Cross-thread from hell

Mark Worthington · 05-23-03, 02:16 AM

I think it's been over 30 years since I've ruined a festener by cross-threading...until the other night. [img]images/icons/frown.gif[/img] I was doing the simplest of tasks: attaching my rear calipers to the mounting ears on the uprights. I was having a hell of a time getting the cap screw to match up with the hole in the upright, and was trying to "pursuade" it with a wrench. The threads caught, and at first seemed OK but then started to feel "funny" and it got harder to turn. I ignored the little voice inside my head that was screaming at me and cranked it down. I realized I was in trouble when I tried to back it out. I was afraid I would break my 3/8" ratchet after I was putting enough force on it to lift the chassis off the jackstands (probably around 200 ft-lb). Since I only had one 10 mm Allen socket and it was for a 3/8" drive ratchet, and I had no breaker bar, I gave up for the night.

On the way home from work tonight I saw a Matco Tools truck and flagged the guy down and bought a 1/2" drive 10 mm Allen socket (and a couple other little goodies [img]images/icons/wink.gif[/img] ). The screw came out no problem with my big breaker bar, and boy is it messed up. Here's a pic:

As you can see, I trashed not only the cap screw, but the mounting hole in the rear caliper. The metal around the hole actually has a little lip that I hit with a file so it would show up. I think the root cause of the problem, other than my carelessness and impatience, was the fact that the calipers are powder coated (clear) and I think the powder coating in the hole in the mounting ear reduced the oversize of the hole such that it was impossible to get a good alignment. It would've been easier to pop the rotor off and relieve the hole a little with a round file, but then again hindsight is always 20/20.

Any recommendations how I should proceed? Should I just drill out and tap the hole for the next-larger size fastener? Should I see if a machine shop can repair it? I don't think this will warrant me getting a new caliper. Any input appreciated.

Bill Bayard · 05-23-03, 04:52 AM

Mark,

Try running the same size tap with a new bolt
first. The hole may not be as buggered as you think. Just make sure that you are more careful with the tap, that you were with the first bolt!If that doesn't work, go one size larger. Good luck!

Bill

Brian Magee · 05-23-03, 05:08 AM

Mark

No need to go one size larger. Fit a Helicoil. Threads in aluminium such as brake mountings should be fitted with Helicoils (or equivelent) to save the threads from binding.

Brian

Editor, Fortyfication.

Mark Worthington · 05-23-03, 09:42 AM

Bill, I think I took out about a third of the threads in the caliper hole and justdon't feel comfortable relying on the remaining threads to hold the cap screw in tension.

Brian, I think I'll go the helicoil (or equivalent) route. BTW, none of these threads are in aluminum. The aluminum upright has oversize holes through which the cap screws pass.

Ron Earp · 05-23-03, 10:57 AM

I almost did the same to mine but cleaned it with a tap first. I still haven't *uckered any holes on mine yet, but I've been over cautious throughout the entire build. I did break one tap with Hershal but it came out. I've been lucky. It was probably because he was egging me on and telling me to quit being so damn slow!! [img]images/icons/wink.gif[/img]

I'd helicoil it too, I think that would be the best option. RF is supposedly watching the paint and powder coat in the threaded and through holes now as it is easy to take care of when you're building the chassis and parts, but a pain to deal with once they are all done.

Ron

Ian K · 05-23-03, 12:01 PM

Say Ron, when do we get to see some progress shots?

You must be getting real close (and subsequently,
really antsy!) [img]images/icons/cool.gif[/img]

Ian

Fran Hall RCR · 05-23-03, 03:43 PM

A timesert is the strongest and most reliable way to repair your little faux pas.
Helicoils are just coiled wires where as a timesaert is a machined steel insert that is far stronger.
Good luck

Robert Logan · 05-23-03, 08:34 PM

Mark,

I will replace the offending item at no cost except you pay for the shipping in the US.

Our next shipment leaves for the US in just over a week and I will include what you require (please contact me to confirm parts required).

Great to see you both at Carlilse and I checked last evening with Jay and the wheel flares are about to be shipped.

Best wishes,

Robert

JayT · 05-23-03, 11:05 PM

Mark, I am to be in Boston next Thursday and Friday. Can we meet and I will bring flairs with me?

Mark Worthington · 05-24-03, 02:01 PM

Robert, thanks for your generous offer, but since I screwed up the caliper I will bear the financial responsibility. I do need a couple odds and ends and will give you a call on Moday AM (Sunday night my time) to discuss.

Jay, I work in Boston (Back Bay) and live in the 'burbs west of the city and would be happy to meet you at either location next week. Shoot me an email and let me know when and where works best for you. Thanks.