[Josue]

Still in the researching phase with what I'd like to do to my '68, today's topic being rear end options.

The car has the original BOP 10 bolt, with 2.56 gears, that's just not going to cut it for me. Seems there are an infinite number of choices though, and it's overwhelming for someone who's just starting out!

12 bolt? Moser XX spline axles? C-clip?? Ford 9"? Tru-trac? And the dozens of rear end gear ratio options??

My plans for the car are to boarderline daily drive it, any time there's no rain in the forecast, the car will be on the road! Plenty of highway use, so I don't want too tall of a gear. It's got the original Pontiac 350, with the usual bolt ons...4bbl Holley 650, Edelbrock intake, mild cam, and headers. Trans is the original 2sp powerglide, that will likely be replaced by a 2004R with the appropriate stall converter for my setup at the time of replacement. Tire size is to be determined. I'd like 18" wheels, but I've seen plenty of stellar examples of cars with 17's that I would have no problem imitating their stance in order to save a few bucks. Tire size is up in the air too.

So, what do you guys think would be the way to go? Can I retain the stock housing and just upgrade the gears and add posi? I'm not even sure if that's an appropriate way to say that...."add posi", because I don't know what that entails. Is it a separate part I need to buy and install/have installed along with the new gears? Or do gears "come" with posi if you wanted it? Would it be easier to just buy a whole new housing with the gears, posi, axles all ready to go? I'm sure that's the more expensive route, but I'd have no problem simply dropping out the original rear end and installing a new one. I don't have the knowledge to rebuild a rear end on my own, I've never done it, so I'd likely have to take it somewhere to have the new gears installed.

I'd also like to add rear discs too at some point. I was going to hold off and just upgrade the front to power disc, to save money, but it would be a good time to do the rears with the rear end blown apart like that, or on a brand new housing.

[MescaBug]

First things first.

What do you have exactly? 8.2 or 8.5? The stock 8.5 is good for 500HP+ motor. With a bonestock 350 and auto trans, 8.2 is plenty sufficient.

If you have 2.56 gears, you have a Series 2 carrier which is limited to 2.56 and less gears. If you want to add steeper gears, you must switch to a Series 3 carrier, its good up to 4.10 I believe.

If the car is a daily driver, and will be used mostly for cruising and spirited highway driving, 2.56 gears are very decent; good mileage, broad acceleration. Good gears for low rev, high torque Pontiac engines. If you dont like it, 3.08 is a good compromise. Some people dont like 3.23 and up for highway because of RPM. Its a nice gearing for street driving though.

Now, swapping the carrier is a job for experienced mechanics. Tolerances are critical. Its usually cheaper to buy a complete axle unit, with the appropriate Carrier and gears.

[Josue]

How can I tell if I have the 8.2 or 8.5? And what do you mean by carrier?

I'll be doing my fair share of highway driving, but still plenty of stop and go city driving, so I'd like to have more pep than 2.56's can give. With the installation of an OD trans, I'm sure I'd be fine with the mileage I'd get on the highway with larger gears. I'd say no more than 3.55's...

[MescaBug]

8.2 or 8.5 differentials can be identified by the diff cover. If you post a pic, we can help identifying it. The shape of the pumpkin is different between models, so that can also help.

You can look for casting codes on the pumpkin and axle tubes. Stampings can help identifiy the maker, gear ratio, and differential type.

The carrier is the unit that 'carries' the ring gear. Its the 'mechanical' term for the POSI unit itself.

The best way to be 100% sure of what you have, is to open the diff and look inside. Of course, you need to drain the fluid, replace the gasket and fill with new fluid.

Here is a few links that might be of some help:

http://www.wallaceracing.com/carrier-id.html
http://www.crankshaftcoalition.com/w...identification

[Josue]

This is the only one I have, for now.

[MescaBug]

That's a BOP 8.2". The irregular cover shape is a dead giveaway of a BOP 8.2. 8.5" cover is round.

I adjusted the brightnesss so we can see the pumpkin more clearly. If you have 2.56 gears, you can go up to 2.73 gears with that carrier type.

http://www.jdrace.com/diff_id/10bBOP_Pontiac.htm

[JLMounce]

I went with a Moser 12 bolt for my application with the Eaton TruTrack, 33 spline axles and a 3.73 ring/pinion. While this rear end is currently overkill for my current setup, I'd eventually like to add a bit more power and it'll let me grow a bit.

The Moser unit while not cheap provided everything I was looking for. They've beefed up the center section over standard GM 12 bolt's, utilize thicker walled tubing that is welded instead of pressed in. You also get the late model torino housing ends and big bearings. This was important to be for a couple reasons. First I didn't want to deal with c clips and the torino ends allow for bolt in axles. Additionally the larger bearings and thicker mounting flanges reduce deflection in cornering. This helps with pad knockback and provides more stable footing in corners. Especially on stickier rubber.

The TruTrac rounds out the package as a true limited slip differential. Instead of locking the drive wheels together like a spool or clutch type posi, the TruTrac can torque split between the two wheels and works opposite of an open differential. It sends power to the wheel with the most amount of grip.

What this does is to allow smoother cornering by allowing the drive wheels to spin at different speeds. By then also transferring torque where traction is the best, you get more traction out of a corner (or from a stop).

It's also a no maintenance unit, so you don't have to replace clutch packs every so often.

If you're planning on driving the car on the highway often, I'd stray away from my choice of the 3.73 axle ratio. I think a 3.08 for a daily driver with a good bit of highway use would be a decent performance compromise. If you spend more time in town, a 3.23 might even be decent.

For me, the car is purpose setup for the majority of the tracks around my area. The car sees only small amounts of highway use, so I can deal with higher revs for a bit. The shorter 3.73's are nice for around town drivin between 30-45 mph where the engine is spinning comfortable at about 1500-1800 rpm in high gear (TH400).

If your plans include an overdrive transmission, I would revise my gear selection from a 3.08 to definitely at least a 3.23. Even a 3.55 may be pretty nice.

That will also depend on tire size as well. I'm currently running a 17" package and overall size is a 26" equivalent (25.7). At 5500 rpm this gives me right at 120mph which will work well for the types of tracks around me, with exception of PMI's half mile straight which having more like 130-135 sealing would be better.

[MescaBug]

Very good info JL.

But a Moser setup, parts and installation, is a few thousands $$$$. The OP as a bonestock Bird with a 350. I think this is WAY overkill.

I'd rather spend some money on a performance engine instead of an overkill axle setup. A good rebuild 8.2" can widthstand the power of a mild 350.

Steep gears with a high revving 350 will surely burn rubbers, but not the best daily driver setup IMO.

[JLMounce]

Originally Posted by MescaBug

Very good info JL.

But a Moser setup, parts and installation, is a few thousands $$$$. The OP as a bonestock Bird with a 350. I think this is WAY overkill.

I'd rather spend some money on a performance engine instead of an overkill axle setup. A good rebuild 8.2" can widthstand the power of a mild 350.

Steep gears with a high revving 350 will surely burn rubbers, but not the best daily driver setup IMO.

Yeah definitely agree on that. I spent close to $3000.00 on my rear end alone. Having the large 455 up front I wanted the added security of a pulletproof rear end.

If I was in the OP's situation, I think I'd probably do a couple things to the factory rear. Have the axle tubes welded, a support girdle and the addition of a posi carrier of choice. My choice since I like corners would obviously be the trutrack.

[Josue]

Originally Posted by MescaBug

That's a BOP 8.2". The irregular cover shape is a dead giveaway of a BOP 8.2. 8.5" cover is round.

I adjusted the brightnesss so we can see the pumpkin more clearly. If you have 2.56 gears, you can go up to 2.73 gears with that carrier type.

So, it seems like it's the bottom of the barrel then, eh? haha Wouldn't surprise me with this car, it's just an average, nothing special about it, built the most of, '68. 350 2bbl, manual drum brakes, powerglide, now the rear end choice.

So, I'd need a new carrier, and set of ring gears then, right? Would the stock housing suffice? Axles? I haven't looked into brands and prices yet, what can I expect to pay for this swap? Minus labor charges if I need to pay someone to install it all.

['ol Pinion head]

Originally Posted by Josue

So, it seems like it's the bottom of the barrel then, eh? haha Wouldn't surprise me with this car, it's just an average, nothing special about it, built the most of, '68. 350 2bbl, manual drum brakes, powerglide, now the rear end choice.

So, I'd need a new carrier, and set of ring gears then, right? Would the stock housing suffice? Axles? I haven't looked into brands and prices yet, what can I expect to pay for this swap? Minus labor charges if I need to pay someone to install it all.

The gray iron 8.2 Pontiac 10 bolt is sufficient for a putt-a-round cruiser/moderate performance streetcar. Desiring to change carriers and gears to lower the gear ratio, you will be sinking $$$$ in parts in the gray iron 8.2, not that smart considering the 8.2's inherent lack of pinion support. Not that big a deal in a cruiser, but if you you ever upgrade the engine and throw a lot of torque at it...wasted bucks.

For under the price of a set of Moser axles, new Pontiac 8.2 posi carrier, set of quality gears, all the small parts and Pro set-up, you are better off having a much stronger HD 8.5 10 bolt or a 12 bolt built. A stock early Camaro 12 bolt or an 8.5 Nova 10 bolt are both going to be a half inch narrower on each side, so can tuck a little wider tire in the wheelwell. A HD 30 spline 8.5 Xbody multi-leaf rear can be built for around $1400. A 30 spline Moser 12 bolt... Jim's price of 2K is fair. Many original desirable code early Camaro 12 bolt, can easily fetch $2500 and up rebuilt...know very well, as I build 'em.

[Josue]

Well...therein lies something else to consider here...

Ultimately, I'd love for the car to see some track use. I'm only an hour and a half away from Mid-Ohio, and Pittsburgh International Race Complex, and I got to run on these tracks with some Mazda's I used to own. GREAT fun, and I'd love to get out there with the Firebird! In reality though, this won't happen for years and years, I just don't have the money to beef up the 350, and even if I took it out there just to hit some corners (after upgrading brakes, suspension, steering, etc) I'd be worried about blowing the thing up and leaving me without a fair weather toy until I could fix it.

So, I'll be adding more power eventually...I just don't know if that warrants going "all out" on a new rear end setup now, or if I should go budget for now and only replace what's necessary to let me have a little more fun on the street, then sell it all to try and fund the upgraded rear end assembly later on. I don't really like doing things twice, ya know...

[JLMounce]

I think you'd be surprised at how robust most engines are. Just because the design and many components date back to the late 50's doesn't mean it's not good. Remember, Pontiac raced these things in NASCAR, Trans Am etc.

Although yes I realize most of hte firebirds ended up running chebby motors in Trans Am.

My point is they can handle a bit of abuse as long as you maintain them and prep them for it.

If you're going to be sticking with the 350, I really don't see the need to spend a bunch of money on a blingy rear end. Per my previous post, I'd just have your axle tubes welded, put in some sort of posi carrier that can hold the gear set you want and maybe look into a cover that is also a support girdle. As long as you're not launching the thing on slicks off a trans brake, I think you'll be fine.

[Josue]

Originally Posted by JLMounce

I think you'd be surprised at how robust most engines are. Just because the design and many components date back to the late 50's doesn't mean it's not good. Remember, Pontiac raced these things in NASCAR, Trans Am etc.

Although yes I realize most of hte firebirds ended up running chebby motors in Trans Am.

My point is they can handle a bit of abuse as long as you maintain them and prep them for it.

If you're going to be sticking with the 350, I really don't see the need to spend a bunch of money on a blingy rear end. Per my previous post, I'd just have your axle tubes welded, put in some sort of posi carrier that can hold the gear set you want and maybe look into a cover that is also a support girdle. As long as you're not launching the thing on slicks off a trans brake, I think you'll be fine.

I just don't know if a 46 year old motor that's never been taken apart and rebuilt, can handle racing around at full throttle on a road course for too long. haha

At this point, I'll be sticking with the 350, but I'd be lying if I said I'll never go with something bigger. Ideally, I'd like to run a set of aluminum D-port heads, put a bigger carb on, and up the cam a bit...400hp seems perfectly attainable and would be fun as hell I'm sure! I'm of the oddball group of guys who thinks it'd be cool and unusual to build up a 350, rather than ditch it for the drones of 400 guys out there. I'd still hope that I could use those parts for a 400 or 455 build later on in life though, I do see limitations with the 350, but increased motor output is low on my priority list right now so I probably won't touch it. The OD trans, stall converter, rear end upgrade, suspension, steering, brakes, and wheels and tires will eat up all of my budget REAL quick. All of the items combined will make for a VERY fun street car I'm sure, even with the low HP output it currently has.

What's the support girdle you're talking about? And welding the tubes on...as simple as it sounds? I was a body man for 15yrs, so I'm handy with a welder...but I don't think my 110 I have at home with be enough to penetrate the housing. Is there anything else to consider; making sure it's supported in a specific way before welding, heat issues, measurements or whatnot? Or is it as simple as cleaning up the weld area, and running a bead around it?

[wovenweb]

Baby got back!

[Josue]

Would this be a decent option? $2000 for a whole new unit?

http://forums.maxperformanceinc.com/...ghlight=girdle

This guy is 45 mins from me too, so no shipping charges. haha

[694.1]

Install 3.08 gears. Easy to find, great compromise, great drivability. Easy to sell in the future. KISS. If installing an OD automatic, a 3.5+ would be golden.

[JLMounce]

Originally Posted by Josue

Would this be a decent option? $2000 for a whole new unit?

http://forums.maxperformanceinc.com/...ghlight=girdle

This guy is 45 mins from me too, so no shipping charges. haha

I'd be all over this. My axle package from Moser was $2800 not including shipping.

[Doug Hopkins]

Originally Posted by Josue

Would this be a decent option? $2000 for a whole new unit?

http://forums.maxperformanceinc.com/...ghlight=girdle

This guy is 45 mins from me too, so no shipping charges. haha

Great price , but your 46 year old never been apart 350 will not last very long with a 3.73 gear. If you plan on a larger engine in the future and mostly street miles, in my opinion you would want no more than a 3.23 gear. My 3980 Lb. 76 TA with a KRE 455 in street trim runs 11.80's @ 114 with a 3.23 gear. With a short street tire I would never use more than a 3.42 gear. The Pontiac street motor is a torque monster, not an RPM screamer. I ran a 3.55 in a 67 326 Firebird. Big mistake ! I could not wait to put in a 3.08 back in the car. That 3.73 would be fun around town (light to light), but on the highway your engine will be screaming. Just my 2 cents.

[Josue]

Great information everyone, I really appreciate it!

I'll have to get in touch with Jim about his axle packages then. Like you guys have said, I don't need top of the line right now, but my future self will probably thank me for spending a little more now rather than having to redo it all later. And for the ease of buying an entire unit like this, rather than finding someone to install gears for me, I think it's worth the extra $.

I honestly don't even know who I would call for this. I have a bunch of mechanic friends, but I don't like leaning on them too much. Schedules clashing so it's hard to even get them over to do the work. Something goes wrong, who do you blame? etc. There are some regular mechanic shops around, but I don't know if they do old school stuff like this...it's probably all diagnostic crap and oil changes nowadays!