5 point harness mounting

[Bill Musarra]

I am about to start the mounting of my 5 point harness. In the DRB chassis, the center and outside mounts are part of the chassis. The upper shoulder restraints are another matter. There is a section of the bulkhead just under the rear bulkhead window that appears to be where they should be mounted. On this part I need to know how far apart they should be?? The seats have a through slot for their passage. But I am not clear where they should actually be mounted. I am 5' 9" with most in the legs(short body syndrome).
The Racetech seats as I mentioned have the pull through. Should the straps be pulled in toward each other a bit or out from each other? Is there a formula for this sort of thing? Mounting the shoulder straps to the bulkhead, will these mounting pieces work or will they need to be replaced? The bolts for the floor mounts are 7/16"-14 thread, unless since the car is Australian it is supposed to be metric and I am just forcing it. Any of you DRB guys set me straight?
The bulkhead piece is not drilled so some tough drilling will be at hand. I can use the plasma cutter to start one or two of the holes from the engine bay side. Since the interior guy has laid down some leather there, I will have to cut plugs in the leather and use starter holes with the plasma unit. I am including some shots of the area and the seats sitting loosely in the car. They will drop down at least 1/2" since there is insulation on the floor.
Speaking of the floor. The floor pan is the 2" ribbed variety. since the submarine stap will be mounted there, do I need to reinforce that area, or will a bolt through the full rib be sufficient?

Bill

 

[Howard Jones]

This is a very good question and you are doing the smart thing asking for correct information.

See below

and http://www.hmsmotorsport.com/docs/Competition_Instructions.pdf

and http://www.jegs.com/instructions/471/471harnessinstall.pdf

and Schroth Racing Harnesses

The mounting point locations are very important as well a being strong. Use nice big backup washers or another reinforcement in you have any questions about how strong the mounts are. Also use grade 8 hardware and only the correct eye bolts that are provided with the harnesses.

 

[Cliff Beer]

Bill, I wouldn't use a plasma cutter anywhere near that cross member - its integrity is important to your car's overall structural integrity (I see you have also installed a roll cage). If eye bolts through the cross member is the way to go then use some high grade eye bolts of moderate size - stay away from the cheesy stuff at Home Depot and check out some marine stores like West Marine for quality fittings. West Marine will have close ended (welded) eye bolts designed to take significant loads. Don't use the open ended eye bolts as they can bend and straighten under load.

For drilling the cross member just use good quality new bits and start with a small bit and work your way up to the necessary ID for the eye bolt. As suggested above use a thick washer on both the engine and the interior sides to distribute the load better. Finally, if you're using metric bolts then go for the 12.9 grade - these are very strong.

 

[Greg Marriott]

Bill, the seat belt eye bolts are 7/16"-14 which is a standard size here in Aus.

The cross member where you intend to fit the shoulder straps is a hollow section. I turned up some bushes with a flange on one end, put them through from the rear and then had a friend tig weld them in position. Just use a hole saw to cut the holes from each side.

I used a 6 point harness and pop rivetted (just to hold it in position) a length of 2"x1/2" aluminium to the underneath of the floor drilled and tapped 7/16"UNF for the eye bolts as I figured that should be strong enough for the crotch straps.

Greg.

 

[Bill Musarra]

Thanks for the quick replys. Howards links are just what I was hoping to get. Not only the angles and such, but the way to use(bend) the retainers.
Cliff, I am carefull not to stress the crossmember. I use the cutter just to put pilot holes and then use a step drill bit to get it to the right diameter. Trying to drill stainless with a hand drill, without a starter hole is near futile. To pop a pilot hole in the tube steel, though thicker, uses a minimum of heat and only takes 2 seconds at most. The drill bit with cutting oil, can then grab hold a lot easier.

Bill

 

[Chris Duncan]

Trying to drill stainless with a hand drill, without a starter hole is near futile.

Not really, if you use the right technique.

to drill stainless takes low rotation speed, high rate feed. In other words you need a variable speed drill holding it at the lowest speed it will turn at and you need to push the bit as hard as you can. Get your whole body behind it and straight arm it. Start with a sharp bit and some cutting fluid, it will go right through. BTW WD-40 is not cutting fluid. I don't know what you're using but you describe "cutting oil". You don't want oil/lubricant, cutting fluid is not lubricant.

What happens with stainless is it work hardens very quickly. If you high RPM the drill bit it rides on the surface and quickly hardens the metal surface harder than the bit can cut. If you cut down faster than you RPM it cuts down past the surface faster than it can work harden.

Work hardening is what happens when a metal is struck or scraped and it becomes harder on the surface.

prefer a 1/2 drill over 3/8, they turn slower and have more low speed torque.

 

[egoman/ Shawn Wedge]

Stainless will drill relatively easy with a quality cobalt bit and proper pressure to keep the cutting edge sharp.