[QUOTE=monzaz;395378]WOW, A lot of OLD wrong info in that down load. PLEASE ask if you need the low down on the 12 bolt olds and what you can and can not do with it.

I have a '69 442 Sports Coupe Im in the process of tearing apart for a restore and wanted to beef up the rearend with out spending too much. I mainly want to add a posi but i want it to be able to handle 500hp all day....any advice? Would 3.73's be too much for a daily driver?

 

I moved your post to it's own thread, as you'll likely get a better response than dredging up a three year old thread. In any case, if you're really making 500 HP "all day long", you've got a lot invested in this car. Spend the money, get a real 12-bolt (not a Type O) and don't look back. The Olds axle has the nice feature of no C-clips, but it's only an 8.5" ring gear held on with 10 bolts. The Chevy axle has an 8.875" ring gear with twelve bolts. You may even want to consider a 9" or 8.8" axle. This isn't a place to cheap-out - one broken axle at launch will ruin your day.

 

Why don't you call Jim (monzaz) and talk to him about options.

 

Im considering building a 470 stroker and have heard those can make some pretty big hp/tq numbers. 500rwhp is probably optomistic...

Maybe I can source a built rear end off craigslist out of another car...but i'd kind of like to keep everything numbers matching if I can. I don't have much experience building rear ends. I'd like to just order all the parts and I'll have a shop put it together.

Can I upgrade to a 31 spline ?

Could I just replace the whole third member ?

 

Call Jim (monzaz) you can find his number on his website, here is the link
He can answer all you questions and supply you with good quality parts. He helped me and many others. Good guy to deal with.

 

If you have an O-Type 12 bolt rear, there are no 3.73 gears for it. The available ratios these days, if you can find any aftermarket gears at all, are 3.90 and 4.10, but you may be able to locate some original GM gears. The closest ratios to the 3.73 you are asking about would be either 3.42 or 3.91.

For posi units, the info below from Brian Trick shows the carrier numbers for the different gear ratios:

Here is a list of the posi units & what gears they will fit:
#673 = 2.56 & 2.78 ratios, 28 spline
#671 = 3.08 & 3.23 ratios, 28 spline
#588 = 3.42 & anything numerically higher, 28 spline
#672 = 3.42 & anything numerically higher, 31 spline
***The 31 spline axles were offered in late 67-68 OAI cars only.

There are new carriers available these days that are Ford 8.8 units that are machined to mate with the O-Type ring gears. Brian or Jim would have info on those as well.

 

Joe- Not trying to step on the toes. Just using the examples you have listed (reason for the quote) for info about the subject of building or not building the 12 bolt 'O' rear or going to something else. (it is not stabbing at you personally )

Here we are again with the 9" ...lol. Folks if we are talking about bolts holding the ring gear.... a 9" is a 10 bolt rear as any other rear. PERIOD. DO also remember that the bolts in the 9" and the Olds 12 bolt and the 8.5 10 bolt rears are 7/16" 12 bolt Chevy uses 3/8" --- BETTER / Worse? does not matter in my book.
If you are talking stock 9" well your not doing any better than that 12 bolt OLDS. pinion shaft size will determine the all out power the ring and pinion will take and how it is supported - AND ALL THAT is a moot point since the spider gears are your true Achilles heal in any and all rears.

ALL aftermarket rears should and are better than stock rears and the reason we pay so much more for them.

ON the street any rear will do the job AS LONG as the rear has been rebuild correctly. It is the STICKY track that will punish the rear and all other drive line components.

I have never seen a pinion gear ever shear properly installed correct length ring gear bolts off of a carrier I have built. I have seen teeth on the pinion and ring blow off.... axle shafts snap and spider gears explode in to bits and a TON OF STOCK 9" FORD pinion supports blow right out the front of the cases. So lets get off the ring gear BOLTS and even the ring gear size for failure points. Ring and pinions rarely fail when installed correctly on the street. IF you do.... You will always find a failure to install correctly or maintenance issue to be the cause of most rear end issues. Pinion nuts will back off... low oil, excessive dirty oil, excessive clutch or cone wear improper torque of bolts caps and ring gear etc.

I DO AGREE In the case of 500HP motor...(actually dyno-ed) if you have pretty good money in a motor to get the HP and torque out you should be spending equal money to upgrade other areas for equal strength to match. That is always the correct way to keep your high dollar machine in one piece and not into the wall of the race tack or a ditch on the side of a country road.

ALL thought must be put into what your car will do for you - will this car be racing ? How much? Freeway driving? street only? stick shift car?trans brake? High stall? TORQUE is the number one factor in breaking parts, weight of the vehicle and how the power is delivered to the rear - this is what rear differential builders like me and others will WORRY about when we have to try to make a lesser sized rear hold to punishment.

So even 500HP I do not fear - it is WHAT torque output and WHEN this torque output is delivered (RPM) and HOW it is being delivered(trans brake, Stick shift etc. ) Then What ground conditions it has to hold to. (Sticky race track with slicks or the street where there much less hook)

These are some things you should ponder when figuring gear ratios - rear end parts and size of rear end you need. Same with your transmission and other drive line and suspension parts.

IF you have the money and can afford the better rear It should be done. How can you afford NOT to do it if your are pushing the envelope. ???

Hope some of the info helps make a better decision.

Jim
J D

 

Actually, you are correct about the bolt torque capability. I ran the numbers on this a while ago (and posted them someplace...), but the bottom line is that the 10 x 7/16" bolts in the Type O can actually carry more torque than the 12 x 3/8" bolts in the Chevy axle, even when you account for the fact that they are on a smaller bolt circle. As you know, however, that's only one factor in the overall ability of a given axle assembly to carry a given torque. A larger diameter ring gear will reduce tooth contact loads, for example. Bearing size and placement also play a role. When you factor in parts availability, it's usually better to go with the more common axle - especially if you plan to run it hard and potentially break parts.

 

Good info Fun71, so it looks like a #672 posi unit, 31 spline axles and a set of 3.90 ring gear would be the parts Im looking for. is that posi unit availabe through an aftermarket company or is it oem only?

How much do you think im looking at to build that setup?

Any recomendations on building the transmission to work with that gear ratio ? Im planning on putting in a shift kit and i'd like to have a trans brake.

I want the car to be able to go done the freeway at a decent rpm....is that out of the question?

Thank you everyone for your time. Your input much appreciated

 

It is unless you get an OD trans or a Gear Vendors unit.

 

Ive heard of a gear vendors unit but i don't think i've ever seen one nor can i say i understand exactly how it works....is it just another set of gears that attatch to the transmission? I'd really like to keep the original transmission. Maybe I should go with a shorter ratio like the 3.42's ....I just want it to hold its own in the quarter mile, and be good for a roadtrip.

Anyone ever seen a 400ci with a fuel injection set up? Ive seen some bolt on units in the Summit catalog...

 

Folks if we are talking about bolts holding the ring gear.... a 9" is a 10 bolt rear as any other rear. PERIOD. DO also remember that the bolts in the 9" and the Olds 12 bolt and the 8.5 10 bolt rears are 7/16" 12 bolt Chevy uses 3/8" --- BETTER / Worse? does not matter in my book.
============
Thank you for pointing that out. Would a 100-bolt ring gear be better... using #8-32 fasteners? Not bloody likely.


...not doing any better than that 12 bolt OLDS. pinion shaft size will determine the all out power the ring and pinion will take and how it is supported - AND ALL THAT is a moot point since the spider gears are your true Achilles heal in any and all rears.
===
Thank you for pointing that out. There is more to a differential than the ring gear securing.


ON the street any rear will do the job AS LONG as the rear has been rebuild correctly. It is the STICKY track that will punish the rear and all other drive line components.
===============
So, more traction/ weight transfer ==> more torque run thru the differential.
If the vehicle spins the tires, then it appears traction is the limiting factor. With infinite torque available to the differential, the torque actually imposed on the differential assembly would still be limited by the traction. Conversely, if the rear axles were locked, then all the torque available at the pinion would be carried by the final drive assembly... or break it.

I have never seen a pinion gear ever shear properly installed correct length ring gear bolts off of a carrier I have built.
....I have seen teeth on the pinion and ring blow off.... axle shafts snap and spider gears explode in to bits and a TON OF STOCK 9" FORD pinion supports blow right out the front of the cases. So lets get off the ring gear BOLTS and even the ring gear size for failure points. Ring and pinions rarely fail when installed correctly on the street.
======
THANK YOU. There is so much more to consider that # of ring gear bolts. Though, these features do make a handy yardstick to assess overall rubustness when shopping.

 

Google Images is your friend. The GV unit is simply a planetary gear set and electromechanical clutch that bolts to the back of your current trans. It just adds another gear set to the output shaft, so you can leave it in normal 1:1 for the strip or shift into O.D. for the highway. These photos are the unit by itself and one installed on a TH400. GV sells all sorts of adapter housings for different transmissions.

 

I am not 100% certain of this, but the carrier bearings / saddles / caps may be different size between the 31 spline HD rears and the standard 28 spline rears. I remember Brian Trick posting about an adapter carrier bearing to allow a 28 spline carrier to fit into the saddles of a 31 spline housing or something along those lines. It's a fuzzy memory and I don't know the details, but it is something to look into before buying parts that may not fit together.

OEM only.


edit: I found my data for the O-Type rears and the STD and HD carrier bearings have different diameters, so it looks as if the HD carrier will not fit into the bearing saddles of a STD housing.

STD (28 spline) carrier bearing: 2.890" OD race/LM501314
HD (31 spline) carrier bearing: 3.061" OD race/LM603049

 

Thanks for the pictures Joe...

Im starting to think the #588 posi unit with 3.42 and the stock 28 spline axles might be the easiest and cheapest way to go...i cant afford 2-3 grand for a gear vendor unit...wish i could.


Ill probably keep the stock suspension setup with the exeption of some 90/10's in the rear.

 

You can upgrade the stock 28 spline shafts to better quality aftermarket shafts.