Why are these extension housing bolts sheared?
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This is my beloved Quaife box:
So, upon finding some oil at the bottom of the transmission - I quickly found some extension housing bolts missing. Upon further inspection, most sheared and left 2/3" thread in the housing. I think only 2 are somewhat 'OK', 4 I've removed so far. The other two are impossible to reach, or are not fully through - making it hard (impossible?) to remove the thread remains. Did they shear because a) they were reused, which should not be done? b) they were overtorqued c) my car makes to much torque (PPF, and such) d) bad carma? |
A) Like most other bolts, you should be able to reuse them a couple times.
B) I see no necking, i doubt it's from over torquing. C) We've seen a million other failures from power, I don't think I've ever seen this failure. D) I vote this one. You said they were reused, was the gearbox taken apart recently? I'd vote first for missing dowel pins and/or UNDERtorqued bolts. This let it twist under acceleration, and shear the bolts. |
Hmmm....I can only speculate here. Does the housing have dowel pins that help align the trans properly? Are they possibly missing?
Does one housing twist enough that it could have hammered the bolts enough to shear them? Perhaps they were not tightened properly. That is my best conjecture. Edit: Curly is faster than me. |
I'm not sure but I'm fairly certain that miserable, POS company Quaife is behind this.
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Originally Posted by hustler
(Post 1007970)
I'm not sure but I'm fairly certain that miserable, POS company Quaife is behind this.
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Are they the OE case bolts? A high grade bolt would fail like that from over torquing. Whereas say a grade 5 would stretch.
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Originally Posted by m2cupcar
(Post 1008116)
Are they the OE case bolts? A high grade bolt would fail like that from over torquing. Whereas say a grade 5 would stretch.
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Yea, OEM grade 8 bolts. They go into the alu, which is still fine.
These are the bolts: (you're looking only at the back half of the transmission, not the bell house) |
Can you get a shot point down the length, like so we can see the face where the break was? From the last picture it almost looks like they were loose and sheared.
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Originally Posted by Leafy
(Post 1008135)
Can you get a shot point down the length, like so we can see the face where the break was? From the last picture it almost looks like they were loose and sheared.
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IMO it looks like over torque on high grade hardware. I realize that Grade 8 is used there as the clamping force is needed, but I suspect they've be torqued before (multiple times?) and gave up this time around. So I vote (a).
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I'll say undertorqued, but that's a non-expert opinion.
I'd buy new bolts, lube & torque them per mazda specs. Make sure dowels are used too. You should be fine if the threads in the aluminum are not damaged. |
I've now been able to replace 6 out of 8. The other 2 I cannot reach/remove the remains.
From the few that were still tight, I can say those were not undertorqued. I was afraid they would snap too. The re-use multiple times - could have been the issue. The torque spec is 34Nm. I'll report back after the next run or two. |
Originally Posted by Spookyfish
(Post 1008155)
Like diz?
The fatigue looks like it is an alternating bending pattern. Blah blah blah, I could go on and on BUT To me it looks like they were undertorqued, or they had lost torque. The undertorque condition led to the bolts being put into a cyclic bending load, one they are not meant to take. I'm guessing the other ones didn't fail because they are torqued correctly. That is my professional failure analysis and there will be a $2000 consulting fee. I'll PM you how you can settle the fee... |
Thanks for the analysis. There are two options
a) Torque maybe was OK initially, then they loosened (vibrations?) and fatigued b) Overtorqued combined with re-use of original bolts Either way, I should be fine with a) Resbond in threads b) Proper torque and new bolts Downside: only 6 out of 8 bolts. There is no more oil sweating from the transmission, so it's tight now. I'll report back |
Originally Posted by Spookyfish
(Post 1009370)
b) Overtorqued combined with re-use of original bolts
In my experience, that sort of failure surface would not be seen in a proper torque condition. Regardless,
Originally Posted by Spookyfish
Either way, I should be fine with
a) Resbond in threads b) Proper torque and new bolts Downside: only 6 out of 8 bolts. |
Thanks for your input, it's on the list already :)
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I'm replacing these bolts faster than changing oil.
I need to check my motor mounts. Something is killing them. |
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Is that part supposed to have any locating pins like the transmission bell housing?
Like maybe one here, and again on the other side? https://www.miataturbo.net/attachmen...ine=1379610475 |
I had one of my fuel rail bolts separate in the middle of the threads like that. I swear I threaded it all the way down by hand. The second I put a little snugging torque on the wrench it felt funny. I pulled it out and it looked just like that. No idea what happened. Called FM and they said they had never heard of that happening. Bad bolts maybe? Maybe try a little strip of white nail polish where the bolt head meets the case and see if the thing is backing out a hair. Vibrating funny.
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