Easy, Simple Broken Tabs Repair

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john keefe
Level 7
Level 7
Posts: 1022
Joined: Sat Sep 02, 2006 1:13 pm
Location: Campbell, CA

Easy, Simple Broken Tabs Repair

Post by john keefe »

As most of you have probably found, 30+ year old plastic tabs don't take much abuse. The main body of plastic might be OK, but those little tabs get brittle, and/or the profile often has natural stress-risers, which over time will shear off. So, how to fix... easily.

Yep, JB Weld/Quick-Weld, 3M stuff, etc. can work great, while most of those plastic epoxy bonders rarely do (for me, anyway). The 3M 34240 is really tempting, but expensive without a long shelf-life once open, which makes it a waste of $$$ if you've only got small things.

What I've found, though, is that a LOT of the Merkur trim and other plastics are a base form of ABS, which means they can be "welded" with the common ABS cement used for ABS pipes and fittings in construction. Not all plastics, of course, but surprisingly quite a few.

It's not an adhesive, but rather a chemical solvent/weld that actually melts the ABS a bit. So, if you're putting a couple pieces together, the finished product is one piece (which is why it works for sewage and drain pipes over a long period of time).

It helps to have a few sheets of different thickness ABS to make your parts/tabs. Just do a small application test on a hidden part of the plastic, and let it sit for a bit. Then, scrape off a little of the cement from your test area, and if the plastic is dulled, or even a little soft, then the cement is working. Make your ABS tab, rough up the contact areas, and use a little of the weld (the fabric ball on the applicator loads way too much at once, and is messy, so use a coffee stirrer, or toothpick to apply).

I've used this for a LOT of repairs lately, including those broken tabs on a Cossie grill. I've even reinforced the tab stress-riser areas with extra ABS filaments. (I think those tabs are usually broken simply when the hood is closed, which can put pressure all along the grill if your gasket is in good shape). You can always smooth it out with a wide-head soldering gun electrode.

While working on my door hinge (another post), I found another use for tab repair, this time with the bottom pocket which usually loses the locator tabs along the bottom, and the reinforcement/bulkhead cracks off where the upper screws bolt in. Couple pics... works great. Just cut 3/8" strips of 1/8" thick ABS, heated lightly with matches, and bent to a Z to where I wanted.
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dimswits
Level 3
Level 3
Posts: 253
Joined: Wed Jan 07, 2004 8:29 pm

Re: Easy, Simple Broken Tabs Repair

Post by dimswits »

john keefe wrote: Wed Jul 07, 2021 5:13 pm What I've found, though, is that a LOT of the Merkur trim and other plastics are a base form of ABS, which means they can be "welded" with the common ABS cement used for ABS pipes and fittings in construction. Not all plastics, of course, but surprisingly quite a few.

It's not an adhesive, but rather a chemical solvent/weld that actually melts the ABS a bit. So, if you're putting a couple pieces together, the finished product is one piece (which is why it works for sewage and drain pipes over a long period of time).

It helps to have a few sheets of different thickness ABS to make your parts/tabs. Just do a small application test on a hidden part of the plastic, and let it sit for a bit. Then, scrape off a little of the cement from your test area, and if the plastic is dulled, or even a little soft, then the cement is working. Make your ABS tab, rough up the contact areas, and use a little of the weld (the fabric ball on the applicator loads way too much at once, and is messy, so use a coffee stirrer, or toothpick to apply).

I've used this for a LOT of repairs lately, including those broken tabs on a Cossie grill. I've even reinforced the tab stress-riser areas with extra ABS filaments. (I think those tabs are usually broken simply when the hood is closed, which can put pressure all along the grill if your gasket is in good shape). You can always smooth it out with a wide-head soldering gun electrode.

While working on my door hinge (another post), I found another use for tab repair, this time with the bottom pocket which usually loses the locator tabs along the bottom, and the reinforcement/bulkhead cracks off where the upper screws bolt in. Couple pics... works great. Just cut 3/8" strips of 1/8" thick ABS, heated lightly with matches, and bent to a Z to where I wanted.

KIMG0133.JPG

KIMG0134.JPG
If you can't find abs cement near you, you can make your own by dissolving scrap abs in acetone. A nice thing about this is you can very easily adjust the viscosity of the resulting slurry for many different purposes. It dries very fast though as the acetone readily evaporates. Instructions abound across the web.

I recently repaired a Scorpio instrument cluster bezel with four completely broken screw tabs using homemade ABS slurry and some woven fiberglass.
Dimitri in NYC
88 Scorpio 2.5 Turbo
89 Scorpio 4.6 DOHC
02 E46 330Ci
17 MKC
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