4:10 is just too low

[TugOwar]

My truck isn't a 4x4 but I figured you guys would know if anyone would.

This is a 68 GMC 2500 - LWB - 305 V-8/th350 2x4

Dana 60 (10 bolt) rear end (leaf springs) with 4:10 posi gears. 31" tires.

As you can imagine, at 55 MPH I'm turning about 3k+ RPM. I live in Texas where the speed limit is 70 and everyone runs 75-80, even on old farm roads. Besides keeping my tired little 305 turned up all the time I've also got people driving up on my back bumper all the time!

I won't be putting it on the drag strip and I don't pull stumps with it either. The ole gal desperately needs higher gears.

Ultimately I want to go with a late model manual overdrive tranny, but thats in the future. The best I can do right now is gear up the rear end, at least 3:73.

So what would you guys suggest? I'd like to keep the job a simple as possible. I'd like to keep the 8 lugs and the big brake shoes. What are my options? Do I look for a whole rear end that will bolt right in? Do I find just the "chunk" in a rear end and swap that out? I'm listening.

[JIMs70GMC]

Find a dana 60 that was behind a big block, they had 3.54 gears.

[sleekster]

first check your tach becouse the math say's 31" tires with 4.10 rear and th350 3rd gear is 1.1 ratio @ 55mph you should be turning 2510 rpm's and same calculation at 75mph you should turn 3422rpm's a 3.73 will not be too much of a diff i would suggest for a 3.42 rear gear this will put you at 2093rpm @55mpn and 2855 @75 mph. hope this helps.

[TugOwar]

Thanks for the info guys. Jim what year model trucks am I likely to find that dana 60 BB rear end? Do I look for GM trucks only or Dodge trucks also?

Sleekster that does help. My numbers aren't exact I know. But the point is I wanna make the truck more street friendly.

[JIMs70GMC]

Well 67-72 3/4 tons for sure or you could just have higher (smaller number) gears installed. The dana 60 has a wide range of gear sets available. You could have your posi freshened up when the gears are installed.

[TugOwar]

eh, can't really afford to pay someone to work on my truck. I do everything I can myself. This is why I need to find either the whole rear end I can swap out OR swap the chunk. I don't have the tools or knowledge to change just the gears.

I'll go junk yard surfin and see what I can find.

[72longbed]

TugOWar,
if you find a 14 Bolt Full Floater, 10.5" ring gear, I have a set of 3.21 ring and pinion for it. The gears are practically new with less than 500 miles on them.

72longbed

[uncle_handsome]

Since your motor's turning over 3000rpm while on paper it should be turning around 2500 rpm, you could be getting a lot of slip from the torque converter in your transmission. A tighter torque converter, like ones for towing will slip less. If your converter wasn't slipping much you should be turning maybe 5 percent faster than the equations for rpm vs. mph say, instead of 20 percent faster. If your converter slips too much and you replace, if the math says you should be around 2500, you may be at 2600-2650. That way you keep your torque.

I think this is the rpm vs. mph equation;

mph x final drive ratio (rear gearing) x 336 x overdrive? (ie 0.70)

divided by

tire diameter

[4bynut]

Hey TUGOWAR, it's to bad shipping would be so high. I have a ford D60 rearend here with 3.54 gears and open carrier. And I'd be glad to swap for your 4.10 posi. I guess that's the way it work's. Jason

[LONGHAIR]

TugOwar,
It sounds like you are being practical about this swap. It takes a lot more to change gears than a lot of guys will believe.

Lets clear-up one thing though. There is no "Chunk" in a Dana60 rear end. The term chunk is used to refer to the removable center section that contains all of the gear parts, not just the differential. These are most common in 9" Fords and the older Eatons. There are others, but these are the ones that apply to trucks (for the most part).

With the Dana60 you will need to swap the entire housing. Just be sure of the new ratio before you buy something.

[goldwing2000]

Get bigger tires.

[uncle_handsome]

I agree with the last message. Since it's 2wd, maybe you could put 33's or 35's in the rear!

[JIMs70GMC]

Also when working on a dana 60 you need a case spreader to get the carrier out.

[TugOwar]

Good information, thanks very much. Good to find out theres no "chunk" and that the entire housing must be changed, which is easier for me anyway. I'm looking for one from a big block like Jim suggested.