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Old 01-11-2016, 05:30 PM   #1
Second Series
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Striped Threads in aluminum housing

I have a 1988 GMC K2500 with the 5-speed transmission. My knuckles hit the dash when I shift to 1st and 3rd. I unscrewed the dust boot to find the top bolts loose. It was leaking there when I got it so I put two longer screws in, I thought it would work, but no, Two of the Four bolt holes the threads in the aluminum housing are striped. The bolts are M6 x 1 x 25. Does anyone have a suggestion for a replacement bolt? Maybe a self tapping bolt thatís slightly larger?
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Old 01-12-2016, 11:44 AM   #2
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Re: Striped Threads in aluminum housing

Helicoil or timesert would be the best way to fix it.
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Old 01-15-2016, 05:14 PM   #3
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Re: Striped Threads in aluminum housing

I'm considering using Helicoils, but I'm concerned about the metal bits falling into the transmission. I could place a piece of tape under the hole to catch most of the shards. I would need to buy the kit, about $35.00. I watched a video about loctite form a thread, but that kit is about $26.00. Has anyone here used this product? I found permatex cold weld compound for $6.00 and plan on trying that. The video showed placing anti seize compound on the bolt followed by the metal epoxy. The bolt is inserted into the stripped housing, and removed after Five minutes. The epoxy cures, and the threads are better than new. Sounds simple enough.
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Old 01-19-2016, 03:02 PM   #4
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Re: Striped Threads in aluminum housing

Well, the glue didn't work. I looked up the conversion from metric to inches and 6mm = .2362". 1/4 inch bolt will be bigger, and I found Two 1/4" self tapping sheet metal screws on my workbench. Now my transmission shifts solid and my knuckles don't hit the dash when I shift to 1st and 3rd.
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Old 07-26-2019, 11:33 AM   #5
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Re: Striped Threads in aluminum housing

Well, that didnít last long. Itís been awhile, but I have driven this truck a dozen times and the bad fix has gone bad. I have never installed a heli-coil, and cutting into an aluminum transmission case is intimidating. After a couple weeks of hemming and hawing, I gathered the supplies and jumped in. I opened it up:
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Old 07-26-2019, 11:34 AM   #6
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Re: Striped Threads in aluminum housing

The two rear holes are the worst. I used a hand drill, the holes kept it perpendicular for the most part. I got a long T-handle for the tap:
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Old 07-26-2019, 11:35 AM   #7
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Re: Striped Threads in aluminum housing

The coil went in easy enough. I actually did one practice run on a piece of scrap aluminum. I was concerned about breaking off the coil pin and preventing it from ending up inside the transmission:
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Old 07-26-2019, 11:36 AM   #8
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Re: Striped Threads in aluminum housing

On my practice run, I used one strand of wire to make a loop and retreived the pin. That worked on the bench, not much fun in the vehicle. I got the pin with a hemostat.
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Old 07-26-2019, 11:37 AM   #9
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Re: Striped Threads in aluminum housing

I used a piece of tape to catch under the hole. Iíll have the transmission flushed sometime, but Iím not too worried about it now. Look at all that metal shaving. I used some thread lock when installing the coils yesterday. I still have to put the top back on. Iím still unsure about this and donít want to run the coils through, not in a hurry, so Iím o.k. with waiting for threadlock to cure. I did find an interesting video about thread repair. I had looked at time-certs since there is no pin to break off, but couldnít locate any locally.
https://www.youtube.com/watch?v=LpDduCVUy6w
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Old 08-10-2019, 09:07 AM   #10
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Re: Striped Threads in aluminum housing

It looks like you have covered all your bases. Heli coil repairs in aluminum are quite strong when done correctly. I think you will be happy with the results. Good job!
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