Another thread repair question. Male threads….

[IndyIan]

You can’t double nut this. This is the access…he can barely get the square nut back in there…

Holding a broken captive nut

On my 1991 mb 350sd I can tell the guide rod mount is loose. So I’m going to replace it, the bushings, and the lower control arm bushing. Everything went well until the captive nut on one of the main bushings broke. There is very little corrosion but apparently enough on this bolt to cause an...

bobistheoilguy.com

Well it's only metal, get out the hole saw... I know he doesn't want to hack this car up.
But for a beater, a significant percentage of the unit body isn't really doing much and could have a hole in it without consequences, but you have to do an educated guess where...
Now that I think about it, if there's space, adding some washers or a larger nut as a spacer, at the bolt head end can get the captive nut onto clean threads of the bolt.

 

[JHZR2]

If you’re looking to save a few $$ on this, @JHZR2 - Measure the bolt carefully (looks like a 12mm?) and then head over to www.belmetric.com to get a flanged bolt of exactly the same diameter and length.

Cut this one in half at the shank and pull it out. Re-use the washer with a new bolt.

Might have to expand the hole, just a touch, to fit the threaded portion through. Which is why you want the flanged bolt - to spread the load over the slightly enlarged hole in the washer.

I’ve replaced several “captured washer” bolts on European cars - they come with a new bolt, and new washer. They don’t come like that one, with the washer fitted inside the threads. So, a new bolt with the old washer will be fine.

Old Kent over at Mercedessource weld the bolts too. You bore out the big washer since it’s captured on the smaller neck bolt and it works fine.

That is an option.

If I didn't have the $60 or needed it to go to work in the morning, I'd double nut it after cleaning up the threads and probably forget about it.

I don’t care so much about the $60. It’s as much about the tools and skills. This one can’t be double nutted.

Buy the new bolt, don't halfazz steering & suspension components.

This isn’t a major steering or suspension element per se. It’s there to push back against movement of the LCA during braking for “smoothness”, as I understand. The holding of the bushing is really done by a nipple that hangs down and inserts into the bushing bore. This just keeps it up in the right place. If it was that critical they would use something more substantial than the captive nut. Im not really concerned with this assuming that it cinches up to the new captive nut.

 

[JHZR2]

I was able to find an m12x1.75 thread chaser and chaser tap. So I went over the bolt, and through the OE captive nut (there are two on this side, so the one that came off and wasn’t destroyed).

The chaser went down easily. The cleaner tap went into the OE captive nut easily.

The two didn’t go into each other easily. I think these captive nuts are the type that are a bit smaller at the end to provide a “locking” function.

The bolt seems readily usable, though part of the thread is still a bit clogged, and a chaser won’t clean it. Should I get a die instead? I don’t really want to remove any of the bolt. But it will thread on easier if I get that junk out… assuming that the bolt needs to thread in that far (which it may not)…

 

[Astro14]

I’d still toss that one and get a new one. The captured nut is, what, four threads deep? Tops? And you’ve got three buggered threads. I would worry about that.

 

[mrbreezeet1]

I was able to find an m12x1.75 thread chaser and chaser tap. So I went over the bolt, and through the OE captive nut (there are two on this side, so the one that came off and wasn’t destroyed).

View attachment 161367View attachment 161368View attachment 161369

The chaser went down easily. The cleaner tap went into the OE captive nut easily.

The two didn’t go into each other easily. I think these captive nuts are the type that are a bit smaller at the end to provide a “locking” function.

View attachment 161371


The bolt seems readily usable, though part of the thread is still a bit clogged, and a chaser won’t clean it. Should I get a die instead? I don’t really want to remove any of the bolt. But it will thread on easier if I get that junk out… assuming that the bolt needs to thread in that far (which it may not)…

View attachment 161372View attachment 161373

Were you able to torque it to the proper spec? If so, I'd call it good!

 

[mrbreezeet1]

Do you weld at all? MIG or a little stick welder? Put a few small tacks on the bracket this bolt is holding!
Ever need to remove it again? Cut your tack weld with a cut off wheel!

 

[JHZR2]

Were you able to torque it to the proper spec? If so, I'd call it good!

I did it in the vice, not on the car.

Do you weld at all? MIG or a little stick welder? Put a few small tacks on the bracket this bolt is holding!
Ever need to remove it again? Cut your tack weld with a cut off wheel!

That would be smart. But I don’t… don’t think it’s worth the money to buy one for this…


I’m not sure stick welding is worth it for my needs which would typically be sheet metal type stuff. And the others just get more expensive and more consumables for what I’d rarely ever use. As much as I love the thought of being able to weld.

 

[JHZR2]

I’d still toss that one and get a new one. The captured nut is, what, four threads deep? Tops? And you’ve got three buggered threads. I would worry about that.

The captured nut went on further than that, I just snapped the photo there…

I don’t know that the bad threads make much of a difference if they tighten properly and torque to spec. The major diameter of the bolt is still there. I may chase it with a die and see if that cleans things more. Worst case it digs too much material out and then I buy another.

I don’t think the bolts were installed more then. 2-3 threads on to start!

 

[JHZR2]

It’s holding the control arm onto the car. Those threads are buggered right where it engages with the nut.

I’d be fine with chasing the threads and smoothing them out, if the engagement took place at a different spot on the bolt.

But with the damage you show, even after chasing them, you’re going to have significantly reduced thread engagement right where it matters on a structurally significant part.

I would replace that bolt.

This is the guide rod mount, not the control arm. The CA has a special eccentric bolt and is a different thing.

The guide rod is just there to reduce forward/aft movement of the LCA under braking, since these cars only have one LCA bushing. The w140 got two, and maybe lost the guide rod?

 

[wrcsixeight]

I buggered some male threads recently, spinning the flanged nut, with powertool , well after it was fully loosened.
Lesson learned.
Thankfully it was just cheap casters on a rolling mechanics stool that i was replacing the casters on anyway, with some urethane wheels. So much nicer.

I was retasking the cheap casters , and the nuts refused to hand thread.
Good magnification and lighting revealed the smeared male threads from my hasty electric powered overzealous removal.

I used a thin diamond cut off wheel on dremel to 'unsmear' them, and they hand threaded, and are now retasked elsewhere.

Not saying this is always the case for all, but i bet many of those new to electric sockets, will smear the maLe threads on removal, spinning the potentially flanged nut with downward pressure, well after it is fully loosened.

Glad my lesson was inconsequential, in the end

 

[JHZR2]

My wonderful wife went to Grainger to pick up a Cleveland M12x1.75 die. Thread chasers weren’t cutting it.

Tried it on my good bolt. It threaded on very easy, just scraped the dirt and surface corrosion on the end, and went easy over the whole thing. I used Tap Magic cutting fluid.

So then I worked in on the one with bad threads. Went back and forth, and got it all the way down.

It really didn’t take off any material.

Came out excellent. The flattened area kind of got reformed to shape, and maybe a bit of a trough cut in it to clear it out. I think she spent $32 for a US made tool to save me $60 on a replacement. The captive nuts now spin right on very readily. Hopefully I can do LCA bushing and guide rod mount tomorrow!