Proof the Opel torque tubes aren't that strong!

[RallyBob]

Found these pics on the German Hecktriebler forum. Ouch! Imagine if that let go on the highway instead of on the dyno.

http://www.opel-hecktriebler-forum.d...6_CIMG2718.JPG

http://www.opel-hecktriebler-forum.d...7_CIMG2720.JPG

http://www.opel-hecktriebler-forum.d...2_CIMG2721.JPG

http://www.opel-hecktriebler-forum.d...4_CIMG2722.JPG

Bob

[namba209]

My God, Bob, that's scary. Wonder where the tube went. There's nothing shown of it except where it bolts to the differential and the forward mount. Any ideas on the cause?

[RallyBob]

Originally Posted by namba209 My God, Bob, that's scary. Wonder where the tube went. There's nothing shown of it except where it bolts to the differential and the forward mount. Any ideas on the cause?

Apparently it had an aluminum outer torque tube, which are inherently weaker. So it probably disintegrated. But the center shaft is what broke it up. Harmonics are usually the issue, and when the center shaft 'whips' it strikes the outer tube. That is why for racing use they will either sleeve the OEM center drive shaft with a tube or make a new one from solid billet steel. It supposedly happened at 6500 rpms from what I could decipher with a 160 HP engine. I presume in 4th gear, as most chassis dynos are run in the gear that is closest to 1:1 ratio.

Bob

[namba209]

I'm glad my dyno run only went to about 5400 RPM in 4th, and I think I've got a steel torque tube. I have noted a minor vibe at around 90 MPH, but I figure that's because my front drive shaft couldn't be balanced, it's so short. Another of the teething problems I've encountered, but an easy fix when I get "a round tuit", with a hose clamp rotated around the shaft until it gets back in balance. A trick I learned from the Gear Vendor folks when they installed one of their units on the motorhome.

[BQS4]

Can you say OUCH!!!!!!

[2 Fast 4 U]

Originally Posted by BQS4 Can you say OUCH!!!!!!

OUCH!!!!!!

[opelwasp]

Bob would cutting the shaft and welding the ends on to some driveline tubing prevent this from happening? I could get it done here for about $75.

[heimue]

The drive shaft in the picture was obviously already reinforced. I got the same one, from Krause Rennsporttechnik (part # HA-00434, 120 Euro). Hopefully, mine holds up in the Kadett! They also have reinforced torque tubes (part # HA-00347, 83 Euro) for racing.

Dieter

[Tru-Craft]

Bob, looks like the maybe the pinion shaft bearings failed?
Or drive shaft out of balance, or U joint failure?
The rotating mass of a shaft at 6,500rpm's is nothing.
Something allowed the shaft to move off center!
Must be a case hardened shaft, sure bent alot, but didn't break.
WOW!
Lyle

[namba209]

Looking at the third pic, it appears the aluminum casting had a crack before the whole tube flew apart. Makes me believe this had been going on for a while. It's still a real scary scenario.

[dcm013]

6500 RPM for that skinny little driveshaft is a LOT! The failure has to do with the driveshaft reaching critical speed and nothing to do with the torque tube itself. Critical speed is the RPM at which the shaft will reach its first bending mode and begin to go into resonance, where ultimate failure results. The torque tube actually prevented catastrophic damage to the floorpan.

It's the reason long wheelbase vehicles like pickup trucks have 2-piece driveshafts and/or large diameter driveshafts. Believe me, I had some first hand experience with this in my past automotive career

Here's an excerpt from the GKN website and a link to the site:

"Every driveshaft has a critical speed. Critical speed is the point at which a rotating driveshaft begins to bow off its
normal rotating centerline.
Driveshafts begin to vibrate as they approach critical speed. If they are operated at near critical speed for an
extended period, they often fail. This can damage the vehicle and possibly injure persons nearby".

http://www.gknservice.com/gkn-ids/re...ion_Guide1.pdf

Don

[jeff denton]

That aluminum casting certainly does appear to have been cracked for some time.
I wouldn't want an aluminum torque tube. My car has been roughed up a little, perhaps you heard about the time the left control rod bracket got ripped out of the floor? Leaving the poor torque tube to take the force of the left side of the rear end being shoved back. It held, but the bolts holding that flange to the diff sure didn't.
There's better ways to reduce both sprung and unsprung weight out back.

[Tru-Craft]

Originally Posted by dcm013 6500 RPM for that skinny little driveshaft is a LOT! The failure has to do with the driveshaft reaching critical speed and nothing to do with the torque tube itself. Critical speed is the RPM at which the shaft will reach its first bending mode and begin to go into resonance, where ultimate failure results. The torque tube actually prevented catastrophic damage to the floorpan. It's the reason long wheelbase vehicles like pickup trucks have 2-piece driveshafts and/or large diameter driveshafts. Believe me, I had some first hand experience with this in my past automotive career Here's an excerpt from the GKN website and a link to the site: "Every driveshaft has a critical speed. Critical speed is the point at which a rotating driveshaft begins to bow off its normal rotating centerline. Don

Don, I agree a long, un-balanced drive shaft located with old/ worn U-joints and high twisting tourque loads could fail in time.
I had a Chevy truck that the U-jouint broke under a towing load, but it was old.

But a 150hp modified Opel motor driving a 2,000 lb car, through a short steel drive shaft, and a short steel pinion shaft and steel torque tube............no way!
Unless something was cracked, worn, damaged or un-balanced.
The rubber locating bushings in the torque could have been bad also.

If GM thought that the pinion shaft would fail at 6,500rpm they wouldn't have a redline of 6,000. I've had my GT to about 140mph/7,000rpm.
A well supported shaft could probably take 10,000rpm.......200mph in a Opel, Bonneville here we come!

I machine custom 5/8" diameter "soft aluminum" shafts varying in length from 2-3ft.
Machine rpm is above 4,000 with a cutting tool side load. They don't bend unless the tool pressure pushes the shaft off center.

For sure, something failed, the shaft was allowed to move off rotating center line, twisted under load and bent.
I am not worried about the pinion shaft failing.
Anyone racing a classic car should be checking parts for cracks, replacing all bearings, bushings and balancing everything.
Just my opinion.
Lyle

[RallyBob]

Originally Posted by opelwasp Bob would cutting the shaft and welding the ends on to some driveline tubing prevent this from happening? I could get it done here for about $75.

Chris, I just weld some DOM steel tubing onto the existing torque tube. I remove the forward yoke, then chuck the t/t shaft into a crankshaft grinder. I grind a small step on the rear splined end to allow the tube (1.75" x .125" wall) to center itself on the t/t shaft. The forward section is tricker, but I get it centered via shims and weld it in one quick pass (after thorough tacking). Then a trip to the balancer is necessary (my friend lets me use his crank balancer), and weld on a few weights as needed.

Bob

[RallyBob]

Originally Posted by jeff denton That aluminum casting certainly does appear to have been cracked for some time. I wouldn't want an aluminum torque tube. My car has been roughed up a little, perhaps you heard about the time the left control rod bracket got ripped out of the floor? Leaving the poor torque tube to take the force of the left side of the rear end being shoved back. It held, but the bolts holding that flange to the diff sure didn't. There's better ways to reduce both sprung and unsprung weight out back.

For hardcore racing, the steel IS the way to go. But mostly just for the cornering loads as a suspension link. In circle track, you will not see 7000 rpms in 4th gear! So the driveline speed is relatively low, therefore the t/t shaft critical rpms won't be seen in 2nd gear.

[RallyBob]

Originally Posted by Tru-Craft But a 150hp modified Opel motor driving a 2,000 lb car, through a short steel drive shaft, and a short steel pinion shaft and steel torque tube............no way! Unless something was cracked, worn, damaged or un-balanced. The rubber locating bushings in the torque could have been bad also. If GM thought that the pinion shaft would fail at 6,500rpm they wouldn't have a redline of 6,000. Iv'e had my GT to about 140mph/7,000rpm. For sure, something failed, the shaft was allowed to move off rotating center line, twisted under load and bent.

You're correct in the sense that if all were perfect, there should not be any issues. Especially with a stock engine (which is all they were designed to handle) and rpm range.

But as you've also said, any variables otherwise can cause it to fail. A swapped driveshaft, a bad u-joint, a worn t/t bushing, or putting too much power into it. If for example, you hammered the car from a standstill one too many times, and put a 'tiny' twist into the t/t shaft, then the next time you run the car to 140 mph+ the rpms and the new t/t shaft imbalance can certainly cause an issue. The shaft diameter is small for sure, so there is little to keep in in line with the application of torque and rpms simultaneously. It will bow, and at some point the bow throws the balance off even more, and then failure.

Bob

[BQS4]

I'm by no means an expert on what ya'll are talking about here, but, I do know, from all my years of driving Opels, not racing, is that the cupped end, at least that's what I call it, the end that fits inside the diff itself, is in itself a weak point. In the pics of Bob's, you can see where the cup is split in several places. Now I don't know if that's what actually caused the whole thing to fail, but, I have pulled a few out of stock street cars that were split.
JMTCW

[Tru-Craft]

Good eye BQS4, I rebuilt my torque tube 3-4 years ago, didn't see any cracks but wasn't really looking that close.

Like Bob said, the drive shaft/ pinion shaft assembly should be fine for our slightly modified Opel's. My GT see's 7,000 for about 10 seconds.
Even most SCCA classic racing Opel's wont see more than 135mph top speed, depending on the track.
The steel torque tube is a good way for the race Opel's to keep all the parts from flying all over the track!
For racing adding a tube is a good easy fix, not adding much rotating mass either.

Bob's Bonneville car won't be able to run the Opel setup, 9,000-9,500rpm sustained high load!? Depending on gear/tire circumference.
That Opel shaft will bend for sure.
Opel did a good job of keeping the parts light, strong enough and inexpensive.
Lyle

[jeff denton]

Originally Posted by RallyBob In circle track, you will not see 7000 rpms in 4th gear!

Oh yeah? What if we were running the superspeedways like Daytona or Talladega?