Olds/Pontiac Rear vs 9" Ford

Any body have any experience with the 8 3/4 Mopar rear axle?

I know I have one behind my 440 R/T Charger making 390hp-400 hp.

I found another one 4.88/posi for a song.

 

the only downfall of the olds/pont that i can see is the heavyness, the 31 spline axle diamiter is too small ,and the availibility of internal diff parts. but my solution is, run a 35 spline spool , 35 spline axles , and a little extra weight is there when you need it .

 

8 3/4 are quite strong to the limit of 30 spline axles, alot of people convert them over to the green bearings but I have never broke one I use to use alot of them years ago.

 

thats why im proud to say that we made everything INHOUSE at summers !

 

Really.... As I said before I only changed the rear axle on that car and it ran the same ET after the change as it did with the Olds/Pont. The car was an awesome bracket car and would repeat very reliably. If it "took any power away", it did not show up in my time slips and I was able to win races instead of towing the car back to the pits from the starting line a couple times a year. Where is this "fact" you speak of? Let me guess.. On the internet somewhere?

I did not get the impression from the original poster that he was trying to run NHRA Pro Stock and was looking for every little bit of power he could get to the ground. I thought he just wanted something reliable, reasonably priced, lots of options, and readily available just about anywhere. I must have read it wrong...

Most folks will make up their own mind. Why would anyone believe me? What do I know? Some people think I am an idiot.

 

I have seen nothing that persuades me Ford rear ends are as inefficient as some believe. "Bad"s post supports that(or maybe his car just doesn't have any power). But......... Where a straight cut bevel gear is the most efficient at one extreme, at the other extreme, and least efficient, is a worm and ring. The efficiency of anything between those two extremes will vary accordingly. And the more the gears are loaded, the the greater the difference in efficiency. That's just a fact of physics.

 

Let me tell you about the horsepower robbing 9" Ford. I have a Henry J with a 9" Ford. It takes all the oomph I can muster to push it around. My Willys had a Olds. It pushed with ease. They are within 100 lbs. in weight.

The P/O of the Henry J built it. He promises to never use a 9" Ford again.

Also, I have a 8.75 mopar in a big heavy 56 Chevy that runs 11's. It works just fine. That old Chevy weights 700 lbs. more than the Henry J and pushes easier.

and another thing, take heed to what Filthy Frank has to say. He is of the famous Summers Bros. company. You know, the Goldenrod streamliner, etc.

 

A variety of things can make one car harder to push than another. While I'm not saying your observations didn't happen, I guarantee you it's not due to Ford's less efficient ring and pinion. Not only is there essentially no difference when there is no load on the gears, if the Ford was that inefficient it would melt in use.

 

No I don't care to fill us in?

 

Would really like to hear more about the 9.25 chrysler carrier swap into the Olds Pontiac. Any details? Doing a little looking I found the carrier bearing themselves to be different sizes. Timken cup/cone olds/pont, 25520/25584. Chrysler 9.25 cup/cone, JLM704610/JLM704649. Bore I.D. and even cup O.D. At the very least the carrier would need to be reworked to fit the olds/pont bearings. Was wondering about ring and pinion, carrier width etc. Or was this a powertrax type conversion into the open carrier. Again any info on the swap would be appreciated. Another question off topic, what size and type rear wheel/tire combo on the '55. Thanks, Johnny

 

Kinda. Carpinet Bros Ran a 12 bolt in an automatic SS/AA hemi Cuda, they did it because it was lighter than a dana, and they figured it might take less hp to drive. I have run a 12 bolt in a fast, heavy, hard leaving, automatic equipped, foot brake street strip car, and broke well set-up, good quality, aftermarket ring & pinions with some constistancy. Broke 2 ring & pinions, and one posi case over 5 seasons. Also bent the axle tubes. Dont get me wrong, I'm not saying the 12-bolt is a weak-kneeded POS, but its not as strong as a well set-up Olds, 9", or dana. I rate them (12-bolts) about the same as a well set-up 8 3/4 mopar. Good rear, but not bulletproof. If you are building a 3500lb, hard-hitting stick car, I would take a pass on the 12-bolt.

 

I would really like more info on this too.

 

Finally, something I can post about I actually have knowledge of. I ran a 56 chev in H/Gas, and as we continually upgraded whatever drive train part would break, we eventually got to an indestructable clutch, ultra strong driveline, and a Doug Nash 5 speed, only to start pulling the pinion gear right out of our 57 pontiac 3rd member, still flopping on the end of the driveshaft. At that stage I said to hell with it, went to a 461 inch with a TH400 and went to brackets. That worked, but at season end we found the case was spider cracked and ready to let go. Your olds/pontiac will NOT hold up to a big block putting out any kind of real power. We were running a pretty good size cam and tunnel ram with 660s, which would lift the front about 10 inches with the auto. If I hadn't got rid of the car to build a pro/gas Monza, it would have gotten a 9 inch.

 

445 ft. lbs. @ 2800 rpm from a 401.

 

In todays world I would use the Ford 9 inch. You need to remember that in the 60's we used the 1957 Pontiac housing because it was a bolt in on the 55 thru 57 Chevy, the Ford was a lot longer and needed to be cut down in length. We didn't have shops growing on trees that could cut down housing and make special axles like today so we had to make do with what we had. Also something to think about is the tires and treated strips of today..in the 60's the traction was poor at best with the old hard slicks and untreated pavement..

 

I have been running Olds/Pont gears for the last 44 years and love them. But they are pretty hard to find any more. Compared to stock O/P to stock 9", I would say they are stronger. If anyone wants to build a cruiser either will do. If anyone wants to build a car for some serious abuse, forget the stock parts on either.

I do not like the 9" , but if someone was to ask me what rear to run, I would tell them build a 9". Only because it is easier to get parts.

In 2007 I put a new combination in my 62 vette. A Four speed and hits really hard on launches. I broke 2 rears in 2 runs. That sucked because the parts are so hard to find.

The first rear blew the two piece Dana Posi case and cracked the housing. The Danas usually crack the housing every time. This is real bad , because the housing is not made by any one. I will never use a Dana again.

The second rear blew the spiders in an Eaton posi. Housing OK.

I gave up on the posi carriers. I put in a 35 spline Strange spool and axles. My 31 spline Moser axles were starting to shear the splines. No problems since the spool.

Fabcraft has lots of parts and RP ratios. They get their spools from strange.

I drive the spool on the street with no problems, But I am not encouraging any one to do the same. There is a learning curve to get used to it.

Dana


Eaton


Hard hitting launch

 

Bump. REALLY hoping to hear more about the Chryco 9 1/4 diff swap.

 

This guy has a lot of parts for the old/pon rear and he's very helpful.

http://stores.ebay.com/fabcraftmetalworks

To make the Ford 9" really strong you have to spend a lot of money. The nodular iron center section cost a lot. The posi are hard to find and also cost a lot. The Olds/Pon rear end is harder to find parts but they are out there it just takes a little more work.

 

I use the olds/pont rears in both my blown Willys...both have been pretty deep in the 8's at 160 mph.....if your trying to keep it old school..the olds will be fine..the only drawback in my mind is the selection of gear ratios.

Rocky

p.s. We use the Ford 9 inch in my funny car and go fast Willys (7.60's) They are excellent but more expensive to build...

 

Fabcraft has gear ratios of :
1957-1964 Pontiac/Olds ring & pinion 3.42, 3.64, 3.90, 4.10, 4.30, 4.56, 4.88, 5.14, 5.38, and deeper gear ratios

 

Is it quite difficult to find 4 series limited slips? Are ring gear spacers available? A spool is not in the cards for my application.

 

i just sold my last olds/pont 35 spline 4 series spool.

 

I have heard the 4 series posi's are just about impossible to find. Thats why the possibility of swapping Chrysler 9.25 guts into an Olds housing grabbed my attention. I am in the parts accumulating stage of a circa late '60s rod, was going to use a late fifties smooth back 9" because I had heard the Olds posi's were so scarce. If theres another way, I would really take another look at running an Olds. I have experience running spools on the street, not something I really want to do again. If a spool is the only option, I would go with the Ford.

 

Ran a '57 Pontiac rear for years in my '55 B/Gas Chevy. 5:38 posi, Summers Bros axles. Never had a problem. Bolt in swap, but I think it was about an inch wider than stock. If you're thinkink about narrowing it, go with the 9". The straight axle tubes make the job much easier than the tapered Poncho tubes.

 

If you guys are patient, I heard Fabcraft is working on "complete" packages. Yes, new housings and posies. They are hoping to have them ready by april and should update their site when it all gets worked out.

 

Oh..one more thing, aluminum third members too!!!

 

Olds rearend, Hilborn injected 426 (440ci) late model Hemi, Torqueflite, never worried about the rearend!

 

Gasser wars magazine #38 has a article about putting a 9" ford internals in a olds/pontiac housing.If anyone is interested i can scan it and post it.Here are some quick pics...

Steve

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In the past I thought that swap would go nicely with a Strange center that takes 12 bolt guts along with ford ends, axles and brakes for parts availability, while still having the look.

Side note:

One thing to keep in mind with the olds/pontiac housing is they are stamped steel sheet. It is best to keep the suspension brackets near the ends to limit flexing of the housing and wrap the brackets 180° so they won't tear. Not so vital with leaf springs, they are less rigid and wont work the housing as much as a ladder bar.

 

I'm interested in what broke, gears, third member axles? If axles, what spline count?