6-Point Harness Attachment Points

[ddd4114]

I know this topic has been pretty thoroughly covered, but considering the importance of proper harness mounting, I wanted to get some feedback before diving into it. I'm probably being a little over-cautious, but... "better safe than sorry".

I already have a rollbar and a fixed-back seat installed, and I'd like to add a 6-point harness in the next couple of weeks. I took some rough measurements today so I can order hardware, and I realized that adding attachment points doesn't look as straightforward as I originally thought.

The shoulder belts are easy since they simply wrap around the harness bar, and I'll most likely use the OEM right-side lap belt location (provided on my seat bracket). However, the left-side OEM location is too far back. That side would have a much longer belt (more stretching), and it would be at too shallow of an angle per Schroth's instructions. Therefore, I'll have to add a new mounting point.

Based on Schroth's 60 degree recommendation, it looks like I'll have to add an eyebolt here, right in the corner of the floor:

I took some rough measurements, and it looks like that will end up somewhere around here on the bottom of the car (marked with the red circle):

However, due to the way the frame is shaped, it's pretty much impossible to add a standard reinforcement place there. My idea was to use an ~8" length of 1.0"x1.0" rectangular tubing (0.120" wall) and place it parallel with the frame rail to spread the load (see the blue outline in the image). However, the floor isn't very flat in that area, so I'm not sure how well that will work. There is as much as a 3/4" difference between the lowest and highest points, so I'd expect that it would deform a lot in anything more than a minor collision.

Next, appropriate locations for the anti-submarine strap mounting points seem limited. Once again, the normal reinforcement plates are too wide to use by themselves, so I'd have to do something different. Based on my rough measurements, the attachment points would have to be around the red circles in this picture to get a 6" distance between them:

It looks pretty difficult to get the attachments points closer to Schroth's 4" recommendation. Even at 6" apart, the floor near the transmission tunnel is (once again) very uneven, and the fuel lines might make the outboard point interesting. I think the 1.0"x1.0" tubing idea might work again here, roughly where I put the blue outlines.

Alternatively, I could make a structure that attaches to the seat bracket and has two eyebolts for the mounting locations. However, I'd rather not go with that idea because I don't want to load the seat bracket more than necessary. While the floor isn't very strong, I can reinforce it, and I'm not limited by the two M8 bolts and two M8 (I think?) studs that hold the seat in place.

Unfortunately, I don't have easy access to a lift or welder, so my options are a bit limited if I tackle this myself. Otherwise, I'll have to pay a shop to do it for me.

If I go with rectangular tubes for reinforcement, I'm also concerned about eyebolt length. I could probably use 1.0"x0.5" tubing with 0.065" walls and reinforce it with a section of 1/8" plate, but it would only give me another 3/8". Schroth only offers 22mm and 38mm eyebolts, so I doubt that I'll easily find something longer.

What have you guys done in the past that doesn't involve welding to the frame? Does my approach seem reasonable? I've spent hours reading things on the web, and I couldn't find any specifics for S197's beyond "drill into the floor".

Thanks.

 

[ddd4114]

Man, no replies in 2 days! Are my questions really that stupid?

I asked a couple people outside of this forum, and the consensus so far is to use the "careful, educated guess and check" route. I guess drilling a few small "inspection holes" and later sealing them with epoxy isn't a terrible approach.

 

[modernbeat]

Well, the inspection holes are a good idea. But I'd also drop the brackets for the lines and space them from the body with a chunk of 2x4 to move them out of the drilling zone and give you some space to put a larger washer and use some tools.

 

[NDSP]

Your placement of holes is very similar to where I would of had to put mine, which is why I didn't drill into the floor. I added angle iron to my seat bracket to install my I-bolts to. Then attached my belts to that. I just didn't feel like I had enough room to drill and/or it would have to be at a slight angle which wouldn't of been optimal. No issues at tech so far. Not a word about it.

 

[neema]

Look here for pics of user Black Boss' lower mounting points.

http://bossmustangsonline.com/index.php?topic=2494.msg106218#msg106218


edit: I'll make your life easier

For the Lap Belts I used the Cooltech harness mounts bolted to the rear seat track bolts:



For the sub belts, I drilled through the floorpan and used eyebolts:



Here's the view from underneath:



The LH bolt is very close to the Fuel pipe -- be sure to drill from underneath:



I used the Planted Seat base, Recaro sliders and Sparco side mounts. Had to drill a couple of holes to match the sliders to the base, but not an issue. I may eliminate the sliders once I've fine tuned the setup.

Used the nuts welded to the plates that came with the Schroth belts for the sub belts and applied silicon sealant to the plate prior to torqueing the eyebolts.

 

[jayel579]

Look here for pics of user Black Boss' lower mounting points.

edit: I'll make your life easier

This is pretty much exactly how I have mine setup. I have the same lap belt loops form Cooltech as well, they are very nice pieces to have. I just put some paint on the backing plates under the body so that they do not rust.

 

[ddd4114]

Look here for pics of user Black Boss' lower mounting points.

http://bossmustangsonline.com/index.php?topic=2494.msg106218#msg106218


edit: I'll make your life easier

Awesome, that's just what I was looking for. It looks like it is possible to use standard reinforcement plates, but of course I'll have to measure the hole locations to make sure they're even and not spaced apart too much. I'll probably still buy some tubing just in case since it's not very expensive.

Thanks everyone for your replies.

 

[neema]

ddd, just FYI, the plates in the post above are schroth units

 

[Arustik]

ddd, just FYI, the plates in the post above are schroth units

Purchased from HMS?

 

[ddd4114]

I was able to install the harnesses, and I figured it would be good to post some information about what I did for whoever finds this thread in the future.

The locations I marked in my first post were almost exactly where I drilled. However, I was able to use Schroth's backing plates as shown in the images that neema posted. I was able to do the whole job with the car on ramps, but it was a pain at times. However, since I removed and reinstalled the seats many times for test fitting, I'm not convinced that a two-post lift would have been much better.

Here is the left anti-submarine strap mount:

Here is the right one:

The left-side lap belt plate did need to be trimmed for it to sit flush:

I wasn't wild about removing material, but since the shape of the underbody in that area naturally adds stiffness, I'm not concerned about it. I had to remove the sealer on the right side of the plate, so I covered the area in an underbody coating before installing the plate.

For all three of those points, I used the supplied eyebolts from Schroth, put some red Loctite on the threads, and coated the backs of the plates with RTV. I did have some difficulty aligning the lap-belt eyebolt, and I found that an oxygen sensor socket fits pretty nicely over it...

For the right-side lap belt, I used the mounting point on my Planted seat bracket. Since I'm going to drive the car to and from tracks, I wanted to retain my factory seat belt, so I needed a way to accommodate both. Here is what I came up with:

I bought some high-strength M10 flange bolts from McMaster (Part #98093A629), and I used Schroth's 3/8" spacer, washer, and B63 bracket to attach the lap belt. For the OEM buckle, I purchased a bronze sleeve from McMaster (shown above, part #6381K457) that fit perfectly in the seat base. I had to enlarge the bore to 13/32" because I didn't have an M10 drill bit.

Using the flange bolt and a flanged nut, I pressed the sleeve into the seat base:

Since the sleeve was a little long, I had to add a 9/16" washer to keep the buckle in place.

Here are the belts before installing the seat:

I bought some 3/32" cotter pins (McMaster part #92375A175) because I didn't feel like messing with safety wire. They look a little goofy, but they work. I just had to make sure I installed them in a way that would prevent them from being pushed back out.

I installed the passenger's seat and harness in the same way.

Here is the finished product:

I didn't use any airbag simulators, so my SRS light is on. I zip-tied the seat track sensors on the seat brackets, and since I retained my OEM seat belt buckles, I also connected the sensors on them.

I didn't feel like ripping apart my passenger's seat to remove the bladder, so I just left that and the OCS module disconnected. I found that while the SRS light stays on, the MIL remains off. In fact, the MIL stays off if you leave the passenger's seat harness entirely disconnected.

Hopefully this will help other people who, like me, want to tackle the job at home. If you see anything that might get me killed, please let me know before I take the car to Mid-Ohio this weekend...

 

[jsbumed]

From what I can see in the pictures everything looks pretty good. You made the right call in trimming that backing plate. By sitting flush it will be able to distribute any load much better than if it had been at an angle. I'm personally not a fan of mounting any part of the belts to the seat bracket, but I understand sometimes it needs to be done. By mounting all points to the car/cage, in the unlikely event that the seat bracket fails, you are still restrained in place. There is nothing in NASA's rules that prohibit you from mounting to the seat bracket, just my personal feeling.

I'll try to get in touch with you in person at Mid-O and take a look at everything in person. From here it looks like you are good to go though.

 

[ddd4114]

Yeah, I'm also not a huge fan of mounting to the seat bracket for the same reason. However, due to the layout of the car, adding a mounting point to the floor would have been very tight (maybe even impossible without the belt rubbing). The only way to comfortably accommodate an eyebolt would be in the transmission tunnel, and I definitely do not like the idea of loading that thin sheet metal in shear - even with a good backing plate.

In case the pictures don't make my car obvious enough, I'm #41. I appreciate the help!