Gonna be swapping gears and adding a posi..got questions.

[Lil Ape]

So when I bought my truck, I was told it had 3.73 gears, which was nice. But I cant can't over the fact that this thing is a dying dog off the line. No stumble, no hesitation..just...slow. even for a fresh 355/th350 and new street avenger carb. My 4.7 jeep with 3.73's and limited slip launches so much faster than this truck. My jeep throws you in the seat with less than maybe 300lb/ft torque. It's certainly doesn't help that this truck has an open diff and bald rear tires, but I figure it's gotta be something else. I know I was gonna get a posi/locker in the future. And I needed to know the axel spline count. So this afternoon I tore apart my rear end. It's a 8.5 10 bolt with 28 spline axels. And behold what I believe to be my big problem. I have 2.56 gears! Counted the teeth on the ring gear and pinion and came to 41/16. Did the math and came to 2.56 ratio. So it appears I was lied to when I bought the truck. And now it makes me question if I really have a 3k stall converter and .30 overbore. So now it looks like i'll be buying new gears with my taxes, was looking to new heads. But I see no reason to build more power when I can't get it planted to the ground properly.

My questions are which gears should I go with. I'm deciding between 3.73's(which it should have already had), or 410's. This NOT a daily driver or track car, strictly a street truck that I would use on the weekend. So I don't care much about gas mileage and road manners. Right now it's still in a resto phase. Which ratio would be better for a street truck and torque? Also, about a locker. Which are some good brands and brands to stay away from. And would it be better to go with a limited slip, or a automatic locker? Any help would be appreciated.

[84chevyguyid]

I have an 84 3/4 ton pickup, started out life as a 6.2 diesel with a 4 speed stick and 4.11 rear gears. Before I bought it, someone had swapped a late 70's 400 small block in it. I live in a rural area and have a 40 mile drive down the freeway to town and with 4.11 gears, the freeway driving sucked but it had good power. Last fall I changed it over to a 700 auto trans and 3.73 gears and now it seems kinda doggy cruising down the freeway. I wish I had left the 4.11 gears in it and just did the overdrive trans. My mileage went from 12 to 15 with the change however. That thing has to be a dog with that rear end ratio! I think I would go with the 4.11 gears if you arent going to be doing much freeway driving. What size tires are you running?

[Lil Ape]

As of this moment I'm running stock 235/75/15 tires. But they are all in desperate need of changing. Since this truck wont be driving all that much, I'm thinking about just running drag radials. probably 275/50/15 out rear. if they'll fit, maybe a 325 wide. And I wont be doing much highway driving in this truck. Mostly short distances because i know i'll get terrible gas mileage right now. My DD jeep only gets 15mpg. I know with a 3spd and 4.10 gears, I'll probably go deaf at 70. And yeah, this this is soooo slow with the 2.56's. Was honestly disappointed when I first went wide open on it.

[79Betty]

Do 4.11's. Mine will roast em through 2nd. Although i do only get 6 mpg :/

[cadillac_al]

I love my 3.08's. I have plenty of power to drive aggressively and tow cars. It still revs plenty high at 70 mph on the highway. I used to run my 3/4 ton with 4.10's at 70 mph but I had 32-35 inch tires on it. These are both no OD. If you have OD then you can easily go to lower gears.

[Lil Ape]

Would there be any performance difference between 4.10's and 4.11 gears?

[cory d]

I have 2.73s so I feel your pain. I am picking up a 3.73 soon so I will give that a try. Maybe 3.42 would be better but I will try the 3.73's. not trying to set and lad speed records so i dont need these darn bonniville gears

[bilfman]

I have been in the same situation before. So here is what I would have done if I could turn back time. If you plan on staying with a 3 speed tranny go with 3.73s . I put in 3.73s with a 32" tire and it was an excellent combo. Fast forward a few months and I upgraded to a 4l80e 4 speed. With the 3.73 it can be a bit on the weak side if towing down the highway. It is so close but just not quite there. The extra 10% that 4.10s would give would make my truck perfect on the top and bottom end. So if planning a non overdrive go 3.73, overdrive 4.10.

Absolutely go with a locker or posi for sure in my opinion the BEST mod for any truck, 2 or 4wd !

[LONGHAIR]

Originally Posted by Lil Ape

Would there be any performance difference between 4.10's and 4.11 gears?

No....the difference between 4.10 gears and 4.11 is in the axle itself. Whether it is a 10 bolt or 12, in a car or truck.

4.10 is a 12 bolt truck and car gear. 41-10 teeth
4.11 is a early 10 bolt car gear 37-9 teeth.
4.09 is a Dana 44 gear 45-11 teeth


Same with the 3.07 and 3.08 thing....truck/car

As far as choice, I would stick with 3.73s, the 4.10s are just too much for any kind of highway driving, especially with thar short of a tire.
Traction device...I would stick with the tried and true Eaton clutch-type posi-traction unit. They are smooth, strong, reliable, predictable and rebuildable.

[kelsfine69]

I had 3.08 and went to 3.73..was a nice difference. Good all around..Then I got greedy and went 4.11...Too low, revs too high on the highway...Will be going back to 3.73 someday...

[INSIDIOUS '86]

I've had 2:73s and 3:08s and 3:73s. All on the same engine. I can tell you one thing for sure. A week engine...is a week engine. 2:73 open diff was a little soggy but I could still run quick but the first gear of the 700r4 helped. Then I swapped to a 3:08 open diff and a th350. It ran stronger and definitely liked it. Then I ponied up for a Detroit true track differential and 3:73s. It loves them and is perfect for the motor but damn I miss my overdrive.
My stepside had 3:73s. The motor just isn't strong enough to make any real use of them speed wise.

If anything. Build your differential then build your trans. Then build your motor to make use of everything else.

3:73s are a perfect street performance gear. 4:11s are better for getting on and off a trailer at a track. I would also recommend an overdrive trans not just to save gas but to also cut wear and tear on the motor....trust me...3000rpm at 60mph for an hour straight isn't doin the motor or your wallet any favors.

[cory d]

calculated that i will be running about 2600 at 60 with 255/70/15's. not bad, i will just do the old double nickle like she use too in the old days at about 2300

[Lil Ape]

I think I'm just going to go with 3.73's. I'm afraid 4.10's will be too much for a 3spd. I'm not concerned with swapping to an OD trans. Not unless something happen to what i have now. This truck wont be driven that much and wont see much, if any highway use. So I'm not too worried about not having an OD, plus the th350 is a freshly rebuilt and I'd like to get some miles outta it. As far as gear sets, what are the good brands to go with? And what pinion shaft diameter do I need to go with? 1.625 or 1.626? And would it be recommended to buy a ring gear installation kit as well?

Appreciate the help, guys.

[MikeB]

I have a buddy whose 77 Nova has a mild 350 with TH350 trans and 8.5" 10-bolt. He decided to replace the 2.56 gears for more performance around town. I suggested 3.08 or 3.23, but he went with 3.43. After a few days of driving it, including some very short stretches of freeway, he said he should have gone with 3.08. Of course, his tires were probably 26" tall, but even with 28" tires, I'd say 3.23 would serve you just fine. Heck, that would be a 26% increase in RPMs over your 2.56 gears!

Best suggestion I have is to use one of the many on-line claculators to determine what your RPMs will be at 65 or 70 mph with a 3.73 or 4.10 axle. Then go out and drive your truck in second gear at that RPM to see if you could live with those RPMs on the highway.

[wilkin250r]

I haven't heard anything about your motor. That's a big, key factor. If you've got a motor built for high horsepower, it is usually accomplished with components that shift the power from the low end up to the higher revs. If so, then a higher ratio like 4.11 will launch you off the line better.

But if you have a motor with lots of low-end grunt and torque, then a lower ratio like 3.73 or even 3.55 would suit you better. The motor would provide the torque to launch you off the line, but you'll need that lower ratio to help with your top-end speed. You don't want to win the battle off the line, only to lose the war to the finish just because you ran out of RPMs.

I had a similar setup years ago, a 72 with a 350, 4.11 gears, 3-speed auto, but my tires were just a tad taller at 31 inches. It was GREAT for what you are talking about, it launched great, real fun truck to drive around town. Freeway speeds were difficult because of the high revs, but not impossible, and gas was much cheaper then. I really think you can get away with 4.11 gears as long as you don't get too small on the tires.

[ont_guy_38]

I run 4:10s. I have a fairly potent motor though and I only drive it about 500 miles or so a year. The speed limit on any highway i drive on is 50 MPH so the gears are not a problem to me. There is one manufacture that makes a 3:90.

[El Toro]

I too am interested in opinions.

Here's what I got 14-bolt Corp with 4.56 behind SM456 with a NP208 (I think that the xfer mdl) behind a 350 with Hedman headers. PO used the truck for mudding hence the low rear end ratio. Don't know if its a locker for sure but could jack it up and test.

This is my son's daily driver but he only drives about 5-10 miles a day. Its torque in 1st and the right rear tire often chirps on take-off. it would be nice for things to be a bit smoother and to behave a little better at high-speed with a lower RPM.

So what's my options? Leave in the 4.56 or go with a 4.10? Does the 14-bolt corp make a difference?

[Lil Ape]

Originally Posted by wilkin250r

I haven't heard anything about your motor. That's a big, key factor. If you've got a motor built for high horsepower, it is usually accomplished with components that shift the power from the low end up to the higher revs. If so, then a higher ratio like 4.11 will launch you off the line better.

But if you have a motor with lots of low-end grunt and torque, then a lower ratio like 3.73 or even 3.55 would suit you better. The motor would provide the torque to launch you off the line, but you'll need that lower ratio to help with your top-end speed. You don't want to win the battle off the line, only to lose the war to the finish just because you ran out of RPMs.

Well it's a 355 with a 3k stall converter. I don't know anything about the bottom end or the compression. But it's got a performer rpm cam, duration 234/244 and lift is .488/.510. Rpm range from 1500-6500. Got the air gap manifold to go with it. But it's got crappy 882 heads that I do plan to upgrade later on. thinking about afr 180cc/65cc. Or something similar. I know my cam is a bit on an outdated design, and I might swap it to something newer. But that would be when I get new heads.

[bigd65]

Ape, looks like we are in the same boat and not far from each other. My 87 should be coming out of the paint shop this Friday ( HOPEFULLY ) then put it all back get her. The plan is start in the back and 3.73 posi and move forward. I am going to keep my 700R4 but have it built. Then play with the motor. Probably just a cam or something... Maybe a better fuel injection.