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  #16 (permalink)  
Old 01-30-2014, 06:29 PM
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Replacing the bearing cap bolts with studs will not hurt the bearings. Tapered roller bearings are not the same as crank and rod bearings. I don't think the studs will make a great improvement in strength, but they don't cost much and it can't hurt.

As long as the tires are spinning the rear end will probably be all right. If you put sticky tires on it then it's probably going to break.

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Old 01-31-2014, 08:34 AM
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Quote:
Originally Posted by rumpfox View Post
what is the first thing to break in these 7.5 rears, the ring gear or the pinon. i'm souping up a monte with one of these rears and have just bought a power trax posi for it but haven't put it in. do you think i sould replace the axles to or waste of money. i put a posi in because this car was so dangeroue in curves, wanted to spin real easy.
I just re-installed my PowerTrax, if you do it like this have some kind of magnet on hand to retrieve the last C clip..., several times.
I´m still running my original 1986 axles.



BTW if you do the install under the car, it´s quite a fiddly job.
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Old 02-03-2014, 01:06 PM
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With street tires you likely won't break it. It will just wear out more quickly than you might like. The small bearings, case, and shafts don't take high torque loads well and even though the tires break loose before parts break, the parts still take a beating. That's why we see more of these units that are chewed up and noisy than actually broken. Cross shaft bores in the diff case become oblong, the cross shaft itself gets chewed. The wear surfaces that support the spider and side gears get ground on(in your case they now support the Power Trax unit), even with the thrust washers. The small ring and pinion gears get ground down and the small bearings fail quickly. Even after just a short time of hard use, they will be noisy. A good gear lube like Valvoline synthetic 70w-140 will help protect against this wear but nothing can stop it. Only real solution is a 9" Ford. That's what I'm saving for now.

BTW, while almost anything is better than the crummy Auburn (cone type) limited slip(posi and limited slip same thing) OE unit, I have never seen road racers use locker rear diffs. Always posi of some kind. The locker can cause inconsistant and sketchy two wheel break away under power in a turn. Not a good way to maintain control when you are racing through tight corners going for lowest lap time. Lockers are designed for straight line traction, not cornering. My 2 cents.
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Old 02-03-2014, 01:24 PM
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all of your cup cars use locker tho. i don' know why mabe a 9" ford thing.
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Old 02-03-2014, 02:06 PM
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Not the ones here in the Portland Oregon area. I see these cars as people buy them at auction. Many taxi cabs in our area are old cop cars. They get beefed up suspensions with bigger sway bars and they get the same Eaton posi units available in the regular production cars. I would think that the maintenance on locker units in cars that spend their days cruising on city streets would be extensive.
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Old 02-03-2014, 02:21 PM
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Your ring gear carrier is the open type for spider gears and very week !!! The Posi gear carrier whether its a locker (Very strong) or limited slip (clutch type) they have a much heavier ring gear carrier and with even the small 10 bolt housing will stand up to power. you just cant put the BIG GEARS in it like 4.56s! On posi carriers they installed posi axles (stress proof), on standard carriers the stock axles break when a posi is installed because they are not stress proof Posi axles ! The Powertrax is cheep !! Its just a cheep way to convert to posi but the carrier is not meant to stand up to real power!! If you installed the Powertrax Lock Right Automatic Positive Locking Differential it ratchets on curves so its street friendly, So enjoy!

I have five sets of posi axles LOL I'm always looking for them because they actually twist under power (not break)! I paint a line down the axle and check it periodically to see how far the line has twisted and replace the axle when it exceeds my limit LOL

Jester
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Old 02-03-2014, 03:06 PM
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Originally Posted by ASE Doc View Post
Not the ones here in the Portland Oregon area. I see these cars as people buy them at auction. Many taxi cabs in our area are old cop cars. They get beefed up suspensions with bigger sway bars and they get the same Eaton posi units available in the regular production cars. I would think that the maintenance on locker units in cars that spend their days cruising on city streets would be extensive.
He said cup cars, not cop cars. The NASCAR cup cars use Detroit Lockers in all races except super speedways.
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Old 02-03-2014, 03:09 PM
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Your ring gear carrier is the open type for spider gears and very week !!! The Posi gear carrier whether its a locker (Very strong) or limited slip (clutch type) they have a much heavier ring gear carrier and with even the small 10 bolt housing will stand up to power. you just cant put the BIG GEARS in it like 4.56s! On posi carriers they installed posi axles (stress proof), on standard carriers the stock axles break when a posi is installed because they are not stress proof Posi axles ! The Powertrax is cheep !! Its just a cheep way to convert to posi but the carrier is not meant to stand up to real power!! If you installed the Powertrax Lock Right Automatic Positive Locking Differential it ratchets on curves so its street friendly, So enjoy!

I have five sets of posi axles LOL I'm always looking for them because they actually twist under power (not break)! I paint a line down the axle and check it periodically to see how far the line has twisted and replace the axle when it exceeds my limit LOL

Jester
Never seen different axles based on the differential that was used. As far as I know all of the axles are the same. There have been minor changes in them over the years. When GM started using AAM axles they got stronger.
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Old 02-03-2014, 04:05 PM
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Originally Posted by big gear head View Post
Never seen different axles based on the differential that was used. As far as I know all of the axles are the same. There have been minor changes in them over the years. When GM started using AAM axles they got stronger.
The early 10 & 12 bolts (GM) had different axles for the posi or spider units into the late 70s depending on HP options and a few after that They included Semi-floating forged and heat-treated axle shafts ,The Wheel drive flange is forged integral with the forged axle. The good axles have a different ring to them like a bell when struck with a small hammer! The " After market" performance axles are better they are heat treated to 3/16 or more while the stock posi axles are only heat treated to 1/8 max! The posi (treated) GM axles will twist and spring back when power is applied for so long before they keep the twist to the point of failure ,where as the standard GM axle shaft doesn't twist it will fracture under real power! Even the Corvette had different axles and universals for the high horsepower options!

Most of the old drag racers Knew there was a difference, I guess it wasn't common Knowledge?

Jester
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Old 02-03-2014, 04:15 PM
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In the 50s the axles were different in the posi and standard units especially GM The posi axles were shorter in GMs besides being stronger, and when converting to posi if you used the old axles you had to grind or machine off the ends, and under power they would usually shear off.

Just a little nostalgia If you have a FACTORY 55-56-57 Chevy rear axle housing and axles (NON-posi axles), and you install a FACTORY style posi (from a 57-64 Chevy) into the 55-56-57 housing, the STOCK 55-56-57 NON-posi axles will be approximately 1/8in too long.
Thus, if you are installing a 57-64 FACTORY posi into your 55-56-57 axle housing, AND IT ORIGINALLY WAS A NON-POSI REAR, then your 57 axles will be about 1/8in too long and will interfere with the posi unit as well as place excessive side loading on the axle bearings which will cause premature failure of the bearings.

Jester

Last edited by painted jester; 02-03-2014 at 04:21 PM.
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Old 02-03-2014, 04:59 PM
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That's good information on the '55 to '64 Chevy rear end, but it doesn't apply to the 7.5 rear end, and I'm not sold on it applying to the '65 and later 10 and 12 bolt. I've rebuilt hundreds of these and I've never seen any difference in the axles in a factory posi rear end and one that wasn't. Around '79 GM started using AAM axles and you can see a big difference in them from the older tapered axles.
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Old 02-03-2014, 08:17 PM
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The thing people should think about is why would GM install the same size and strength axle shafts in the 6 cylinder and low HP cars during the muscle car years when you could order big blocks and small blocks putting out gobs of horse power and torque when they installed heavier bell housings , 4 bolt mains, heavier stronger drive shafts, ETC But didn't do any heat treating to the posi axles! And axle shafts don't have to be heavier or non tapered to be stronger or have more splines it depends on the casting, the forging or the heat treating and the quality!! You can by crappy axle shafts with fine spline and they look heavier but are weaker then a coarse spline tapered heat treated OE axle.

I learned about the difference while on the pit crews in the 60s & 70s maybe some of the old guys remember this, Or maybe I just thought it would be fun to make it up, Except the COPO and YENCOs came with the heat treated factory axles. The Yencos weren't allowed to race in the Factory classes because they weren't built at the factory but the COPOs were! Central Office Production Order, or COPO. The orders included power disc brakes, a 4.10 Positraction rear end with heat treated axle shafts, (to avoid breakage), a Z-28 front anti-sway bar, and a heavy-duty 4-core radiator. Buyers of the car had the option of either the M-21 four speed or the Turbo Hydramatic 400 automatic transmission. A total of 201 cars were sold in 1969

And some of the cars leaving the factorys had these axle shafts with the high HP options like the GTOs, Trans AMs, 302 YZs, etc etc especially the factory sponsored cars , I never said all posi s had them That's why when I ran across them I grab em. And they are impossible to tell apart but the tell tale ring will give them away if rapped with a small hammer!

Take all this with a grain of salt. Its no big deal anyone can buy after market heat treated axles pretty reasonable now! Me when I saw a rear housing years ago with a posi tag on it at the junk yards I would pull the axle and listen to the ring, if the yard let me, And the axles I have now will probably be still in the corner of my garage when I'm long gone

Jester

Last edited by painted jester; 02-03-2014 at 08:28 PM.
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Old 02-03-2014, 09:21 PM
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Chris,let me know when you are leaving?
I had a 67 Camaro and I broke a couple axles. I remember 1 parts guy asking me a lot of questions way back.I thought he didnt know what he was talking about,maybe I missed out on learning? Taper was a big concern. stock 12 bolt axles were not that strong,I can see axles from a 7.5 inch diff being likes paghetti
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Old 02-03-2014, 09:58 PM
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9" ford parts are cheap and strong. 7.5's are the same rear end they put in vegas out of the factory. I like 12 bolts and 8.5 10 bolts. If you drag race it with slicks you may have to go pick up your ring gear off the street. I would sell it and spend the money on a junkyard pickup 9" ford. Local stock car guys have tons of parts for them cheap. See "Speedway" catalog also.

PS. I would never run an 8.5 chevy rear with factory Gov-Lock because they are JUNK. The small parts fall out and get stuck in the big parts and bang.
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Old 02-03-2014, 10:16 PM
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Vinnie

I like the 8.5" 10-bolt, the axles shafts are the weak point of the 8.5 10-bolt but the " ring gear is less than ½” smaller in diameter (.375”) than the 12-bolt 8.875" rear. The 10-bolt is capable of handling 9-second Buick Grand National blasts (I stole that Grand N. remark LOL), the ring gear is less than ½” smaller in diameter (.375”) than the 12-bolt rear.” and the pinions are the same diameter. But you know that LOL The small 10 bolt 8.20" is ok for street use and playing around but I would suggest to anyone who is a weekend warrior to go with one of the 2 bigger 10 and 12 bolts and for all out power a Ford Nodular 9" or a Dana.

I have fooled with a 7.5 in a Monte Carlo, welded the small 10 bolt axle tubes and gusseted the housings and installed a Locker, ladder bars and aftermarket axles running slicks and it stood up pretty good at the strip but with only about 500 HP applied to it. But it was driven with clenched teeth and butt cheeks!

Its funny the things we old farts remember and try to pass on to the younger generation and they think we make stuff up #%$&
LOL

Jester

Last edited by painted jester; 02-03-2014 at 10:22 PM.
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