Suspension mount built into a unibody

[Motorcitydak]

I have to build the upper mount for my rear 3 link into the unibody floor. Can you guys put up some pics of this? According to Billy Stropes website, this mount will see about 1500# of tension under acc. It has to be 5 inches off center and I have a specific height where the mount needs to be so I will have to build around that. I am probably going to build it using 1/8 and 1/4 steel plate. Should I put in a bar or two to anchor it to the frame rail? I saw the 3 link that XV motorsports has a mount that just welds to the floor.

[Norm Peterson]

If the upper arm sees 1500 lbs axial load. there will also be a moment applied to the unibody floor equal to 1500 lb x whatever the distance between the UCA and the floor. IOW, at the floor you need to resist more than just 1500 lbs in shear.

I can't imagine adding a bracket for a 3rd link that is not backed up by at least some local stiffening/strengthening. Perhaps in some floorpans the shape, thickness, and existing panel stiffening is sufficient, but I would not count on that being the case.

In any event, you should keep the stresses are relatively low (due to fatigue effects).


Norm

[Bryce]

I plan on running a cross member between the frame rails for my chassis side 3-link mount. this may also tie into the subframe connectors. I dont think I will attach to the floor at all.

[Motorcitydak]

Just wanted to update this thread with what I ended up building to hold my upper link. The bracket itself is made from 1/8 cold roll steel, the sides are 2 pieces laminated together. The tube is 1x2 0.125 wall. I cut the ends at 5 degrees each giving it 10 total. Since this bracket will see tension, this will force the tubes even harder into the frame rails making sure that they will never go anywhere

https://static1.pt-content.com/images/pt/2010/11/DSCF1015-1.jpg

https://static1.pt-content.com/images/pt/2010/11/DSCF1016-1.jpg

https://static1.pt-content.com/images/pt/2010/11/DSCF1021-1.jpg

https://static1.pt-content.com/images/pt/2010/11/DSCF1027-1.jpg

https://static1.pt-content.com/images/pt/2010/11/DSCF1024-1.jpg

https://static1.pt-content.com/images/pt/2010/11/DSCF1023-1.jpg

https://static1.pt-content.com/images/pt/2010/11/DSCF1053-1.jpg

[19,69camaro]

How long do you plan on making your upper link? Also where are you going to mount your lowers? Many of the triangulated 4-links use the stock leafspring forward mount to catch the chassis side lca. Then again Im not familiar with early chargers

[Motorcitydak]

The upper will be about 8.5. I know its short, especially compared to the 22 inch lowers. I checked out the suspension travel, the pinion angle will change 6 degrees thru out suspension travel

https://static1.pt-content.com/images/pt/2010/11/DSCF1031-1.jpg

[67zo6Camaro]

Good concept Steve, you have the right idea. The 1x2 .125 wall sq tube might still flex unless you add some triangle supports to that. The piece you have used looks about +-36" long. Try taking another 36" long piece and laying it down on the ground angled up to a curb or step...now bounce up and down on the middle. I suspect you will see deflection. In that case, you can up the size if you have room, or use some type of backing frame work under the seat area on the other side so that it will reach and attach to onther core support in a direct line. Remember the force will be in the direct line of which direction the upper 8.5" arm is pointing (in both directions forward and back). Ill have to dig out a picture of a backing support I have put under a seat with a 4 link.

Brett
fab53.com

[Motorcitydak]

Thanks Brett, I did forget to mention that. That was part of the reason I put that foot on the mount. I will weld it to the floor pan and put a larger backing plate on the inside that will be welded directly to the foot by drilling a few holes thru the backing plate and floor. Ill plug weld those holes up and I think that should about take care of it.

I really wish I could have mounted that bracket on something and huge 2000# or so on it to see how much it would flex. I do not doubt that it would move a little, just hopefully not too much. I close to lay the 1x2 down that way because the 2 inch long sides will resist flexing in that direction a lot more than if I had mounted it standing up or if I had used round tube

I guess if it does flex too bad I can put in a tube onto that backing plate that can run forward and down thru the floor to attach to the frame rail or the frame rail connector

Here is the drawing I did of the rear end

https://static1.pt-content.com/images/pt/2010/11/DSCF1038-1.jpg

[67zo6Camaro]

Is that at full drop to full compression. You will only see +-1.5" to 2" of real travel at ride height depending on a leaf spring or coil-over application.

Brett
Fab53.com

[Motorcitydak]

Yeah that was a full cycle of the suspension iirc. The circles drawn on the vertical lines showed the axle centerline. That was 1/4 scale so 1/4 inch (1 box) represents 1 inch. I think I used 7 inches of suspension travel. I think I planned for 3 up and 4 down. Actually 2.5 up until contact with the bump stops

O, and ill be using some type of coil over shock

[67zo6Camaro]

Sounds good. Also a side note....looks like you can turn up the power on your welder to lay down the "worm" looking weld. Just a little hotter should do....or dial back wire speed slightly and go slower.

Good luck.
Brett
fab53.com

[Motorcitydak]

Cool, I will do that since I still have about 30 more pounds of welding wire to put into this car until its done

[Bryce]

Steve, It looks pretty good. I would also try to add some triangulation. Check out my build thread. We are almost at the same point.

[JohnUlaszek]

Fully gusseting and welding from the upper link mount to the frame rails is going to be essential.