Seat Bolt Floor Inserts

E28 technical advice asked and given! Troubleshooting, modifications and more.
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ARico08
Posts: 61
Joined: Jul 27, 2017 9:00 PM
Location: Mesa, AZ

Seat Bolt Floor Inserts

Post by ARico08 »

I've got an interesting issue that I'm hoping someone can help me with. I swapped out the front seat of my 535 and when bolting the new seat in, one of the threaded inserts in the floor fell through. I tried searching, I tried to see if I could get at the insert but haven't figured out a way.

If anyone could assist me it would be greatly appreciated, three bolts seem to hold the seat fine but I would be more comfortable with all four.
Mike W.
Posts: 26872
Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: Seat Bolt Floor Inserts

Post by Mike W. »

Yeah, you want all 4 bolts holding it in place. Normal driving, no big deal, but in an accident, it might be.

Anyway, I'd have a go with a magnet, crossing your fingers of course. If you can retrieve it you might be able to glue it in place to install the seat, goop or something. It wouldn't be structural, just to hold it in place to bolt up. Barring that, there was a similar thread not too long ago, I don't recall the details even though I had some input, but spend some time on the search button and try to dig it out.
ARico08
Posts: 61
Joined: Jul 27, 2017 9:00 PM
Location: Mesa, AZ

Re: Seat Bolt Floor Inserts

Post by ARico08 »

Mike W. wrote:Yeah, you want all 4 bolts holding it in place. Normal driving, no big deal, but in an accident, it might be.

Anyway, I'd have a go with a magnet, crossing your fingers of course. If you can retrieve it you might be able to glue it in place to install the seat, goop or something. It wouldn't be structural, just to hold it in place to bolt up. Barring that, there was a similar thread not too long ago, I don't recall the details even though I had some input, but spend some time on the search button and try to dig it out.
Do you remember any key words from the thread? I've tried searching "seat bolt insert" and variations on that but couldn't come up with anything.
Mike W.
Posts: 26872
Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: Seat Bolt Floor Inserts

Post by Mike W. »

ARico08 wrote:
Mike W. wrote:Yeah, you want all 4 bolts holding it in place. Normal driving, no big deal, but in an accident, it might be.

Anyway, I'd have a go with a magnet, crossing your fingers of course. If you can retrieve it you might be able to glue it in place to install the seat, goop or something. It wouldn't be structural, just to hold it in place to bolt up. Barring that, there was a similar thread not too long ago, I don't recall the details even though I had some input, but spend some time on the search button and try to dig it out.
Do you remember any key words from the thread? I've tried searching "seat bolt insert" and variations on that but couldn't come up with anything.
Man, I'm all over this place like a bad rash, I can't remember that stuff!

Might want to include mount, insert doesn't ring a bell. Just keep trying different combos, Jeremy shortened the search again time after we griped too much. So you can keep throwing new search terms in there.
WVe28
Posts: 2125
Joined: Jul 29, 2007 8:57 AM
Location: Charleston, WV

Re: Seat Bolt Floor Inserts

Post by WVe28 »

I've seen one drilled all the way through the floor and a bolt inserted through the bottom. Just make sure it's well-protected and undercoated if you go that route.
vinceg101
Posts: 4802
Joined: Jun 20, 2007 2:40 AM
Location: Los Angeles, CA

Re: Seat Bolt Floor Inserts

Post by vinceg101 »

The loss of these seat bolt mounts is pretty common in my experience (at least in an informal poll with a bunch of folks here on this forum). There is something about the make-up of the steel of the support box frame the seat sits on that makes it kind of weak. Given the constant loading and unloading of the seats along with the torque those bolts and capture T-Nuts are under, it is only a matter of time before one or more of them give out.
I just went through this and knew my inside driver's side bolt mount was failing, but when I took my seat out for something I saw that it was only hanging on by a thread. A small touch made it drop through the box frame before I could try a JB Weld temp repair. Your condition probably looks like this:
Image

And the other side looks like this: the beginnings of a failure:
Image

The proper solution is to patch the hole and replace the T-Bolt mount with a graft from either an intact parts car or fabricating a new piece from steel stock. I did see someone simply weld in a bolt in lieu of a capture nut, and while that can work, you still have to do the same amount of work so why not weld in the proper capture nut. (Sorry I don't have or can't find a picture of the capture T-Nut; to be clear it is the steel that the nut is attached to that fails not the nut so you can in theory re-use the capture nut as long as you give it something to mount to.)

In my case I had a lot of help from my trusted comrade Ralph who just so happens to know his way around a welder (or at least enough to do this job). He also had the grafts from a car he was breaking so he cut them out and brought them down. We ended up doing both the Driver's sides mounts since I didn't want to do this again in a year when the other side failed. For the Driver's outside mount, we ended up just doing a reinforcing weld around the existing position rather than a replacement. I might eventually get around to do this to the Passenger's side but I'm sure it is no where near as bad as the Driver's (to be expected).
Image
Image
Image
Image

After that was some primer for now to seal it all up. I will get around to re-painting these when I re-do the interior next year. For now the seat is stabilized, strong and most of all safe. You really need to have all four mounting points because if you don't the stresses on the other mounts rises exponentially and will cause premature failure. Besides, do you really want to drive around knowing that during a minor collision your entire seat can be ripped from the floor?
Last edited by vinceg101 on Apr 21, 2019 10:36 PM, edited 1 time in total.
Mike W.
Posts: 26872
Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: Seat Bolt Floor Inserts

Post by Mike W. »

Mike W. wrote:Welding would be the preferred choice, but I'll throw out another option too. Now I think it's boxed in from underneath and this assumes that.

You'd have to make the exact size determinations on site. Get a piece of flat bar steel, steel, not aluminum. Probably 3/16" thick by 1" wide and ideally 3 or 4 inches long. You might have to enlarge the hole a bit width wise, but get it so you can slide the piece of flat bar in. Have tape on it or something so you don't drop it and have an unfixable rattle. Figure out exactly where you need the hole to be, remove it, then drill and tap the hole to the correct size. Now how you affix it below is up to you, you could drill and tap smaller holes, at least 2, ideally 4, 6MM or 1/4", or pop rivet it in with long (and make sure they're long enough) steel pop rivets. Most common is aluminum, but get steel, they're not that hard to find. You can then predrill everything from above, sliding in rivets to locate, without riveting while you drill the other holes. Then slide the flatbar in, with a bolt in the seat bolt hole to hold onto, and bolt or rivet it in place.

The reason of course the rear is double metal layers is front end accidents are much more common and at higher impacts, meaning the seat would tear out easier. Not to mention the seat belts are bolted to the seat frame.

A couple of hours work, but not all day. For access you could even cut the carpet slightly as it's under the seat there and glue it back in place or put some fabric/vinyl backing under it and glue it to that to keep it together.
http://www.mye28.com/viewtopic.php?f=2& ... &p=1453405

I should add to Vince's comments, his car is a special one, and I say that with respect, not sarcasm, it's not exceptionally nice, it's extraordinary nice. :up: Which means depending on your car, resources and abilities, his fix may be overkill.
vinceg101
Posts: 4802
Joined: Jun 20, 2007 2:40 AM
Location: Los Angeles, CA

Re: Seat Bolt Floor Inserts

Post by vinceg101 »

^^^
Why, thanks Mike I appreciate the compliments.

I have to point out that what I did was really no different than the method you quoted in your copied caption albeit with a few less steps. I was prepared to do exactly what you described: get a piece of steel bar stock, weld the nut onto the bar stock and then weld onto the box frame over the original hole. It just turns out Ralph had access to an E28 in a yard and grabbed that section of the box frame so we eliminated a few of those steps. (I forgot to mention in my post above that Ralph also hit the capture T-Bolt on the replacement graft with a weld bead for reinforcement.)

I approach these repairs from the standpoint of not wanting to deal with it ever again; therefore I tend to invest a lot of effort in going for the longer, more thorough methods. Of course it helps that I don't drive this car every day so if it takes twice as long to do these tasks, who cares? But the OP's situation may be different.
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