Halfshaft Bolt Answers (all threads merged)
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richardhead
GT Owner
- Sep 19, 2006
- 169
Hey Everyone....
When replacing the half shaft bolts, using the Accufab kit or Ford parts, be sure and carefully clean the two inside spline shaft holes with an 8MMX1.25Pitch tap before installing the two new washer/hub retention bolts. The factory used a red thread locking compound on the original bolts. If this red compound is not removed from the treads in the hole before you torque the new retention bolts, there is a very good possibility your torque application will not be to spec. In two of my bolt holes, the torque required to turn the bolts in the last quarter or so of their length was in excess of 40 ft.-lbs. This would have made torquing the bolts against the washer to the ACCUFAB spec torque of 24-27 ft.-lbs. impossible. After cleaning all four holes with a lightly oiled tap from True Value Hardware Stores (American made), and cleaning the holes with Brake/Parts cleaner spray (you should have seen the crud that flushed out), and letting dry....the new bolts, with Blue Loctite compound on the threads, turned all the way in by hand and seated on the washer surface easily. Torquing to spec clearly worked properly. It takes a little extra time, but it is worth it to be sure your bolts are in to proper specification.
When replacing the half shaft bolts, using the Accufab kit or Ford parts, be sure and carefully clean the two inside spline shaft holes with an 8MMX1.25Pitch tap before installing the two new washer/hub retention bolts. The factory used a red thread locking compound on the original bolts. If this red compound is not removed from the treads in the hole before you torque the new retention bolts, there is a very good possibility your torque application will not be to spec. In two of my bolt holes, the torque required to turn the bolts in the last quarter or so of their length was in excess of 40 ft.-lbs. This would have made torquing the bolts against the washer to the ACCUFAB spec torque of 24-27 ft.-lbs. impossible. After cleaning all four holes with a lightly oiled tap from True Value Hardware Stores (American made), and cleaning the holes with Brake/Parts cleaner spray (you should have seen the crud that flushed out), and letting dry....the new bolts, with Blue Loctite compound on the threads, turned all the way in by hand and seated on the washer surface easily. Torquing to spec clearly worked properly. It takes a little extra time, but it is worth it to be sure your bolts are in to proper specification.
- Aug 25, 2006
- 4,436
analogdesigner
GT Owner
good info
Richard,
Yeah, thanks for the info. I had already purchased the tap (just in case of a problem, like you just mentioned) even though I have not upgraded my bolts yet. My car is quarantined until I get this done, hopefully soon.
Jay
Richard,
Yeah, thanks for the info. I had already purchased the tap (just in case of a problem, like you just mentioned) even though I have not upgraded my bolts yet. My car is quarantined until I get this done, hopefully soon.
Jay
Bolt Failure Follow-up in Seattle
Hi Guys,
I just got my car back from Ford of Bellevue tonight. No surprise, the problem was failure of the halfshaft bolts. Ford apparently wants to analyze the parts, so they wouldn't let me keep them. For the purpose of collecting data for the forum, I did photograph them so that you could see them. The washers didn't have any visible deformity. We placed them together and they seemed perfectly flat (unlike the photos that were posted earlier). You see how the heads of the bolts have popped off. Fortunately no other damage to the car. To get this done under warranty, they had to use the Ford upgraded parts. The tech (Howard, who seemed to know his stuff), said he would be happy to install the Accufab parts later if I wanted (he thought the idea of a shoulder bolt made sense), but it wouldn't be covered under warranty. He estimated it would be about a 6-10 hour job. Does anyone know of anyone who has had a failure of the upgraded bolts?
JAM
Hi Guys,
I just got my car back from Ford of Bellevue tonight. No surprise, the problem was failure of the halfshaft bolts. Ford apparently wants to analyze the parts, so they wouldn't let me keep them. For the purpose of collecting data for the forum, I did photograph them so that you could see them. The washers didn't have any visible deformity. We placed them together and they seemed perfectly flat (unlike the photos that were posted earlier). You see how the heads of the bolts have popped off. Fortunately no other damage to the car. To get this done under warranty, they had to use the Ford upgraded parts. The tech (Howard, who seemed to know his stuff), said he would be happy to install the Accufab parts later if I wanted (he thought the idea of a shoulder bolt made sense), but it wouldn't be covered under warranty. He estimated it would be about a 6-10 hour job. Does anyone know of anyone who has had a failure of the upgraded bolts?
JAM
Attachments
- Aug 25, 2006
- 4,436
Hi Jam
First of all thank you again for taking the time to share the process from end to end.
Now as a side bar; if it takes 6-10 hours to provide the swapping of half shaft bolts then darn it......... line them up because his clock must run at 4 times actual speed as I could likely complete at least 3 gals in the course of a very casual and methodical 8 hour day
Takes care
Shadowman
richardhead
GT Owner
- Sep 19, 2006
- 169
I agree with Shadowman. Having done this once very carefully, the whole job could be easily done in two hours or less without rushing.
analogdesigner
GT Owner
finite element analysis
JAM,
Thanks, as this correlates well with my FEA (finite element analysis). Even my FEA program pointed out exactly where the peak stress point is (not shown here, so I manually circled it). This dual fastener design is a bad idea due to lack of symmetry around the head of the fasteners. Jay
JAM,
Thanks, as this correlates well with my FEA (finite element analysis). Even my FEA program pointed out exactly where the peak stress point is (not shown here, so I manually circled it). This dual fastener design is a bad idea due to lack of symmetry around the head of the fasteners. Jay
B O N Y
MODERATOR & FGT OWNER
Had an interesting conversation with John at Accufab yesterday. I ordered an extra set of bolts to keep in the FGT. We discussed the need to remove old Locktite and that the threads must be ready to accept the new bolts. He recommended running a TAP in and out, but was reluctant to put it in writing.
If someone is not careful, and have experience with taps they could break it off in the hole and it would be extreamly difficult and costly to remove. I share this information for what it is worth...
If someone is not careful, and have experience with taps they could break it off in the hole and it would be extreamly difficult and costly to remove. I share this information for what it is worth...
Gulf GT
GT Owner
I think your FEA results are fine but we need to remember that there is no torque on these bolts when they are in place. It's admittedly hard to make a conclusion based on pictures.... but I can't help but notice how clean the threads are with no sign of Loctite. I still believe that the breaking bolts may be a symptom and not the cause. Still a very plausible theory is that the bolts were not torqued correctly during assembly and the walk themselvs out over time. As soon as they walk out far enough to release the spline engagement, then there's going to be a butt-load (that's a lot) of torque on the bolts and ANY bolt will shear under these conditions.
Signs of this being the cause:
1. Very clean threads
2. Lack of cupping of a known soft washer. The update I performed last week on an '05 car had tight bolts which had cupped the washer. (See pictures a few posts up.) If these bolts were tightened to the same torque - it would seem that the washers would be cupped as well. They are not. Hmmmm.
3. Odd looking flat spot on the threads. May lend credibility to the theory that the bolt was way loose before breaking.
Note to Ford: I have the bolts and washers from my preventative maintenance upgrade. If they can help you, contact me.
analogdesigner
GT Owner
Tapping advice
Good Info! Use a high quality, two flute, tap (NOT made in China, German made are the best!). Use a T-handle on the tap to minimize side loading. Be conservative by threading the tap inward until there is some resistance. Stop and then back it out about 1/2 to 1 full revolution. Then go back in further and repeat. Someone could have a small (hardened) metal burr in one of the threaded holes, so be cautious! When the tap bottoms out it should be very noticable, so do NOT try to cut beyond the factory threads! I have removed more broken taps for friends AND myself than I care to think about. Hopefully we will not have any broken tap stories on this forum. Jay
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Empty Pockets
ex-GT Owner
Indy GT
Yea, I got one...too
Bolt Shear
Nota4re, interesting post and a thought provoker.
The FEA results posted show equivalent stress (ie Von Mesis) so no definition of where the stress is tensile or compressive. From my experience and looking as best I can at the fracture surface shown in the post#626 pictures the failure appears to be tensile overload at the thread fillet-to-head area. It would have been helpful to take a zoomed in picture of just the (under) bolt head fracture surface for better diagnostics. If the bolt is subjected to bending (which is clearly what the FEA indicates by the high stresses (red in color) on one side of the bolt thread) then the Kt effects of the fillet would most likely lead to this type of failure.
I am not sure what "mechanism" you might propose for why the bolts would walk themselves out over time. Sure under torquing the bolts would lead to lower than anticipated preload in both the washer (and drive yoke thru the washer) and the bolt proper, but if Riccardo and or Ford had any QA procedures and locktite was used on the threads, I personally see little chance of bolt relative motion. Yes I know the #626 post does not show any residual locktite on the threads, however it is unclear from the text if these were just as they had been extracted or if a clean-up rag was wiped over the threads. Further, it might be a leap-of-faith to assume bolt under torque condition just because the silver washer does not have a permanent cup. The silver washer was at some time in the design process "bought off" as acceptable for this application and was used in significant numbers in our cars. Production run changes happen all the time which may unknowningly have altered the washer strength so some silver washers were ok and others were not ok in this application.
Accepting your loosening scenerio, if the bolts did loosen (am not sure how far they would actually have to back out, maybe someone can comment) a sufficient distance to allow the splines to disengage (thus the half shaft drive line to the wheel is disconnected from torque output from the transaxle, see Gimbal drawing post #497) there is no torque transmitted. The splines have decoupled. The only way you might possibly get drive torque to the bolts is if the transaxle torque output is channeled through the two bolts loosly screwed into the drive shaft (they have worked loose at this point allowing spline disengagement), the bolts would then channel the torque through the washer and try to drive the decoupled yoke attached to the wheel drivetrain. But since the bolts are loose (ie the washer is loose against the yoke) there is no normal force between the washer and the yoke and thus no means to transmit torque through this interface via friction (mu times normal force which is zero).
Were the bolts failing in torsional shear or just gross torque applied to the upper part of the thread from the transaxle torque migrating to the wheel through the bolts the bolts would show more twisting deformation in my opinion.
Lets hope Ford will come out with a fix for this problem soon.......
Bill
Nota4re, interesting post and a thought provoker.
The FEA results posted show equivalent stress (ie Von Mesis) so no definition of where the stress is tensile or compressive. From my experience and looking as best I can at the fracture surface shown in the post#626 pictures the failure appears to be tensile overload at the thread fillet-to-head area. It would have been helpful to take a zoomed in picture of just the (under) bolt head fracture surface for better diagnostics. If the bolt is subjected to bending (which is clearly what the FEA indicates by the high stresses (red in color) on one side of the bolt thread) then the Kt effects of the fillet would most likely lead to this type of failure.
I am not sure what "mechanism" you might propose for why the bolts would walk themselves out over time. Sure under torquing the bolts would lead to lower than anticipated preload in both the washer (and drive yoke thru the washer) and the bolt proper, but if Riccardo and or Ford had any QA procedures and locktite was used on the threads, I personally see little chance of bolt relative motion. Yes I know the #626 post does not show any residual locktite on the threads, however it is unclear from the text if these were just as they had been extracted or if a clean-up rag was wiped over the threads. Further, it might be a leap-of-faith to assume bolt under torque condition just because the silver washer does not have a permanent cup. The silver washer was at some time in the design process "bought off" as acceptable for this application and was used in significant numbers in our cars. Production run changes happen all the time which may unknowningly have altered the washer strength so some silver washers were ok and others were not ok in this application.
Accepting your loosening scenerio, if the bolts did loosen (am not sure how far they would actually have to back out, maybe someone can comment) a sufficient distance to allow the splines to disengage (thus the half shaft drive line to the wheel is disconnected from torque output from the transaxle, see Gimbal drawing post #497) there is no torque transmitted. The splines have decoupled. The only way you might possibly get drive torque to the bolts is if the transaxle torque output is channeled through the two bolts loosly screwed into the drive shaft (they have worked loose at this point allowing spline disengagement), the bolts would then channel the torque through the washer and try to drive the decoupled yoke attached to the wheel drivetrain. But since the bolts are loose (ie the washer is loose against the yoke) there is no normal force between the washer and the yoke and thus no means to transmit torque through this interface via friction (mu times normal force which is zero).
Were the bolts failing in torsional shear or just gross torque applied to the upper part of the thread from the transaxle torque migrating to the wheel through the bolts the bolts would show more twisting deformation in my opinion.
Lets hope Ford will come out with a fix for this problem soon.......
Bill
RSR1975
GT Owner
A near-term solution from Ford would be nice!
"Lets hope Ford will come out with a fix for this problem soon.......". Aggreed, a near-term solution from Ford would be nice. I would like to take the GT on its first long trip in June to Watkins Glen, NY for the vintage races, but I'm not comfortable with the idea of getting stuck somewhere between PA and NY with a half shaft bolt failure. Has there been any back channel discussion on progress toward a solution? If not, the GT stays in the garage and the old reliable Posche will make the trip as it has in the past.
"Lets hope Ford will come out with a fix for this problem soon.......". Aggreed, a near-term solution from Ford would be nice. I would like to take the GT on its first long trip in June to Watkins Glen, NY for the vintage races, but I'm not comfortable with the idea of getting stuck somewhere between PA and NY with a half shaft bolt failure. Has there been any back channel discussion on progress toward a solution? If not, the GT stays in the garage and the old reliable Posche will make the trip as it has in the past.
ENZO BTR
GT Owner
First I have to say how impressed I am with the technical know-how being displayed in the analysis of this problem. I even understand a good percentage of it (5-10% :ack ).
One non-techncial point I have to offer is the timing/mileage of the failure. My GT has had no bolt upgrade. It is a 2005, #1456 and it just turned over 8,300 miles. I'll readily admit there's an element of wishful thinking here, but is there any thinking regarding the likely time-frame/mileage for this failure. From my purely anecdotal observations it seems most failures happen before 2,500 miles (between 800 and 1,500 seems the real target zone). When the list of failures (with mileage) was up in the first post I think I remember only one failure above 3,000 miles (BTW, where did the list go???).
Obviously I'd love to think there's a "if it hasn't broken by now you're okay" element here, but who knows? I do have a Ford replacement kit on hand in the car, and I am going to order an Accufab kit ASAP, but part of me is hesitant to initiate the "repair" (if it ain't broke don't fix it).
One thing that really bums me out is the thought of all those owners who are not driving theirs because of a fear of breakage. I was feeling the same way last fall when this problem became apparent, but my car was already over 6,000 miles at the time. I now have another 2K with no issues and it's honestly getting harder and harder to obsess over it (though, honestly, I still think about it regularly).
Of course, now that I've posted this I expect to momentarily be posting my own axle-bolt failure experience... :willy
One non-techncial point I have to offer is the timing/mileage of the failure. My GT has had no bolt upgrade. It is a 2005, #1456 and it just turned over 8,300 miles. I'll readily admit there's an element of wishful thinking here, but is there any thinking regarding the likely time-frame/mileage for this failure. From my purely anecdotal observations it seems most failures happen before 2,500 miles (between 800 and 1,500 seems the real target zone). When the list of failures (with mileage) was up in the first post I think I remember only one failure above 3,000 miles (BTW, where did the list go???).
Obviously I'd love to think there's a "if it hasn't broken by now you're okay" element here, but who knows? I do have a Ford replacement kit on hand in the car, and I am going to order an Accufab kit ASAP, but part of me is hesitant to initiate the "repair" (if it ain't broke don't fix it).
One thing that really bums me out is the thought of all those owners who are not driving theirs because of a fear of breakage. I was feeling the same way last fall when this problem became apparent, but my car was already over 6,000 miles at the time. I now have another 2K with no issues and it's honestly getting harder and harder to obsess over it (though, honestly, I still think about it regularly).
Of course, now that I've posted this I expect to momentarily be posting my own axle-bolt failure experience... :willy
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analogdesigner
GT Owner
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