Rear End Posi Help!

[leftybass209]

So, i just decoded my rear axle and it's an HB which if I am correct, is a 3:07 rear end, and I cracked it open to confirm it's posi. Unfortunately, the truck has a 700r4 which is no bueno with the rear end gears for overdrive. My question is, can I swap out the rear gears without swapping the posi unit? I see 3:73 gears through companies for anywhere between 150-200 which isn't bad at all, I just don't want to have to dump another 500+ on a posi unit. Any help is greatly appreciated, thanks!

[Sklptrljay]

I'm not an expert at all on this, but I have been researching options for my own rear end.

I am pretty sure you can change the gears and not change the posi unit, but since you have 3.07's you have a 3 series carrier. A 3.73 requires a 4 series, but......

They make thicker aftermarket 3.73 gears that should fit in your housing.

Good luck.

[leftybass209]

I just started to understand the 3 and 4 series carriers and I understand that they have all the gears in 3 and 4 series (summit racing has them). Thanks for the info though!

[70blackfish]

Don't go Cheap on the gears,cheap gears are made in China. and 3.73 is a good ratio for the 700r4.

[leftybass209]

Good advice, I won't be going cheap. It just seems most all brands are similar priced. I checked Richmond, and a couple others. This truck is just a cruiser so I'd be pretty hard pressed to even chirp the tires. Thanks for the replies!

[Bigdav160]

India is a major supplier of gearsets. Even name brand ones are made there.

[67chevy1series]

ok heres what you can do thy make an adapter ring to gtom from 3.07 to 3.73 and keep your orignal 3 series carrier if you buy that adapter ring along with a new 3.73 ring and pinnion as well as a new crush sleeve and while your at it bearings for the carrier and pinion and new seals then you should be able to install no problemo


carrier breaks:

3 SERIES CARRIERS: 3.07, 3.42. (3.42 and lower are all 3 seies)

4 SERIES CARRIERS: 3.73, 4.11. ( above 3.42 in ex: 3.55 are all 4 series)

there is no way to use a 4 series carrier with 3 series gears. it will not happen. hopefully this will be a referece for anyone in the future.

[cdowns]

brand new gears and a 40 year old posi ?? that doesnt sound like a great plan

[straps57]

If it is just a cruiser why even worry about posi?

[leftybass209]

Originally Posted by cdowns

brand new gears and a 40 year old posi ?? that doesnt sound like a great plan

I plan on having the posi rebuilt as well, I just didn't know if the posi is specific to the ring and pinion as in, I'd have to buy a new carrier, and new ring and pinion. Having it rebuilt saves about 300 bucks.

[SS Tim]

To keep thi simple.
The 12 bolt truck cases (open or posi), from the factory, were sized for 3.73 ratios and up (higher numerically) such as 4.10. Or 3.40 down numerically like a 3.08.

If you have a factory 3.08 then that would be a 3 series case and to install a lower stock ratio (higher numerically) like a 3.73 or a 4.10 from another truck would require a case chage.

However the aftermarket has stepped in and offers truck gear sets in 3.73, 4.10 and 4.56 that will fit the 3 series case due to dimension changes in the gear sets.

A quick check of about any parts catalog (Jegs referenced) will show gears that would allow you to keep your 3 series case.
Jegs has both Eaton and Jegs branded sets from 3.73 up to 4.56 on a 3 series case.

Depending on wear or damage it might be cheaper to replace the case with a new unit, maybe even step up to an Auburn.

If money is really tight almost any 6 cyl C10 will have 3.73 gears if swapping a rear axle out buys you time to build a dream axle up.

Finally before you go ripping everything apart I would recommend doing the math for your intended tire and gear selection in OD then finding/borrowing a set of used tires sized to mimic the gear changes. This will give you a real world feel before spending a lot on hard parts then wishing you had gone a little lower or higher.

[leftybass209]

Thanks for the info, it really helps. I'm about 2 months shy of buying one but I need to start budgeting for this stuff now.

[Fitz]

Originally Posted by leftybass209

So, i just decoded my rear axle and it's an HB which if I am correct, is a 3:07 rear end, and I cracked it open to confirm it's posi. Unfortunately, the truck has a 700r4 which is no bueno with the rear end gears for overdrive. My question is, can I swap out the rear gears without swapping the posi unit? I see 3:73 gears through companies for anywhere between 150-200 which isn't bad at all, I just don't want to have to dump another 500+ on a posi unit. Any help is greatly appreciated, thanks!

The ring and pinion can be swapped without changing your posi center section. You will find it easier to work on if you pull the diff out but it can be done in the truck if you have a lift. The photo is my posi 12 bolt. You will need to pull the axles then remove the carrier bearing caps on either side of the center section. Turning the driveshaft yoke will allow the pinion gear to "climb" the ring gear and push the center section out. there are shims on each side of the center section. Don't get those mixed up. Remove the eight bolts holding the ring gear to the center section and it might just slip off. If it doesn't, get a BUTANE (not acetylene) torch and GENTLY heat the ring gear around it's perimeter to get it to expand enough to slide off.

When you go to put the new one on, preheat the wife's oven to 400 degrees and bake that thing for 20 minutes. It will expand enough to slip on but be sure you have the bolts handy. You will need to get two in finger tight before that ring gear shrinks! Then it's just a matter of pulling the pinion gear and pinion bearing and replacing the old pinion with a new one.

Mark Williams has a pretty good tutorial on how to do this here: http://www.markwilliams.com/bulletproof.aspx but there are many others. If you happen to have the overhaul manual for your truck it's in there with pictures! If you don't have that book you can get one on CD Rom here: http://www.faxonautoliterature.com/1...al-P20755.aspx

Gearsets, bearings, install kits and new springs and clutches for your posi can be had at reasonable price at Drive Train Specialists. DTS uses ONLY American made parts so you aren't getting Chinese crap for bearings and gears.
A 3.73 R&P set will be about $190.00. http://www.drivetrainspecialists.com/ If you decide to rebuild your posi carrier, use the 600lb springs, not the 400's or 800's.

[Sklptrljay]

Good info! Thanks Fitz.

[67chevy1series]

Originally Posted by Fitz

The ring and pinion can be swapped without changing your posi center section. You will find it easier to work on if you pull the diff out but it can be done in the truck if you have a lift. The photo is my posi 12 bolt. You will need to pull the axles then remove the carrier bearing caps on either side of the center section. Turning the driveshaft yoke will allow the pinion gear to "climb" the ring gear and push the center section out. there are shims on each side of the center section. Don't get those mixed up. Remove the eight bolts holding the ring gear to the center section and it might just slip off. If it doesn't, get a BUTANE (not acetylene) torch and GENTLY heat the ring gear around it's perimeter to get it to expand enough to slide off.

When you go to put the new one on, preheat the wife's oven to 400 degrees and bake that thing for 20 minutes. It will expand enough to slip on but be sure you have the bolts handy. You will need to get two in finger tight before that ring gear shrinks! Then it's just a matter of pulling the pinion gear and pinion bearing and replacing the old pinion with a new one.

Mark Williams has a pretty good tutorial on how to do this here: http://www.markwilliams.com/bulletproof.aspx but there are many others. If you happen to have the overhaul manual for your truck it's in there with pictures! If you don't have that book you can get one on CD Rom here: http://www.faxonautoliterature.com/1...al-P20755.aspx

Gearsets, bearings, install kits and new springs and clutches for your posi can be had at reasonable price at Drive Train Specialists. DTS uses ONLY American made parts so you aren't getting Chinese crap for bearings and gears.
A 3.73 R&P set will be about $190.00. http://www.drivetrainspecialists.com/ If you decide to rebuild your posi carrier, use the 600lb springs, not the 400's or 800's.

What is the benefits of 600lb springs versus the others? How much is it for new clutch packs and springs?