Well, this kinda sucks. Was trying to get a final fun run in tonight to get this pig running right for next weeks HAMB Drags festivities, but nature threw a wrench in the works....or, well, a driveshaft. The car had been having a few problems while trying to get dialed in just about every Friday night for the last month and today it was really cooking. Great throttle response from the new carbs, really coming alive at the top end, and tracking straight as a string on the big end. But tonight, on my second pass, the driveshaft snapped off flush right at the rear yoke. Felt the slightest vibration around the 1000 foot line and BOOM! Twisted that thing in two and the rear half nearly came through the rear floor. Still managed to do a 14.5, which is the best it has run so far...(as embarrassing as that is).Very glad I have a safety loop up front (which is slightly mangled now), but I think I am definitely going to make a loop for the rear this week while I hopefully can find someone willing to make a new driveshaft before next Saturday. Definitely going to do whatever it takes (especially since I just got my packet in this week!). The way the driveshaft broke at the back makes me wonder about the pinion angle, but I checked, checked again, and once more for good measure before I ever took the car on the track for its first run. 3 down in the rear and 3 up in the front with all 4 wheels on the ground. Up until tonight, I never had a vibration and I have made probably 10 or so runs so there isn't too much to go off of, but I do know that the very last run was the first vibration and that was a split second before it came apart. So who knows, maybe some much more knowledgable people could chime in. Have a lot to do this week now. Hoping to see you all there next Saturday!
Sorry about the bad luck. I have used Joplin Driveshaft in the past. Prices were fair and no problems with their work. John
That's a blessing in disguise. Gives you insight on plenty of things. First is you weren't hurt, the safety stuff worked, and you'll race again. Most interesting is that it went faster with the rear 1/2 of drive shaft acting as a nunchuck while eating energy and trying to slow the rear axle/car instead of driving the rear axle. That's something to look at. Breaking a drive shaft with a 14-15 second car wasn't from brute torque. The drive angles should be parallel - for racing and launching static setup is off a bit off so that spring wrap and acceleration force bring the angles parallel. Verbal explanation of pinion angle is better done with pictures .
Could have just been weak at that point. Maybe a pinhole in a weld let water in, and it rusted through from the inside. Only driveshaft I ever broke was on launch, not going down the track. Your's probably broke on launch too, then finished tearing apart as you went farther. The vibration was probably when it started ripping apart.
Thanks WZ JUNK, I am going to try to get in touch with him on Monday. He does great work. He did my driveshaft for my 65 C10 a few months ago. I just hope he's caught up enough to maybe do some fast work. We went ahead and ordered another 52 1/2 inch one from Speedway and if it gets here in time, we will have him balance it. If not, I think it will be good enough for one day for the Drags, then I will just use it as a spare after I get a beefy full size one built. And thank you for your input 31Vicky. And yes, definitely wasn't due to brute force, especially with the humble running a its been doing lately. I am running leaf springs and ladder bars. I was thinking that the rear would stay more in place and help transfer the torque forward a bit but I could be wrong. I checked this morning again and as you said, that rear section acted as a nunchuck and beat everything to hell under there. I am glad it didn't hit a brake line or the fuel pump, filter, etc. could have been a lot worse, that's for sure. Even though it's not a requirement, I am thinking a rear loop is just as important as a front loop. BamaMav, I think you are on to something there. Your explanation makes a lot of sense. I had been working a lot on harder launches and really punishing the burn outs so if there had been a weak weld back there, that could have helped open it up. I would much rather break on launch than at the end of the track again.
Hell yeah! Love the car, and the carnage. 14.50's ain't nothing to be ashamed of, I think everyones' race car is off the pace first few times out. Mine was for a couple years.... Posted using the Full Custom H.A.M.B. App!
rick doesn't have a balancer at Joplin drive shaft, has not for awhile now.... fleet pride out off 249 can balance them , or make you a new one. Ive been using power train industries out in spring field. awesome service, cheap shipping, way cheaper then riving the 1.5 hrs to get it, and usually have it in my hands 2 days after ordering it.
Have you thought about why the car went faster or fastest when it coasted thru the traps after loosing a DS at 1000 feet
I have and I'm thinking I was probably a little past the 1000 ft line. I just remember still seeing the 1320 line when I heard the boom and I took a guess relative to time. After losing the driveshaft I would have immediately started losing momentum, so 1000 ft might not be completely correct. I passed the traps doing 91 at 14.5 if I remember correctly, so I'm thinking if I had not broken, I might have had a lower 14 and closer to 100 mph. It's all bench racing and conjecture now. I'll try to dig up time slip tomorrow because I think the 1000 ft time was 12 something in the mid 80s. If I get all of the variables and sit down, I could probably figure out exactly where it happened.
My thoughts sort of go along the line like this. The drive shaft broke = car went faster. A logical explanation would be you were on a monumental run after some major change, the shaft broke from the extra power and coasting still made the fastest time. Seems to be along what you were thinking. What was that major change ? I didn't see that you mentioned one. Without some major power building change that really doesn't explain it . A comparison to earlier time slips would show you going much faster at all points until the shaft broke and then actually slowing down. A fast enough rate to over come the coast with a faster ET. Another explanation is that due to some circumstance that applies too much conflicting forces into the shaft. The drive shaft could not hold the conflict and broke. Releasing the conflict by breaking the shaft and then the car was free to coast thru at a higher ET Because it was free of this conflict. The flailing drive shaft stub surely was devouring energy and trying to slow the pinion shaft and there fore the wheels yet the car still ETs higher. It's interesting for sure because the car is not going to ET quicker without an increase in positive energy or a decrease in negative energy. You lost positive energy when the connection from the engine separated. Should slow mph and raise Et. You gained negative energy by trying to stop the wheels thru the pinion with a DS trying to be stopped by floorboards and the track, this should also slow mph and raise Et. Hard to explain a drop in ET (going quicker) by inducing negative energy and stoping the flow of positive energy. That is unless an energy conflict great enough to snap a drive shaft dropped a even greater amount of negative energy.
I'm not sure what drive train your running but just glancing thru I tend to agree with 31 Vicky. A week or rusted driveshaft should have busted during initial launch, but drive train binding will kill a shaft at higher speeds. I busted two years ago in a 1946 Chevy with incorrect pinion angle. Dung BOTH FAILURES. I also cracked the transmission bell housing (350 turbo in my case).... SO MY ADVICE IS TO CHECK THE BELL HOUSING FOR CRACKS before you put her back on the road.
Very good points. The thing is, there wasn't a major change other than some more timing and higher octane fuel. None of which would have contributed to the driveshaft directly. As far as the conflicting forces on the driveshaft, I really don't know. I wish I would have checked the driveshaft angle along with my checks of the pinion angle + tailshaft angle, but again, they were at -3 and +3. I know that measurement doesn't really mean much if the driveshaft is still in a bind, but I would have thought that would have killed U-joints before breaking the driveshaft. The driveshaft was a new 52.5 inch shaft from Speedway and I had it dynamically balanced before installation. Also, I had made several runs before and never had an incling of vibration, so I am thinking something along the lines of weak weld at the back and it gave up at high speed, which would have had obvious catastrophic results at that high of RPM. The Speedway driveshaft was smaller in diameter than factory driveshafts so I am curious of the difference of centrifugal force as compared to a bigger factory GM shaft (I picked up an 81 Monte Carlo shaft yesterday). I really enjoy you trying to figure this out with me. Reminds me of my physics classes in college that I haven't really had much opportunity to use since then. For sure man. I was worried about the transmission too. I have been under and over with my flashlight checking for cracks in the housing. Everything appears to be good, but I put more emphasis on the rear of the transmission, so I will take a look up at the bell housing tonight. I was very surprised that the tailshaft housing didn't break. As I stated above, I can't rule out driveshaft binding at all because I am not 100% positive of the driveshaft angle relative to the rearend and transmission, but I never had any vibration until all hell broke loose last Friday. So I am not really sure. It will be checked and confirmed this time though.
Why don't you draw out the -3 +3 orientation. Reason being the Trans should go down to the rear (-3) and the pinion also go down to the rear.(-3) That would be parallel and keeping the Cl of crank parallel with CL of pinion. While under a car measuring these things guys will turn themselves around along with turning the gauge around and then say the pinion is up 3 but leave out the fact the reference changed from down to the rear for the engine and is now up to the front for the rear end. Ill tell you that if you told any fabricator or look at any protractor that you want " -3* and +3* you'd get something like this \ | / They aren't parallel. However if you marked -3 and flipped the protractor over ,,,reading the numbers in reverse ,,, You want to be parallel under acceleration in a drag car. Ok so depending on spring wrap you may need to set pinion static at Zero or something else.
Looking at your pictures it does look as if it broke at or near the welds of the rear yoke. I would definitely check for poor weld penetration or poor fusing of the two components. One other thought on the angle is possibly the pins that locate your axle may have broke and changed your pinion angle.
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