Regearing Advice... What do I need?

Camar068 · Jul 3, 2024

Grit dog said:
My advice. If your axles are both good shape, bring your truck over here. I’ll literally you swap your 3.42s for the kids 4.10s. For free.
If you paint them black and swap my brakes and hubs (unless yours are nicer lol) I’ll provide the beer too.
Don’t even need to bring tools.
You must have overdrive or you wouldn’t be swapping.

can't beat that.....and it's free. If you don't like it, then go to your shop. Of course, if your close to each other.

Grit dog · Jul 4, 2024

shep151 said:
Tempting as that is, I'm not 100% confident in the rear axle overall. The PO had a tendency to haul HEAVY and I have a slight wheel vibration that I've isolated to the right rear, but can't see the cause. I've gone over all the usual suspects and am coming up blank.

So I've decided to have a reputable shop regear the rear diff and go through the whole rear axle from drum to drum so I'm starting with a clean slate. Later I'll do the front diff, it's a 10 bolt corporate.

Bummer dude…
Well good luck with er.

shep151 · Jul 4, 2024

Grit dog said:
Bummer dude…
Well good luck with er.

If the shop says they're in good shape, do you want the 3.42 ring & pinion?

Grit dog · Jul 4, 2024

shep151 said:
If the shop says they're in good shape, do you want the 3.42 ring & pinion?

Maybe? Honestly I’d likely not make the swap otherwise. Truck is a Sunday driver and it would be a ways down our list of projects.

Plus, yours is a 78 so presuming it’s a 14ff and Dana front. His is an 86 so 14sf and 10bolt front or whatever it is. Not sure they’re the same.
Appreciate it though.

shep151 · Jul 4, 2024

Grit dog said:
Maybe? Honestly I’d likely not make the swap otherwise. Truck is a Sunday driver and it would be a ways down our list of projects.

Plus, yours is a 78 so presuming it’s a 14ff and Dana front. His is an 86 so 14sf and 10bolt front or whatever it is. Not sure they’re the same.

I'm not sure of the year of either axle. Rear is 14FF, front is corporate 10.

mattsk8 · Jul 5, 2024

If you don't have overdrive and do a lot of towing you might hate 4.10 gears on the highway. I had a TH400 trans with 4.10 gears and at about 80 it was screaming, IIRC I was over 3,500 RPMs. That was with 33" tires, if yours are smaller it'll be worse.

I swapped my TH400 to a 700r4 and absolutely love it, now at 80 mph I'm turning about 2k RPMs.

trukman1 · Jul 8, 2024

I used East Coast Gear Supply. I called them to make sure I got everything right. Great customer service, fast shipping. Need I say more?

cmichels83 · Jul 8, 2024

You must be registered for see images attach

I found this chart helpful for decided gears. Ignore the blue circles. That was me calling out the difference in a past text conversation I was having with someone when I re-geared my suburban.

mattsk8 · Jul 8, 2024

cmichels83 said:
You must be registered for see images attach

I found this chart helpful for decided gears. Ignore the blue circles. That was me calling out the difference in a past text conversation I was having with someone when I re-geared my suburban.

I'm trying to figure out what this actually means. It's beneficial if you have 31" tires and 3.42 gears to know that going to 4.11 will bump your RPM 400, but I don't understand the mileage/performance rating. I guess according to that chart, the idea is to get close to 2,400 RPM on the highway?

gmbellew · Jul 9, 2024

http://www.grimmjeeper.com/gears.html this is the best calculator I've found. Use your actual measured tire size on the truck, not the spec sheet.

gmbellew · Jul 9, 2024

http://www.grimmjeeper.com/gears.html this is the best calculator I've found. Use your actual measured tire size on the truck, not the spec sheet.

Craig Nedrow · Jul 9, 2024

Lots of good input, what a great group. Yukon Gear is in Everett by Paine field, been there a few times. They also do rearends. My K20 14FF with 4:10 gears 1:1 (no overdrive,) was 3300 at 70, been running the 454 like that for a while, but I am swapping to a 4l80e, like matt said, hope you have OD. I am in Selah, you must be close.

mattsk8 · Jul 10, 2024

Craig Nedrow said:
Lots of good input, what a great group. Yukon Gear is in Everett by Paine field, been there a few times. They also do rearends. My K20 14FF with 4:10 gears 1:1 (no overdrive,) was 3300 at 70, been running the 454 like that for a while, but I am swapping to a 4l80e, like matt said, hope you have OD. I am in Selah, you must be close.

How long until you do the 4L80? Do you have to modify the transmission tunnel on our cabs? Someday if (or more likely when) my 700r4 craps the bed I'll probably go that route.

Hunter79764 · Jul 10, 2024

mattsk8 said:
I'm trying to figure out what this actually means. It's beneficial if you have 31" tires and 3.42 gears to know that going to 4.11 will bump your RPM 400, but I don't understand the mileage/performance rating. I guess according to that chart, the idea is to get close to 2,400 RPM on the highway?

Basically, its saying ~2400 RPM is MPG special but a dog in town, ~2750 is compromise, and 3000+ has you passing everything except a gas station... All of that of course depends on your exact setup and your definition, but it's a guideline.

Note, I'm assuming that chart is based on a 1:1 final transmission ratio which is completely accurate for a non-overdrive manual transmission or a lock-up converter in a non-OD auto transmission like a TH350C.
Non-Lockup automatics like a regular TH350 or TH400 will have a little more RPM than the chart shows, probably just 150-200 RPM or so, depending on the converter and a ton of other factors.
Overdrive will reduce those numbers by the overdrive ratio. I.E., if you have a .75 overdrive gear and the chart shows 2800, your actual RPM will be closer to (2800) x (.75) = 2100 RPM

cmichels83 · Jul 11, 2024

Sorry about the long delay. I believe the chart is showing rpm at 65mph without overdrive. I couldn't find the original, just my screenshot I took 9 months ago. The chart is useful if you are changing gears and/or tires to make sure you are getting in the range of what you're intending. When I was reading through other people's comments about what gears they were running, a lot of them were failing to mention tire size. Without knowing what tire size they have, the recommendation of gears doesn't mean much. My dad use to always say, it is cheaper to change your tire size than your gears.

Regearing Advice... What do I need?

Camar068

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Grit dog

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shep151

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Grit dog

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shep151

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mattsk8

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