Single leg to a Posi unit ?

[ck5566]

I have a 68 C10 coils all 4 corners, with that said I would like to know if or how easy it is to turn a single leg rear end mine (3.73) into a Posi rear third member unit. I am not real found of my 3.73's would like to go with 3.42's. The eng is a (for now) 305 with a 700R4. I would like to go 3.07's for when the 350 gets "built" but for now with the 305eng I think the 3.42's will get along better with each other (305/700R4/3.42) So what do you all think. thanks in advance

[davepl]

I had a locker (actually a Helical) installed when I had my rear end rebuilt. It's actually a little aggressive in parking lots for my taste, but works well.

With a 700R4 are you sure you want to be that steep? I'm running 4.10s with overdrive and it's about right on the highway. Remember to multiple the gear ratio by your overdrive (about 0.7) to get a feel for what it will be like, and 3.07 would be like 2.10 with overdrive.

[Malo83]

http://www.powertrax.com/

[ck5566]

Originally Posted by davepl

I had a locker (actually a Helical) installed when I had my rear end rebuilt. It's actually a little aggressive in parking lots for my taste, but works well.

With a 700R4 are you sure you want to be that steep? I'm running 4.10s with overdrive and it's about right on the highway. Remember to multiple the gear ratio by your overdrive (about 0.7) to get a feel for what it will be like, and 3.07 would be like 2.10 with overdrive.

What do you RPM cruise at when at 70 mph? I am not following you on that "multiple the gear ratio" thing? can you explain how that works. with a 305/700R4/3.42 would that come out too be around the 3.07 range?

[ck5566]

Originally Posted by Malo83

http://www.powertrax.com/

Thanks but trying to stay with stock parts, GM only.

[Bigdav160]

Most newer GM trucks use the 3.42:1 rear axle gear. It's fine for general use and stock diameter tires. It's not idea for towing, or large diameter tires.

[Overdriven]

Originally Posted by ck5566

What do you RPM cruise at when at 70 mph? I am not following you on that "multiple the gear ratio" thing? can you explain how that works. with a 305/700R4/3.42 would that come out too be around the 3.07 range?

700r4 has a .70:1 gear ratio in overdrive and let's say your rear is 3.42:1 years. 3.42 X .70 = 2.39:1 final drive ratio. There were some cars (vette and Fbody) that used 3.08's with the 700r4 but they're tires were smaller in diameter. Plus you don't want to have the rpms too low. I have a gear calculator I use for all sorts of stuff but there are automotive specific ones out there too. I'll look for one and update if I find one. If I plug in 28" tall tires and the 2.39:1 gear ratio 2000rpm equals 70mph. If you have a lockup torque converter in your 700r4 this is spot on, if it's a regular converter add 300rpm. FYI 27" tall tires, 2000rpm = about 66mph.

Don't quote me on this but I seem to remember reading this about truck 12bolts. They are 2 or 3 different housings and each has a specific gear range it can accept. For instance one housing takes 2.73-3.42 while another takes 3.73-4.56 gears. I'll try to double check on that while I find you a good online gear calculator.

[Overdriven]

Couple of gear/rpm/mph calculators. You can find more just by using Google and those terms.
http://www.wallaceracing.com/gear-speed.php
http://spicerparts.com/calculators/t...rpm-calculator

According to following page it seems I was right about there being different housings for different gears.
http://www.drivetrainspecialists.com...-12bolt-truck/
Series 2 takes 2.73 or lower numerically, series 3 for up to 3.42, series 4 for 3.73 and up. That site also lists lot of different Limited slip differentials. GM uses Eaton so that's an option.

While it is something you can do yourself, personally I'd have it done. There's a crush sleeve on the pinion that needs to be torqued to something over 100ftlbs if I recall correctly. Then there's the gear backlash that needs to be set with shims and measured with a micrometer. The backlash will change if you change to a new differential or new gears. After that's done you need to check the wear pattern. It looks fairly simple on videos, but it's probably not that easy and you need some more specialty tools. Probably better off ripping it out of the truck (so they dont charge you to do it) and dropping it to a pro to do correctly.

[ck5566]

Originally Posted by Overdriven

700r4 has a .70:1 gear ratio in overdrive and let's say your rear is 3.42:1 years. 3.42 X .70 = 2.39:1 final drive ratio. There were some cars (vette and Fbody) that used 3.08's with the 700r4 but they're tires were smaller in diameter. Plus you don't want to have the rpms too low. I have a gear calculator I use for all sorts of stuff but there are automotive specific ones out there too. I'll look for one and update if I find one. If I plug in 28" tall tires and the 2.39:1 gear ratio 2000rpm equals 70mph. If you have a lockup torque converter in your 700r4 this is spot on, if it's a regular converter add 300rpm. FYI 27" tall tires, 2000rpm = about 66mph.

Don't quote me on this but I seem to remember reading this about truck 12bolts. They are 2 or 3 different housings and each has a specific gear range it can accept. For instance one housing takes 2.73-3.42 while another takes 3.73-4.56 gears. I'll try to double check on that while I find you a good online gear calculator.

Thank you, I Appreciate the explanation and the help with a Online gear calculator. great!

[ck5566]

Originally Posted by Overdriven

Couple of gear/rpm/mph calculators. You can find more just by using Google and those terms.
http://www.wallaceracing.com/gear-speed.php
http://spicerparts.com/calculators/t...rpm-calculator

According to following page it seems I was right about there being different housings for different gears.
http://www.drivetrainspecialists.com...-12bolt-truck/
Series 2 takes 2.73 or lower numerically, series 3 for up to 3.42, series 4 for 3.73 and up. That site also lists lot of different Limited slip differentials. GM uses Eaton so that's an option.

While it is something you can do yourself, personally I'd have it done. There's a crush sleeve on the pinion that needs to be torqued to something over 100ftlbs if I recall correctly. Then there's the gear backlash that needs to be set with shims and measured with a micrometer. The backlash will change if you change to a new differential or new gears. After that's done you need to check the wear pattern. It looks fairly simple on videos, but it's probably not that easy and you need some more specialty tools. Probably better off ripping it out of the truck (so they dont charge you to do it) and dropping it to a pro to do correctly.

Again Great, thanks

[71meangreenc10]

I personally like 3.42's in my trucks and I run 275/60/15 tires with them. PATC has all the speedo parts if you use mechanical speedometer. Didn't catch it in this thread, but if you have never built a rear end before I would not suggest doing it yourself. You do need special tools to do it right and there is more than just torqueing the crush sleeve to get long life out of what is already an expensive job. I build my own and it is always fun...

Smitty

[ck5566]

Originally Posted by 71meangreenc10

I personally like 3.42's in my trucks and I run 275/60/15 tires with them. PATC has all the speedo parts if you use mechanical speedometer. Didn't catch it in this thread, but if you have never built a rear end before I would not suggest doing it yourself. You do need special tools to do it right and there is more than just torqueing the crush sleeve to get long life out of what is already an expensive job. I build my own and it is always fun...

Smitty

Are you a Man or are you a meow man. LOL Get rid of the wife and get more trucks just that simple.

All kidding aside If I was to go the 3.42 way then I would need the 350 eng much faster and then that puts me in the same position as you "the wife thing", god I hope your or my wife doesn't read this. LOL

[RenoKeene]

Its actually the carrier that changes, housings are the same. Forgive me if I read something wrong here.

[71meangreenc10]

Originally Posted by ck5566

Are you a Man or are you a meow man. LOL Get rid of the wife and get more trucks just that simple.

All kidding aside If I was to go the 3.42 way then I would need the 350 eng much faster and then that puts me in the same position as you "the wife thing", god I hope your or my wife doesn't read this. LOL

Interesting response.

[ck5566]

Originally Posted by 71meangreenc10

Interesting response.

Just having a little fun here. You did leave your self wide open though. To give you a little background on me I had/have a nick name that I still live up to today, my nick name was & still is The "Joker". Now you see why I still have a Demented Mind. LOL LOL.

[ck5566]

Originally Posted by 71meangreenc10

Interesting response.

You know you don't live too far from me, give me a heads up and stop in and we can have a bear or "coke" (I don't drink) or milk and cookies, what do you say.

[Overdriven]

Originally Posted by RenoKeene

Its actually the carrier that changes, housings are the same. Forgive me if I read something wrong here.

Nope you are right, did more digging and confirmed it. It is the differential/gear carrier itself that changes according to gear ratio. The rear axle housing remains the same. That does make more sense than how I interpreted it originally, thanks for the correction. The information I posted above about the gears that the different series of carrier can accept is true though.

There are manufacturers who didn't go this route with multiple carriers to accomodate a wider range of gear ratios. Late model toyotas use a center section style axle and that center section is gear specific while the carrier remains the same. I just assumed GM did this with their housings as well.

For those wondering why there are different series of carriers or in Toyota's case center sections, it's due to the thickness of the ring gear. Lower numerically gear ratios have larger diameter pinions which could end up making the ring gear thin with the vice versa being true. So GM adjusts the ring gear mounting point on the carrier so that the ring gear didn't have to get too thin or too thick. The only other option for doing this is to move the pinion to prevent the ring gear from getting too thick or too thin which is what Toyota is doing with their late model center sections.

[Bigdav160]

Technically, the ring gear bolts to the case and the case bolts to the carrier. Older Toyotas, Ford 8 and 9" (and others) had removable carriers. Most GM's had integral carriers as the carrier is part of the housing. I know everyone uses the term "carrier" to describe the case but I like to use the correct terms. As the gear ratio gets steeper the pinion gear gets smaller. The ring gear has to get thicker or the ring gear mounting has to move to accommodate. GM and Dana axles usually have 3 "case splits". Ford 8.8" only has one differential case size.

Back the original question. Changing to a posi case is relatively easy. Very little specialized tools are needed. Changing gear ratios is more involved.

[ck5566]

Originally Posted by Bigdav160

Technically, the ring gear bolts to the case and the case bolts to the carrier. Older Toyotas, Ford 8 and 9" (and others) had removable carriers. Most GM's had integral carriers as the carrier is part of the housing. I know everyone uses the term "carrier" to describe the case but I like to use the correct terms. As the gear ratio gets steeper the pinion gear gets smaller. The ring gear has to get thicker or the ring gear mounting has to move to accommodate. GM and Dana axles usually have 3 "case splits". Ford 8.8" only has one differential case size.

Back the original question. Changing to a posi case is relatively easy. Very little specialized tools are needed. Changing gear ratios is more involved.

I probably should have worded my question differently to say/ask can a one leg'ed/open carrier stay in and just add parts too make it a Posi unit?

[ck5566]

Free Bump TTT, need to have a further answer.

[un4gvn!]

You need to change out your carrier. I installed a Auburn Pro Posi carrier with USA 3:42 gears. I use 29 inch tall tires all around. When I take it to the drag strip, I use Mickey Thompson 29x15x15 inch slicks. My 69 CST with a ZZ454 and Hughes 400 turbo runs mid 12's. The lowest it ran was 12:33. I have all the slips to prove it. My opinion, not to bad for a 3800 pound truck. I enjoy my street and strip set up. My original 12 bolt was also a one leger once.

[Tiger Joe]

no you can't keep the one legged carrier and make it a posi. Only way to keep your current carrier would be to use a locker. thats what I did and has been working fine for a few years now

[davepl]

You can re-use your existing gears if you buy the posi unit in the same series carrier as the old one. Don't know if you want to, just saying.

I'm still worried you're going to wind up with too steep of gearing with truck tires and an overdrive though. I sure wouldn't go any taller than 3.42, because as pointed out above, with overdrive that's like a 2.40 or something.

[ck5566]

Originally Posted by davepl

You can re-use your existing gears if you buy the posi unit in the same series carrier as the old one. Don't know if you want to, just saying.

I'm still worried you're going to wind up with too steep of gearing with truck tires and an overdrive though. I sure wouldn't go any taller than 3.42, because as pointed out above, with overdrive that's like a 2.40 or something.

At a later date I will put in a 350 in the 450 HP range, thinking that much HP will pull a lot better than the 305 (200'esh HP) would. The change in gear ratio & posi wont be until the engine swap. Maybe you or someone else gave me 2 links for how to do the Math (well it calculates for you) on Tires, Rear Gears, Trans "OD", and other stuff I Cant Remember At This Moment that I have looked at and am now seeing what changing thing does to the overall package. Thanks Guys

[ck5566]

Originally Posted by Tiger Joe

no you can't keep the one legged carrier and make it a posi. Only way to keep your current carrier would be to use a locker. thats what I did and has been working fine for a few years now

This "Locker" thing I have heard mentioned but don't know what it is. I guess I could Google it and learn something new today. I will Google it but for the moment can you give me some info to start me going on it. thanks