I have thought the same thing about this. A couple more reasons could be the additional cost, plus the reality that most of their customers never go under the vehicle, so wouldn't see it anyway.
Why are some parts not painted or protected from rusting?
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I understand parts that get very hot don't need to be protected from rust. But others I don't get. For example, the Pinion flange for the rear diff.
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Or for example, the backside of the rear diff mount
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Both of these were severely rusted on my vehicle. I understand sometimes parts are not coated because they are meant to be "sacrificial" so that they would rust instead of others, but I don't think that is the case for these.
I'm guessing the answer is "because it doesn't need to be" as in the car will be junk before the outer part of the pinion flange or diff mount actually matters.
Or for example, the backside of the rear diff mount
Both of these were severely rusted on my vehicle. I understand sometimes parts are not coated because they are meant to be "sacrificial" so that they would rust instead of others, but I don't think that is the case for these.
I'm guessing the answer is "because it doesn't need to be" as in the car will be junk before the outer part of the pinion flange or diff mount actually matters.
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Some of you may remember’ back in the day ‘ they used to spray undercoating, sometimes it was standard other times Extra charge…was it worth it? Sometimes it just made pockets for the water to sit in, But. At least they “ tried “I understand parts that get very hot don't need to be protected from rust. But others I don't get. For example, the Pinion flange for the rear diff.
![]()
Or for example, the backside of the rear diff mount
![]()
Both of these were severely rusted on my vehicle. I understand sometimes parts are not coated because they are meant to be "sacrificial" so that they would rust instead of others, but I don't think that is the case for these.
I'm guessing the answer is "because it doesn't need to be" as in the car will be junk before the outer part of the pinion flange or diff mount actually matters.
The introduction of periodic emission testing took most of the 'clunkers' off the road up here (Ontario, Canada). It ended my habit of buying a 'winter beater' for a couple of hundred bucks to get me through the salt season. Now that affordable old cars are gone, they scrapped the testing program. Oh well.
Sure do. Similar consistency to roofing tar. Had to park on the street for a few days after or you had a real mess on the driveway. Ziebart was the big name for that around here, but there were others. Not sure if it did more harm than good for rust, but it was a decent sound deadener. Added a couple of hundred pounds to your curb weight to boot.
Yes it does harm. The moisture gets trapped underneath and rots the car. Just look on youtube.Sure do. Similar consistency to roofing tar. Had to park on the street for a few days after or you had a real mess on the driveway. Ziebart was the big name for that around here, but there were others. Not sure if it did more harm than good for rust, but it was a decent sound deadener. Added a couple of hundred pounds to your curb weight to boot.
For that reason I chose fluid film under my car which is just an oil based undercoating.
Mickey's and Ziebart were the only rustproofing companies that worked back in the 70s. The tar stuff was just technically undercoating that was often sold as "dealer rustproofing", and it was useless. That stuff was never meant to be anything other than sound deadening. Crooked dealers even tarnished the rustproofing reputation.Sure do. Similar consistency to roofing tar. Had to park on the street for a few days after or you had a real mess on the driveway. Ziebart was the big name for that around here, but there were others. Not sure if it did more harm than good for rust, but it was a decent sound deadener. Added a couple of hundred pounds to your curb weight to boot.
If you had your car rustproofed by Mickey's or Ziebart when it was new, it really didn't rust out, but it had to be done before it got soaked in salt spray.
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