Broken Driveshaft
10-26-2004, 11:37 AM
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Broken Driveshaft
Has anyone had their driveshaft break? The mechanic called it the "Stub Axle", but it's part of the driveshaft. I broke mine in last weekends DE. The strange part is that I broke the wheel bearing about a month ago and had everything replaced (driveshaft and wheel bearing). Anyway, coming out of the fastest turn, I felt as if I had a flat. As I rolled into the pits, the car suddenly came to a stop, like I had the brakes on. When I put it in gear and let go of the clutch, nothing happened (I don't have a LSD). When I went back and looked at the wheel, it was only being held on by the caliper. The part of the drive shaft that goes through the carrier (the part with the teeth) was missing, including the nut.
What do you think could have caused this? Too much or too little torque on the nut? I'm baffled as it was a brand new driveshaft.
George
What do you think could have caused this? Too much or too little torque on the nut? I'm baffled as it was a brand new driveshaft.
George
10-26-2004, 06:57 PM
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The nut must have come loose prior to the stub axle part of the drive shaft snapping off. Once the nut is loose, the stub axle is loaded in bending. Since it is not made to be loaded in bending it fails pretty quick.
Before you yell at the mechanic, be advised that the wheel bearing nuts come loose even when they are properly torqued. After a bearing replacement, the nut should be checked again after one session in case one of the parts moved a little. Once this is done, the nut probably won't come loose again.
The nuts on the left side of the car will eventually come loose if they are never checked. Porsche provides a system to prevent this on its more sporty models.
Chris Cervelli
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Before you yell at the mechanic, be advised that the wheel bearing nuts come loose even when they are properly torqued. After a bearing replacement, the nut should be checked again after one session in case one of the parts moved a little. Once this is done, the nut probably won't come loose again.
The nuts on the left side of the car will eventually come loose if they are never checked. Porsche provides a system to prevent this on its more sporty models.
Chris Cervelli
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10-26-2004, 08:18 PM
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Yeh... what Chris said;
Stub axle failures are VEEEERY uncommon, and usually only happen when something is loose or severely worn. Since it all was new, I would think as does Chris.
With all new parts, it is not unheard of for them to not be familiar enough with each other to take a good set. With any suspension piece, I usually like to give it another tweak after the first session since it has been apart. This goes TRIPLE for new parts. A little stress on new stuff has a tendancy to free it up. Old experienced parts are usually ornery; taking a set, never to budge.
Bummer, but At least you didn't trash the car.
Stub axle failures are VEEEERY uncommon, and usually only happen when something is loose or severely worn. Since it all was new, I would think as does Chris.
With all new parts, it is not unheard of for them to not be familiar enough with each other to take a good set. With any suspension piece, I usually like to give it another tweak after the first session since it has been apart. This goes TRIPLE for new parts. A little stress on new stuff has a tendancy to free it up. Old experienced parts are usually ornery; taking a set, never to budge.
Bummer, but At least you didn't trash the car.
10-26-2004, 09:34 PM
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Thanks guys. That does make sense. I am going to be re-checking new parts from now on. I'm just really happy nothing "bad" happened, and not upset with anyone. I heard several different theories at the track and just wanted some more opinions.
Chris, do you have upgraded driveshafts on your 993? I've heard that the cupcars came with extra hardware that would prevent the nut from coming off.
George
Chris, do you have upgraded driveshafts on your 993? I've heard that the cupcars came with extra hardware that would prevent the nut from coming off.
George
10-27-2004, 07:42 AM
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I run RSR axles in all my race prepped 993s. They are shorter, which allows the axle to remain in the comfortable part of the CV's range at extremely low heights. Also, the inner CV joint is tougher and more expensive. The shorter length makes installation and removal much easier as well. The part you had trouble with is no different.
The Cup car Centerlock parts do 100% prevent the axle nut loosening, as Phil said. Putting these on a non-Centerlock car would be possible but expensive. I can get you a set of locknuts which will prevent this from ever happening again. The locknuts are cheap and easy.
Are you going to NPR? If so, I can install them on your car there. I am leaving for Sears Point today and will return on Nov 2.
Chris Cervelli
Premier Motorsports
The Cup car Centerlock parts do 100% prevent the axle nut loosening, as Phil said. Putting these on a non-Centerlock car would be possible but expensive. I can get you a set of locknuts which will prevent this from ever happening again. The locknuts are cheap and easy.
Are you going to NPR? If so, I can install them on your car there. I am leaving for Sears Point today and will return on Nov 2.
Chris Cervelli
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10-27-2004, 08:00 AM
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In my old 935 I snapped 2 stub axles clear off. However, that was due to power, grip (big slicks), and age of the stub axles. Funny thing that they both happened in the same turn on the same track. They happened right when the car is loaded and exiting the caroussel at MidOhio.
Additionally, I saw someone snap one on a normally aspirated RSR replica type car a Putnam a few weeks ago too.
Since I run high HP cars, I proactively now replace just about everything including stub axles both inner and outer as well as the axles & CVs. Boy are GT2 axles expensive :-)
Breaking due to torque and load is much less of an issue on lower HP cars. As Chris mentioned, it is most likely loosening up that causes those problems...
Just thought I'd mention my experiences.
Norm
Additionally, I saw someone snap one on a normally aspirated RSR replica type car a Putnam a few weeks ago too.
Since I run high HP cars, I proactively now replace just about everything including stub axles both inner and outer as well as the axles & CVs. Boy are GT2 axles expensive :-)
Breaking due to torque and load is much less of an issue on lower HP cars. As Chris mentioned, it is most likely loosening up that causes those problems...
Just thought I'd mention my experiences.
Norm
10-27-2004, 10:47 AM
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Norm,
That's interesting because I talked about it with a couple of friends and they actually think it might have been over-torqued and eventually snapped. I'm not looking to lay blame, I just want to figure out what happened. I wish we would have found the bolt. They had the corner workers looking for it, but they found nothing.
Here is the scenario: I just put on a new to me set of Dunlop slicks because the Pirelli slicks I had been using picked up a vibration in the front. The car felt smooth as butter. I remember thinking to myself how good it felt. Now, I was right at the apex of the fastest corner, when I felt the backend come out from under me. It felt like a violent snap. I had no vibrations, no nothing, before that turn and the turn in was smooth. It was the loaded side (right rear on a left turn). That means I would have lost the nut on the previous right hander (I was told that it must have happened when the wheel was unloaded, as force was pushing it out. I actually question this part). The problem is that I went through two left turns (there are actually three, but I take two as one) after the last right. That means I would have traveled a third of the track without the nut. Is that possible? Wouldn't I have felt it? Or do you think that the snap I felt was nut coming off and the stub axel broke off afterwards? Luckily, pit entrance is about 50 yards after where this happened.
George
That's interesting because I talked about it with a couple of friends and they actually think it might have been over-torqued and eventually snapped. I'm not looking to lay blame, I just want to figure out what happened. I wish we would have found the bolt. They had the corner workers looking for it, but they found nothing.
Here is the scenario: I just put on a new to me set of Dunlop slicks because the Pirelli slicks I had been using picked up a vibration in the front. The car felt smooth as butter. I remember thinking to myself how good it felt. Now, I was right at the apex of the fastest corner, when I felt the backend come out from under me. It felt like a violent snap. I had no vibrations, no nothing, before that turn and the turn in was smooth. It was the loaded side (right rear on a left turn). That means I would have lost the nut on the previous right hander (I was told that it must have happened when the wheel was unloaded, as force was pushing it out. I actually question this part). The problem is that I went through two left turns (there are actually three, but I take two as one) after the last right. That means I would have traveled a third of the track without the nut. Is that possible? Wouldn't I have felt it? Or do you think that the snap I felt was nut coming off and the stub axel broke off afterwards? Luckily, pit entrance is about 50 yards after where this happened.
George
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10-30-2004, 01:58 PM
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George A (Hey, Neighbor), can you attach a macro photo of the end of the broken stub? The photo might help analysis if it was result of over-torque or a loose fastener. Essentially, if it is a very smooth break (looks like a lathe cut with a tit in the center), that is a an axial break (no pun). This is from mis-alignment or incorrect loading. If is is a relatively rough break, over-torque could be the culprit.
Kevin-Richardson
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10-30-2004, 04:06 PM
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Kevin,
Here is a pic I took today. They haven't started working on it. I wanted to take some pics with the wheel off. I'll take some more when I go back.
BTW, if you look closely, you will notice that the hub is broken. Now, could the hub have broken first?
The end of the axel looks smooth, so I guess it's mis-alignment or incorrect loading. Let me know what you think.
Here is a pic I took today. They haven't started working on it. I wanted to take some pics with the wheel off. I'll take some more when I go back.
BTW, if you look closely, you will notice that the hub is broken. Now, could the hub have broken first?
The end of the axel looks smooth, so I guess it's mis-alignment or incorrect loading. Let me know what you think.
Last edited by George A; 10-30-2004 at 08:27 PM.
10-31-2004, 07:00 PM
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George,
The photo supports what Chris Cervelli and John Hajny said at the beginning.
Let me clarify, I have never experienced this *particular* failure, and my statements were based on generalities for metal fatigue/failure. It does appear over-torque was not the problem for the stub. The exposed stub end does not exhibit the typical appearance of tension or torsion failure, but of axial/rotational bending. The alignment/loading scenario comes in as the hub slides on the spline applying greater pressure on the end of stub axle, causing the stub failure, leading to the cracked hub.
One thing that does catch my eye, is the battered appearance of the washer bearing surface, further supporting a loose fastener. This indicates the hub and washer slapping around.
The cracked hub poses an interesting chronolgy of failure. Examining your photo, I cannot ID the crack. I do see an area inside the splined area and on the outer edges of of the hub bore.
A couple of questions:
1) Did you experience any handling anomalies prior to the "flat" sensation
2) Was the retainer castlleated or of a ny-lock/crimp-lock type?
Anyway, my $0.02. Good luck!
Kevin
The photo supports what Chris Cervelli and John Hajny said at the beginning.
Let me clarify, I have never experienced this *particular* failure, and my statements were based on generalities for metal fatigue/failure. It does appear over-torque was not the problem for the stub. The exposed stub end does not exhibit the typical appearance of tension or torsion failure, but of axial/rotational bending. The alignment/loading scenario comes in as the hub slides on the spline applying greater pressure on the end of stub axle, causing the stub failure, leading to the cracked hub.
One thing that does catch my eye, is the battered appearance of the washer bearing surface, further supporting a loose fastener. This indicates the hub and washer slapping around.
The cracked hub poses an interesting chronolgy of failure. Examining your photo, I cannot ID the crack. I do see an area inside the splined area and on the outer edges of of the hub bore.
A couple of questions:
1) Did you experience any handling anomalies prior to the "flat" sensation
2) Was the retainer castlleated or of a ny-lock/crimp-lock type?
Anyway, my $0.02. Good luck!
Kevin
11-01-2004, 10:16 AM
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Kevin,
Thanks for the reply. As I look at it more and more, I'm inclined to agree that the nut was loose and fell off.
I didn't really feel anything out of the ordinary before it broke. It actually felt good. Keep in mind that I did have a student in the car and was talking about the line, so the car did not have my full attention. And finally, there is no ratainer.
BTW, the crack is real easy to see. You notice how there are two sets of splines? There should be only one. It looks like it cracked after the wheel bearing.
George
Thanks for the reply. As I look at it more and more, I'm inclined to agree that the nut was loose and fell off.
I didn't really feel anything out of the ordinary before it broke. It actually felt good. Keep in mind that I did have a student in the car and was talking about the line, so the car did not have my full attention. And finally, there is no ratainer.
BTW, the crack is real easy to see. You notice how there are two sets of splines? There should be only one. It looks like it cracked after the wheel bearing.
George
11-01-2004, 08:31 PM
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George,
The "two splines" was where it appeared the crack was, but I could not quite tell from the photo. Regarding the "retainer", another name for a nut, fastener, etc.
The main thing is your student, you, nor the car suffered any catastrophic injury/damage.
Kevin
The "two splines" was where it appeared the crack was, but I could not quite tell from the photo. Regarding the "retainer", another name for a nut, fastener, etc.
The main thing is your student, you, nor the car suffered any catastrophic injury/damage.
Kevin
11-01-2004, 11:22 PM
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Originally Posted by George A
Thanks for the reply. As I look at it more and more, I'm inclined to agree that the nut was loose and fell off.
11-02-2004, 11:13 AM
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Chris,
I'm going to replace everything around that area. Now it looks like the carrier won't hold the bearing. So, I'm getting a new carrier, hub, bearing and driveshaft. Should be ready by the end of the week. I've got a DE next weekend, so it'll give me a chance to test it out. Trust me, I'll be watching it.
George
I'm going to replace everything around that area. Now it looks like the carrier won't hold the bearing. So, I'm getting a new carrier, hub, bearing and driveshaft. Should be ready by the end of the week. I've got a DE next weekend, so it'll give me a chance to test it out. Trust me, I'll be watching it.
George