Body to Frame Bolts

[Dennisfly]

1935, Tudor Sedan.


I want to remove a body to frame bolt near the battery box to use as a ground for a master electrical cut-off switch. On the underside is a nut and lock washer. The top end of the bolt that is under the floor mat is domed like a carriage bolt. There is nothing on top that you can get a wrench on and the bolt turns when you try to remove the nut.

How is this properly removed?

[DavidG]

It is indeed a carriage bolt and obviously the original square hole in the floor or sill is now round. About what's left in the way of alternatives is to weld something to the head of the bolt such as a hex nut to give you purchase on the head of the bolt.

[Pete]

Use a cut off wheel or an oscillating saw and cut the nut end of the bolt off. Replace with a grade 8 bolt.
If there is a wood spacer block involved, replace it with a piece of aluminum. Scrape all contact areas around the bolt down to bare metal. Use a COPPER star washer between the cable lug and the frame. Apply NoOx (a corrosive preventive goop) to all electrical contact areas before assembling.
Remember, this connection can be carrying up to 200 amps under starting conditions.

[Tinker]

I use basic connections with 00 welding wire. Off battery ground to body as usual. Then added a body to engine jumper. Then a transmission jumper to frame. Sometimes a 12guage off the frame for rear lights help.

Side note. Was going to take my 36 down to a neighbors for a camp fire. Thought I should check the lights. No go. Pulled the fuse and ran some sand paper through the connections. Fixed...

You can just have a disconnect at the battery. I just run a "loose" ground on the battery and discount it when sitting for long periods. As said, the first couple are solid mounts. No springs. Cut the old out and get a new one if that is the way you want to go.

[rockfla]

You can use a round head machine screw in its place, it will "closely" duplicate the round head (though slightly taller head) but will give you, either a slot or a phillips drive (most likely slot) to hold on to and will be covered by your mat. IF you like, PM me the size and your address and I will send you a couple of them IF you like.

[Ray in La Mesa]

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I've used a Dremel to cut a slot in the carriage head to fit a large screwdriver.

[Mart]

I have used a clamp and lever to put a lot of downward force on the carriage bolt heads. If the nut is not too tight, it can sometimes hold it still while the nut unwinds. Better to do it right from the start so you don't round it at the first attempt.

[Dennisfly]

Thanks guys.
I couldn't get good access with a saw or grinder. The bolt was in a corner where a cross member connected to the frame rail. I ended up center punching the top of the dome and drilling it out from the top. In any case, I will attach the cable as Pete suggests. Tinker, I had a 1 gauge cable made, and I like the switch because I turn it off every time I walk away from the car. Rockfla, thank you for the generous offer. I already bought the grade 8 bolt and it will sit in a small recess and be covered by the mat so I think it will be fine. Ray, you had the easiest solution of all, but it just didn't occur to me!