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73-87 Chevy _ GMC Trucks => 4 Wheel Drives => Topic started by: Magic1 on August 19, 2015, 11:24:21 pm
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My 82 Sierra 4x4 is running a 350/th350 with 35 inch tires, 3.08 gears, an open front diff and a locker in the rear. The spider gears were shot in the rear end and to save money I installed a spartan locker which I hate. I'm going to replace the differentials with limited slip front and rear and regear the truck. I won't say it's terrible at takeoff and power now but it could certainly be better. The question I've got is what are a lot of you guys running as your gear ratio with the same tire size/transmission that I have? I've looked at several gear calculator charts and they all show for a broad range of power and mileage to go between 4.10 up to 4.88 for that particular tire size. That seems like quite a jump to me but I'm not sure. I wanna do it right the first time. Just looking for some opinions from those that are running a similar setup.
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I think I would go with 4.56 or 4.10 if you don't have overdrive.
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I appreciate your response. I talked to a Drivetrain-Differential shop yesterday and they advised me to go with the 4.56. Said they do a lot of them.
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4.56 and 35s you will be screaming trying to keep up with traffic with no od. i had 4.10 with 38s and no od wish i had 3.73. now if you mud yeah you might miss it but thats what 4low is for
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4.56 is going to make your truck seem a lot quicker in the zero to 55 speed slot. It's a good choice.
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I have a 4.56 in my Yellow extended cab. I dislike (HATE) it. Even 50 mph the engine is screaming. If you never had to go on the highway, probably be ok. If you were running 38's or 44's, a 4.56 would be a good gear. My $.02
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even in my 91 i have 4.10 and only 29s i think if not smaller. with od im around 2k just going 60. might not be too bad in a gas motor but im losing my mpgs with the cummins.
with 4.56 and 35s you'll be at 3k going 65 and at 55 youll be close to 2500
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Zieg what size tire are you running with those 56's.
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Zieg what size tire are you running with those 56's.
LT265/75R16
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Yea I see what you mean 4.56 gear is in the basement for that tire size.
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Wonder how much difference I would be able to tell in going up to a 3.73? With it being so much I wanna do it right the first time and have no regrets but I also don't want to spend the money and not be able to tell much of a difference. Seems like now I'm running around 2200 rpms at 70 or so with the 3.08s. I don't want it to be screaming on the highway but I don't drive it at 70 all that often either. Just want to find a good balance. Also I built the truck for all around use; hunting, hauling trash, getting to work in bad weather. I don't intend on mudding it but rather have something that'll get me there and back if I have to get in some slop.
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I have 4.10s on my '91 with 35s, but I have OD. I can fly down the highway with ease. At 75 I am only turning about 2,100. For you, without overdrive, the same effect would be close to what you have now. If you went with 3.73s you would be turning about 600 RPM more and in my opinion, wouldn't be too bad if you driving on the highway fairly often. I turn about 2,900 in my '69 Chevelle going 75 and it is more than comfortable doing that.
In my '77 I also have 4.10s, but without overdrive and with 33s. In that I am turning about 3,100 to go 75 and it is just too much to drive that fast on the highway for long periods. It is loud and it is fatiguing! Around town it is just fine!
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The more I think about it the more I'm leaning towards 3.73. I think anything lower would be a waste of money and the 4.56 would be too low without od. Jury's out on the 4.10, may like it better but I think the 3.73 would probably work the best for what I use it for
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4.91 that's what I have. She jumps pretty good but revs ( 3000) at highway speed. 33" tires.
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I'm running 3.73 with 31s on a K truck. Mostly around town, but the occasional 200-300 mile run and back. I think it's about perfect. 2500 rpm at 60, give or take. So 4.10 would be my bet.
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i have 3.73's with a limited slip out of a suburban in the rear. I have 33" tires and a 6" lift. It's great. Great response off the line and feels like good top end.
I don't have a tach, but the motor def is not screaming. it feels good at 65 mph. Then again i don't drive it at 70 or 75 so i can't say how that would be, especially daily if you had to. This is just a weekend cruiser truck. I could easily stand 4.10 or 4.56 ... i think ...
But that's my story and im stickin to it. ;)
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Lol. Think I'm gonna try the 3.73s. New truetrac rear diff with fresh bearings and call it good. Appreciate all the input. Be nice if it didn't cost so much and ya could experiment a little but I guess you gotta pay to play right?
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I vote for 4.10's.
My 81 stepide has 4.10's with 35" tires. With a turbo 350 trans this seems like a great set up. I haven't drove the truck in years, so I can't remember the rpm's at highway speed. It just felt right.
My M1028 has 4.56 gears with 285/75R16 tires (32" +/-). With a turbo 400 trans this truck is good for about 60 mph on the highway. Any faster, and the 6.2 diesel sounds angry.
Is your truck running 10:bolt axles?
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10 bolt up front and 12 in the rear. Not the strongest setup I know, but will work fine for what I need.
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3.73 is very common
Should be able to find that in a used axle if you feel
Comfortable swapping the whole axle
I think 3.73 would be a good choice
We run that with 35 inch tires
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Man...just when I think I may have things figured out my wife throws something else in the mix. She brought up pulling a camper to the lake. That's got me wondering if the 3.73s would be good enough or if I'd be better with the 4.10s or would there even be any real advantage one over the other. I'll definitely add a auxiliary transmission cooler.
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typical lol just when you thought you had it. but how big of a camper are we talking? how far of a travel? hills?
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typical lol just when you thought you had it. but how big of a camper are we talking? how far of a travel? hills?
Like a 30ft travel trailer that would be left at the lake. Not pulled back and forth but only occasionally. I live in Kentucky so it's fairly hilly. I'd say probably around 50-60 miles one way.
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You'll most likely end up disappointed with anything less than the 4.10. Unless your motor been massaged our small blocks are usually just decent on power throw in a taller tire and it's like losing 50hp.
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You'll most likely end up disappointed with anything less than the 4.10. Unless your motor been massaged our small blocks are usually just decent on power throw in a taller tire and it's like losing 50hp.
Are you talking about while towing or just in general? See that's what has me concerned about going to such a lower gear like a 4.10 or higher. It is slow on take off but really not bad going down the road with the 3.08s. I've got a crate goodwrench 350 with an edelbrock performer manifold and headers. Supposedly it's making around 260 hp but who knows. I want better towing ability and basically just want the truck more usable and fun to drive but not be stuck in permanent granny gear. Looking at gear calculator charts online say with a 35" tire to get it back to stock I should go with a 4.10-4.88 but it doesn't specify whether or not that's with an overdrive transmission. I've got the th350 and don't plan on going to the 700r4. If I'd planned a little better or knew more about what I would be doing when I bought the truck I would have got one and had it beefed up but I already had the th350 rebuilt with a mild shift kit and converted the old np203 over to a 205. I could sell the combo and get the overdrive but I don't want to start all over again and I'm satisfied with the way it works now.
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All the charts I've seen online are based on a 1:1 transmission ratio, which is what you're TH350 has in 3rd gear with the np205 in high. Considering a 35" tire is really around 34.5" at 65MPH you're 3.08 should be around 2000RPM switching to 4.10 would put you around 2650RPM, 4.56 would put you at almost 3000RPM. 3.73 at 65MPH is around 2400RPM.
I would say, go with the 4.10s as it's going to get better into the torque curve and still stay reasonable on highway
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4.10 :)))
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I also vote to go with the 4:10. It will help you when you are towing. The truck won't be a slug with a camper behind it. I would also suggest a transmission cooler if you are going to tow with your truck. That is just cheap insurance.
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yeah with the trailer and not having a manual trans i have to change my vote to 4.10
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If your towing is just a one time deal
Install a good Trans cooler and haul your camper
Just don't get in a hurry and remember it's better on the engine and the Trans to wind it up fast than to lug it so you may need to drive some or most of the way in second gear depending on the hills and how bad your trailer sways
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I sure appreciate all the input guys. I'm sure it's a worn out subject but when it's yours you always wanna make sure you're getting what you need. Do any of y'all have any suggestions towards a true Trac vs an Eaton posi? I've read that the true Trac is a little more bullet proof than the Eaton due to it being all gears but the Eaton is smoother because it has clutch disks that will slip. Maybe a non issue but I figured I'd ask while I'm at it cause I'm considering the true Trac. Price is basically the same for both. Also, I've got the transmission lines routed into the radiator. Will a transmission cooler make much difference?
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I don't think you will have an issue with either. I am probably going to try a true trac next, I don't think either is going to be smoother than the other...
A cooler is always a plus if you are pulling or putting a load on the truck.