Door check strap renewal

Rodger

True Classic
My check straps on my '79 were getting tired and one of the ones on my '81 had a broken spring. The original style of these are hard to find and the replacements seem a little on the cheap side, quality wise. I bought one of those years ago from Art Bayless, but have never used it as I just never liked it as it was mostly all plastic.
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I was able to get a new spring from Obert's for the original style, but that was a couple of years ago and I don't see them currently available. But if your springs are still intact as on my '79's, and the strap just doesn't hold the door open as well, then you can replace the bobbin to restore them. What happens is that the narrow part of the bobbin where the spring rubs, wears over time and so the spring does not clamp it tight enough to hold the door open. New bobbins are available from Obert's as well as MWB and Henk.
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Here is the strap housing that had the broken spring. The bobbin is held in with a long rivet that can be easily removed by drilling off the spread end.
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I found this down at my local hardware store. It is a 1" x 1/4" shank with a threaded internal that a screw goes into. Here it is compared to the stock rivet.
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The 1/4" fits through the hole in the housing, but I had to drill out the center of the new plastic bobbin slightly to fit it. The 1" is about a couple of mm's too long, so I just filed it down until it was just below the surface of the housing.
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Here are the two different kinds of bobbins that I got. I can't remember who I got the white plastic ones from as that was a couple of years ago when I bought them, but I recently bought a couple of NOS ones from MWB, that were in a Fiat parts bag, but are gray.
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What is interesting is the difference in the internal narrow part of the bobbin where the spring goes. I measured the old ones at the widest unworn diameter that I took out of the worn strap. One measured 15.5 mm and one was 17 mm. The white bobbin in the photo measured 14.64 mm and the gray one measured 17.75. Kind of like Goldilocks here.

I compared the two new bobbin fits to a new original style complete strap that I had found a while ago but had not installed yet. The replacement white bobbin was looser than the NOS one I had, but the gray bobbin was very tight and did not allow any play in the spring. It would be very difficult to install it in the car due to amount of spring compression needed to fit it into the holding loops on the door frame. I would be concerned that the spring would either break, or the force to open the door and flex the spring would be too much. I elected to go with the white one.

Here it is put together with some thread locker on the threaded part of the center shaft.
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Thank you Rodger, excellent work.

I wonder if any of those bobbins are actually the ones used on the engine cover and/or rear trunk lid holders? That might explain the differences in sizes? Or some might be from various years or models of Fiats (or related vehicles) that had slight differences?

The bolt you used from the hardware store is called a "binding screw" or "post screw" I believe. If they come in some type of steel it would likely last longer than aluminum. These check straps have a lot of force on them.

I seem to recall back when the replacement springs ("hair pins") were available from one of the vendors, they were actually from a slightly different application (850??) and the instructions said to bend them a little to fit the X. I always thought a heavy spring steel piece like this would not be easily bent. If it could be then it wouldn't last long as a check strap. Might be why they are no longer offered?

It would be interesting if you mounted the repaired unit on one door and the "new style" one on the other door and see how they compare after awhile.

Gotta love this. Even Fiat's plastic rusts :D ....
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Also known as a sex bolt (seriously) or barrel nut.

Great little tutorial. Simple and nicely thought out.
 

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The bobbins I took out of the worn out ones are the same as the trunk and engine cover ones.

The post screws that I got are steel. There really doesn’t look to be that much load on them.
 
That is really interesting, and funny in a way because it is exactly what I did 30 years ago, right down to the binding bolt..in aluminum. But sadly it lasted no longer than an original. Still if we could just get a bobbin of the right dimension it might be worth another go now that I know I was not just me being stupid.
 
Again, excellent job. I really enjoy these kind of projects. Not only did you succeed in repairing the part, but it is as good as the original and better than most replacements. Plus it did not cost a lot.

I believe the trunk/engine lid bobbins are available as replacements. So are you saying they are a better fit?

My mistake on the bolt, at first look it appeared to aluminum in the photos. But now that I look back at it I can see differently. ;)
 
Fiatplus has both new and used bobbins. Chris calls them Strap or Prop Plastic Roller. Fiat part number 4263566. His bobbins are white, like the originals, not gray like the ones from MWB. My guess is that they would be the correct size. The white ones that I used are more translucent whereas the originals are more opaque white. I think the ones I used were some I ordered from Henk a couple of years ago.
 
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