View Full Version : Different approach for seat and belt mounting
JohnUlaszek
05-26-2010, 01:02 PM
Some work in progress for an upcoming GM High Tech Performance story.
This is the drivers side floor pan of a 89 Firebird. I removed the seat support structures and recessed a 1x2.25x.120 structure into the floor to attach a new seat adapter bracket with pickup points for belt
hardware.
These are work in progress, the seat adapter bracket is an earlier photo and doesn't show the crossmember for the sub straps or the additional gusseting.
https://static1.pt-content.com/images/pt/2010/05/4642209402_73318600b5_o-1.jpg
https://static1.pt-content.com/images/pt/2010/05/4642212880_b4a46c7122_o-1.jpg
JohnUlaszek
05-27-2010, 06:38 PM
I had really hoped to tie lap and sub strap belt mount points into the seat adapter, but it doesn't look like that's going to work out. I did some calculations and the bending stresses are higher than I can account for in the limited amount of space I have for gusseting the lap belt attach points. If I could have kept the load path a bit straighter it would been fine, but then I would have had issues with the belt rubbing.
I started over on a simpler adapter and will tie the lap belt and sub straps into plates welded to the floor and tied into the cross member.
I am still planning on using the OEM lap belt attach points as extra attach points for the seat adapter bracket.
The upside is that the seat is still over three inches lower than it would have otherwise been.
JohnUlaszek
05-30-2010, 07:43 PM
Decided to retain sub strap mounting on the adapter. Lowered the bracket another quarter inch, ditched the lap belt mount points, but kept attach points for the Schroth six point's sub straps.
According to Schroth, the sub strap(s?) see up to 1,200 lbs -- unfortunately the documentation doesn't mention duration or if this is for a five or six point, so I designed around a static load of 1,200 lbs at each attach point with the belt at a 45 degree angle which is conservative as the installed condition should be closer to 20 degrees.
Except for a bit of gusseting at the lap belt fastener location at the back of the bracket. (photo right) going this is the final revision.
https://static1.pt-content.com/images/pt/2010/05/4654484517_e989af3758_b-1.jpg
64Chevelle
05-31-2010, 01:17 AM
Interesting, I'm planning for something similar in my 64 Chevelle. I hope to greatly increase the structural rigidity of the floor pan while I'm at it.
JohnUlaszek
06-01-2010, 06:43 PM
Interesting, I'm planning for something similar in my 64 Chevelle. I hope to greatly increase the structural rigidity of the floor pan while I'm at it.
The floor pan is much more rigid now and has very little deflection even when standing on it. Of course it's hard to say what this really does for total vehicle stiffness.
The idea for a crossmember came from Detroit Speed's transmission crossmember -- I would have happily bought one from DSE instead of piecing one together if they made one for third-gen f-bodies.
https://static1.pt-content.com/images/noimg.gif
64Chevelle
06-02-2010, 04:26 AM
The floor pan is much more rigid now and has very little deflection even when standing on it. Of course it's hard to say what this really does for total vehicle stiffness.
Well, I think it can contribute quite substantially combined with other mods and stiff body bushings.
The idea for a crossmember came from Detroit Speed's transmission crossmember -- I would have happily bought one from DSE instead of piecing one together if they made one for third-gen f-bodies.
Of course, but we're not always that lucky, are we.
silver69camaro
06-02-2010, 10:24 AM
The floor pan is much more rigid now and has very little deflection even when standing on it. Of course it's hard to say what this really does for total vehicle stiffness.
The idea for a crossmember came from Detroit Speed's transmission crossmember -- I would have happily bought one from DSE instead of piecing one together if they made one for third-gen f-bodies.
Give us a call. We're pretty decent at bending box tubing.
PhillipM
06-02-2010, 12:32 PM
The floor pan is much more rigid now and has very little deflection even when standing on it. Of course it's hard to say what this really does for total vehicle stiffness.
The idea for a crossmember came from Detroit Speed's transmission crossmember -- I would have happily bought one from DSE instead of piecing one together if they made one for third-gen f-bodies.
https://static1.pt-content.com/images/noimg.gif
I just can't bring myself to justify $725.00 For 4 bends and a few othersmall pieces. As for making the body more rigid, the seat pans are probably one of the strongest areas in the center floor section so my opinion is that, it is adding stiffness but not in a super crucial area. But hey, I'm no engineer.:guilty:
John Wright
06-02-2010, 01:04 PM
I think what it(bracing across the seat pans) helps do is tie the ends of the subframe together.
JohnUlaszek
06-02-2010, 06:32 PM
Give us a call. We're pretty decent at bending box tubing.
I completely forgot about you guys, and after the custom work you did for John Parson's IIMuch, I can't believe I didn't think to call. A pre-bent shape would have saved a lot of time; I probably have over 100 hours into this floor and seat brackets.
If a cross member is bolted in on the ends or even welded in on the ends I don't think it stiffens things up much unless triangulated in some way, but recessing into the floor and fully welding the sheet metal to the tubes turns the floor pan into a bit of a shear panel and the difference in floor pan stiffness is very significant especially if the member crosses over the tunnel thus working in multiple planes.
Third-gen f-bodies like the 89 Formula above are really tough to tie together effectively, but a crossmember would make a great place to tie in real subframe connectors.
Stiffening the car was secondary to getting the seat lower for me and ditching the factory crossmember was worth almost an inch.
JohnUlaszek
06-05-2010, 06:56 PM
I decided to ditch the factory lap belt attach points as they weren't in an optimal location and the backing plate was actually in the way of where I wanted the new one. While I shouldn't have been surprised, there was significant rust between the hardware and the 18 gage sheet metal.
https://static1.pt-content.com/images/pt/2010/06/4673662756_71b49d104c_b-1.jpg
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