how tough are our rearends

[Holt]

how tough are 67-72 rearends? Not exactly sure what year i have, truck is a 67 but i have 5 lug axles and disc brakes in the front that matched up perfectly with 72 calipers when i had to replace. i have 3.73 gears, so back to the question how tough are these rearends?

[vectorit]

Mine has been kicked around so many times these past 40+ years, I sometimes feel like super man since I am still kicking other rear ends and takin names...

To answer your question.

Some of the toughest around, and still highly regarded as a standard when it comes to strength.

[67ChevyRedneck]

Mine has probably over 200K on it, it's almost 45 years old, and when I changed the fluid a couple years ago there were NO visible signs of wear or leaks! Seems pretty tough to me.

[Holt]

good to know, thnx

[oldblue1968chevy]

still running an original rearend from a 72 from a guy off the forum here.

changed oil and put new rtv on thats all so far

[prostreetC-10]

My rear end is pretty tough........and according to my wife.......quite stinky at times!

[earlthegoat2]

Ill assume we are talking about 1/2 ton rears since the 3/4 and 1 ton rears are so tough I think their reputation speaks for itself.

A lot of the 4x4 crowd will likes to say C clip axles are not worth a salt but I have never had on go bad on me. The 12 bolt rears that were put in 396 Camaros have stood up excellently to the high torque that engine is capable of producing.

On to trucks though, my only real experience is, once again, with 12 bolts and like I said, I have never had on malfunction in any way from anything I have done to it. 4wd and 2wd applications.

[WAAF]

a few thoughts..
the truck 12 bolt is not the same as the 12 bolt under a camaro or chevelle..
the truck 12 bolt is stong.. untill you slap slicks on it.. and beat on it...
the truck 12 bolt has a smaller pinion shaft o.d. than the car, why g.m. did this.. who knows..
there are other differences, from what I've heard the car diff will not work in the truck housing..
my understanding is they are a little stonger than a chevy 10 bolt, but weaker than the car 12 bolt..
still mighty strong. but wasn't made for todays big block power levels..
also remember back in the late 60's early 70's tires didn't have the grip they have today..
todays goodyear eagles street gator backs have more hook than most recapped slicks of the day.. nevermind todays drag radials.. or heaven forbid slicks..
only reason manual trannys lasted back then is because the tires where the weal link..

[cdowns]

12bolt truck rears will not last but 2seconds in a top fuel car// many lasted over 45 years and are still going strong in warmed up vehicles with bonzai driving

so it all really depends on horspower, tires, abuse and other factors / none of which was addressessed in the original question

[mbgmike]

pretty tough for a stock vehicle considering how much care most owners did NOT give them. for racing no. they lasted this long

[GASoline71]

Mine in my 1972 GMC C1500 Super Custom has an Eaton posi, 3.73's, and Moser axles. I beat the snot out of it. Comes back for more...

Gary

[WorkinLonghorn]

If we're talking 1/2 tons, my last '69 had a 350 engine with a serious RV cam that developed unbelievable torque. Load the truck with a couple yards of wet decomposed granite, select granny low (6.55-1) and floor it. Broke a few U-joints in it but never had a diff. problem in 6 years of use and abuse.
Same story with the current 3/4 ton without the U-joint problems.

[Mike C]

In my experience, the truck 12 bolt is sufficient for a 1/2 ton 2 wheel drive truck that is used as a 1/2 ton 2 wheel drive truck. OK in a 4x4 if you don't put big tires on it or have a manual trans. And if you have an orignal Eaton posi and not a Gov-Bomb.

When we got the '72 Jimmy in '77 it had 113k miles on it. My dad was turning it off in the driveway and letting the clutch out simultaneously when it backfired. And broke two teeth on the pinion gear crazy enough. Put a junkyard one in at that point, 130k miles or so, and ran it up to around 200k at which point the pinion bearing went out. Combined all the parts into one and ran it until 270k or so. Swapped in a Gov-Lok and a set of 4.10's from a parts truck once I put 33's and then 35's on it. Broke ring gear in about 15k miles, my brother had borrowed it so who knows what he was up to. Had diff rebuilt with 4.10 thick gear on the original Eaton posi. Was gettin' on it a little and it wheel hopped. Twice. And broke the Eaton posi in 1/2 across the window. Swapped other original Eaton in on new gear set, and broke ring gear. Turns out two much runout on the posi unit and the first new gear set install I had done. Had posi trued up in lathe and ANOTHER new 4.10 gear set. Ran that until 340k miles or so. Then ditched the 12 bolt completely which now had ridiculous amounts of bearing wear and bent spring perches as well . Put in a semi-float 9.5" form a 3/4 ton Suburban which is unbelievably stout compared to the 12t , and it will most likely go the distance considering how truck gets driven now.

So, 7? 8? 12 bolts in the truck. I may have missed one somewhere, but not what I consider "stout". Will see how long the 3.73 posi lasts in my new short bed, but considering TH350 and 307 power with 28" tires, probably within its design paramters.

The 8.5" 10 bolt with 30 spline axles is a strong as a car 12 bolt (12p). The fewer ring gear bolts are larger in diameter and reversed threaded compared to the 12t or p, so that is a push. The ring gear diameter at 8 1/2" vs. 8 7/8" is almost a push, and pinion diameter on the 8.5 is same as the 12p. Big tires will do in all of them with stock style/strength components.

[texnician01]

Depends on how you are going to use it. My 69 was used as a chassis with a camper on it, I have no idea how many miles it has on it, the odometer has rolled over at least once and judging by the wear on the original 292 maybe twice. I have never had a problem with it and it is now behind a 327 making about 400ft/lbs of torque. I used to be quite...spirited with it when I was in high school. The axle is rated for 3750lbs. I once by mistake hauled 2 tons of pea gravel in the bed for 40 miles and it has never given me a problem. I have an original Eaton Posi to put in it and I'm going to replace all the bearings as a preventative measure but I plan to keep running it. Just a few specs, 327 400ft/lbs tq, sm465 granny low 4 speed, (soon to have us gear overdrive), 3.73 gears, 31x10.5 tires.

If that wasn't enough, my grandfather was a heavy equipment operator/mechanic, he had a 67 half ton, sm420 granny low trans, and 3.73 posi. It hauled over a ton of fuel, tools, fluids and parts every day of it's life over some pretty tough terrain for years. The truck was wrecked and then the box and rear were made into a trailer, they just junked it because the box rotted out, but the rear is still fine. In fact, that is what my posi is from. I took it out and put in an open carrier and a junk set of axle sidegears just to keep the axles in.

I have no question that it will handle anything I will throw at it. But i'm not drag racing either.

[ChevLoRay]

If you have a need, Currie makes their Ford 9-inch rear ends with whatever lug pattern you want on the axles. I've read plenty of times, of folks using those 9-inch rear ends in plenty of high-perf apps.

We used Taylor-Dunn electric vehicles at ALCOA. They had narrowed 9-inch rear ends, modified to run electric motors. I have seen them abused in just about every possible way and never a failure. Motors did fail, but not the rear ends. Oh, those were 36-volt motors and they had plenty of torque, so the gears would have taken the brunt of the load.

Alway wanted to get one and change out the "punkin" and use it with some wide wheels and tires in a narrowed chassis....seems like those rearends were less than 40 inches, hub-to-hub.

[AusTx68]

I took for granted that my 1/2 ton rear (12 bolt 71-72) would go one without checking on it. It was literally the only thing I didn't refurbish or replace with new. The first time I tried to take it for a 2 hr road trip she died on me. It was a mess! Only the housing was salvageable. I had it completely rebuilt with Eaton posi, 4.11s, new axles, bearings and seals. Now I feel she'll go another 40+ years.

[Holt]

guess i didn't give enough info on the original post...69 half ton 2 wheel drive. just had engine rebuilt 350 bored .060, cam, not sure what kind of hp or torque its gonna make. Just curious about weak links in drive train. Trans is a th350 with shift kit.

[oldno7]

I'll chime in here, My 72 has a 69 12 bolt posi in it i run at the track i bought the 69 for parts for 250.00 and then found it had the posi. so anyways my truck runs 8.90's 1/8 mile all day with a 350 aluminum heads 750 holley with a small cam pretty damn peppy so the only thing ive done to the rearend was install 4.56 behind the tci street fighter 400 tranny it still has c-clips and a two piece drive shaft that ive tried like hell to break leaving the line at 3000 rpm with 8-10 pounds of pressure in my mickey thompson et streets I havent been to the track for awhile been workin on my 67 alot So as far as im concrened these 12 bolts kick a55

[bosco200]

I have a HO-52 and its a TANK!

[Mike C]

Big tires along with big power, or at least reasonable power in a high traction environment will find the weak link. Wheel hop will destroy it pronto.

I've built 8 1/2" 10 bolts for drag cars. The last one ran 10 teens at 126 mph behind a 462 Pontiac in a 3000# Firebird. No parts were stock, but I've built several for high 10/low 11 second cars with all stock parts but gears and some of them had hundreds of passes on them. So they can be built to take some power, and so can the 12t.

One way to look at it, is the 12t is not in demand to be swapped into anything to beef up what's already there...

[Dunenutt]

Just swapped out the original 10 bolt in my 69. It had over 500,000 miles on it, and I remember replacing the wheel bearings twice. As I was taking it apart for it's demise, it had a tooth missing from the ring gear.

They are pretty tough!