wanting to change the 3.42 gears. Have a lot to think about, advice?

[weider1717]

my 87 is an open axle 4x4 with 3.42's it came with 31's stock and i've ran 32x11.50 for years.

I'd like to eventually go 33x12.50 and a 2-2.5" lift. And in the back of my head I may even go 4" ad 35's I like the looks just hate the strain on a 1500 drivetrain.

I am also an original kidna guy so besides the lift and tire size it will stay stock and might even go back to stock one day just knowing me……

with that said what is the best gera option I am thinking 4.10's because I think those are perfect with 33's and CAN work with 35's and CAN work with even down to 31's so it should be a one time gear swap.

or should I go 4.56's?

[mongocanfly]

My vote is 4.10s..I've gotem in mine with 33in tires..it does tend to run higher rpm but I put a 5spd in mine to take care of that...there are gear ratio calculators you can use to determin what rpm you would be running..I would get as close to what your comfortable with. High rpm=empty tank.http://spicerparts.com/calculators/e...rpm-calculator

[N2TRUX]

Good info weider1717 but you failed to mention what transmission you have. That will help determine what final gear works best. Regardless, I think 4.56 is going too deep.

[Rubble]

I'm running 35s with 4:10s in my 86. It has a 465 & runs about 2500RPM at 60mph. It's a decent combo for what I use the truck for.

[weider1717]

Originally Posted by N2TRUX

Good info weider1717 but you failed to mention what transmission you have. That will help determine what final gear works best. Regardless, I think 4.56 is going too deep.

Sorry, it is the original 4sp/OD that came in it. Engine is stock also 350 FI 210hp I believe.

[Jake Wade]

4.56 would be my pick for 35's and a 700R4, cruise RPM at 60 MPH in OD with converter locked up will be around 1900.

[hotrodder]

Until the converter locks up, you will be turning the ole motor, not to mention the fuel mileage.

[weider1717]

So whats the verdict guys 4.10s? or go to the 4.56's? i talked with the guy going to do the work he promise they won't whine when he gets done with it runs a really clean shop feel good about him doing it just on the fence about what set to get.

ARE 4.56'S excessive with 33's?

[mongocanfly]

4.10...2cents

[mongocanfly]

4.10...2cents..4.56 will run aprox 200 more rpm at around 60mph

[weider1717]

Thanks, 4.10s is where I was leaning from the get go think thats what i'll do.

[Greenlee]

The k5 blazer on the left has 4.56 gears (1 ton military axles) and a 700r4 on 35's. It drives great. Seems like a perfect match to me.

My truck on the right has 3.42 gears and 31's. It used to have a 700r4 until it crapped out on me. Now it has a TH400 out of the same military truck the axles came from.

[enaberif]

Originally Posted by weider1717

Sorry, it is the original 4sp/OD that came in it. Engine is stock also 350 FI 210hp I believe.

Hmm 4spd/OD? The only transmission that was in these trucks that had that option was the A833 transmission which was more commonly found in the 2wd trucks.

You sure about the shift pattern?

[slotard]

Originally Posted by enaberif

Hmm 4spd/OD? The only transmission that was in these trucks that had that option was the A833 transmission which was more commonly found in the 2wd trucks.

You sure about the shift pattern?

I suspect he means 700R4 but who knows.

I can say that with no lockup or OD, my 350/350/4.10 with 30.5" tires isn't much fun on the freeway. Will it go faster than I should? Sure... but it sounds like it doesn't like going more than 60ish. OD will help a lot but I'd probably go 4.10s for now.

[Ski-me]

I have 4.10's with 33's, 350 TBI, 700r4. At 65 I'm right around 1800 rpms and the truck seems to do good. Pickup is good and get pretty decent mileage. I had 35's before and it did have to work a bit more....but nothing too major.

I'm at 6500 feet so the lower the elevation, the more "zip" you have. And being in SC, it looks like your elevation would be a good advantage.

So, I thing 4.10's are good. If your goal was 35's for sure, then 4.56, but if you're going back and forth and mainly 33's, 4.10's are the way to go.

My truck has stock rally wheels, 33's and 2.5" lift. Nice, mild stance.