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4.10 to 3.42 gear swap?

O

old clunker

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i have 4.10s with a 465 and 35 mud kings and a 14ff. I have to rebuild the rear cuz its got lots of miles on it. I like to run down the highway and the 4.10s kinda suck. Has anybody ran 3.42s with 35s? my motor has plenty of power and have low range if i need it. The truck is a 78 long box with 6" ez ride springs. Thanks for any help
 
What you are proposing is a setup that will do nothing but suck your gas tank dry. If you really want higher highway gears I'd go with a Klune-v overdrive. Then you still have some adequate gearing for off road excursions and it might even be cheaper.
 
I've got 3.42's and 33's, (as do many here I'm sure) and with the 465, it is no problem getting it rolling. I'd have no hesitation to run 35's with the gears in it. Not saying you will win any speed contests, but it will move.

You aren't going to hurt in town mileage with gears. The truck weighs 5000+lbs, THATS the reason they get bad in town mileage.
 
I'm a tall-gear fan with the SM465. I run 3.21 and 33's with a 6.2L/SM465 in a 6000# suburban.

I used to run 4.10 with a 350/SM465 and 33's. It was also too much gear for the highway IMHO.

EDIT: I also run 35's/4.10 on my Powerstroke, which is about all I'd go because I don't have a granny gear. I intend to run 39's with 4.10s after I do the 6.2L swap on my '91. If I need slower speeds it will come with extra t-case reduction.
 
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what about doing 3.73s? I used to run 3.73s with my sm465 and 35s and liked it ok. still low enough to get it rolling pretty easy but high enough to do ok on the highway. and if by chance you decide to go with 3.73s I know someone who has a 14bff and dana 44 with 3.73s that would love to trade you for your 4.10s if they are in decent shape.:D
 
Personally I don't think the difference between 3.73 and 4.10 is worth it. I think that is why you see so many people recommend 4.56's over 3.73's.

It's a difference, but not that much. Two other aspects of changing to numerically lower gears though, is that you lose crawl ratio (not too bad with the 6.55 first of the 465 of course) but you also loose compression braking. Depends on what you do with the truck, it may or may not be a factor.
 
Im going to just stick with the 4.10s and rebuild it. I like to wheel it but have no way to trailer it so drives take awhile. How are the yukon gears? i have heard good things about them. Anybody know what they may cost? Im going to put some 36 ground hawgs on and the 410s and detroit work great with my truck combo. Thanks for the help
 
My last combo was 35's with a 465 and around town it was fine. Off road wasn't too bad either. The big problem was on the highway. As long as it was flat it was ok but not great and if there was any hills you could hang it up. Too fast to downshift, not enough torque to keep the speed up. One of the main reasons I changed axles. I would not go lower than 373's
 
I ran a 465/3.42/33" combo for many many years and never had any problems with power. And highway rpms were reasonable. The truck ('80 K-10) got about 12mpg after I put on an edelbrock q-jet.

I put the same axles into a Blazer with TH350 and 35's and it still did pretty good.

I put 4.10 axles under that same Blazer and my mileage dropped from 8-10 mpg to 7-9 mpg (yes, I calculated actual speeds and distances, not just speedo readings) but it has gobs more power, according to my ass-dyno.

I think with a manual, the 3.42s would be a good all-around ratio, since you have the low gear to use when you need more low end power.
 
SM465 with 35's and 4.10's is about right, IMO, unless you're going to run down the interstate at 75+ all of the time, and then I still don't think it's worth it to do the swap. I had 3.42's and 285's on a rig, and it was almost unbearable. That was with a 305, though- albeit one that ran pretty good. I would suggest going to 37's, getting OD, or leaving it alone.
 
old clunker said:
Im going to just stick with the 4.10s and rebuild it. I like to wheel it but have no way to trailer it so drives take awhile. How are the yukon gears? i have heard good things about them. Anybody know what they may cost? Im going to put some 36 ground hawgs on and the 410s and detroit work great with my truck combo. Thanks for the help
Click to expand...

Im running yukon gears in my front axle and I like them. I got them from randy's ring and pinion. Randy's has excellent customer srevice and is overall a great company to do business with. Ive got the 4.56 variety and I believe the gears were about $130. No problems with them yet and ive been running them for about 4 years in a locked 10 bolt with 37's.
-Harrison
 
+1 vote for Randy's. I got my Detroit from them and the customer service was outstanding.
 
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