Gearing advice opinion

I have a 69 commando.

With 3.73's in it, am switching to wide trac d30 front from cj 7.
I have the option of putting in 4.10's

running 225 sm420 , D20 rebuilt stock,and 32inch tires.

Would it be worth it or nessasary to switch for better low end grunt,
or not that much differance?

 

IMHO that is not much of a movement. I would stick with 3.73.

 

I would keep the 3.73 gears if they are already in the new front axle. With the SM420 you shouldn't need the lower gears for crawling, and without overdrive on road they will help cruising speed. Unless you have a lot of hills around you..... I have factory 4.27s in my 68 and wow does it climb hills well with the 235/75/15s especially compared to my 66 with 4.56s and 36" iroks (hill in last sentance is a 2000 foot climb at 6%)

Of course you might not see the high speeds I do in CDA that I do in southern NM (75 mph freeways to get most places or 75 mph back roads as the locals like to drive)

Heck when I lived in Moscow ID going to the University I had 5.38s and an SM420 with 35s, around there you could drive 50-55 on the highway (made about 18 mpg) and not get run over most of the time.

Nice thing is you can always change gears later if you want a little more.

Both of my :v6:s seem to like to climb at 2700 rpm or better on the highway, under that and they lug pretty bad.

One last thing I might throw in is that with the jump from 3rd to 4th, if you find yourself downshifting at highway speeds get ready to slow way down. When I have to downsift on the hill above I run 55 mph at a little over 4000 rpm with the 4.56 and 36" tire combo. I wish I would have gone a little deeper than I did for that reason. Part of this is the heavy aggressive rubber, I didn't usually have to downshift with the 35 ATs.

I can't really think of a 32" that should slow down a :v6: with 3.73 gears, I would stick with them for now. Unless the 4.10 was already in the new front and I only had to change the rear. Then I would just change the rear and enjoy the speedo being closer to stock again.

This rambling probably didn't help much, but I hope you found something usable.

 

I think the 3.73's will be fine. I've got 4.10's, 35's and a SM465, good on the highway and good offroad.