8.75 rear end/ axle questions?

[daytona kid]

Due to budget cuts I'm am going to have to use the 8.75 rear end that came in my 68 charger. I'm hoping to get a 500hp, or so, motor for it in the near future. My questions are #1- Are my stock axles going to be ok as far as nhra legal and able to hold up to the power? #1.1- If not, what's the best deal for the dollar on stronger/legal axles? And #2- Do I need to install some special lug studs for nhra or the power? #2.1- If so where's the best deal on those?

 

[383man]

I can tell you I am still running stock axles on my 63. I do want to upgrade but they have never said anything about them at the track. If your cars an automatic it will be much easier on the axles then if you have a four speed. My 63 is an auto with a Dynamic 9.5 converter that will flash to about 4200. Ron

 

[bobtile]

If youre running a stock 727, you'll break it before the rear or axles. That power should put you in the 11's with thatt car. You won't need aftermarket axles. Ask me how I know

 

[daytona kid]

If youre running a stock 727, you'll break it before the rear or axles. That power should put you in the 11's with thatt car. You won't need aftermarket axles. Ask me how I know

Thanks, I assumed the trans would need some mods., I'll research that and mod as needed, when I get to it., trying to button up the rear end now..
And don't your lug studs have to be bigger or longer for nhra? Anybody know the details on that rule?

 

[Cranky]

Running a spool? If so, aftermarket axles should be in your budget. How fast do you plan on going? Been awhile since looking at a rule book but iirc, 10.99 and faster dictates them according to the NHRA....

 

[Budnicks]

I can relate to a budget, especially lately,
I'd highly suggest getting a rule book for the class/ET you planning/expecting on running...
Some classes/et's as soon as you dip into the 10's IIRC, all faster classes require hardened & more even splines,
than stock type 30 spline 8.750" axles, depending on et's/class...

Stock axles may live just fine, for a while,
you may get away with it in tech for a while too,
it's not 1970's anymore thou, safety & reg.'s have changed,
it really depends on what track, even what tech official you have & what type event, local or a national event
& even on how much bite you actually get, how heavy the final car is & how much HP/TQ you will actually have...

I've ran them {stock axles} on some relatively fast cars that went into the 9's occasionally, that weren't really raced regularly,
that were more of a street/strip type cars, with relatively stock type rear suspension or leafs w-CalTracs & w-drag radials
or that didn't have a big wide &/or tall "racing slick"...

IMHFO If it's a dedicated racecar, especially with racing slicks,
it really should have some good hardened axles & lugs...
cheap insurance/safety issue...

NHRA approved hardened Axles aren't "really" that expensive,
in the scheme of the overall costs of building your car,
they start about $350-$400 a pair,
custom lengths & more splines are more $$,
Yukon Axles are relatively cheap try Mancini Racing maybe,
or Strange Engineering,
Mark Williams,
Moser,
Summers Brothers,
Doctor Diff maybe,
{Currie Ent ?, not sure if they have any for 8.750" Mopar's}
Google search; Racing Axles
all have different alloy axles, drilled or solid & various different splines, studs & nuts...

If you run Racing Slicks or Drag radials, you have {Mandatory} to run open ended lug nuts
& the studs must stick outside the nuts, appr. the same distance as the diameter of the studs, in the rear,
depending on what types/thickness of wheels, will dictate what length of studs you will need to run...

 

[daytona kid]

Running a spool? If so, aftermarket axles should be in your budget. How fast do you plan on going? Been awhile since looking at a rule book but iirc, 10.99 and faster dictates them according to the NHRA....

Excuse my ignorance, but what is a spool?

 

[Cranky]

A spool is a solid diff (carrier) that takes the place of a limited slip unit (Sure Grip) or an open diff. The ring gear bolts to it and then the axles are installed and then everything is locked up. No differential action what so ever.

 

[daytona kid]

Ok, no I'll be running a posi-trac unit.

 

[Hemi Rebel]

A sure grip.

 

[daytona kid]

OK, didn't know the proper name, thnx. My stock chunk is a limited slip, or one wheel drive, I believe. With the wheels off the ground, I turned them and they spun in opposite directions. I have found a sure-grip chunk in a used speed shop for about $300. It's spline sockets turn the same direction when you spin one., so that makes it a sure-grip, right? So are my assumptions correct here? Is there another sure way to tell which is which? And is that a decent deal for the sure-grip chunk?

 

[actionange1]

OK, didn't know the proper name, thnx. My stock chunk is a limited slip, or one wheel drive, I believe. With the wheels off the ground, I turned them and they spun in opposite directions. I have found a sure-grip chunk in a used speed shop for about $300. It's spline sockets turn the same direction when you spin one., so that makes it a sure-grip, right? So are my assumptions correct here? Is there another sure way to tell which is which? And is that a decent deal for the sure-grip chunk?

Yes both spin same direction it's a Sure Grip.
Price is usually dictated by gear ratio and casting #. Last 3 digits on the side of the chuck:
742- 1 3/4 pinion- up to 1968/69 clutch type unit
489- 1 7/8 tapered pinion 69/70 and up cone type unit
741- weakest chuck- stay away
$300 is great price if it is on of the first 2 listed above

 

[Budnicks]

Excuse my ignorance, but what is a spool?

here's an example Yukon Spool for the 8.750" rear $179.95 from Mancini Racing

 

[Cranky]

Yes both spin same direction it's a Sure Grip.
Price is usually dictated by gear ratio and casting #. Last 3 digits on the side of the chuck:
742- 1 3/4 pinion- up to 1968/69 clutch type unit
489- 1 7/8 tapered pinion 69/70 and up cone type unit
741- weakest chuck- stay away
$300 is great price if it is on of the first 2 listed above

What makes the 741 so weak? Magazine stories is the answer. How many of these have you seen broken at the gear head of the pinion? I've never seen one broken at the so called weak spot. The weak spots on any 8 3/4 3rd member is the gears then the next weak spot is where the yoke fits. Please send me all the 41 units instead of throwing them away. Thanks.

- - - Updated - - -

OK, didn't know the proper name, thnx. My stock chunk is a limited slip, or one wheel drive, I believe. With the wheels off the ground, I turned them and they spun in opposite directions. I have found a sure-grip chunk in a used speed shop for about $300. It's spline sockets turn the same direction when you spin one., so that makes it a sure-grip, right? So are my assumptions correct here? Is there another sure way to tell which is which? And is that a decent deal for the sure-grip chunk?

A Sure Grip is the Mopar name for it's 'posi' units and is a limited slip unit just like a PosiTrack is GM's name for their limited slip unit. An open rear where one wheel spins is not a limited slip rear. Can you post of pic of the back of the chuck you found?

Btw, even an open rear drives both wheels on a level surface with equal amount of grip on the road way until one wheel loses traction and then that wheel will spin but the reason why the passenger wheel spins when power is applied on a level surface is because the rear end tries to torque over counterclockwise and tries to lift the right side wheel which will then let it spin.

 

[daytona kid]

So, if the chunck that I'm thinking of buying is a good # sure-grip, Is it going to be ok with 500hp & auto trans. Or is it going to spin one tire and go into the wall or something detrimental to my drag strip racing plans? I do want to be able to drive it on the street also, very little tho probably.

 

[Cranky]

A tight SureGrip should work well on the strip. I maintain a cone type unit (there's a clutch type too) for a buddy with a 6 pack fully loaded Challenger that's fairly heavy and it runs mid/low 11's. In the past 15 years, I've machined the cones twice and added shims the 2nd time and so far, it's still working well. He doesn't run it every weekend nor does he drive it on the street that much but from what he does run at the track (with slicks) is pretty rough on it. They were not designed for that type of abuse but with proper maintenance, they can hold up. Just make sure when you feel it not working right, don't keep hammering it and chances are you won't feel it spinning one wheel. You just about need to have someone paying attention to you when you do your burnout.

 

[747mopar]

So far so good with my factory posi, I'm somewhere in the 500hp area and it leaves nice posi burnout every time haha. I learned something new helping Kahn search for a posi at the Nats, you want the old clutch style posi because the newer cone posi's aren't rebuildable. The cone digs into the housing so when it's done it's done, you can spot this style by looking threw the opening where you'll see a plate and springs inside.

.

- - - Updated - - -

O'K cranky just posted at the same time and it appears you can machine them but the older style is just a simple rebuild. These guys know more about it than me but I'm pretty happy with mine so far.

This is the cone style



This is the older clutch style

 

[womanator]

Not arguing here.
But 100 plus pass's into the 10's with a 741 case 4.10 gears.

 

[Photon440]

Daytona Kid, the NHRA doesn't really care if you have 500hp, or 600 or 200. They care about speed and times. If you break 10.99, they require aftermarket axles.

 

[nitrojunkie]

As a point of interest didn't the early Ramchargers run the 741 case? I think they were only 9" tires and run low to mid 12's. Somebody correct me if Im wrong.