new hemi swap = what rear end?

[Evelbist]

Putting a 392 hemi from a '14 challenger into a '69 charger. I have a 3:23 8 3/4 non-SG rear, but will that live behind the 470 hp engine?

If not, what should go back there?

[BLK 68 R/T]

Your current 8 3/4 will be just fine.

[Kern Dog]

Unless you want a 1/4 mile 1 wheel peel, you will surely want to consider a limited slip differential. Some call it a "Posi" but that is a term that really only applies to Chevrolets. It is short for their own brand of limited slip differentials called Posi-Traction. Like many things, the Chevy terms are popular and get used elsewhere.
When our cars were new, the LSD option was called Sure Grip. Pontiac called theirs Saf-T-Track. Ford had a few: Detroit Locker, Traction Lok.
Several options are out there for you but personally I like the original style clutch type SG that was available from 1958-68. It has clutch plates that can be replaced when they are worn. In 1969 they changed to a NON rebuildable design that is available new today. This "cone" type diff is okay when new and lasts awhile but is most often thrown away when it is worn out. Some claim to have rebuilt them with success but a greater number of people consider that a bad idea.

[justcruisin]

Do you know why they say it is a bad idea to rebuild the cone type rear. I have never had the need to do one but I know what is involved and if you can do the work yourself and the case half's are OK  I can't see why not, maybe I am missing something.

[c00nhunterjoe]

Do you know why they say it is a bad idea to rebuild the cone type rear. I have never had the need to do one but I know what is involved and if you can do the work yourself and the case half's are OK  I can't see why not, maybe I am missing something.

Typically they are not really rebuilding them. The cones wear down so they cram spacers in the tighten up the gaps. Not exactly the right way to do it.

[justcruisin]

I agree they should be replaced but I can't see an issue machining the face of the cone and using a spacing washer made from a good quality stainless. I wouldn't pay some one to do it, I would put the money into a new unit but for a cheap as chips, do it yourself approach, when I look at it - I still can't see a problem. The only thing I see is the spacer wont be splined to the axle. (Don't think that will mater).

Reason I ask is if needed I will do the repair to mine, just looking for reasons why it's not a good idea.

[Kern Dog]

The further the cones dig in, the spider/bevel gears move inboard making contact in a slightly different area. What was once a mated and matched contact area now is not. Sorta like putting new brake pads on grooved rotors.

[cdr]

The only time I would put money into an 8 3/4 would be a very low performance car 

[c00nhunterjoe]

The only time I would put money into an 8 3/4 would be a very low performance car 

This.

[justcruisin]

Exactly - that's why the repair - I don't want to spend any money on it, but still the majority of true street mopars out there are running an 8 3/4. I really don't have anything to point to but I would say that a reason for sure grip cone type failure (apart from normal wear on the cones) was from using a unit that was close to being bottomed out and consequently not having full contact loading on the side gears - can't help. Although from what I understand an axle will let go first.
Anyway, I can see all your points,and if I had an engine with enough balls I would probably ditch the 8 3/4. It has stood up so far but when the car goes back on the road after some body work I will be adding some drag radials to try and get a better ET.

[Kern Dog]

The only time I would put money into an 8 3/4 would be a very low performance car 

This.

??
DEfine very low performance....?
Lots of guys are running the 8 3/4" axle with more than stock horsepower. Mine has never gin=ven a moments trouble except for the bullshit non adjustable axle bearings that I thought were a better idea.
If the 8 3/4" was the default axle even for HEMI automatic cars, how can you dismiss the axle so quickly?
Sure...If you have a dedicated drag car that takes a pounding, I can see that. The other 90% of us may rarely race but like the lighter weight, ease of swapping in different ratios and cheaper cost will stick with the 8 3/4".
I have a 440/493 that surely would not be defined as low performance. I have no plans to use anything else.

[cdr]

The only time I would put money into an 8 3/4 would be a very low performance car 

This.

??
DEfine very low performance....?
Lots of guys are running the 8 3/4" axle with more than stock horsepower. Mine has never gin=ven a moments trouble except for the bullshit non adjustable axle bearings that I thought were a better idea.
If the 8 3/4" was the default axle even for HEMI automatic cars, how can you dismiss the axle so quickly?
Sure...If you have a dedicated drag car that takes a pounding, I can see that. The other 90% of us may rarely race but like the lighter weight, ease of swapping in different ratios and cheaper cost will stick with the 8 3/4".
I have a 440/493 that surely would not be defined as low performance. I have no plans to use anything else.

In 1980 my GTS 383 Dart I broke a clutch sure grip, the spider gears exploded & the shrapnel broke the ring gear, 383 mild cam & headers auto trans, ran low 13 's
1/4, my friends 68 RR stock 68 440 4 speed,out of a Charger, has broken THREE  8 3/4 's never had sticky tires, my 68,512 with drag radials killed my new 8.3/4 wasted money!!!!

[justcruisin]

Man - there seems to be some story's for both sides. I recall a prior thread -  Ron(firefighter) gave a story of a friend using a 8 3/4 in 3800lb plymouth that ran 10's. Coonhunterjoe gave a story of snapping axles on a mild 440 build.
My personal experience is they are pretty tough and I have never seen one let go when using street rubber.
Maybe set up and condition of the center section has something to do with it?

[c00nhunterjoe]

Man - there seems to be some story's for both sides. I recall a prior thread -  Ron(firefighter) gave a story of a friend using a 8 3/4 in 3800lb plymouth that ran 10's. Coonhunterjoe gave a story of snapping axles on a mild 440 build.
My personal experience is they are pretty tough and I have never seen one let go when using street rubber.
Maybe set up and condition of the center section has something to do with it?

Mild 383... broke many sets. Scattered the 489 cone suregrip on bfg radial ta tires in similar fasion to what cdr stated, not quite as violent though. Lol. Broke several axles with the 727 behind it. Broke a hell of alot more with the 4 speed and sticky tires. And it was no race car.

[cdr]

Man - there seems to be some story's for both sides. I recall a prior thread -  Ron(firefighter) gave a story of a friend using a 8 3/4 in 3800lb plymouth that ran 10's. Coonhunterjoe gave a story of snapping axles on a mild 440 build.
My personal experience is they are pretty tough and I have never seen one let go when using street rubber.
Maybe set up and condition of the center section has something to do with it?

My friend that I have been racing with for many years has a very nice 78 Trans am, 3750# 455 pont auto runs 10.90, still has the 10 bolt rear end & stock axles & never broken it, does that mean the stock 8.5 gm 10 bolt is a strong rear end, I dont think so,he has just been lucky.

[Mike DC]

  
A Dana 60 swap would certainly fix the strength questions.  But it's not a 100% no-brainer.  There are downsides with it too.  

The D60 will add something like 50 lbs of unsprung weight over an 8.75" rear.  An aluminum chunk for the 8.75" (not possible for a D60) would spread the difference another 10-15 lbs wider.

The gearsets for D60s only go down to 3.54 ratios.  Nothing "taller" will fit in the case.  You can find 4.10 sets for D60s all day long but you can't give it anything like a 3.23 or 2.94 for highway cruising.    

---------------

As for whether the stock 8.75" rear will live behind that modern Hemi, it probably will on the street.  What really breaks rearends is curb weight + torque + traction + shock loading.  An automatic tranny and (honest) street tires will do a lot to save it.

[John_Kunkel]

The first question should be.....automatic or stick?

[c00nhunterjoe]

I broke them with a pump gas 383, 727, 11" 3k converter and 275/60/15 bfg radial ta tires. Broke several axles, and a 489 sure grip. The 742 lived for years but axles continued to break and got worse with the 4 speed. Finally built the dana and no more problems.
  To those who argue the weight, are you running billet specialty wheels? Cause they are alot lighter then stocker rims? Its just money right? Arguing 50 lbs of axle housing is ridiculous on these cars.

[justcruisin]

Did you notice any difference in your time slips going to the D60. Presuming just the rear swap.

[ACUDANUT]

The first question should be.....automatic or stick?

Next question, is what is your budget ?[/b]

[alfaitalia]

Does anyone have the official figures as to what an 8.75 can actually handle as far as power and torque....and weight as that must affect things. I don't mean someone's guess or that there mates mate broke two whilst parking...but real Dana quoted figures...I googled it but did not come up with a definitive answer. I think I will be going 60 for my plans....but still it will be interesting to know the FACTS re the 8.75.

[c00nhunterjoe]

Did you notice any difference in your time slips going to the D60. Presuming just the rear swap.

No.

[c00nhunterjoe]

Does anyone have the official figures as to what an 8.75 can actually handle as far as power and torque....and weight as that must affect things. I don't mean someone's guess or that there mates mate broke two whilst parking...but real Dana quoted figures...I googled it but did not come up with a definitive answer. I think I will be going 60 for my plans....but still it will be interesting to know the FACTS re the 8.75.

There is no number for any rear regardless of manufacture. The bottom line is if you are going to dump a ton of money into building a rear, you should build the dana over the 8.75. As stated earlier, if you want 2.90s or 3.23s, then you have to do the 8.75. If you are worried about weight, then buy the lightweight dana parts. You can build a dana lighter then an 8.75 if you want to spend the money to do it, but its not necessary.

[Mike DC]

To those who argue the weight, are you running billet specialty wheels? Cause they are alot lighter then stocker rims? Its just money right? Arguing 50 lbs of axle housing is ridiculous on these cars.

Arguing that an 8.75" rear is inadequate for a 383/727 street car is a little ridiculous by many people's standards.  Different strokes.  There are 500" strokers driving around on 8.75" rearends every day.  Some people are harder on their cars than others. 

Anyone who cares about unsprung weight at all will care about 50 lbs of it.  Some people buy aluminum brake calipers & fiberglass leaf springs to save a fraction of that.

[c00nhunterjoe]

To those who argue the weight, are you running billet specialty wheels? Cause they are alot lighter then stocker rims? Its just money right? Arguing 50 lbs of axle housing is ridiculous on these cars.

Arguing that an 8.75" rear is inadequate for a 383/727 street car is a little ridiculous by many people's standards.  Different strokes.  There are 500" strokers driving around on 8.75" rearends every day.  Some people are harder on their cars than others. 

Anyone who cares about unsprung weight at all will care about 50 lbs of it.  Some people buy aluminum brake calipers & fiberglass leaf springs to save a fraction of that.

I never said it was inadequate,lots of people run them with success. my arguement is based on when you are building it from basicly the bare housing, the dana is a no brainer regardless of your engine.  You suggest the aluminum 8.75 chunk. That alone is 1000 dollars. Then to run your 3.23s requires custom machining on top of that. You can buy lightweight dana parts, you can get lightweight tubes. Then on top of it all, the dana uses less horsepower. If that slight difference in weight was that critical compared to hp used, especially in racing, then the dana wouldnt be under the majority of the stock and super stock drag cars. When it comes to the street cars and arguing unsprung weight; thats what i am refering to in my arguement on billet wheels. You are splitting hairs saying to stay away from the dana because of 50 lbs, yet the same cars are running over 50 lbs worth of 11" cast drums compared to a lighter disc setup and heavy steel wheels vs light weights.