gears

[BigWill]

hey every body i just joined the site and i like what im reading so far. ok the question that ive got is dealing with gearing my truck is a 1/2 ton 87 chevy p/u with a 4"lift a mild sb400/th400/np208t-case with front and rear gm 10 bolt diffs and 38.5x15x15 boggers. the guy i bought the truck from built it to this current state but he didnt make any changes to the diff gears so needles to say its a dog at the mud hole so i wanted to ask what do yall think i need to change the gear ratios to Thanks in addvance for any info

[junior3382]

5.13 would be a good ratio to gain some power, but not KILL gas mileage horribly. But I have heard of Much stronger like 5.71. Depends what you are going to use the truck for.

For a good idea of where you may want to be visit

4Lo.com :: Gear Ratio & Tire Size Chart

It will set it up for you.

[75K30]

Welcome to the site:
Junior has provided a reasonable solution to your gearing problem. I like his aggressive approach to this. I am a firm believer in aggressive gearing, and believe that you really can't run too much gear. You do have a 208 T-case, which has a pretty decent low range, and you are only running 38.5" tires. You are also running an auto trans, so there may be a little compromise on the highway, but you are probably not searching for a gas mileage master here, or you would be driving a honda or something. Your truck should make decent torque with the SBC 400, and the lower ratio of the t-case may help a bit, but for mud, I feel that you would be better suited with 4.88, or 5.13's with aired down 38's and an auto transmission.
Needless to say that before you spend a bunch of money on 10 bolt drivetrain and 38" tires, you may consider that by making the truck a little more capable, you are right at the maximum capacity of the axle limits. Probably might consider upgrading axles to larger / stronger units before you sheel out some bucks on light drivetrain. In the long run you will probably have to upgrade anyway, so at least keep it in mind now.
Most axles will have a better gear ratio already, so while you upgrade, you can also get a better idea of how steeper gears are gonna get.
Have seen 14B's with detroits and 4.56's for less than 500 bucks. This is probably less than you could install a gear set into a 10 bolt, and with a mild SBC 400, you will never have to worry about breaking it.
Just a thought before you spend around 1500 to change gears in small axles that could (will) break.

[BigWill]

Hey 75k30 thanks for the info i am fully aware of the limited strength of the 10 bolts. But im having to work with what ive got for now b/c of budget reasons and parts findability. Eventually i will build the truck into a full on mud truck with bbc, front rear Dana60's and so on. As it stands now im not in the best spot to buy a front Dana60 as that is what i lack to complete the total package. Right now i have 3 Dana60 rears and 1 Dana70 rear. But there isnt much since in putting in just a rear and having a weak front holding me back. So for now ill just build what ive got and not beat on it too hard. Yeah right Thanks

[75K30]

Well, if you do not mind my honest opinion, I would really consider holding off on the gears and such with the small axles. Here is why:
you stated that you already have a D70 rear, and just need to find a D60 front. Since you are fortunate to have a chevy, you can find them for a reasonable price. Probably for less than you will spend on a set of gears. I say this because like so many I have done the exact thing that you are doing, and I have a few regrets. What I mean by that is that I have spent money twice on a modification, only to have to spend the money again after I upgraded the axles. Gears are not cheap, and changing them twice can really add up.
Instead of spending the money on the 10 bolt gears, why not buy a front 60, and install the 70 that you already have. I would not run a 60 out back because most 60's are tappered shaft 30 spline units that are pretty small, and break easilly. The 70 (depending on which one) may have up to 1.5" 35 spline shafts. Probably not going to break this any time soon. If traction is what you want, weld the diff out back, and call it good. For now it will probably have a 4.11 ratio, and there is a carrier break at 4.56, so after you get the whole thing together, you can later install a locker and the right ratio. You can do this in steps so you do not have to shell out the cheddar all at once. This means you can do the upgrade on a budget, and add the upgrades a little at a time as money permits. This way, every upgrade you do is actaully a stepp in the right direction, and not a side step that just eats up money.
Believe me, I have been there,and done that. When you break a 10 bolt, and have to spend even more money to get it fixed, just to get back to where you started, you will question why you did not invest in the larger drivetrain from the beginning.
Just my opinion, and maybe a helpfull suggestion.

75

[BigWill]

you know i like your thought process so i think ill go on that route now i just need to find a front 60

[75K30]

My intentions are not to completely change your mind, only share with you some of my experiences that have cost me money.
Your old axles will cost a pretty penny to upgrade, and even if they survive, once you make the move to 1 tons, you will ebentually sell the small axles, and they never bring great money. The cost of the 1 ton upgrade remains the same, so you might as well save the money now, and start working towards the final goal. The one ton swap is almost a bolt in deal, so you should not have too many issues.
Some things to think about for your swap;
Bolt pattern for wheels will now be 8 lug, and not 6.
Driveshafts will be too long, and they will need to be modified.
U-bolts are a different size since the axle tubes are larger.
After a D60 install, the crossover steering upgrade should strongly be considered.
U-joints are a different size, but can be changed during the d-shaft mod.

You should have no problems with finding a front 60. The chevy is the strongest and the least expensive of all the front 60's, and I have purchased these complete for less than 1000 bucks US.
Good luck, I am sure you will be very pleased after you go this direction, and at least that hard earned money will be going towards something positive, and not just getting you by.

[junior3382]

Not that I want to hijack a thread, but I am curious. 75K30, I know we have had an extensive conversation about SAS and gearing and my S-series trucks, but can this same concept be applied to mine? What i mean by that is I was going to upgrade my gears too to compinsate for the larger tires, but I would hate to spend the money on gears if they are not going to last me. I was going to upgrade to 4.56. And more then likely, for a while, keep the IFS, since I mainly like the trails and ocaional mud hole. But, Is this not a good idea?

[75K30]

Still applicable to this thread kinda.
Anyway, these are two fifferent trucks with two differnt styles of front axles, and one with a big horsepower advantage.
The OP's truck is already a solid front axle, and converting this to a 1 ton is a bolt in deal. The choice to go to a one ton drivetrain is simply because of cost VS effort.
The advantages of a stronger drivetrain when linked to a 400 cubic inch SBC, and a rather larger tire is not outweighed by just installing a set of gears in a small axle.
A guy can find a ex-military truck and have all of the components they need to build a real quality truck. These 1 1/2, or 1 1/4 rated full size trucks came with a stout 14 bolt rear axle with 4.56 gears and a detroit locker, and well as a 35 spline front Dana 60. These axles will bolt right up to any early checy truck with a few mods to the drivelines, thats it. These can be found at auctions for a rather inexpensive price. The sheetmetal is the same, so there are many other parts that can be used.
Now for a late model S series truck with IFS, this becomes a little more of a problem since there is no axle that is gonna just bolt right up. There will be much more fabrication involved to even start any SAS.
Now, as we discussed some time ago, before I would spend any money on an IFS lift, I would really consider the SAS. Most guys do not wheel like I do, and the IFS lift is plenty strong, but this is not the case for 100% of the drivers out there.
I believe we had determined that you already had spent money on a lift, and you have some bucks invested in tires and wheels, and that you will probably never see larger tires than you have now. You mentioned that your off-roading in this vehicle was going to be limited to light trails and some mud holes, and that you were a pretty responsible driver, and could make the lighter drivetrain survive.
I am a big fan of the SAS, but if it is not going to ever see its full benifits, then it might be an investment that can't be realized for it's full potential.
Now, if you had a bone stock truck, and had not purchased any lift yet, and you could buy tires and wheels one time, and knew ahead of time the amount of work involved, you could probably spend about the same amount of money performing the SAS as you would for a quality IFS lift. I would really lean towards the SAS before I shelled out a few thousand dollars on just a lift kit for this.
Anyway, I suggested the 1 ton gear for this thread and this vehicle, based upon the fact that the OP has 38" tires, and already has a solid front axle, and the chevy trucks are the easiest to upgrade to 3/4 ton, or even 1 ton gear.
Little different on an S series truck.

[junior3382]

So, keeping what i have, but apgrading the gears for a little more power from my comparitive small 4.3l will be okay? I got a little worried since this is next for me, and you had mentioned them not holding up, and if i am going to spend that kinda money, I would hate to blow them out later and have to redo it.

At that time, and to now, yes, i have the IFS lift. I chose it because in the end, it was doable. I did not want to chance an SAS with out the right knowledge and in my little circles I could not find anyone to do the swap for me. However, I did appreciate ALL the insight you gave me. My truck is all but done, but I am working on my Blazer now. That I am probably going to stay with the IFS lift due to again, not knowing enough people. And you are right, these particular rides, I have no interest in the extreme that I would NEED the solid axle for anyways. Though for durablitly and looks, it would be nice.

I have also angaged in a project with a friend of mine. We found and old jeep for a few hundred bucks and we are going to make off-road only. I will practice on that first. MY two trucks are my babies. I run them, but not beat on them.

Anyways, I know this was long winded and a bit off target, but seriously, am I safe just swapping gears, or do I NEED and upgrade?