Will my stock axles hold up?

[darktone]

I mean if I get traction at the strip with those hoosier DOT's? I only plan on running in the mid 13's with it but it might take a pretty hard hit of torque with that 3,000 stall and hoosier's. Moving almost 4,000 pounds of mass might I encounter a broken axle? Or am I reasonably safe on a car that will only see 20-30 passes a year?

[scredneck]

What rear end? Gear ratio?

[darktone]

8 3/4 with 3.55 gears.

[nhdriver]

They won't last forever but they will take a beating

[RacerHog]

Strat buying stuff now.....Beat'em till it breaks.....

[darktone]

Originally Posted by RacerHog

Strat buying stuff now.....Beat'em till it breaks.....

A good idea. When the axles break don't they take out the sprag too? I have a bolt in sprag so I should not have to worry about that but others reading this should be warned.

[aarracer]

They have lasted for years and years of abuse with slicks, 340's - 440's and 426's, and all the other engines Ma Mopar has thrown at them. They will probably be just fine.

Cheers

AARRACER

[TrashedCharger]

If in doubt, run some bigger numbered gears, like some 3.91's.

The 8 3/4 is actually the most efficient rear axle ever made. It dramatically decreases use of HP and torque multiplication created from torque converters and because of it's efficient design over other rear axles, has less drag.

What kind of car is this in? If you don't have custom axles in your running gear, if this is a narrower axle/ housing combo for bigger tires or like something that would have been slapped in an A-body, one trick you can do without spending the cash on custom axles is run cut down truck or full size wagon 8 3/4 axles.

The step up in diameter on an A-body 8 3/4 axle is relatively close to the bearing/ flange. Truck and full size wagon axles have the same diameter step, but the step up in diameter is towards the other side of the axle, closer to the splines, making the rest of it out to the bearing and flange thicker than the stock A-body (and maybe even B-Body axles) overall. The truck/ wagon axle is long enough that the step down towards the splines is past the point of cutoff for what is needed in an A-body housing. And that's with the narrower wagon axle, compared to the truck axle. You may even be able to cut a pair down to fit a B body housing.

I think the wagon axle (narrower than the truck) we measured against a factory A-body axle had at least 1/2" to spare in length before the step down, actually. That would give at least 1" more width that they could be used for a housing that was wider than an A-body. I think if you got axles from a truck 8 3/4", it would give you even more usable width to cut down for a B-body and the truck axles can be had everywhere for next to nothing.

[MOPEkid]

Hmm, that's interesting. Is it a lot more efficient than an 8 1/4" rear? If so I might go to an 8 3/4" when I swap rearends.

[Paul Precht]

It is common knowledge in NHRA Superstock that the 12 bolt GM is probably the most efficient. Many SS Mopar racers use it because of that. It has less friction due to the mesh angle which is also what makes it weaker. The 8 3/4 is a great choice though, it's almost as efficient, stronger and easier to set up and change, Paul.

[TrashedCharger]

That is correct, the GM 12 bolt is weaker than the 8 3/4, not to mention it's added weight compared to the 8 3/4, making the unsprung weight in the back of the car far less with the mopar axle. The benefits from a 12 bolt in it's added mesh taper and lack of resistance are far outweighed by their downfalls with weakness and weight, making the 8 3/4 the most efficient/ reliable axle. There have been documents of cars getting more fuel economy with an 8 3/4 over a GM 12 bolt in the same vehicle.

You could argue that the 12 bolt is a more efficient axle for transferring HP and torque to the wheels in perfect conditions, but you could also argue that because of an 8 3/4's added strength, you are more capable with it, because you could exceed the HP and TQ threshold of a 12 bolt, leaving it in the dust and cutting quicker times with less weight to boot. For the capabilities in threshold of HP + TQ and weight of any rear axle, the 8 3/4 is by far the best. You simply can't find an axle that is as capable as the 8 3/4 for the same or less unsprung weight.

The reason that the SS guys use the 12 bolt is because they are cheap and have less drag than a Mopar axle, but they don't get as much use out of them. You could compare it to Dick Landy neutral dropping his race cars for a better launch from 5000 RPM.

He came up to the track with a truck full of 727's and had a removable transmission tunnel for ease of changes. Ironically, they were the only transmission able to survive a run like this at the time, but the point is that this method was the most efficient way to launch a car and completely sacrificed all practicality and reliability. Just because something works on the track, doesn't mean it's the better way to go.

As far as the 8 1/4 goes, you just have to pick your poison. An 8 1/4 will deliver about as much drag as an 8 3/4 with a little less strength and weight. So, if you think your car will exceed the HP and TQ threshold of the 8 1/4, that's when it's probably best to move up, but if you aren't going to make use of the added strength, the 8 3/4 just added weight and a little more drag.

The SS guys also use heavily modified 904 transmissions over 727's, because they are more efficient, but again, they aren't getting as much use out of them as ones that see 100,000+ miles before getting rebuilt.

This is why I'm choosing to go with an A-500 for an overdrive, versus the A-518. I just don't need the strength and would rather have the lack of weight and size of moving parts to be the most efficient in my desired range of HP and TQ. And I can do it without sacrificing reliability up to and beyond 100,000+ miles worth of use, which is completely moot to consider with a racecar.

[dave571]

Originally Posted by darktone

I mean if I get traction at the strip with those hoosier DOT's? I only plan on running in the mid 13's with it but it might take a pretty hard hit of torque with that 3,000 stall and hoosier's. Moving almost 4,000 pounds of mass might I encounter a broken axle? Or am I reasonably safe on a car that will only see 20-30 passes a year?

Stock axles will live a long time behind a 13 second car.
Mopar axles are pretty decent.
I certainly wouldn't worry on a 20-30 pass/year car.
My .02

[darktone]

Thanks for the advice guy's. I am going to leave the axles stock and not worry about them.

[TrashedCharger]

Good call. If you ever want an inexpensive upgrade, go with a set of cut down truck or full size (C-body) wagon axles. They are a bit thicker and can be had for next to nothing, as well as cut down and splined for next to nothing.

[lazarus]

I snapped a stock axle last year in my '66 Charger. Mid 12 second car. I think your asking for trouble keeping the stock axles.

[aarracer]

Originally Posted by lazarus

I snapped a stock axle last year in my '66 Charger. Mid 12 second car. I think your asking for trouble keeping the stock axles.

Lazarus

Do you still have the broken Axle. It would be interesting to see pics of the fracture! Were you using a spool type diff? What's the cars weight? Is it a trans brake car?

Thanks

[RacerHog]

Run Them...There Fine.....

[lazarus]

Originally Posted by aarracer

Lazarus

Do you still have the broken Axle. It would be interesting to see pics of the fracture! Were you using a spool type diff? What's the cars weight? Is it a trans brake car?

Thanks

I still have about a 2" section of the splines on my desk at work. You can see the splines twisting about 1/2" from the break. I have no camera so no pics. I use a Detroit Locker and launch off the convertor at 2000 rpm. Dont know the weight, all steel '66 Charger. 7.80's in the 1/8 mile, it's a big fat slug just something to play with.

[Mopower71]

I had a stock set of axles in my 440 Dart for years, running mid 12's and 8 1/2" slicks, never had a problem with them. The wheel studs are a different story.

[Mopower71]

The 340 Demon I bought did have an axle issue. Before I even ran the car I pulled the axles to find the drivers side axle was twisted at the spline.
I believe they were resplined C body axles.

[Mopower71]

I found the picture

[Mopower71]

The Demon was a 340 4spd car. I wonder now if the axle was fulley seated. It had a sure grip, running green bearings, and the spacer in the center of the rear was never removed.