 3.07 = 4.57 you'll be shifting out of third around 45 mph
4th is 1.00 x 3.07 = 3.07 and you'll be shifting out of fourth around 60mph
5th is .86 x 3.07 = 2.64 and if you have 27 inch tires and you're on a flat stretch you'll be cruising at 65 at around 2200 rpm and with a 235 in a pickup, that's as good as it is going to get. If you're in hilly terrain or battling a headwind, you'll stay in 4th, but in 4th at 65 you're going to be running around 2500 rpm. 2500 rpm is just fine, by the way but so is 2200. Your torque has peaked around 1600 rpm you know.
The overall ratios of the T5 (as I've said many times and proved above) can be very close to the original ratios that were used with the 3 speed and torque tube rear end. Now if on the other hand you just run out and buy any T5 without doing any homework at all, you might wind up with ratios like these:
1st ratio of 2.95
2nd ratio of 1.94
3rd ratio of 1.34
4th ratio of 1.00
5th ratio of .63
Now let's see what your overall ratios will be with a 3.07 rear end:
1st...2.95 x 3.07 = 9.05
2nd...1.94 x 3.07 = 5.96
3rd...1.34 x 3.07 = 4.11
4th... 1.00 x 3.07 = 3.07
5th... .63 x 3.07 = 1.93
With this transmission coupled to a 235 and a 3.07 rear end, you won't be able to carry anything heavier than an empty beer can, you'll burn clutches out frequently, and 5th gear will be something you never get to use, because at 65mph, your rpm will be around 1500 and that simply will not work.
But with the proper T5, some thought/planning, you absolutely can use it with the 235 and a 3.07 rear end. You can see it in the figures above.
