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lust4speed · 02-28-2005, 09:45 PM

We were running the red '67 GTO on the chassis dyno at the automotive technical institute, and had completed two abbreviated runs without incident. We then went pedal to the metal on a full load 3,000 to 6,000 run in high gear. At 5,300 RPM and 129 MPH all hell broke loose. Half a driveshaft makes a fair amount of racket coasting down from that speed as it thrashes the underside of the car. Surprisingly, the 3" exhaust system took almost all of the blunt trama, and while the exhaust pipes were squished flat, the floorpan suffered very little. The driveshaft safety loop held the force for awhile until the bowing driveshaft became too short to stay inside. The trans totally seperated around the bellhousing and in front of the tailshaft area. Note that the driveshaft had absolutely no rust, and there was no vibration at all until the instant catastrophic failure. Totally destroyed was the Turbo 400 trans, stock driveshaft with HD universal joints, and the 3" exhaust system.

Sort of like the chicken-or-the-egg-debate trying to figure out where the problem started. Best guess is either a C-clip broke allowing the universal to slide over starting the imbalance, or the driveshaft bowed and started the failure. Scary thing is this is our cruiser running nothing more than a healthy 400 -- and I now cringe when I think about the blue goat running the 4-speed and 428 also with the stock driveshaft.

lust4speed · 02-28-2005, 09:45 PM

We were running the red '67 GTO on the chassis dyno at the automotive technical institute, and had completed two abbreviated runs without incident. We then went pedal to the metal on a full load 3,000 to 6,000 run in high gear. At 5,300 RPM and 129 MPH all hell broke loose. Half a driveshaft makes a fair amount of racket coasting down from that speed as it thrashes the underside of the car. Surprisingly, the 3" exhaust system took almost all of the blunt trama, and while the exhaust pipes were squished flat, the floorpan suffered very little. The driveshaft safety loop held the force for awhile until the bowing driveshaft became too short to stay inside. The trans totally seperated around the bellhousing and in front of the tailshaft area. Note that the driveshaft had absolutely no rust, and there was no vibration at all until the instant catastrophic failure. Totally destroyed was the Turbo 400 trans, stock driveshaft with HD universal joints, and the 3" exhaust system.

Sort of like the chicken-or-the-egg-debate trying to figure out where the problem started. Best guess is either a C-clip broke allowing the universal to slide over starting the imbalance, or the driveshaft bowed and started the failure. Scary thing is this is our cruiser running nothing more than a healthy 400 -- and I now cringe when I think about the blue goat running the 4-speed and 428 also with the stock driveshaft.

LouisianaGuy · 02-28-2005, 10:04 PM

Well dont feel too bad I dropped the sprag in my TH350 today :/ Getting it out tomorrow and having it rebuilt to go back in Thursday so I can make it to the track on Friday

On another note I had the exact same thing happen to me doing 130 mph down the interstate in a friends chevelle ...dropped the front U-joint with no safety loop...needless to say there was only about 1 foot of drive shaft left when we stopped...and no damage to floor pan or exhaust system, shaft dug in and got chewed up.
You may wana check your pinion angle out, it may be off some seen cases crack like yours did at the top...as matter of fact the same Chevelle cracked a case like that and pinion angle was off a good bit, we corrected it and havent broken any more cases.
Sorry to hear about your loss.
Mike

Ryche400 · 02-28-2005, 10:30 PM

Same thing happend at my buddy's shop a few weeks ago. They were dynoing a guys 2002 Chevy P/U. The guy had just done a cam swap and wanted to check out the improvement. All was fine, until about 5500 RPM, the driveshaft let go. For no appearant reason. The truck only had about 20K miles. Hey, Sh*t happens sometimes we cant explain... Luckily nobody got hurt....

uneasyrider · 03-01-2005, 05:22 AM

Way back in 1969 we were on are way home from a picnic outside Eugene OR when we had a U-joint break at ~125mph in a '65 Catalina. I was 4yrs old and I can still remember it! My mom, aunt, and I were singing and the louder we sang the faster my dad would go. We were on a four lane highway and when we hit about 120mph my dad put it to the floor. A second later it felt like I was in a cannon. The car jumped about 1ft in the air shoving me and everone else of course down into the seat so had I think my butt slammed against the floor board. The people behind use said that all four wheels were six inches off the ground. My dad let the car coast down keeping it between the shoulders until we rolled to a stop. The back of the tranny had broken off and tranny fluid had spred all over the back tires and all under the car. WHAT A RIDE! I can tell you that everyone was singing a different tune.

Txbobcat · 03-01-2005, 05:28 AM

Wow glad you werent on the road doing that test

JEFF KING · 03-01-2005, 05:49 AM

WOW.. Inside the shop that must have sounded like pure Hell!!
I've Seen this before, infact I have a driveshaft that looks like it, s sister. It, s the product of slicks and too good a Hook.
Torque is twisting force and when it finds an easy way out you get the carnage you have now.
Still it never fails to amaze me.
Sorry about your Loss.

Half-Inch Stud · 03-01-2005, 07:48 AM

Failure Mode looks to me the "Safety Loop" cut the driveshaft. Engine&Exhaust Vibration may gotten the Safety Loop into a Tuning Fork mode.

HIS

ponjohn · 03-01-2005, 12:46 PM

im not familiar with the operation of chassis dyno- does the operator establish the amount of load? See what i am getting at.....?

Ryche400 · 03-01-2005, 04:44 PM

No, the car is strapped onto some "Rollers". The back tires turn the drums, and the computer anylizes it, and gives you the results. I had a similar incident at the track years ago. I took off hard, and felt a slight vibration. But me being young and foolish, didnt let off. As soon as I let off at the end of the 1/4, I hear, and feel a loud bang under the car, then all hell breaks loose. After I coasted to a stop, I looked under the car, the driveshaft was nowhere to be found, and half of the tranny was hanging, almost touching the track. Ended up costing me a new tranny, driveshaft, exhaust system, flywheel, starter, and broke a small chunk of the block off.... Been there, done that, and bought the t-shirt..

Billy177 · 03-01-2005, 07:49 PM

what rear end gears did you have? just trying to get an idea of how fast teh driveshaft was spinning

Ryche400 · 03-01-2005, 08:16 PM

I only had 3.73's, but I was running a 26x10.5 ET Street. Damn those things hook. Also I was running Nitrous, so I had alot of MPH. I crossed the lights at 113. Also Stock driveshft, which I kick myself in the ass over. But you live and learn.

beamy45 · 03-02-2005, 06:12 AM

ive heard of these stories happening, but this is the first time ive ever seen what it looks like.
scary!

Half-Inch Stud · 03-02-2005, 06:16 AM

Strappin-down makes me think the Driveshaft was brought real close to the Safety-Lathe-Loop.

Signatures below all featured Stock Driveshafts (11.0 was a reweld unit)..and slicks.

Skip Fix · 03-02-2005, 07:08 AM

Another potential cause , strapping down may have shoved the driveshft into the tranny a little more. Might double check that on teh next one.

Rugratman · 03-02-2005, 07:13 AM

Your lucky the engine didin't over rev and blow that too.

ponjohn · 03-02-2005, 10:51 AM

yes but there has to be resistance- without resistance the there is no hp or tqe made.

It would like putting an engine on a dyno with no load.

lust4speed · 03-02-2005, 12:23 PM

I just recently replaced the MSD 6A box with a 6AL box with the limiter. The next day at work the thought occurred to me whether the untested limiter had worked as advertised. It was tough waiting out the remainder of the work day so I could get home and fire it up -- and yes, the limiter did work. I would bet that since the engine was already at 5,300 at full throttle load and basically snapped into neutral, that it was firmly up against the 6300 RPM chip.

I installed the safety loop a dozen years ago, and it is located just behind the front universal and actually touches the underside of the floor, and has plenty of clearance from the driveshaft. The transmission, 10 bolt posi rear, and the driveshaft are (were?) original to the car. The car has air bags, and the height after being strapped down looked normal - and there were two runs made previously without any strange noise or vibrations. Only marks on the driveshaft were made by the two stock safetybelt bolts that protrude through the captive bolts on top of the tunnel. Pictures are on the home computer, and I'm at work or I could post the shot of the underside of the car.

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