Check Strap Assembly

[Rob Glasgow]

The threads on my right hand door check strap assembly have stripped so I’m going the replace the left hand bolt and nut. The original is a course thread but I’m thinking of replacing it with a fine thread. My thought is that it might have better grip and the adjustment would be less exaggerated when turning the nut from one flat to the next when adjusting the tension. Maybe I’m over thinking it.
Any body care to offer their experience or opinion on course vs. fine thread?

 

[Healey Nut]

Either will work , but the fine thread will give you a more precise adjustment of the resistance through the friction disc .

 

[BobHaskell]

Rob,

As the door opens, the nut tightens on the bolt. With a fine thread, you won't apply as much pressure to the friction disk. So I don't know if it will work as well. I'd be interested to hear what you find out.

 

[red57]

I'd stick with coarse thread. As Bob said, the fine thread would not tighten as much when you open the door. Since these cars were built with fine thread fasteners everywhere, I think the use of coarse thread in this application was a deliberate engineering choice. I too, will be intested in hearing the results of fine thread if you make the change.

 

[Rob Glasgow]

UPDATE - Today I repaired the passenger check strap. After thinking about the comment red57 made about Healeys using plenty of fine thread fasteners so the engineers decision to use coarse threads for this application was on purpose. I chose to stay with the original design, with a twist. I purchased a 5/16" -18 x 1-1/2" grade 8 left hand bolt and matching Grade 8 LH nuts from McMaster-Carr. I spot welded 3 nuts together to give me the equivalent of a coupler nut, figuring the more threads in contact with the bolt, the less likely for it to strip. I had done this 20 years ago with the driver side door and it is still working perfectly. For the driver door I was able to buy a right hand thread coupler nut so that was more straightforward. I couldn't find a left hand thread coupler nut in 5/16" size so I built my own. The finished product works well even with the added weight of the side curtains. Here are some photos. If anyone needs any Grade 8 5/16"-18 left hand nuts, let me know. I had to buy 25 and I think this is the last time I will need to do this repair........

 

[John Turney]

Good work!

One thing that I did was to make new "wrenches" out of 1/8" steel. I think my check straps may have been reproductions because the "wrenches" kept bending and opening up.