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Thread: Mag 915 Throttle Relay Bolt Snapped Off

  1. 09-12-2018, 11:50 AM #1
    EsGeht
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    Mag 915 Throttle Relay Bolt Snapped Off

    (As posted on Pelican, I need all the advice I can get)
    Oh Boy. The driver side CV joint bolts backed out (a whole story in and of itself) and the axle came loose from the trans at 35mph. The spinning, flailing CV joint caught the throttle rod aft of the relay lever and pulled the lever backwards, snapping off the mounting bolt in the process.
    The trans was just rebuilt and is exceedingly clean, and the mounting bolt in question was spotless and re-installed only months ago, so it is not stuck or oxidized in place. It should come out without a lot of coaxing. I just can't get a grip on the thing.
    I have several ideas about how to remove the broken bolt, but I need the advice of a more experienced mag trans person. Matt Monson? Pete Zimmerman? I am specifically intimidated by the magnesium trans case. I have successfully removed a broken stud from an aluminum engine case by MIG welding a washer and nut to the bolt. It took a few tries, but it worked. However, in that case, the bolt was snapped flush and the surrounding material was aluminum. I know magnesium, once aflame, is nearly impossible to douse. Is it safe to MIG weld on a bolt threaded into magnesium? How volatile is magnesium? I know magnesium gets welded all the time, but I'm leery having had no experience with it. Has this been attempted by anyone else? And in this instance the bolt is snapped off a few millimeters below the surface of the trans case.

    Here are examples of methods I'm considering:

    https://www.youtube.com/watch?v=dJfkCj3FWBs at 3:40 Centering bit drilling method using reversing bit. There is very little clearance between the trailing arm and the trans for a drill and centering bit. Most likely engine/trans removal is necessary.

    https://www.youtube.com/watch?v=P0vakRH-bpY at 3:10 Simplified welding technique, just building up the deposited metal into a nub large enough for vice grips to grab it. With proper shielding of trans and nearby fuel lines, this can easily be done with the trans in car.

    https://www.youtube.com/watch?v=bXz-chvw-90&t=109s Welding washer and nut to stud. This method seems difficult with the trans in place and working on a vertical surface. This method, too, seems to entail pulling the motor and trans and doing the welding horizontally with the trans on it's side.

    I like the simplified method, but again, I'm intimidated by the magnesium. Has anyone else done this? Thoughts? Thanks!
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    Mike O'Meara
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    72 911T
    56,59 356s gone
    67,68 912s gone
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  2. 09-12-2018, 02:47 PM #2
    edmayo
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    Just drill it out, important part is getting hole centered, it's an 8 mm bolt, so drill out to 6 mm or so and try eze -out, if that won't do it just keep drilling out until you get to 8mm tap drill size. Usually by that time you can pick out the remains. As you drill out to 6 mm or so try left hand drill bits, might even spin that stub right out. This is just a daily occurrance in a shop, no big deal. If threads get chewed up install a time-zert.
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  3. 09-12-2018, 03:19 PM #3
    EsGeht
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    It looks like there is enough room for a right angle drill or right angle attachment on a conventional drill. I have a set of these centering drill bits. The sleeve around the bit looks to provide some protection to the threads in the mag case. Thanks, Ed. I'm reassured to hear it's a common shop issue, figured it must be. Is there a history of errant axles lopping off this bolt?
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    Mike O'Meara
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    72 911T
    56,59 356s gone
    67,68 912s gone
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  4. 09-12-2018, 04:56 PM #4
    30westrob
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    I use reverse twist drills for this type of problem. As you drill larger the drill will dig into the broken piece and usually spin it out. Rob
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  5. 09-13-2018, 03:41 AM #5
    edmayo
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    We've never had it happen to any cars that left our shop, but we are careful to use new lock washers, and even over tighten those c.v. bolts a little. I've seen it happen on a 914 once, even broke the starter!
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  6. 09-13-2018, 05:32 AM #6
    EsGeht
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    I will drill. I've had those axles on and off multiple times over the last 20 years and have never had one loosen up. This happened in less than 500 miles, so I obviously did something wrong. I used new Schnorr washers and a torque wrench, but I had an issue with one of the locating dowels and probably didn't have the CV seated correctly. Blame the mechanic (me). I'm just glad the damage isn't worse. Thanks for the help!
    Mike O'Meara
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    72 911T
    56,59 356s gone
    67,68 912s gone
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  7. 09-13-2018, 06:06 PM #7
    EsGeht
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    Got it! This had me intimidated, but it actually came out very easily, with no thread damage. Thanks to all!
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    Mike O'Meara
    Reg #1043
    72 911T
    56,59 356s gone
    67,68 912s gone
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