KMCBOSS
RED GT owner
I'm not a mechanical engineer but IMHO the problem may be nothing more than an over torque condition of the bolts from the factory. Remove the bolts and replace with new bolts.
Halfshaft Bolt Answers (all threads merged)
- Thread starter dbk
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AZGT
GT Owner
Thanks Shadowman, good explanation.
But still a question in your statement that was part of my question. If the purpose of the bolts is to secure things, why is there the movement?
You mentioned axial rotation. Fine, but unless there is slop in the washer where the bolt goes through which would allow some back and forth movement and therefore wear, I still don't see how you would get to a shear position. If we are talking bolts that can take 140,000 psi (for each bolt), I can't believe the torque of the GT can even approach that mark. I would also expect to see elongation of the washer holes to indicate an issue, but I don't think that is there.
I think one thing that would be interesting is that when (sorry - if) someone else breaks a bolt, we should measure how much of the bolt needs to be backed out - would give an idea if in fact the bolts are "walking" out or if they are not backing out and truly shearing right at the head.
Just another thought as I am sitting here. Maybe rather than shear they are being popped off. Don't know how the rear suspension really works in the GT without taking a hard look and thinking hard (ouch - too old for that). But what if the suspension "squats" under acceleration, like an old independent rear supension Corvette (mine squated like crazy and the insides of te tires were always bald). Could there be a vertical "pull" created by the squat that "pops" the bolt head because of limited give or play? Maybe something where there needs to be a slip joint, like a drive shaft yoke, in line? Or maybe rather than the bolts being there, the half shaft bolts to a free floating splined shaft going in to the transaxle? The actual geometry of the rear suspension should be able to hold a floating shaft in place with no bolts to the transaxle axle (sorry hard to straight between the half shaft and transaxle shaft). Support for the popping idea (I think) is isn't the transaxle shaft already splined? If so, popping becomes even more likely than twist off (geez - sounds like a beer commercial) :cheers
Maybe we are looking at the wrong issue. :confused
This kind of takes me back to teaching days when we would dscuss problem solvng. The first thing is that you need to understand the problem otherwise luck is the only way to find a solution. On ocassion you have to come in backward to find the solution. Sometimes you also need to deal with people that are not so smart (like me) because they will have a different perspective than a smart person (I used to demonstrate a problem that small kids could easily solve but adults couldn't because their frame of reference was too sophisticated). OK, so the problem is the bolts break. The question is WHY. I know that is what everyone has been thinking about, and the logic has been something right there - at that point (i.e. bolts, washer, axle). But could the problem be caused by squatting, alignment, too short of half shaft, heat generation in the transaxle causing the washer and bolts to expand which causes them to pop (there goes my popping idea again), etc .......
Has anyone with a transaxle cooler broken a bolt? Are the bolts broken in warmer (and therefore greater heat) rather than cold climates (well, you guys in the cold are not drivng, so forget that - guaranteed no breaking right now).
If there are the "uneven gaps", are they breaking on the close side since that may have more vertical pull? So maybe a spacer would take away some of the vertical pressure? Do the six bolts of the half shaft "pull" the half shaft to the transaxle, or is the half shaft more "pushed away" when placed against the transaxle? Pulling in up would imply that vertical pressure again. Maybe a circular shim between the half shaft and the transaxle shaft held in by the six bolts to give it just a smidge of "push" or zero pressure.
The squat / pop (if they do squat any) could also explain why they let loose going from a start and not while on the road or downshifting (which would also cause a twisting force, but you have nose squat not rear).
Anyway, just the brain starting to think outside the box.
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- Aug 25, 2006
- 4,436
I am very sorry as I tend to ramble
What I was attempting to say is there should be "NO" measureable axial rotation of the couple once fit onto the splines and if there is the results would be as have been experierienced in which case the mish mash of bolt and washer swaps are simply a stop gap when compared to the cure.
Now as with most; this is my opinion and based on experience in similar situations and has little if any bases in fact when speacifically addressing our GT's.
So as not to ramble I will leave it at that
Shadowman
AZGT
GT Owner
OK, so I rambled and you clam up? Geez ........ :cheers
I think the sharing of opinions is OK. Yes, we know, they are like a_sholes - everybody has one. But if enough opinions come out, the SMART guys that really can figure it out might just see something that was said and it will give them an idea of something to try that maybe they had not considered.
I've got a feeling there are not too many stupid people on this forum (I apologize to those of you that are and I just offended :eek ), so the opinions are probably based in more than just a reach.
- Aug 25, 2006
- 4,436
You did very good and your opinions are as certainly as valid as the next persons. I for one think that it is very cool that you were willing to take the time to share them.
There is no doubt that the concern is a real one (particularly for those that have gone through the process of pushing their gal to the side of the road) however at the end of the day I suspect that a very few folks (comparatively speaking) have been or will be affected. Now whether I will be able to dodge the radar or not is yet to be seen however I will slide my half shafts out to get a closer look and for (if nothing else) peace of mind.
Thumbs Up
Thank you
Shadowman
Gimbal
GT Owner
You just might be right. After changing the driver side the only thing I observed was that the 2 bolts seemed over torqued. I had no backlash in the splines, the CV joint moved axially eliminating axial load on the bolts, I had hard washers showing no bending that would tend to cause a high load on the outside portion of the bolt head. The fully threaded bolt is also a no good thing and I replaced with bolts with a filleted radius at the bolt head. If the CV joint ran out of travel during driving and imparted a slamming load on the bolt head then if the bolts don't break the CV joint will. I don't think this is the case but short of that the only other failure method might be a constant fatiguing load on the bolts as the axles continues to rotate. This would only be confirmed with some life testing at Ford or something like that.
quick time
GT Owner
- Jul 27, 2006
- 90
FWIW: I have a 06 with an April build date. I just had the TSB done that addresses a slight leak at the output shaft seal. Of course they replaced the 2 bolts and washer on both sides including the other long bolts involved.
The bolts were fine and the washer, which was the hardened version, showed no sign of distortion. The only comment that the tech made was that the amount of torque called for in the TSB on those two small bolts was not much. I think he said 22 lbs. However all those bolts do is hold the output shaft in place and as there is no torque at all on these bolts they should hold fine unless the splines are moving around quite a bit as has been suggested here. I am still hoping that Ford eventually does the right thing and comes up with an definitive answer and fix for this issue so we may all drive our GT's without the stress of a shaft falling out at any time.
The bolts were fine and the washer, which was the hardened version, showed no sign of distortion. The only comment that the tech made was that the amount of torque called for in the TSB on those two small bolts was not much. I think he said 22 lbs. However all those bolts do is hold the output shaft in place and as there is no torque at all on these bolts they should hold fine unless the splines are moving around quite a bit as has been suggested here. I am still hoping that Ford eventually does the right thing and comes up with an definitive answer and fix for this issue so we may all drive our GT's without the stress of a shaft falling out at any time.
Gimbal
GT Owner
Another thing I noticed when replacing the bolts on the driver side is that it did not have any sign of oil leaking out of the splines. I had no backlash in my splines so I am hoping the tightness of the splines is keeping the oil from leaking out. I wonder if broken bolt situations have had oil leaks also? I performed the TSB to seal the splines anyway since I had it all apart.
KMCBOSS
RED GT owner
The bolts were designed to take only so much torque so if the person who assembled this part of the trany had the torque wrench on the wrong setting or maybe the wrench was way out of calibration etc. the bolts could have been over torqued - in some cases. It is also possible these bolts can only handle so many smokey burnouts before failing.
Gimbal
GT Owner
Another crazy thought... I read in the manual that the outer CV joint has a larger angle capability than the inner one near the tranny axle. If the inner CV is angling to near its limit then every time the axle rotates it imposes a load. With the axle rotating round and round it might just take a matter of time before it snaps a bolt head off.
Gimbal
GT Owner
Can anyone confirm that they have actually seen or measured any backlash between the axle and hub splines?
When I replaced the bolts on the driver side I used two lever arms, one attached to the tranny axle and the other to the hub so that I could feel for any backlash. At least my driver side had none that I could detect. I pulled the hub out about 1/4" or so to get a feel for the sliding fit and it basically felt about as perfect as I assume it should.
When I replaced the bolts on the driver side I used two lever arms, one attached to the tranny axle and the other to the hub so that I could feel for any backlash. At least my driver side had none that I could detect. I pulled the hub out about 1/4" or so to get a feel for the sliding fit and it basically felt about as perfect as I assume it should.
Gimbal
GT Owner
OK, well I replaced the 2 bolts on the passenger side today.
1) The bolts were tight, seemed tightened about right.
2) That side also had the hard washer
3) No oil leaking out of the splines
4) Rotationally I was unable to feel backlash between the axle and hub splines
5) However, here is where it gets interesting. Since the TSB to seal any oil leaks says "DO NOT REMOVE THE HUB", I did not pull the hub off the driver side. When doing the passenger side I decided to pull the hub off just for the hell of it. Only a very small amount of oil came out, 10 drops maybe. What I then noticed was a very large amount of up and down and left and right backlash in the splines. The futher I pulled the hub out the more backlash, way more than I think there should be.
I then decided to re-do the driver side since I did not pull the hub off when changing those bolts last week. As I pulled the hub off I notice just about the same amount of backlash up and down and left and right, maybe a little less than the passenger side. I also tried swapping hubs and the results were about the same.
I video taped this backlash but can't figure out how to attach a video file to this forum. It's quite obvious noticing the backlash in the video. If someone can tell me how to attach a video file I will do that for anyone who wants to see. I can edit it down to about 15 seconds or so.
I now have a strong feeling the culprit is this extreme backlash causing broken bolts as several people have suggested. It is the washer shoving the hub up against the inner race of the axle bearing just inside the tranny sort of holding everything in place, but if the hub has this loose backlash it makes sense that some high loads could be produced on the 2 little bolt heads eventually snapping them off.
I took many measurements. I have a larger gap on the passenger side than the driver side. From my measurements it turns out that the distance from the end of the axle to the inner race of the bearing inside the tranny is the same on both sides. The hubs are nearly identical. The difference in gaps is caused by the axle bearing and axle being further out on the passenger side. I have no idea why but it is inside the tranny. Hopefully it is just a shimming process during the tranny assembly. I feel these gaps have nothing to do with broken bolts.
I takes only about .80 inches for the hub to slide off the axle. It seems like enough spline engagement but I would feel better with more.
If the axle splines were manufactured with very tight tolerances perhaps new hubs could be made to fit tighter. If the tolerances are too large then custom hubs would need to be made for each axle. If this is the problem then the only real fix is new hubs or axles, neither being cheap or easy.
Stronger and better bolts would help but not sure it is the long term fix.
I guess I will drive and hope the bolts don't break. Ford needs to hurry and come up with a fix.
1) The bolts were tight, seemed tightened about right.
2) That side also had the hard washer
3) No oil leaking out of the splines
4) Rotationally I was unable to feel backlash between the axle and hub splines
5) However, here is where it gets interesting. Since the TSB to seal any oil leaks says "DO NOT REMOVE THE HUB", I did not pull the hub off the driver side. When doing the passenger side I decided to pull the hub off just for the hell of it. Only a very small amount of oil came out, 10 drops maybe. What I then noticed was a very large amount of up and down and left and right backlash in the splines. The futher I pulled the hub out the more backlash, way more than I think there should be.
I then decided to re-do the driver side since I did not pull the hub off when changing those bolts last week. As I pulled the hub off I notice just about the same amount of backlash up and down and left and right, maybe a little less than the passenger side. I also tried swapping hubs and the results were about the same.
I video taped this backlash but can't figure out how to attach a video file to this forum. It's quite obvious noticing the backlash in the video. If someone can tell me how to attach a video file I will do that for anyone who wants to see. I can edit it down to about 15 seconds or so.
I now have a strong feeling the culprit is this extreme backlash causing broken bolts as several people have suggested. It is the washer shoving the hub up against the inner race of the axle bearing just inside the tranny sort of holding everything in place, but if the hub has this loose backlash it makes sense that some high loads could be produced on the 2 little bolt heads eventually snapping them off.
I took many measurements. I have a larger gap on the passenger side than the driver side. From my measurements it turns out that the distance from the end of the axle to the inner race of the bearing inside the tranny is the same on both sides. The hubs are nearly identical. The difference in gaps is caused by the axle bearing and axle being further out on the passenger side. I have no idea why but it is inside the tranny. Hopefully it is just a shimming process during the tranny assembly. I feel these gaps have nothing to do with broken bolts.
I takes only about .80 inches for the hub to slide off the axle. It seems like enough spline engagement but I would feel better with more.
If the axle splines were manufactured with very tight tolerances perhaps new hubs could be made to fit tighter. If the tolerances are too large then custom hubs would need to be made for each axle. If this is the problem then the only real fix is new hubs or axles, neither being cheap or easy.
Stronger and better bolts would help but not sure it is the long term fix.
I guess I will drive and hope the bolts don't break. Ford needs to hurry and come up with a fix.
- Aug 25, 2006
- 4,436
THANK YOU
Sadly this is exactly what I and for that matter many others have been speculating on for a long time.
The fact that you took the extra time to validate this is very much appreciated even though for some; in fact maybe all of us this is not a good thing.
I indicated in an earlier thread that I suspected that the total spline engagement was likely no more than an inch or two however you stating that it is only .800 is both surprising and a bit troubling because the ability for the flange aka coupler to rotate off center becomes much greater.
I will now begin to speculate on whether the flange aka couple actually begins to oscillate around the primary shaft akin to watching a crank shaft when in motion and how much it twist as such the process of working the bolts and washers is never ending when as has been stated; there should be “zero-zip-nada” operational stress applied to the bolts and the washer. They should simply be along for the ride however they are beginning to appear as the basis of the ride.
Regards
Shadowman
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Gimbal
GT Owner
Maybe Ford purposely wrote "DO NOT TAKE OFF THE HUBS" in the TSB so you would not find out how f loose the hub splines were!
BlackICE
GT Owner
Gimbal, great investigation and write up. This confirms the theory many have had on this board. Do you know the type metal used and hardness of the flange? I would be interesting to get a new flange to compare with the old one as to the fit. I could be that the flange originally was tight fitting, but may of soft material that deforms and loosens with use. If that is the case Ford could release new stronger flanges to solve the problem. If the shaft's spline tolerances are poor, then the fixes are really expensive!
Gimbal
GT Owner
Axle and Hub pix
Here is a couple of photos of the passenger side of the axle and hub. The splines on each do not look deformed. So I suspect that the loose fit is just bad design tolerances and not being caused by slowly being deformed or reshaped. I now wish I looked at the hub under a microscope, I have one too, dangit!
Here is a couple of photos of the passenger side of the axle and hub. The splines on each do not look deformed. So I suspect that the loose fit is just bad design tolerances and not being caused by slowly being deformed or reshaped. I now wish I looked at the hub under a microscope, I have one too, dangit!
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analogdesigner
GT Owner
Thanks from me too!
Gimbal,
Thanks from me too!
I will be tearing my car apart on Tuesday or Wednesday and I will measure the amount of slop (notice I didn't refer to it as play) and completely document everything. The fasteners will be replaced with ARP brand.
I was never comfortable with the axle diameter to spline length ratio. Thanks for the images.
Jay
Gimbal,
Thanks from me too!
I will be tearing my car apart on Tuesday or Wednesday and I will measure the amount of slop (notice I didn't refer to it as play) and completely document everything. The fasteners will be replaced with ARP brand.
I was never comfortable with the axle diameter to spline length ratio. Thanks for the images.
Jay
dbtgt
One lucky SOB to own a GT
Gimbal and Shadowman, is it possible that the tolerances reduce when the transaxle gets up to operating temperature? I know that good designs provide for expansion of the metals at operating temp.
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Gimbal
GT Owner
dbtgt, Good point but I would assume both axle and hub flange expand at about the same rate as temp increases. In fact it might not be a good idea for one to expand more than the other, this itself could cause high stresses, etc. I am sure Ford knows or could easily figure out if the splines and slop is excessive per the design. Ford could double check drawing tolerances. Is there any way to get a copy of the actual drawings of the axle and hub flange splines? Or would this info be proprietary? Seems much of the speculation by everyone could be confirmed quickly with a relatively small amount of information from Ford if there were a way to get it.
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