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I've got a 2007 Pontiac Torrent that I (mostly) installed a hitch on. The hitch mounts to 8 points. 6 points are existing welded in nuts.

4 of these welded nuts are causing me trouble. They've rusted so badly I can't get a bolt through them... They are in the frame, so I don't think I can remove/replace them.

Any wonderful suggestions?

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    This question has two parts - how to clean the threads so they work better, and how to stop the rust from coming back the same way. Existing questions focus on cleaning. I'd look at a product like RustBuster or POR15 or possibly a fish oil in through the bolt holes after they're cleaned up but before fitting. – Criggie Aug 31 '16 at 7:37
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A tap/die is not the same thing as a thread chaser - while it can be used that way, you have a higher risk of cutting new threads instead of renewing old threads.

A proper thread chaser will clean up old threads with a much lower risk of cross threading. They can save threads that appear destroyed and are well worth the expense. Here is a Craftsman set that I use with great success (as of a couple years ago, still made in the USA):

Craftsman thread chaser

EDIT: Confusingly, this set is labeled as a "tap and die set" but you can see in the picture that the threads are much less aggressive than a regular tap or die.

I bet if you use some penetrating oil like PB Blaster and one of these thread restorers, those welded nuts would clean right up.

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    One of the sometimes-overlooked benefits of using these v/s a regular tap is that the heads of thread cleaners will work with a wrench or socket (usually the same size as the corresponding bolt), meaning you don't have to figure out how to rotate the tee handle of a pin vise or regular tap handle in a confined space; you can use a socket and extension just like on the bolt that will eventually go into the hole. – dannysauer Aug 30 '16 at 20:41
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    Only difference between a Tap and thread chaser is the chaser will not remove any of the original thread material and will push (swaging) metal back in place when threads are distorted, taps on the other hand vary depending on manufacture quality control, they can actually remove metal from the original threads, especially if the threads are distorted. – Moab Aug 30 '16 at 23:03
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Have you tried completely drenching them in PB Blaster or a similar penetrating oil? I've seen it work wonders in the past for me.

enter image description here

I'd cover them in a layer of that, and let it sit for several hours. Odds are, it'll dissolve enough rust that you'll be able to work a bolt into it.

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    PB Blaster is the shiznitz. It works especially well on rusted exhaust bolts. – Pᴀᴜʟsᴛᴇʀ2 Aug 30 '16 at 15:39
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    @Pᴀᴜʟsᴛᴇʀ2 risking going off topic here, but I always start spraying a day ahead of time when the exhaust bolts are cold, then again when they are hot, then again when they are cold. The heat cycling allows the 'shiznitz' to seep in and get down to bidniz. – MooseLucifer Aug 30 '16 at 15:54
  • Also Certified Labs Free certifiedlabs.com/certified/viewArticle.asp?article_id=1969 – Steven Penny Aug 30 '16 at 22:35
  • Add a little heat and shazzam! – Moab Aug 30 '16 at 23:06
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Save for the trouble of going to the store this is a pretty easy fix.

Take one of your bolts and go to a hardware or auto parts store and ask for a tap to match. Then run the tap through the holes.

The tap should go pretty easily. If not double check that it's the right size and then work by turning it in a turn it so and then backing out just a bit.

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    Provide enough lubrication while repairing the thread. As for lubrication: Since this is just some rusted steel even some drops of engine oil will suffice. – Martin Aug 30 '16 at 14:17
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Taps come in different styles. A starter tap will have a taper on it, rather than being parallel. So you can let it feel its way into the rusted captive nut. Finish off with a parallel. Failing that, taper the bolt end on a grinding wheel, and work it into the nut, a bit at a time. That's a good move anyway to start a tricky-to-line-up bolt. Obviously using lubricant all the time.I'd also try some extreme heat, as in oxy-acetylene, if there's no risk of anything catching fire.

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