Well I have now that worked my way around to the rear of my car, I'm wondering what to do with my 12bolt rear end. From all that I've read in this thread, upgrade parts for these are difficult to locate? This will be behind my BB. Would I be better off changing to a Chevy 12 bolt or Olds 10bolt? I posted these pics in case they are needed for reference...

 

The Type O axle (12 bolt cover, 10 bolt ring gear) was only used for the 1967-1970 model years. It would not have been factory installed in a 1972 Olds. What does the rear cover look like? How many bolts are on the ring gear?

 

Contact Brian Trick (507olds on realoldspower) for info on the Type O rear. In general, it is fairly strong, much better than the 8.2" Pontiac and Buick ten bolts. With street tires, it is probably fine. If you want to build a diff more or less bulletproof for slicks and high power, it will cost about the same for a 12 bolt chevy, Strange Dana 60 (housing is repro with ears for A body suspension arms), or 9" "type F" "Dearborn" [Ford].

 

http://www.supercarsunlimited.com/Ca...epartmentID=33

 

Joe
I counted, it does have a 10 bolt ring gear, so I'm assuming like other parts on my car it was not original... The cover is the smooth one, not the "eyebrow" cover.

 

Yep. In addition to the other sources, here's one more:

http://www.drivetrainspecialists.com/categories/gm/

The Type O is no stronger than the "corporate" ten bolt. The Chevy twelve bolt is much stronger. Both of these have excellent aftermarket support. The problem is that A-body axles, particularly 12 bolt, are apparently made of solid gold these days.

 

Thanks for the link. I guess I was hoping every part for this rear end didn't cost a gazillion dollars....LOL

 

I would put the correct 71-72 style 8.5" 10-bolt in there.It is also your cheapest option,& you are not sacrificing any strength. I would put a stock style 8.5" up against a 12-bolt Chevy any day of the week.The "10-bolt" got a bad rep from the 8.2's of the 60's.The 8.5's are much better,plus they have bolt-in axles,& are actually thicker than a stock 12-bolt Chevy axle shaft.

 

X2 Well explained, too!

 

monzaz, aka: JIM, of J D Race & Restoration, is also an excellent source of information for rear axle & differential stuff...

 

It is unfounded legend that the 12 bolt Type C is so strong. It can be made strong, but that takes high $. The c-clip axle retainers are dangerous, the axle shafts are small diameter, and the 12 ring gear bolts are only 3/8" diameter. The type O has bolt in axles, 7/16" bolts. It is, however, an "orphan" with less stuff around for it. The correct 8.5" ten bolt is good, as Brian said, and correct for your car. Just don't get a Chevy version with c clip axle retention.

 

Ok facts... 12 bolt has 3/8 bolts fine spline, but there are 2 more total bolts for extra hold strength... MAKES a pretty big difference in stability all SERIOUS REARS ON THE MARKET TODAY have 12 bolt ring gears. dana 60 70 and 80, 8 3/4 mopar, 14 bolt truck, 9.5 truck, 11.5 truck, ford 9 3/4 and 10 1/4 truck... even the olds pontiac gasser drop out third member was 12 bolt with YES 3/8" bolts... Gee which of these rears that almost the whole world thinks is so great is missing???? 9" (that is because it is 10 bolt rear) Which one of these rears had to be totally rebuilt by the aftermarket to actual make it strong. Ford 9" (10 bolt rear)

12 bolt chevy does not have any aftermarket mods to make it stronger cause it never needed it. Period

The diameter issue on the axles. That was when the 12 bolts first design rears which had the taper after the spline...If you look at any late 60 and early 70 rear you will not see the taper as in the early rears like the 65-67 nova and chevelles.
Even all your 10 bolt 8.2 rear had the same heavy hour glass taper behind the spline of the axle... But as far as thickness goes, the thickest 10 bolt axle shaft on the 71 72 axle is 1.382 the chevy axles thickest part is 1.40 so there you go.

Bolt in axles are a good design for sure, but as for street cars deemed NOT necessary because of higher cost to machine etc. How many new cars with RWD have bolt in axles from 1973-1987.... axles breaking because of RAW torque on the street just is not that common. Evidence usually found for this breakage leads to other issues of the rear carrier bearing overheating and low oil maintenance issues causing overheating of the axle shaft end. If your slamming in to curbs and bouncing off cars and walls in a race track WELL that is a different story. Even Ford gave in with the 8.8 ford rear ...they literally copied the GM rears 8.5 and 12 bolt chevy to make the 8.8 ford 10 bolt (C-CLIP REAR). which is a pretty solid rear BUT has a crappy posi unit (looks like a 8.5 posi but they failed with the clutch plate system) from the factory.

Any of the rears 12 bolt olds, 12 bolt chevy and 10 bolt 8.5 will be a good match for your car on the street and some weekend track runs (YES even with slicks) make sure it is put together correct and they all work well. Failure to assemble the rear correct will cause catastrophic damage in any and all drive line components and is the number one leading failure, next to maintenance issues as stated earlier

Things you need to think about are when buying a rear:
1. how much you want to spend?
2. how correct matching do you want/need your car to be?
3. what will be done with the car mostly? (drag race, cruise, burn out machine etc.)
4. If you do go with a 8.5 rear you will need to modify the drive shaft shorter so you will need to figure that into the works ...For most of us that is NOT a huge deal...but again it is there and will cost some money again.
5. Any 10 bolt 8.2, 12 bolt Olds, 12 bolt Chevy, 10 bolt Chevy from 1967-1972 will be a direct bolt in to your car...Chevy rears will require a u-joint conversion joint at the most 12 bolt Chevy came with 4 different yoke and even came with a bop yoke if your lucky enough to find one from a BOP car it will bolt in with NO mods.
6. lastly a rear is only as strong as the proper assembly of parts in the rear. On used rears age on the the build and maintenance will also determine what the rear can handle.

example: you have a 12 bolt Chevy that is 25 years old untouched and then you have a 10 bolt 8.5 or even a 8.2 newly rebuilt CORRECTLY. both are 900.00 which would you buy?

well depends what your needs are??? number matching Chevy SS car your gonna buy a 12 bolt .... street cruiser burn out machine I would get the 10 bolt as all the new parts and reliability... 25 years I am sure the parts are getting sloppy even if it is low mileage a sitting rear with all the weight on the bearing surfaces from 3000-4000 pounds sitting on them is not good either.

Buy a rear that will fit your needs... there are a lot of good choices but a lot of bad products... I wish you all the best on your quest for the diff that will bring you the smile on face come BURN OUT DAY!....lol

Take care, Jim

J D Race.com

 

Good discussion.
The Ford 9" uses 10 7/16" bolts but the pro gears also have 10 1/2" fine thread holes if you want that upgrade. Some 9" were not too strong, but if you got a 60s--early 70s Ford performance model, you got 31 spline axles and a nodular center section. A few had Detroit Locker; some had 4 spider posis. You can still get a soft locker for 31 spline axles, No Spin for 35 spline. You can get a nodular or aluminum case easily now, with bigger side bearings for 35 and 40 spline axles. Nice thing is that for virtually all 9" aftermarket parts, they are the same price regardless of the upgrade level: 31 or 35 spline axles, which Locker, which case, etc. Pro gears cost the same with 28 or 35 spline pinion stem. The Daytona front bearing retainer costs the same for either pinion size too.

To make my 12 bolt strong, I got the tubes welded to the center with Ni rod, steel left bearing cap with allen bolts, Mark Williams axles and c-clip eliminators, Moroso posi, pro gears. NHRA rules require getting rid of c clips for a reason. Sure, street use is different, but if you break a C axle, you will ruin the quarter panel at a minimum. NHRA class cars tha have to use the 12 bolt replace gears etc. regularly whereas 9" owners seldom do so.

True, the 9" does have more friction so not as good for that last .05 sec. e.t. However, you can make yours bulletproof for the same money to make a 12 bolt pretty strong. Another option is the Dana but it is a lot heavier and a pain to set up with the pinion shim under the outer race, and the side shims under the bearings.

There are lots of parts for the 8.5 also, and it is a good rear. My main concern I guess is that you have to weld the tubes to the center for good reliability with slicks, and this operation is not straightforward for most welders. Welding cast iron/steel is always somewhat iffy. You can buy any of the housings ready to go into your Olds, but if you are trying to use stuff you already have, this welding concern will pop up if you are going to make good power and use slicks.

 

I just do not understand why eveytime we get to talking about rears that everyone thinks it has to be 10sec drag race strong???

This is what makes buying a diff for the person driving a street car spend more money than needs.

All rears work very well with any size motor on the street. Even some track time is fine. The over concern of part breakage concerns me. We ran a 10 bolt 7.5 MONZA rear on the strip for 4 years mini spooled 3.73 26 spline axles. NO issues and to this day it is still going on a street car. It was only 2500 stall but got the little stock Monza into the 11.90 time in the 1/4. Now this is NO major feet with a 2800 pound car...but it is still done.

We also see 7.6 camaro rears take punishment even with NOS...NOW I am not saying every weekend BUT with reasonable risk taken you can play. PAy attention to the car and listen to what it is saying...

The nhra axle retention is for safety of the people driving at the track and your competitor in the other lane too. 11.90 and faster cars require it.
As stated for racing bolt in axle are great. Remember c-clip elim kit is for the track ...on the street the heat from freeway driving will cause failure in the aluminum housed bearing. These c-clip elim kits are made with ball bearing and are for straight line performance mostly . If you want elim for a street car go with ford ends tapered bearings and aftermarket axles.

Trust me c-clip axle will be more than fine for most street applications. If your engine puts out extreme torque and horses you obviously spent the money to get it to do this and you should be able to afford to spend some good money on a comparable built rear to handle this expensive upgraded engines torque. Yes? Point here do not be cheap in one place of your car build because you spent too much money in another... THAT WOULD BE FOOLISH!!! right?

HAppens way too often.

I do understand budgets I am NO RICH MAN.

 

That's why I suggested the 8.5" 10-bolt. Compared to the 12-bolt Olds & 12-bolt Chevy,it is the cheapest alternative,but yet plenty strong for his application.The 12-bolt Olds cores are cheap,but the parts are somewhat costly.The 12-bolt Chevy has parts availability everywhere,but the housings/cores cost more,since all of the Chevelle world thinks you can't exist without one.Every time I build a rear,I get all the info from the customer,as far as the car,power output,including any future plans,& what his purpose will be with the car.That way I can determine what suits him best.I do not want to build something that is "just good enough",or something to get the person by.If he has to do it all over again in the future,then it isn't exactly money well spent.I could suggest DANA 60's for all,but that is not practical.
There's been plenty of debates over the number of bolts & the sizes.That will be debated forever.My point about the axle shafts was that most people think just because the 12-bolt Chevy has 30-spline,compared to the 8.5" 10-bolt 28-spline,it is better.The fact the factory 12-bolt Chevy axle shafts taper-down before the spline defeats the purpose,as now that thinner diameter is the weak link in the shaft,& where I have seen all of them break.I have plenty of 70-72 Chevy 12-bolt rears that still have those tapered shafts.Maybe not as severe,but they still get skinny.Does that mean they are useless?NO.There are plenty of applications that they can be used for,but just don't expect the world out of them.I do think the whole c-clip thing is a little over-rated,but again,it depends on the application.I don't care for c-clip eliminators though.I would rather cut the ends of the housing off,& weld new ends on,but again,that is more expensive than just doing the c-clip eliminators.
Yes,the 8.8" Ford rears pretty much mimmick the GM c-clip rears,& yes the factory 8.8" Ford units are duds.That must be why they decided to use those to remachine for the 12-bolt O-axle.There have been a few of those that have scattered behind 12:50ET Cutlass/442's,but they seem to do a little better behind the Mustangs,so keep them there,unless you have a cruiser/family car & just want a posi.If I need a serious unit for the Olds rear,I machine mine from Eaton blanks,or machine a spool,but neither one of those are cheap dates,& you must be die-hard to want to do that.I've even managed to remachine the whole goddam housing to stuff 12-bolt Chevy guts in it,but that was for my own purposes,and I would not suggest that.

 

I use steel MW c clip eliminators on my 12 bolt. If an axle breaks, you and your car are in danger of damage, not just others.
As for how much to spend, that depends on what you are doing, as Brian has eloquently stated. On a strict budget, I'd rank the 8.5 first, then Type O. Parts costs and originality for your 72 are significant factors. I have seen too many cases where someone goes for cheap, then just wants to make a couple passes on his 4 speed car with borrowed slicks. I broke the spiders on the first takeoff at 5000 rpm that way (10 bolt P axle, yeah, I know it's weaker).

 

Yah and how old was the 8.2 10 bolt you used...My point exactly. Nothing wrong with the 8.2 the spider gear system as it is as big as a 12 bolt chevy and 8.5 and 12 bolt Olds. side gears are a bit bigger in the chevy... so failure either was from raw torque...NOT likely...compared to years of fatigue heat up and cool down cycles breaking the metals tinsel strength down.

We all need to make choices...Just hope you make good ones. Good luck

 

Brian, calm your self...lol. Were just discussing stuff. It is all opinions and people are reading for enjoyment on the subject... to curse God over the matter....lol. These debates will go on till the end of RWD car time...lol.

Just enjoy and point out your arguments and we all will hash out on them and have some FUN and get some GOOD info for all to use in decision making.

Some times I will argue a point just to reassure the facts and points being made.

Enjoy the holiday break all. Jim

 

Sorry about the God word.That particular adventure I embarked on was a real trip.
Yes,I do realize that these are all opinions,& I am not offended by any of them.I once had to learn all of this too.I also see a lot of situations where a person simply wants a posi,but thinks he needs to order a Moser 9" or something,just to accomplish that.Not so.I try to keep everything as simple as possible,when possible.

 

Yep, I hear yah TOTALLY. Not to say we all would want a super car rear...

Jim