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"Sombrero" mount



Hello All,

Yesterday trying to reassemble the crossmember and differential of my car I stripped the nut that is welded inside one of the "sombreros" where the crossmember is mounted. :( What can I do now??? So far I gathered a few "solutions", but of course I won't try anything unless I'm absolutely sure it is safe.

1. The obvious thing to do would be to get a new sombrero and replace it. That would mean paying some good $$$ for the new part, paying more $$$ to a welder to go there and do the job (this is way beyond my abilities!), and refinishing the frame (which is now beautifully painted). Of course this is the right thing to do, but I'll try to avoid it, if possible. But if there is no other option, well, you gotta do what you gotta do...

2. Retap it. The bolt size is 7/16" (I think). I bought a 1/2" tap. I think I should try it before I go to option #1 above. Ya know, nothing to lose... Or maybe I could try an intermediate metric size?

3. Maybe it would be possible to drill the upper, flat part of the mount, and use a long grade 8 bolt that would go all the way to the top of the mount, and use a regular
nut on the top? That's totally feasible, but would that compromise the integrity of the mount??? Would it be safe?

4. Others???

Your advice will be greatly appreciated! Thanks in advance!


If I were confronted with the same dilemma, I would choose choice #2 and drill and tap it a larger size. There would be no degradation in safety with this choice.
Second choice would be to install a longer bolt and nut like in #3. However, this would obviously (to a real NCRS nut!) would be a major change. If that does not faze you then it too would be a good choice.
Both of the above solutions are safe and much less expensive than option #1.
Windy but you asked for it!! LOL :)

Thanks for your reply! I guess I could always try option #2, and if doesn't work, then try #3, right? My only concern with #2 is that I'm afraid the nut would be weakened--I mean, there wouldn't be too much left after tapping it for a larger bolt.

Would you accept a ride in my car after I fix it using option #2 or #3? :)

I haven't done that area on my car yet so I'm not real well versed on the working room that you've got, but I along with thousands of other mechanics have had thier butts saved by the helicoil kits mentioned by 516manny. That would be, by far, my first choice.;)

So I'll show my ignorance now: what is a helicoil? I have no idea! :eek:

Thanks a bunch, guys!


The helicoil is a spring/coil type device you insert into the nut or where you need the threads. It replaces the original threads. They are used a lot, instead of using oversized bolts and having to tap the thread. Some work extremely well. Most auto-parts if not all carry them. Good Luck with your "Sombrero" mounting.

HeliCoil aka thread repair insert

HeliCoil is a brand name for a thread repair insert...you drill out to larger size...tap with SPECIAL helicoil tap...wind in the HC with SPECIAL HC tool...now you can use original bolt / stud. The HC is a spring-like device. I suggest you also look at other brand names E-Z LOK and XACT as these are SOLID (not spring-like) thread repair inserts and should permit you to apply far more torque to the fastener; they're installed in similar manner to HeliCoil. You can find these at Nolan Supply...here's a link http://www.nolansupply.com/ Get a free catalog from Nolan and it'll show you the tooling used for metal fabrication. Hope this helps.
Thanks guys! Now, that bolt takes a severe load, it's a grade 8 bolt and should be torqued to approx. 60 lb ft. Would this kind of insert work under this conditions? (Specially considering that there will not be much left of the nut after drilling it for the insert.)

Thanks again!
inserts safe?

IMHO, use of a thread repair insert for this application MAY be feasible...IF after being on the road you can monitor it / torque for a while. Keep in mind that the inserts are cheap; their installation tools / taps are not. I don't know the sombrero...can the welded nut be removed and a grade 8 or tool steel nut be tack-welded in place? How much for another sombrero?

The "sombrero" could be removed and a new nut welded inside, but since it's welded to the frame I would have to hire a welder to go to my garage and do the job--probably it woudn't be cheap. Also would have to trust the guy, since a bad welding job would probably be more dangerous than a thread insert or option #3 above, right?


on-site welding nixed

On-site welding would be pricey...otherwise might've been a $10 permanent fix...but safely welding a nut isn't rocket science. If, only if, you can keep an eye on the insert, I'd probably try it...and ride in it myself.
option 3

Can you also keep an eye on bubba option 3? Again, IF...IF...you can keep an eye on it...I'd try that one FIRST...yes, I'd ride in it. It is rumored that Bubbas were first propagated in Carolinas

The nut of the "sombrero" is completely hidden. Impossible to see or reach. Welding a new nut would involve removing and rewelding the sombrero back to the frame. After retapping or using a insert, the only sort of "control" I'd have would be checking the torque of the bolt. So option #3 would be the easiest to keep an eye on--I would at least see the nut. I wouldn't mind doing a "Bubba", as long as I can safely put my car back on the road soon. (Is there suck a thing as a "safe Bubba"? :))


Safe Bubba?

I'm afraid you're gonna have to make a judgement call here...unless someone who has done this very task comes along with advice. A fellow CAC member ssvett at http://ssautovett.homestead.com/home.html
may have run across this very problem. As for safe Bubbas...we can get away with murder in Florence County SC...literally...our Coroner (aka county medical examiner) is named Bubba Mathews...humorous maybe...but true! Try Steve / ssvett.

Hubby here,
finally got the keyboard away from Mrs. Silver.
Anyway, I have used these devices on many different applications and have even seen them used in some very precarious applications by engineer types.
In my experience and of my observations the helicoil is a sound solution.
I would recomend however that if you decide to take this route as a repair when inserting the replacement thread you use some locktite. After torquing drive it on a hot day let the thermals from the road do their thing and recheck the torque after you have parked it overnight and cooled down.
Should be good to go.


I got the keyboard back...he was gonna sign it "Bubba"!

Mr. & Mrs. Silver :)
Sorry if this is not relevant to the original post.

Heidi, you're not one of THOSE are you? (One of those situations where the husband never gets a word in edgewise.) :L

C'mon, you gotta share the keyboard more often. It sounds like you're keeping a very knowledgeable person from sharing with us. ;) I for one, want to hear more from "Hubby"; your husband Ken that is, not "Bubba". :L

...if the shoe fits...

I just couldn't let him sign the post "Bubba", I just COULDN'T!


Just heard from Jack Hill, from Hillco Fasteners, who sells fasteners for Dick Guldstrand, and he recommended drilling all the way through and using a long grade 8 bolt, with heavy duty flat washers at both ends and a grade 8 all steel lock nut. He says he's solved similar problems in this way with no problems.

Good, since that's the easiest and cheapest fix I can imagine! The only drawback I can think of is the possibility of water getting inside the sombrero, in which case it would be trapped inside and it would rust its way out. So I guess after I torque the bolt, drive it some, and retorque the bolt, then I'll have to seal it with some caulk or RTV. Or do you have any other suggestions?

Have an additional question: I've seen grade 8 bolts in hardware stores, but don't remember seing grade 8 nuts or heavy duty washers. Where can I find this kind of stuff locally?

Thanks for all the help! So please tell me, would you accept a ride in my car after this fix? :D


Let your fingers do the walking :D go to the Yellow pages of your phone book and look under Fasteners...
There will be a "Bolt Shop" somewhere listed there. That's what I did when I put new bolts in my rear spring assy.


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