[Chase Rath (70wss)]

Title says it all, I'm planning to build a 450-500hp 440 for my new Challenger, it will also have a 4-spd, would it be possible to use a 8 3/4 rear and not have problems. I thought about a Dana 60 but read only 10 sec. or faster cars really need those. I plan to run drag radials on the car and maybe slicks occasionally.

[Dave-R (Roppa440)]

There are different 8.75 axles some of which are stronger than others.
My mate MoparKev summed it up very well;

There were 4 centre sections; 657, 1 3/8" pinion ('57-'64); 741, 1 3/8" pinion ('65-'74); 742, 1 3/4" pinion ('57-'68); 489, 1 7/8" pinion ('69-'74). Of these the best are the 742 (Shimmed preload) and 489 (Crush sleeve preload). There were two SureGrips; Dana Power Lok ('62-'69) (clutch type) and Borg-Warner Spin Resistant ('69-'74) (cone type). The cone type is not easily rebuildable, the clutch type is.

The strongest of these (489) as stock will cope with that much power and an auto trans. Not sure about a 4-speed though. You might get away with it but I think you would be safer to have the 8.75 beefed up. There are many places that will build it tougher for you. Places like Mancini will even sell you complete limited slip diffs built to higher spec. Better axle shafts might be a good idea as well.

I have over 500hp going into my stock 489 axle through the auto trans and nothing has broke yet. But I would not be surprised if something in there broke one day.

[Tig (Cathtig)]

Depends on how much traction you have, how much torque, and how heavy your car is. Also a manual car will shock the drivetrain more. Go for a Dana now and it'll last, you also won't have to worry about it when you go to upgrade again.

[Hans (72challenger)]

A guy over here is running 500+ hp 440 in a roadrunner with a 4-speed on the strip on slicks and it runs fine, already for a longer time. This car has a 83/4 suregrip 3.55 gears. He's even running his 440 with a cast crank... something I wouldn't do I quess.

[John P (Blue)]

I would run the 8 3/4 until you break it, and then upgrade to a Dana. With that amount of horsepower and a 4 speed, even if you beef the rest of it up you are still liable to rip teeth off the crown wheel or break spider gears in the sure grip. For that reason I don't see the point of spending any money on the 8 3/4, some years ago I had a 383 / 4 speed Duster with 10'"slicks, it had less horsepower than you are planning, and I managed to chip gears, break the sure grip, twist the stock halfshafts and break the rear UJ ( not all on the same occasion!) it ran 11.7 and weighed 2800lbs by the way.

[Chase Rath (70wss)]

I decided to go ahead and get a Dana, since I have to buy a rearend anyway, might as well spend the money once, I am going to have a truck case narrowed, I get get one for about $150 from a junkyard, a lot less than $2000 for an original and $1750 for a new one.

[Joel Bennett (Joel)]

How can you tell a Dana from a non-sure grip type rear-end? My brother is running a 440 452 crate racing motor with 450hp+ with 4.10" gears with a 727 in a '68 Fury III. It origninally had a 383 2bbl and 2.76" gears in it.

[Dave-R (Roppa440)]

You seem confused Joel.

Are you wanting to know how to tell if an axle has a sure-grip in it or not? There is a couple of threads that cover this.

Or are you asking how to tell a 9.75 inch Dana from a 8.75 inch or 8.25 inch axle? That is easy as the 8.75 has no cover on the back. The Dana is a BIG axle. You can't mistake it - it is that big.

The axles have casting numbers on them too.

[Joel Bennett (Joel)]

Nevermind. I answered my own question by looking under neither the car and compared it to the examples shown in my Year One service manual. The rear end on my car has a removable carrier and no cover, which I take it means its a 489.

Besides, it was part question and part statement and it didn't make a whole lot of sense, cus I was in a hurry to leave for work. Sorry.

Man, the 9 3/4" sure has a lot of parts. I'm looking at an exploded picture of one.

Dave, do you know of any manufacturers that produce a 1.5 way limited-slip differential for a 489, 1 7/8" pinion? I know that you could order a 8 3/4" car with SURE-GRIP, but I don't want full posi when I go around corners or let off the throttle, just on acceleration.

[Dave-R (Roppa440)]

Joel. You may indeed have a 8.75 axle but you do not have a 489 axle unless it says so with the last three digits on the casting number on the carrier. There were three different 8.75 inch axles with different diameter pinions. Read the second post in this thread.

When it comes to the limited slip question you really are confusing me and yourself. For example why on earth would you... oh never mind.

I don't think you quite grasp what a limited slip is for or how it operates. Just stick with the sure grip. It is a very good unit that does everything expected of it.

[Joel Bennett (Joel)]

Ok, I'll check the casting number kater today after church.

There are several types of limited slip. The 1-way limited slip allows both wheels to drive the car on acceleration, but one wheel disengages on deceleration, allowing for safer and easier turning. 1.5 limited allows both wheels to drive the car, but the effects of having full posi on deceleration is somewhat diminished, helping to slow the car to some degree. Then there is 2-way limited slip, which is basiclly what we call SURE-GRIP. Both tires are ingaged fully on acceleration and on deceleration. When the differential is engaged fully on deceleration, it helps to slow the car down faster. The 2 way type has a tendencey to be a little tricky for most people to control in wet and icey conditions. Also, when you go around corners, both wheels want to turn at the same speed, so outer wheel will churp, making the turn more difficult. Normal limited-slip is more like .5- way or half-way limited slip, because it only drives one wheel until a certian speed is attained and then both wheels drive the car and then disengages on deceleration. This helps to make turns around tight corners easier and prevents the outer tire from churping, aswell as to prevent fish tailing in wet and slippery conditions. The mass majority of people aren't that good at driving. When the car begins to fishtail, most people have a tendancey to over correct and they end up getting into accidents. That's why only sports cars and trucks come standard with posi, or a.k.a SURE-GRIP. SURE-GRIP, posi, or anyother name you want to call it, are actually 2way limited slip.

This is what I gathered from the sources that I've read.

[Alex (Alex)]

I gather the sources are GT3 on the playstation!

Apart from the usual pre loaded lsd you get in mopars and other muscle cars which will allow the wheels to move independantly at a given torque, i.e. going round a corner in the dry, the only other type of lsd I know of which is manufacturer supplied is the 'torson' stlye, which uses hydraulic force to work, this style works the other way round, it normally ats as an 'open' diff, but when one wheel starts to spin the hydraulic action inside the diff progressivly locks the other to it, this also works as a constant variable, i.e. it can work anywhere from 20-100% lock. They are very clever and quiet in operation and as they come in slowly are a dream to use, examples of cars using this type of diff are Maserati and TVR, although I think many of the Jap supercars (Skylines etc) are using a similer system now.

[Dave-R (Roppa440)]

Joel. In the real world you will not notice you have a sure-grip LSD during normal driving. However when you push it hard in a straight line or on a corner you will notice that it does it better without one wheel breaking lose and slowing the car down. It will cirtainly not chirp one tire as you drive around corners like a locked diff.

[Luke (Luke)]

lighten up dave let the young fellers catch up.

[Dave-R (Roppa440)]

Am I nothing but sweetness and light?

OK so I am a dry grumpy old fart. I eat babies and small children too you know.

[Roger Bettoni (Roger)]

I'll throw my two cents in now...
In my 4x4 I have installed a "Lock Right" diff-lock device. This thing is guaranteed for life, made of titanium and works a treat. Locks positively if more than 20% slip is recognised, but otherwise acts like an ordinary open diff. You must power the vehicle when articulating (turning) so as not to engage the locking device. This requires some concious application of throttle while driving around round-abouts and the like, but otherwise you just drive normally. These are standard fittment in the Hummer or "Humbie" as used by the US military. My 4x4 is now a 3x4 as opposed to the manufacturer's set-up with two open diffs, which makes it a 2x4 in reality.
I believe you can install one in an 8.75 diff so would this make it like a sure-grip?

[Dave-R (Roppa440)]

Fair enough in a four wheel off road application but in a Challenger?

Sounds an expensive way to do it to me when the stock, cheaper suregrip does the job without any problems? Made from titanium? Good grief!

[Roger Bettoni (Roger)]

Dave, not sure how much a sure grip costs but a mob called Ring and Pinion are advertising a "sure-grip positraction" as 'available soon' and price starts at US$363 The lock-right, which replaces the spider gears for all 8.75 cases sells for US$299
As I know how good this product is, I would seriously consider putting one in the arse end of my chally. The one in my 4x4 has done 200,000 km's and got me out of some pretty bad situations, ones that I would never have gotten out of without it.

[Dave-R (Roppa440)]

Only $300? That is cheap. The only bit that would worry me slightly is having to keep power on around every corner (which I realise you should anyway) with an automatic and a high gear in the axle.

Plus it is not that hard to source a used suregrip.

How can something made from titanium be that cheap? A guy showed me a 5-inch titanium bolt from a Top Fuel car he was building once and he told me a single bolt cost 60 quid (about $100 US).

[Dave-R (Roppa440)]

Just checked out the prices on limited slip units for the 8 3/4 from places like Mancini. You are talking $400 US for a new one. The units that fit the 8 1/4 inch axles are much cheaper though. Like half the price. Bandits!

[Andy Neal (Tweety)]

As to practical limits for an 8 3/4-well it depends how far you want to go, me and some drag racing friends are currently embarked on a mission to see how much they will take before they explode!
The current leader is running 9.3's in a 2860lb ( less driver) Dart that really hooks up.
The weakest link once you eliminate the limited slip bit are the gears.
If you want an 8 3/4 to survive you need to put a brace on the case, they move around all over the place other wise.
How fast do you plan to go with this thing? 400 HP will put you some where in the 12's I guess? and on street tyres, the standard bits should last a while.
I've destroyed PLENTY of 8 3/4's so if you want any pointers as to what snaps e-mail me.
Good luck Andy