Twisting drive shafts in two?

[roybeckett13j]

Ok, had this happen twice now, in two weeks...I need answers! *sorry, long post*

Blew up my 355, put in a 14:1 383, with a 500 cfm carb. Had a 6.33 gear, car weighed 3504 pound. First night out ran great, stupid amounts of power.

Second night out, put about 53% wedge into the car, and 140-150 lbs of LR bite...she had some NASTY traction. I could just bury the throttle about halfway through, was carrying the LF half the time. Last lap of the heat...rear end BLEW...UP right at 6900 rpm. Broke the driveshaft. I pulled handfulls of pieces out of the housing...it was dead.

I ordered a new driveshaft from southwest speed, borrowed a set of 6.20 gears, checked for binding, clearance...everything I could think of....and went racing the next saturday.

Made it through the heat race, but had a slight vibration start on the last lap at about 6600. All bolts were tight so we went back out. Hooked HARD the first lap of the feature, then at the end of the front stretch at lap 2 it chucked the driveshaft at about 6400.

Now, my confusion. It looks like the driveshaft was held on one end, then twisted and pulled down until it was two pieces.

A few old racers said its not possible...at all! But is it possible with this big engine, a really good hooking set up and a car that weights 3504 pounds to twist a driveshaft in two?

please give me some input!

[dirttrackrocker]

Sounds to me like your gaining too much pinion angle or something. I don't have any experience with a car that weighs that much, but, I have used Southwest Speed driveshafts for the past couple of years and had 600 + horsepower and never had a problem.

[turner]

We had a similar issue to start the year. We put in a new rearend after about 5 years. Went out and broke driveshaft in two on the first nite.I finally traced everything that i had changed, and it ended up that i had bought a new yoke that was 1.5" longer. It fit fine on the rack, but it was to long and was causing the driveshafts to break. I dont think you are breaking them because of power. I dragrace a 3835 lb buick, and it dynos at 744 hp and 669 lbs tq, and i launch it with slicks and it has alot lower gear than you are running. I have never broken the driveshaft in it.Just have heavy duty u joints.I would make sure your fdriveshaft isnt to long. Good luck and keep us posted.

[racingford]

if you are running trans mount make sure it is solid or at least polly type mount.I had a stock mount in street car once that had enough movement it would get the driveshaft wipping and do just what you are seeing.

[roybeckett13j]

Solid mount on the trans.

When the new one was put in I let the rear shocks loose, and run the car through all the suspension travel it would see, and saw nothing binding up.


Could I just of got a funk driveshaft?

[Egoracing]

Check for anything that it could be hitting. Remember your chassis is NOT rigid and is twisting and if you are lifting the LF something may be getting close enough to hit the shaft. I never had ANY luck running a solid trans mount, broke the trans or drive shaft in every car that had one. The Factory chassis can not be built rigid enough to keep it from twisting. If your car is twisting enough the front could be twisting down and away toward the LF adding a large amount of drive shaft angle.

[DaveBauerSS6]

Urethane trans mount , it's the best of both steel and rubber.

[roybeckett13j]

Car is build super rigid, LOTS of bracing and X's underneath the floor pans.

We were running with some 2970-ish pound cars, with one that weighs 3504. Thats a lot of weight to be moving on the same stuff the people that weigh 500+ pounds less.

[Egoracing]

If you are using ANY part of a production chassis it is not rigid and if the chassis was solid rigid, get rid of it before you die in a wreck as a proper built car is supposed to flex and give to allow the car to absorb impact and not kill the driver. Not to mention that the more rigid the chassis the more precise the setup has to be for EVERY track condition. This is why late models are designed to flex, if not you could never keep up with chassis adjustments during a race much less a weekend. I agree on the urethane mount.

[carowner73]

If you are using ANY part of a production chassis it is not rigid and if the chassis was solid rigid, get rid of it before you die in a wreck as a proper built car is supposed to flex and give to allow the car to absorb impact and not kill the driver. Not to mention that the more rigid the chassis the more precise the setup has to be for EVERY track condition. This is why late models are designed to flex, if not you could never keep up with chassis adjustments during a race much less a weekend. I agree on the urethane mount.

That is some serious bullshiot right there.

[Egoracing]

That is some serious bullshiot right there.

Please explain.

[Dirtman29]

That is some serious bullshiot right there.

I agree with ego on this one, you want the chassis to have some give to it. Build it solid in the 4 point area of the cage (in case of a rollover), but IMO the front & rear of the car should be built (braced) to take a 'moderate' hit, otherwise you can snap your neck if you have a real bad crash.

[sj valley dave]

Professionally built Late Model manufacturer's call them crush zones..The cage is rigid and solid but the front and rear clips are designed to "crush" in a large impact so it does transfer to the driver...

[roybeckett13j]

Car was built, like a racecar should. LOTS of bracing and cage around driver. Bracing under driver, under the floor pans like I said. The center of the car should not be flexing.

The front is built light, not dangerous, but light. The rear has good bracing surrounding the cell...

...How the car is built was not the question.

Is it possible with a heavy car, really heathly engine and a goood setup...to produce the forces necessary to break a driveshaft in two. thanks...

[blncfn57]

Car was built, like a racecar should. LOTS of bracing and cage around driver. Bracing under driver, under the floor pans like I said. The center of the car should not be flexing.

The front is built light, not dangerous, but light. The rear has good bracing surrounding the cell...

...How the car is built was not the question.

Is it possible with a heavy car, really heathly engine and a goood setup...to produce the forces necessary to break a driveshaft in two. thanks...

NO..........