1 Topic by proto17 (edited by proto17 2016-11-26 11:42 AM)

  • Registered: 2015-09-09
  • Posts: 31

Topic: Lap and sub belt mount check

I'm very new to prepping a car for racing.  I was hoping for some input to the mounting points for my lap and sub belts.  The car is an 88' BMW 535i.

Here are some pics of the mount points.  The shiny bit is the drivers side rear floor.  The rear seat mount (the thicker seat mount) is about an inch tall and I'm using a long eye bolt there.  I'm assuming that it's okay to just tighten that down in place without anything other than the required 2.5 inch washer and grade 8 hardware even though the seat mount is hollow.  Is that correct?

https://drive.google.com/file/d/0BzpbYv … sp=sharing
https://drive.google.com/file/d/0BzpbYv … sp=sharing
https://drive.google.com/file/d/0BzpbYv … sp=sharing
https://drive.google.com/file/d/0BzpbYv … sp=sharing
https://drive.google.com/file/d/0BzpbYv … sp=sharing
https://drive.google.com/file/d/0BzpbYv … sp=sharing
https://drive.google.com/file/d/0BzpbYv … sp=sharing

Here is a video of me pushing up on the floor pan near the left side eye bolt:
https://drive.google.com/file/d/0BzpbYv … sp=sharing

The concerns I have are:

1. The structural integrity of the rear floor for mounting the left side lap belt (check the video).  I'm wondering if it's fine for the 45 degree angle that it will be pulled from in an accident.  The actual floor has a rather large drain plug in the middle.  A small 1/2" strip near the plug is rusted out. 
2. Is it okay for the lat belts to come inward behind the seat?  I can't mount to the door sills because that's where the brake lines run sad  There are no jagged edges on the seat, so I am not worried about fraying for that reason. 
3. Is it okay to have the sub belt eye bolt where it is?  My only other choice is to drill into the frame rail which I was hoping to avoid.

Thank you very much for any input!

Fingers crossed that the links work O.o

-Dave

Edit: the links have now been fixed

2 Reply by proto17 (edited by proto17 2016-11-26 11:42 AM)

  • Registered: 2015-09-09
  • Posts: 31

Re: Lap and sub belt mount check

Well, the images didn't come through properly.  You should be able to right click and open the image in a new tab.  The rules don't let me post links yet sad

Edit: got enough posts now to change to URLs.  Should just be able to click the links now

3 Reply by ppressle (edited by ppressle 2016-11-26 09:33 AM)

  • Registered: 2011-04-07
  • Posts: 279

Re: Lap and sub belt mount check

You can't use the stock outboard lap belt mounting spot?

I would avoid using the floor as it is not very strong.  Perhaps a very large backing washer if you don't have other options?  I assume you have good sized backing washers on the tunnel and sub mounts?  I would put a spacer (washers?) to fill any air gap on that sub strap mount.

On my car, Pagel's shop welded a 4" x 7" plate onto the center tunnel and then welded a nut to the back of that..  Basically a large welded in plate to distribute the load.  They did the same thing for the sub belt mount.


I would send pictures to John Pagel with your question.

Pete

Cerveza Racing

ppressle's Website

  • From: Greenville, TX
  • Registered: 2009-09-11
  • Posts: 169

Re: Lap and sub belt mount check

I'm with Pete on the LHS stock mount. It's been great for us. We also welded plate to the tunnel and came in with the bolt between the heat shield below. Since the floor is flimsy, I welded a strip of the same material for the spreader plates all the way across and drilled through it for the anti-sub mount. Your floor looks to be in great shape, too!

I'm pretty sure I have a few OEM belt bolts, if you need the info for its dimensions or want to pay to ship one. Feel free to PM me with an email if you have other e28 questions.

Plain Jane '86 BMW 535i - Current
RIP People's Elbowed Protege - 2010
  • Registered: 2015-09-09
  • Posts: 31

Re: Lap and sub belt mount check

I am using the https://www.summitracing.com/parts/gfr-109l/overview/ and https://www.summitracing.com/parts/gfr-109h/overview/ eye bolts for the lap and sub mounts.  The washers are 2.5" which AFAIK is within spec for Lemons.  I could try welding some plate to the inside of the tunnel, but that's going to get *really* close to the drive shaft as the best mounting point that I have found is very close linearly to the center bearing.

I was really hoping I could use the existing seat belt mount on the left side, but the cage is in the way.  It's something that I didn't even think about since I didn't have the seat rails on hand at the time the cage was started.  I can get a screw on it, but an eye bolt wouldn't work as it wouldn't be able to turn and even if it did it would stick out the diameter of the tubing which seems like it would make a really weak set mount.

Thought has been given to welding brackets onto the cage, but I've been reading around the forums and I get the idea that making your own seat belt mount is rather frowned upon.  Reinforcing the floor and mounting that way seems to be the way to go.

On the topic of reinforcing, how would I go about making the left side lap belt mount stronger?  Seems that I would have to run plate steel all the way behind the back seat, or to the tunnel, or maybe to the frame rail.  Is it simply surface area that will do the trick?  Would something thinner like 1/4" or 1/8" plate work as well?  3/8" is gonna be a bear to get right O.O  It really sucks that the best place to put the mount just happens to be the home of all the brake lines.

I would put a spacer (washers?) to fill any air gap on that sub strap mount.

I'll see if I have anything on hand to make that happen.  Thanks!

I will also send John an E-Mail to get his advice.  Found his E-Mail address in another thread. 

Thanks for the advice!!!

-Dave

  • Registered: 2011-04-07
  • Posts: 279

Re: Lap and sub belt mount check

1/8 or 3/16 spreader plate would probably be fine.

What about getting a bolt in end on the lap belt and just bolting it in and not using the eye bolts?  Would that fit? 

Even with the large washer on the sub mount, with that air gap, it will likely distort if ever put under load.  Fill the gap or weld a plate to the top and bolt it to that.

Pete

Cerveza Racing

ppressle's Website

7 Reply by racinrob (edited by racinrob 2016-11-26 07:45 PM)

  • From: Shippensburg, PA
  • Registered: 2010-11-18
  • Posts: 1,963

Re: Lap and sub belt mount check

ppressle wrote:

What about getting a bolt in end on the lap belt and just bolting it in and not using the eye bolts?  Would that fit?

That is what we did.  I used the OE shoulder bolts on both sides. 

On the tunnel side the factory belt mount was too far forward, so we just used a nut welded to a 4" OD washer.  I then riveted the washer to the trans tunnel so I could remove the belts without needing someone underneath to hold the nut.


Edited:

After seeing the video and looking at the pics, particularly the next to last one, I can see that you have a bar that appears to be parallel with your door sill that is right in front of the OE belt mount.  I'd consider welding parallel pieces of steel to that bar.  Weld them just far enough apart to  allow the belt hardware to slip between them, with a little extra clearance.

"She's a brick house" 57th out of 121 and 5th in Class C, There Goes the Neighborhood 2013
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  • Registered: 2015-09-09
  • Posts: 31

Re: Lap and sub belt mount check

What about getting a bolt in end on the lap belt and just bolting it in and not using the eye bolts?  Would that fit?

I'm having a hard time visualizing your idea.  Would you mind explaining that another way?

After seeing the video and looking at the pics, particularly the next to last one, I can see that you have a bar that appears to be parallel with your door sill that is right in front of the OE belt mount.  I'd consider welding parallel pieces of steel to that bar.  Weld them just far enough apart to  allow the belt hardware to slip between them, with a little extra clearance.

I understand the the idea.  I'll make some cardboard templates and take pictures later today. 

Thank you both the the ideas!!!

  • Registered: 2015-09-09
  • Posts: 31

Re: Lap and sub belt mount check

After seeing the video and looking at the pics, particularly the next to last one, I can see that you have a bar that appears to be parallel with your door sill that is right in front of the OE belt mount.  I'd consider welding parallel pieces of steel to that bar.  Weld them just far enough apart to  allow the belt hardware to slip between them, with a little extra clearance.

Here is what I think you're talking about.

Two ideas for location:
https://drive.google.com/file/d/0BzpbYv … sp=sharing
https://drive.google.com/file/d/0BzpbYv … sp=sharing

Two ideas for how far inside to weld (one is a little more toward the middle of the tube):
https://drive.google.com/file/d/0BzpbYv … sp=sharing
https://drive.google.com/file/d/0BzpbYv … sp=sharing

I tried threading one of my longer eye bolts in and that wouldn't even reach the exiting mount hole before fouling on the cage.  To show the clearance issue I made this video:

https://drive.google.com/file/d/0BzpbYv … sp=sharing

The big issue I see is that I can't get to the back side of the cage to weld there.

I'm a little confused about how the belt would be secured.  Is there a bolt going through two plates (the white cardboard cutout in this case) and the belt mounts to that?

Thank you!

  • Registered: 2015-09-09
  • Posts: 31

Re: Lap and sub belt mount check

Can I get away with making the cardboard template out of 1/8" steel plate and welding it (single sided as I can't get to the back side) to the cage and then securing the belt to that with a large grade 8 bolt?

  • From: baltimore.md
  • Registered: 2014-03-04
  • Posts: 21

Re: Lap and sub belt mount check

If It was me. I would get the guy who put the cage in the way fix it. smile

  • Registered: 2011-04-07
  • Posts: 279

Re: Lap and sub belt mount check

Why not just drill through the spreader plate in a good location and install the eye bolt there?  On that bent section for example?  Put a nut on the back of that and it should be very strong.



I'm having a hard time visualizing your idea.  Would you mind explaining that another way?

If you can get a bolt into the original outboard seat belt mount location, then you can get your lap belt converted to have a bolt in style end.  With that type, you just bolt the end directly to the chassis and do not use the eye bolt style.  Like stock seat belt mounts.

Either of those could work.

Pete

Cerveza Racing

ppressle's Website

  • Registered: 2015-09-09
  • Posts: 31

Re: Lap and sub belt mount check

kapplegatejr wrote:

If It was me. I would get the guy who put the cage in the way fix it. smile

Well, if I had hired someone to do it, yes, I might go back to them.  But, this was done out of kindness for free by a friend.  His schedule was really tight and I told him to just go ahead and weld everything in and I would bring the seat mounts later.

So, having gotten the cage installed for free, and being the one who didn't have the seat mounts to check things out, it's my fault and I'd be an ass to send it back to him.

  • Registered: 2015-09-09
  • Posts: 31

Re: Lap and sub belt mount check

ppressle wrote:

Why not just drill through the spreader plate in a good location and install the eye bolt there?  On that bent section for example?  Put a nut on the back of that and it should be very strong.



I'm having a hard time visualizing your idea.  Would you mind explaining that another way?

If you can get a bolt into the original outboard seat belt mount location, then you can get your lap belt converted to have a bolt in style end.  With that type, you just bolt the end directly to the chassis and do not use the eye bolt style.  Like stock seat belt mounts.

Either of those could work.

Pete

I would love to either drill into the spreader plate or the actual rocker (I think that's the right word).  Trouble is that the brake lines (and maybe the gas lines too) run directly under the flat bit just before the slight bend to the floor.  I measured and found that the angled bit was not large enough for the mandatory 2.5" washer.  I could bend the washer around the angles, but I had assumed that would be a no-no.  Also, am I allowed to drill into the spreader?  Another thing that I had assumed to be a bad idea.

Thank you very much for the ideas and detailed description!  I'll have a look at these today.

  • Registered: 2011-04-07
  • Posts: 279

Re: Lap and sub belt mount check

If you are drilling into the spreader plate, that is much more substantial than the washer and you would not need the washer.   Confer with Pagel, he'll get you set up properly.

I don't know if there are rules against mounting the seat belts to the spreader plate.

Cerveza Racing

ppressle's Website