Re-gear 14B FF from 4.10 to....?

[Dropped88]

I have a dually here getting a 8.1 and 3.42 gears, I can come back with a update when it's done

 

[someotherguy]

I have a dually here getting a 8.1 and 3.42 gears, I can come back with a update when it's done

Sounds like a great cruiser that will have enough guts to still tow! I wish I had an 8.1 instead of a TBI 7.4. and I could make it happen, but probably not in the cards for this truck.

Richard

 

[b454rat]

What about taller tires? Put some 235/85s or 255/85s on the back. The 235 will bring it down to 2500 rpms. The 255s lil lower....

 

[someotherguy]

What about taller tires? Put some 235/85s or 255/85s on the back. The 235 will bring it down to 2500 rpms. The 255s lil lower....

Dropped. 225/75/16 is what it's got.

Richard

 

[Sean Buick 76]

No I wouldn’t change the gearing. Sure try tall tires, you could run taller when not towing. Use a gps app on your phone for your speedo. Although the rpm is a bit high when going 80 mph+ it’s just not a vehicle that’s designed to go 100 mph. Or stop from 100 mph. Also it’s less about the RPM it is at and more about the load. Switch to a 3.42 gear and sure it will rev less but it will fight on hills empty. It’s a heavy truck that’s geared correctly, leave it alone lol

 

[1998_K1500_Sub]

What was the OE tire diameter?

You’ve got ~29” tires now.

Divide 29 by OE diameter.

Multiply that by 4.10 to yield the new rear gear ratio.

It’ll provide “OE” performance.

(Edit) Ah, the OE tires for a 1993 C3500 dually ARE 225/75 R16, same as on it now. So much for my suggestion above.

For Comparison: My 1998 Suburban's OE tire is 245/75 R16. It weighs 6210# and came w/ L31 4L60E and 3.42 gears. It's reasonably responsive. I've since put on larger tires (265/65-18), and later re-geared it to 3.73 to make up for the larger tire.

 

[Caman96]

No I wouldn’t change the gearing. Sure try tall tires, you could run taller when not towing. Use a gps app on your phone for your speedo. Although the rpm is a bit high when going 80 mph+ it’s just not a vehicle that’s designed to go 100 mph. Or stop from 100 mph. Also it’s less about the RPM it is at and more about the load. Switch to a 3.42 gear and sure it will rev less but it will fight on hills empty. It’s a heavy truck that’s geared correctly, leave it alone lol

They did come with 3.42’s, not arguing for or against.

 

[boy&hisdogs]

This might be helpful for those that don't know about it yet. It's a very detailed gear ratio calculator that takes into account your entire drive train and spits out lots of good usesble information (rpms at given speed in each gear, etc)

Gear Ratio Calculator

Finding and axle in a non-standard gear ratio will be very hard but not impossible, but you might go years without it just to end up doing something else anyway. That's what I ended up doing trying to find a unicorn rear end (6 lug 14bSF with 4.10) and ended up going with bigger tires than i originally planned for and 4.88s.

My truck came stock with 3.42s and it was wimpy, but I think yours being lower, with smaller tires and a bigger engine will probably drive pretty nice with 3.42s.

 

[b454rat]

I mentioned the tires cause its the easiest to do. Just a matter of putting them on. I used to hit junkyards ALL THE TIME, and never found a 14ff with 3.42s or 3.21s. Could be the area, lot of hills, but only seen a Dana 70 with 3.42s in an 88 1 ton I had years ago.

 

[1998_K1500_Sub]

I mentioned the tires cause its the easiest to do. Just a matter of putting them on.

See Post #14