Car Buying Tip: A Gauge to Check for Bondo

"Tohru" (tohrurokuno) 11/04/2014 at 22:48 • Filed to: car buying, bondo

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I honestly can't believe I forgot about this one.

We used them all the time at the salvage yard. When we would go to the salvage and used car auctions and we had specific cars in mind to buy (i.e. a shop needed sheet metal or an engine for a customer job), we would bring along these little magnetic gauges to check for Bondo. Which is what I called it for the longest time, a "Bondo checking gauge".

Thanks to Denver looking at an AMC Eagle wagon, I found what it's actually called: a Magnetic Coating Thickness Gauge. O'Reilly's sells them under the brand name ProGauge II for $59.95.

How the gauge works is simple. It has a magnet on one end, attached to a barrel body and spring. The barrel body is calibrated in mils of thickness. The end of the spring not attached to the body is attached to a metal sleeve which goes over the body. Then, it works kinda like a tire tread depth gauge:

1. Put magnetic tip of gauge against sheet metal.

2. Slowly and steadily pull the metal sleeve away from the sheet metal.

3. When the magnet lets go, the reading of the barrel body at the edge of the metal sleeve is the paint and Bondo thickness in mils. Lower is better.

When using one, test first on the roof (where odds-are there's little to no Bondo work) before testing the suspect areas of the vehicle.

Happy car buying!

biker > Tohru 11/04/2014 at 23:14

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so what about guys that mix in powdered iron into the body filler?

Tohru > biker 11/04/2014 at 23:19

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Is that a thing? Because I've been working on cars and working with body shop guys for a long time and I haven't heard of it.

miadaman? yes please > Tohru 11/04/2014 at 23:36

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This is going straight to my Christmas list. A must have for any proud owners of 90s Honda really.

Rec'd for helping me spend car money.

biker > Tohru 11/04/2014 at 23:36

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I have heard of it in cheap "restorations" where car is done to pass off, & even engine numbers built up with iron added to the putty, or new numbers tig welded to make a matching number car, even seen 1 set of heads torch welded, this is to get the quick easy bucks, & a pro will think they need to correct stuff & make easy money, for example wrong belts hoses, tires, & small stuff, but car may be more incorrect than they realize. the iron in putty for numbers people got wise & use picks to see if they can poke into it, & so welding became the preferred method.

I been in the automotive scene around 30 years, worked in many shops under the table, & small restoration places, done body & mechanic work as side line to my primary job most of my life.

you probably wouldnt believe half the stuff I have seen done between Harleys, & automobiles. craziest is Harley cases, "broken"ahem, repaired, new correct bearing for the title year installed, different year cases use different style bearing races, so along with the "broken" section repaired & to not to "damage any numbers" however all new metal where the numbers go, & new numbers stamped in, with the correct fonts, & now a number matching bike, this being done by "professionals"

crowmolly > Tohru 11/04/2014 at 23:56

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Yes, it is, but I haven't seen it personally. That's "more calculated" fraud so it will be tough to catch.

AddictedToM3s - Drives a GC > Tohru 11/05/2014 at 01:06

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That's a neat tip. I never knew these existed. Definitely going to pick one up when I get the chance. I'd also add a paint thickness meter if the person can swing it. There's composite and metal thickness meters so it could help identify resprays or body work.

Tohru > AddictedToM3s - Drives a GC 11/05/2014 at 01:15

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The electric ones? I saw those when looking for this one. They're pretty cool. Knowing my luck though, every time I would grab the damned thing the batteries would be dead. This one has no batteries.

Klaus Schmoll > Tohru 11/05/2014 at 09:52

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This is the pro tool, for DIY stuff I simply use a cheap fridge magnet that once was in a cereal box. It can't hold more than 2-3 sheets of paper to a fridge, so it's good at finding bondo too. No help for finding thick paint though!