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Fitting a towbar in rusty holes
JoelP - 4/1/17 at 10:03 AM

My Jeep has not had a towbar fitted for 12 years, and now the mounting threads in a chassis rail are rusted beyond use. I'm thinking of drilling it up and replacing it with an m12 thread. Anyone done this, or any dire warnings? I can't see an alternative tbh.

designer - 4/1/17 at 10:23 AM

Just run a tap through it.

nick205 - 4/1/17 at 11:41 AM

quote:
Originally posted by designer
Just run a tap through it.


That would be my first action - lube it and run a tap through to clean the thread.

The difficulty I see with drilling /tapping it larger is ensuring the drill / tap run squarely through the material. Out of interest what is the existing thread...M10?

JoelP - 4/1/17 at 02:13 PM

Yeah m10. I got a bolt into it fine, but it wobbles even when fully through. The threads have rusted away, not just rusted up. In the process now of tapping it to m12.

nick205 - 4/1/17 at 02:54 PM

Fair enough - I assumed the existing thread would be rust covered.

David Jenkins - 4/1/17 at 03:45 PM

Can you get to both sides of the rail? If so, why not thread a longer bolt through and back it up with a nut?

907 - 4/1/17 at 04:45 PM

quote:
Originally posted by JoelP
Yeah m10. I got a bolt into it fine, but it wobbles even when fully through. The threads have rusted away, not just rusted up. In the process now of tapping it to m12.




Tapping to M12 is the way Joel.

!0.2mm is the drill size and this will take the old thread out completely.
Just make sure there's enough metal remaining after the M12.

llionellis - 4/1/17 at 06:27 PM

Depending on age it could be UNC 10mm bolt would be slack (very slack) in a 7/16 unc tapped hole.

bi22le - 4/1/17 at 06:58 PM

quote:
Originally posted by llionellis
Depending on age it could be UNC 10mm bolt would be slack (very slack) in a 7/16 unc tapped hole.


Its a 12year old Jeep. This was my thinking when I first read this. It won't be M10!

coyoteboy - 4/1/17 at 11:17 PM

Interestingly a search through forums suggests the engine and transmission bolts may be metric but a lot of the body bolts are UNC.

nick205 - 5/1/17 at 08:58 AM

quote:
Originally posted by llionellis
Depending on age it could be UNC 10mm bolt would be slack (very slack) in a 7/16 unc tapped hole.


I hadn't considered this and it could be on the money. If the hole is now drilled then tapping to M12 may be the only resolution.

As mentioned a nut on the other side could increase security of the fixing. Would a plain (untapped) hole then be batter?

02GF74 - 5/1/17 at 08:32 PM

quote:
Originally posted by nick205
Would a plain (untapped) hole then be batter?



It'lll be fine in that plaice.

steve m - 5/1/17 at 09:03 PM

Am I not the only one, who thinks, "the holes are so rusty that the bolts pull through" and .................
If so the metal around, the said rusty threaded holes will be so rusty, that its wafer thin, the first tug on the towbar will rip the whole rear end of the car ?

maybe, its just me then

gremlin1234 - 5/1/17 at 09:15 PM

another way to do it might be thread inserts / helicoils , but I don't think they are appropriate here.

Adamirish - 5/1/17 at 10:02 PM

quote:
Originally posted by 02GF74
quote:
Originally posted by nick205
Would a plain (untapped) hole then be batter?



It'lll be fine in that plaice.




It cod be trouble.

bi22le - 5/1/17 at 11:19 PM

quote:
Originally posted by nick205
quote:
Originally posted by llionellis
Depending on age it could be UNC 10mm bolt would be slack (very slack) in a 7/16 unc tapped hole.


I hadn't considered this and it could be on the money. If the hole is now drilled then tapping to M12 may be the only resolution.

As mentioned a nut on the other side could increase security of the fixing. Would a plain (untapped) hole then be batter?


Nuts in the other side would be fine if you can get there. You could lift your car from them 4 x M12 with bolts!

As long as the rust bit is bolted to hold ups. As previously mentioned.

nick205 - 6/1/17 at 11:51 AM

quote:
Originally posted by 02GF74
quote:
Originally posted by nick205
Would a plain (untapped) hole then be batter?



It'lll be fine in that plaice.



Oooops! A typo there

JoelP - 6/1/17 at 01:09 PM

Sorry for the slow reply guys, didn't see all these posts. I think you're right that it wasn't m10. Drilling it with a 10.5mm drill didn't remove all traces of rust, which I think rules out m10. My googling showed that an m12x1.75 thread starts from 10.5mm hole. As an aside, 'what hole...' on google throws up some amazing predictions - sex education isn't what it used to be!

So it now has 5 m12 bolts done up tight (6th is obscured by the exhaust, I'll get my mate to do that at the next service), and it pulled a tonne trailer fine.

Cheers for all the help.

JoelP - 6/1/17 at 01:11 PM

Oh yeah, no access to get a nut behind.