Rear ratio question.

[krue]

I'm putting a 6.0l/4l80e combo in my 70. I currently have a 3.07 ratio rear end and wonder how well this will work with the engine/tranny combo. When I was planning a 5.3l or 4.8l conversion I planned on going with a 3.42 ratio rear end. I wonder if the added torque will make the 3.07 work. Plan on daily driver with occasional towing duty (pulling my tractor or vehicles around).

[nlped]

How tall of a tire will you be running? If it isn't really short, that 3.07 gear is going to cause the truck to go in & out of overdrive at highway speed.... unless you're going to be driving 100+ mph

[Eddie H.]

I went with a 3:73 on the last overdrive conversion I did. It was geared way too high with the 3:07.

[Shinysideup]

You'll want the 3.70, luckily that came stock so you can find a complete rear to swap.

[Daves70]

3.73 seems to be the sweet spot gear with an overdrive. I have a 3.42 and it's still a little too tall for my combo.

[ozarks hunter]

I'm doing the same swap in my 72 but with a 410 rear gear. Hopefully I'll be able to let you know how that combo works in a few months.

[LockDoc]

-
I also vote for the 3.73. The 3.07 will be too steep. It may cause your trans to overheat.

LockDoc

[Wrenchbender Ret]

I had a 70 with 350 engine, 3:08 rear gears & 700R4. It was a pleasure to drive. It would pull long hills on the Interstate with A/C on & never downshift. The engine was quite & the MPG good. If you were pulling a load you just left it in direct drive & it still worked good. The best of 2 worlds.

[MattPSU]

I have a 5.3 with a BTR stage 3 cam, 4l60e and my truck originally had 3.07 gears. With the 3.07, I felt like it was searching for gears all the time and the trans ran hot unless I was cruising on the highway at 70mph. At highway speeds it was great, but not a great combo for around town. I actually considered going back to a stock cam because I felt like it wasn't ever in the sweet spot RPM-wise for the cam.

I just put in 3.42's mostly because I picked up a posi unit cheap and that was the lowest ratio it would accept. I have just over 100 miles on it so far, but I'm liking it a lot more. It seems to have woken the truck up considerably. It seems quicker at the light, it's not searching for gears, and my transmission seems to be running cooler.

My researched found that 3.73 seemed to be the ideal LS swap gear, and that's what I would have gone with had I not picked up the posi so cheap.