Good rear gears

[84GMCSierra]

Good Afternoon members. Just got my truck back with the "new" Vortec 350. I want to do some long distance driving with it but was told it's geared too low. It's an 84 C2500 with the TH400. I don't know what are in it now, but want to change them out in the next few months. I'm just doing in town driving now. What's a good setup? I don't do any pulling or heavy hauling.

 

[legopnuematic]

Figure out what ratio it is now and what your tire size is. That information would give us something to work off of.

 

[75gmck25]

Stock tires on a C2500 are probably about 30-31” (245/75R16?), and you don’t have overdrive. Figure out your current rear end ratio and then run one of the many online calculators to figure out what ratio seems to work best for you.

My K25 has 4.10 gears and about 30.5” tires, and it runs about 2800 rpm at 60 mph. The noise level is not great at that speed, but it will run for hours on the highway with no issues. It just depends on what you are looking for.

 

[CountKrunk]

I don't see any reason why you can't drive it as long as you want. My c20 has an sbc with a turbo 400 heavy duty trans w/ 4.10 gears and ive driven it on a 8 hour road trip. I was maxing out around 60-65 mph but yeah, driving just fine.

 

[bucket]

Good Afternoon members. Just got my truck back with the "new" Vortec 350. I want to do some long distance driving with it but was told it's geared too low. It's an 84 C2500 with the TH400. I don't know what are in it now, but want to change them out in the next few months. I'm just doing in town driving now. What's a good setup? I don't do any pulling or heavy hauling.

Who told you it was geared too low?

If you like how it drives right now, that's all that matters.

 

[Ricko1966]

Good Afternoon members. Just got my truck back with the "new" Vortec 350. I want to do some long distance driving with it but was told it's geared too low. It's an 84 C2500 with the TH400. I don't know what are in it now, but want to change them out in the next few months. I'm just doing in town driving now. What's a good setup? I don't do any pulling or heavy hauling.

People drove these trucks everyday,cross country,just like they came from the factory,sure someone may have ordered it or installed some tall gears in it. As @legopnuematic said find out what ratio you have and your tire size. Or get us rpm at 60mph and your tire size.

 

[legopnuematic]

4.56 was the lowest ratio available for an 84 2500 series, even with a 30.5" tire that is about 3500rpm at 65mph. 4.10s with the same size tire is about 3150rpm at 65mph.

So worst case scenario it is not really that bad. Compared to new vehicles with 5,6,8,10 speeds yes it might seem like its screaming, but as far as old trucks are concerned its fine.

 

[bucket]

4.56 was the lowest ratio available for an 84 2500 series, even with a 30.5" tire that is about 3500rpm at 65mph. 4.10s with the same size tire is about 3150rpm at 65mph.

So worst case scenario it is not really that bad. Compared to new vehicles with 5,6,8,10 speeds yes it might seem like its screaming, but as far as old trucks are concerned its fine.

Yeah, my old '86 C20 454 Suburban with 3.73 gears cruised the interstate with ease, even at 80mph. It was a fantastic cruiser for out of state trips. I actually would have preferred that it had a 4.10 gear.

 

[84GMCSierra]

I'll try the online calculator I got off this site to figure out what I have. Unfortunately right now I pushed the engine past it's limit and threw a rod so the replacement engine is toast. It wasn't a rebuild, just a used drop in.

 

[ali_c20]

Jack the rear up and put it on stands. Make a mark on the driveshaft so that you can count the revolutions. Make a mark on 1 tire. Put the tranny in neutral and release the parking brake. Rotate the tire 1 time and count the turns the driveshafts makes. E.g. 1 turn on the tire nearly 4 turns on the driveshaft would be 3.73:1 This is an easy method to find the rear end ratio without pulling the cover.
With knowing your ratio you can do your calculations to get the gearing you want.

 

[Ricko1966]

The above needs some qualifying. That will work provided it has a posi or welded diff etc. If it's an open diff you need to turn the tire through 2 revolutions. When you start spinning the tire look at the other side,is the other tire spinning the opposite direction? If so it is most likely an open diff,spinning g same direction? Most likely some type of locked diff. You can just mark one tire, and push the truck forward and count turns,this eliminates posi or open diff from the equation, taping a piece of string to the drive shaft will help you count,as in 3 wraps of string means tge driveshaft spun 3 times. Partial spins you can estimate based on what gear ratios are available. 3 plus barely part of a turn 3.08 3+3/4 turns = 3.73 etc

 

[bucket]

I'll try the online calculator I got off this site to figure out what I have. Unfortunately right now I pushed the engine past it's limit and threw a rod so the replacement engine is toast. It wasn't a rebuild, just a used drop in.

Unless you were out doing 5500 rpm burnouts or doing top speed testing, that engine of yours was not healthy and was about to expire no matter how you were driving.

 

[SquareRoot]

Welcome. It's been lonely down here.