Rear end advice for racing with a 4 speed

[340MPR]

Hey guys,

I just got into drag racing my 69 dart last year broke my first parts, the rear end crapped out on me. My car has a 340 that makes 440HP at the crank, 4 speed, 741 case 8-3/4 rear end with 3.91’s, Mickey Thompson ET Street SS tires. After taking the rear end apart I found that the drivers side axle splines twisted and the inner side gears of my sure grip were wiped along with that portion of both axle splines, the outer side gears were fine. To get the car back in action and to make the last race of the season I rebuilt the sure grip with new, one piece side gears, new clutch plates, and found an old pair of factory axles. The ‘66 dated ring and pinion looked to be in good shape and I left them as is.

The last race of the the season was just this past weekend and I raced without issue and now I want to properly come up with a game plan. A lot of the local mopar guy’s think that the 8-3/4 will do just fine for my power level and that I should just get a new pair of axles and keep running it. I will say that they all run automatic’s and aren’t racing a 4-speed. I talked with Dr Diff and Cass figures if I’ve twisted axle splines than it will happen again, even with new axles so he’s leaning me towards a dana60.

I made around 50 passes last year and about the same this year and I’m hoping to keep that pace up. Down the road I’ll probably get slicks for the car and maybe coax some more power out of the car but nothing too drastic. It’s a true street/strip car.

I appreciate any advice from guys who race 4 speeds, thanks. Mike N

 

[ch1ll]

While a Dana is going to hold up to slicks and a glued track, your going to notice the heavier rear end while on the street. It’s not going to handle as well. Usually the weak spot on an 8 3/4 is that the housing flexes and that can be solved to a point by bracing the back side, but that may not be your problem. Race duty axle’s may solve your problem. A Chrysler 9 1/4 rear axle while still is heavier than an 8 3/4 rear axle may be an option.

It’s always a compromise for a street/strip car. Either you give up street manners for racing durability or you live with parts fatigue while racing for street manners.

 

[lead69]

A lot depends on the type of clutch you are running, if you don't have an adjustable one than check out the clutch tamer @weedburner . I went with a dana 60 @Newbomb Turk s advice since he figured I would be stepping up the power levels later and it turned out to be sooner so he was right.

 

[PROSTOCKTOM]

If want to save yourself a lot of time and money put a Dana 60 or 9" Ford in there with 35-spline axles and you'll never have to think about issues again.

Tom

 

[AJ/FormS]

I got about the same power, but I don't race. Well one day I did, back in 2004. I made 4 passes on an old airport runway, no prep. Car went 93 in the Eighth.

My axles are Resplined C-body axles, in a narrowed rear; I don't have your kind of problems.
I gotta get me a pair of those tires!
What else are you running back there?

 

[GTX JOHN]

I would suggest the Dana 60 for sure.

When I ran a 440 4 Sp 1970 Barracuda Gran Coupe back
when they were new, I broke several 8 3/4s
the first year until I sprung for a Dana.

I do not think you will notice the weight difference very
much.

 

[PROSTOCKTOM]

I do not think you will notice the weight difference very much.

People argue and fight about this all the time. The bottom line is a Dana 60 will weigh more, but that weight is also putting more weight on the tires.

So you actually get better traction because of it. If you do it right a Dana 60 can be done very reasonably.

Tom

 

[72bluNblu]

While a Dana is going to hold up to slicks and a glued track, your going to notice the heavier rear end while on the street. It’s not going to handle as well. Usually the weak spot on an 8 3/4 is that the housing flexes and that can be solved to a point by bracing the back side, but that may not be your problem. Race duty axle’s may solve your problem. A Chrysler 9 1/4 rear axle while still is heavier than an 8 3/4 rear axle may be an option.

It’s always a compromise for a street/strip car. Either you give up street manners for racing durability or you live with parts fatigue while racing for street manners.

Adding a Dana will not hurt handling or street manners.

These cars are all nose heavy in stock trim or anything close to it, and better balance improves handling far more than a small increase in overall weight will hurt it. If anything the Dana will improve F/R weight bias and may even lower the CG a smidge.

There’s a small increase in driveline losses, but that would hardly be noticeable, if noticeable at all, on the street.