Snapped welded nut off inside subframe/crossmember

So in taking my Control arms out I realized I needed to remove this bracket to let the furthest rear portion of the control arm free. the furthest 2 bolts cracked free easily, and the third which actually locks the plate down had huge resistance so I went slow at it. Then it stripped (at least I thought.) but I wasn't able to get the bolt to come out so thinking its attached to the nut and flopping around in the control arm.


How can I go about repairing this. It appears cross member is hollow I won't have access to the bolt either.


I can weld alright so I am thinking I need to cut the bolt and get the nut either out of there or tacked somewhere its not gonna rattle around and then weld a new nut in place? I doubt this has happened to anyone else! but any input is appreciated. I don't want to change the crossmember or subframe. I just read on a FJ forum that I could drill 3 small holes around the bolt get the nut back into place and then weld it. After this I would still need to remove the bolt, and do thread repair on the nut and that may work. But it would be a better repair using a fresh nut in my opinion damn my luck.





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Rust central

Alright I will be updating this post tomorrow but I have found a solution. Basically you need to drill 3-4 small holes in order to weld the nut back into place. At which point I will douse the bolt in penetrating oil every half hour as I finish the control arm job on the other side of the vehicle. Hopefully this will allow the bolt to spin free of the nut without breaking the welds I will be basically doing blind through the small holes. Hopefully I will have decent thread left on both pieces.

If the nut is stripped I will be able to drill it and tap it oversize. Or may replace the nut / bolt completely with some grade 8 Hardware. But this would require cutting a hole large enough to remove and replace the nut reducing structural integrity a lot more than 3 small holes drilled and filled with a mig when the process is complete.

I will take pictures, may make a slight tutorial. I think this is where Japanese cars fail is under rust conditions. There is not one P5 up here in Canada that does not have the Mazda, and protege logo and at least one rear fender ruined by rust. That being said all the bolts came loose a lot easier on the P5 than on my WRX swapped Legacy except for the one where the weld failed. Due to rust

I'm interested to see what you come up with to deal with this. You may be able to access the nut by cutting a small hole through the floor under the dash also.

duffbuster243 said:

I'm interested to see what you come up with to deal with this. You may be able to access the nut by cutting a small hole through the floor under the dash also.

Click to expand...

this is how the dealer fixes the problem when they break that nut or bolt.

bikingpro5 said:

this is how the dealer fixes the problem when they break that nut or bolt.

Click to expand...

Good to know. I lowered my subframe to replace front sway bar bushings, the bolts came out good but I might have overtightened the one too much and broke the welds on the nut because the bolt will keep spinning. When I have to replace a control arm I'll have to go in through the floor.

I didn't break the bolt or the nut. I broke the bad tack weld they install the nut with. if there selling cars in the Northern Hemisphere they should do better tacks we pay more for vehicles anyways. the fact that a 2002 is rusting to s*** is kind of embarassing for Mazda.

Well I dropped the crossmember only to find out ya its hollow. But the bolt is inside the frame / Unibody.. sooo I did all of that for nothing.


So now I don't know what to do. thinking If I get a drill bit long enough to drill up into the floor and then feed a longer grade 8 Bolt down with a nut. as Duff and Biking suggested. and as I was originally thinking I started to grind a small box to allow me to remove the bolt / nut (already grinded head of bolt off so I could remove the plate and actually see what was up there.) But found I got through the fender and inside there is more metal and I don't want to damage the integrity of the unibody.


I now have a chisel lost up there as well as half the bolt and the nut.. So If I just feed a bolt down how badly is it gonna bang around? I had to take a break after dropping the crossmember for nothing. time for a undeserved beer.




*Update. I can not drill straight up to the floor. If it was the bolt next to it I could but the one I messed up goes up and then angles so I don't feel it would be a sturdy place to put a load bearing bolt down.

So I did option 2 which I didn't want to do but hate being at a standstill. I drilled a small hole in the wheel well probably 2 inches up and a little the left of the bolt I circled in my picture.

With a little flash light I can see the bolt and the chisel I pushed into the hole and lost, tomorrow going to get a bendable magnetic "snake" this should help me get the chisel out. To get the bolt with half nut out I would need to make a huge hole. SO I am thinking I want to get a new nut in there, weld it into place and then install the other bolts after that I can find a place for the broken piece that won't interfere with the other bolts, I will then weld it in place inside the frame where it will be forever forgotten. Will finish off by spraying inside with rust paint, and welding the hole shut and then protecting the outside with more paint. Hopefully won't be to noticeable when I am finished, Actually it will look much better because anything painted flat black does