Marsden Nuts
What is the purpose of the 8 marsden nuts that hold the rear bumper to the frame and brackets? Why are marsden nuts better than using regular hex nuts?
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Re: Marsden Nuts
Joe, a marsden nut is a self locking nut that threads on easily. Gary....
NCRS Texas Chapter
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Re: Marsden Nuts
Marsden nuts have a narrow recess machined on the bottom, adjacent to the threaded hole; the nut turns easily on a threaded bolt until the joint tightens up and the nut is torqued. When the nut is torqued, a force is generated along the hole's axis in the nut which is greater adjacent to the outside of the nut than it is adjacent to the hole (due to the recess). That force tends to squeeze the segments at the (slotted) top of the nut against the threads on the bolt, applying a radial self-locking pressure against the threads. The slots separate the segments, allowing them to be individually distorted inwards to apply the pressure.
They were rarely used due to their cost; the most typical high-volume applications were on rear leaf spring rear shackle plates (Chevy II, Camaro, Nova, etc.).Comment
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Re: Marsden Nuts
Apparently GM used 8 of them to afix the bumper of the 1960 to the brackets. Bubba removed all 8 and now I will need to figure out where the 8 go; nuts on order from CC. Thanks for the explanation.Comment
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Re: Marsden Nuts
I just repainted my brackets on the rear, the Marsden nuts were on the 4 studs that hold the bumpers to the brackets. I don't recall using 8 on the rear bumpers. Also, there is a ground wire that attaches to the left bracket, if you are repainting the brackets make sure you clean the area for the contact.Comment
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Re: Marsden Nuts
Phillip, at least 2 more marsden nuts hold the rear bumperettes to the bracket. I looked through the narrow crack between the bumper and the bumperette and saw a marsden nut on the passenger side. Bubba forgot to throw that one away! <grin> The remaining two may be under the body; haven't explored that yet.Comment
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Re: Marsden Nuts
Joe-----
Aren't these nuts shown by part number in the AIM? If the part number is shown for one application is a known Marsden nut, then when the same part number is shown for any other application that will also, of course, be a Marsden nut.
What is the part number shown in the AIM for the Marsden nuts?In Appreciation of John HinckleyComment
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Re: Marsden Nuts
Joe, you are correct about the part number being associated with a number and then you can see where that part is used on the same AIM sheet. The nut part number is 126012. AIM Section 14, Sheet 3.00 shows the nut in 3 places, but I believe the illustrator missed the 4th location, rear bumper bolt closest to the exhaust tubes. Drawing shows the single bolt passing through the rubber seal and then it gets lost at the back of the drawing, behind the side brace.
There is possibly a 5th marsden nut location. Two hex head bolt hold the bumperette to the bumper, but the drawing does not show what type of nut is used on the 2nd bolt. I am guessing it is a marsden nut since the adjoining bolt (part #122300) is capped with a marsden nut. I don't really want to remove the bumper to change a couple of nuts, but probably will anyway.Comment
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Re: Marsden Nuts
Joe-----
From what I can find, these nuts were never available from GM in SERVICE. However, they are very old "Standard Fastener" part numbers. So, these were once in the "repertoire" of GMs "standard parts bin" and not "special parts" with a part number assigned to a car or truck line.In Appreciation of John HinckleyComment
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Re: Marsden Nuts
Joe,
There is a marden nut on the bumperette, the side bolts into a tapped plate on the bumper there were no nuts. I had all the brackets off and the bolts looked to be run into nut plates in the frame and the lower part of the bumperette was also a nut plate. That would account for 6 of them.
Phil PorterComment
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Re: Marsden Nuts
Phillip, aren't there 2 bolts inside the bumperette? Both with nuts or just the one with the marsden nut? What is the second bolt fastened to inside the bumperette?Comment
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Re: Marsden Nuts
Joe if there are 2 bolts in the top portion of the bumperette I do not recall, I went out to the car and removed the lamp assemably and could only feel one bolt, but getting my "paw" in there was not really easy. The AIM only shows 1 bolt at the top but it does look like there may be another but it is not spelled out which they were pretty good about. I am looking at section 14 sheet 3.
Phil PorterComment
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Re: Marsden Nuts
i removed both rear bumpers last night; actually an easy task. There is one bolt inside each bumperette that has a marsden nut. One of the few places that remained unmolested on my car. I dipped both bolts/marsden nuts in naval jelly and then buffed with steel brush. Shiny as new!
I decided to take the left and right bumper braces (bolts to frame) off to remove rust and then repaint. The 3/4" bolt on the left twisted off and the nut is a welded on nut! The capture nut plate can be unbolted from the frame so I will remove the plate and have the old bolt drilled out and a new nut welded onto the plate.Comment
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Re: Marsden Nuts
Joe,
That sounds similar to what I did except I was fortunate not to have anything break, that being said, this is while you have it apart, I replaced all of the rubber items seals. MY orignal project started with exhaust replacement and of course needed to replace tailpipe retainer in the bumpers and well you know it keeps going.
PhilComment
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