Which gears to run?

[2wheeler]

I have 38.5" tires on my '86 and now I don't know what gears to go with. I just rebuilt a 355ci and have a 700r4... I was thinking 5.?? because it's not going to be around any highways and it would be a bonus to bark the tires or leave a patch or something. What do you guys think? Anything is appreciated. Thank you

[b454rat]

Take your 38s and divide that by the stock size tires, say a 31. Mulitply that by the current gears, we'll say 3.42s, which comes up to 4.24, so you can go down to 4.10s, or up to 4.56s. Depending on what axles you have, going to a 5.13s will make the pinion real small, and with 38s and a healthy motor could make them and the joints go pop.

[vtblazer]

Originally Posted by b454rat

going to a 5.13s will make the pinion real small, and with 38s and a healthy motor could make them and the joints go pop.

Naw, it's done all the time and holds up just fine.

I've been wheeling pretty hard with 5:13's and 39.5's without issue.

Pretty common set up among the 4x4 crowd, wouldn't be if it didn't work.

2wheeler, go 5:13's or higher with that over drive.
Did you have the 700r beefed up?

Any pics?

[2wheeler]

Originally Posted by vtblazer

Did you have the 700r beefed up?
Any pics?

I was told that the transmission was rebuilt when I bought the truck and I've only driven it once or twice around the block. The only decent pic I have...

[vtblazer]

Nice ride.

Leaving it black for wheeling? (looks good IMO)

Or is it about ready for paint.

[2wheeler]

It's wheelin' paint right now but I haven't even got that far and then one day I hope that it'll be nice enough for a gloss black

[lilpup69chevy]

i'd say 4.56's or 5.13's

[2wheeler]

I found this: Good "rule of thumb" calculation is to mutiply .12 by your tire diameter. (.12 X 38" = 4.56)

So that's probably what I'll do but would it be worth putting the gears into a 12 bolt that I can get or the stock 10 bolt?

[see ten]

Originally Posted by 2wheeler

I found this: Good "rule of thumb" calculation is to mutiply .12 by your tire diameter. (.12 X 38" = 4.56)

So that's probably what I'll do but would it be worth putting the gears into a 12 bolt that I can get or the stock 10 bolt?

I wouldn't regear a 10 bolt for a tire that tall! If you have a foot of any weight, the axle would be junk in short order. You're borderline on needing some 3/4 or ton running gear there.

[1969K10]

Originally Posted by see ten

I wouldn't regear a 10 bolt for a tire that tall! If you have a foot of any weight, the axle would be junk in short order. You're borderline on needing some 3/4 or ton running gear there.

You're getting ready to drop a heap o' money on some 1/2T axles that aren't even close to being up for the abuse you're getting ready to hand them.

[LONGHAIR]

I agree........If you really are going to 'wheel this truck, up-grade the rear-end at a bare minimum. You can step up to a 12 bolt and keep the 6 lug wheels, as a lower dollar option. This is not the best way, but the most cost effective for a minimal use non-competition vehicle.

The biggest thing, reguardless of which axles you end-up using, is proper break-in procedure. This is even more important in lower ratio gears like these. First of all use a synthetic lube. Second, drive no further than around the block on the first voyage. Park it and let it cool for a while. Then drive a mile or so and wait again. Then no more than 5 miles or so, cooling again. After that some in town driving w/o highway speed for the next twenty or so. Then you should be good to go. Personally I would pull the cover, inspect the gears (looking for metallic particles in the lube) and change the lube after 100 miles or so.

Again as I always say, do do the gear change yourself. Pay a reputable shop to do it for you. Inquire about their break-in procedures and warranty.

[2wdBlazer]

5.13 or numerically higher. I would go with at least a 5.29 beacause you want more power and you have overdrive. That other formula only works for a 1:1 final drive.

[kwmech]

Originally Posted by 2wdBlazer

5.13 or numerically higher. I would go with at least a 5.29 beacause you want more power and you have overdrive. That other formula only works for a 1:1 final drive.

That would be my vote also. The 5.13s in overdrive (700 is 28%) is 3.69 final

[2wheeler]

The more and more I look at this, the more and more I get confused.

TH 700R4
1st 2nd 3rd 4th
3.06 1.62 1.00 0.70

NP 208
Lo Hi
2.61 1.00

The reason I put all the ratios is because right now I don't have a front driveshaft so I put the transfercase in four-lo and drive around with 3.08s. I think the gear ratio that I'm looking for is pretty much the truck in 1st/Lo

Sorry about all the questions... This is what I do before I invest, research it and go accordingly and I've never done gears before