Frame under axle - Thought?

[cornfedbill]

I have found that after relocating the front control arms and channelling the front subframe 2 inches upward, that the rear axle will run right through the framerails to sit level with the front. At a level ride height, the axle will sit on the bumpstops.

I need to completely gut the rear frame and floorplan around the rear axle and start over.

I am seriously considering running the frame below the axle as in some circle track cars and the Lotus 7. It will give me a good place to mount the Watts link that will sit horizontally below the axle, and will also support my belly pan. I plan to use 2X3 rectangular tubing laying on its side so it only takes up 2 inches under the axle.

The belly of the car will be 4 inches off the ground from bumper to tail with a flat belly pan the whole way (except where it curves up in the rear to form a diffuser.

It means that I will only have the rear of my roll cage above the floor in the rear, and will need to mount my springs and shocks to it. I will be using conventional Bilstein shocks and coil springs, not coilovers.

The rear leaf springs will be cast off in favor of an adjustable 3-link with to top link offset about 8 inches to the right.

I know I am crazy, but what are your thoughts on the concept?

156113

[Peter Mc Mahon]

Not sure if we can mention competing sites? But check out American Motors experimental full frame on that other G site. Full under slung frame

[dhutton]

It’s here too:

https://www.pro-touring.com/threads/84756-American-Motors-Xperimental-full-frame?highlight=

Don

[justanova]

I believe No Limits Hellboy truck has an arrangement similar to what your talking about

[cornfedbill]

Thanks. Both projects have some good ideas I can use.

[mikedc]

Offhand thought:

If that car gets hit hard in the rear/side then it might shove the axle into the rear of the passenger compartment. The OEM frame rails above the axle normally keep that from happening.

The same problem would apply if you did a 'Dukes of Hazzard' move and bottomed-out the rearend hard enough to break whatever bump stop setup you built.



I think the answer is just an old-school C-notching job like the lowered pickup truck crowd does.

Cut as far into the frame rail as necessary to get the clearance. Leave a sliver of the OEM rail intact at the top if you can. Cut out the sheetmetal above the frame in that area, add a reinforcing piece onto the top of the rail above the notch (to recover the lost rail height), and fabricate new sheetmetal over that bigger hump.

This article gives you the idea. IMO it would help to make the changes to the rail's path more gradual than their drawings.

http://www.how-to-build-hotrods.com/c-notch.html

[mikedc]

Also, the bumpstops:

If you try to keep the bumpstops squeezed directly between the axle & framerail, then you are liable to be running very small stops that get severely mashed on any hit. For a given amount of net-total "spring rate" in the stopper, it's better to have a larger piece of rubber doing it. The stops last longer and work more smoothly.

It might help to relocate the axle's bumpstops. Maybe do a side-saddle kind of deal that perches a rubber stopper next to the framerail instead of under it. Combine this with another very slim/hard backup stopper directly under the framerail so you never risk going metal-to-metal even on a bad hit.

[cornfedbill]

Offhand thought:

If that car gets hit hard in the rear/side then it might shove the axle into the rear of the passenger compartment. The OEM frame rails above the axle normally keep that from happening.

The same problem would apply if you did a 'Dukes of Hazzard' move and bottomed-out the rearend hard enough to break whatever bump stop setup you built.



I think the answer is just an old-school C-notching job like the lowered pickup truck crowd does.

Cut as far into the frame rail as necessary to get the clearance. Leave a sliver of the OEM rail intact at the top if you can. Cut out the sheetmetal above the frame in that area, add a reinforcing piece onto the top of the rail above the notch (to recover the lost rail height), and fabricate new sheetmetal over that bigger hump.

This article gives you the idea. IMO it would help to make the changes to the rail's path more gradual than their drawings.

http://www.how-to-build-hotrods.com/c-notch.html

I guess I’m not too worried about the axle entering the passenger compartment.

There will be a roll cage above it. Also there will be no rear seat to protect.

The springs, shocks and bump stops will be attached to the roll cage itself.

[krom]

The chassis will be much stronger/stiffer with structure below the axle

[cornfedbill]

The chassis will be much stronger/stiffer with structure below the axle

That was my thinking also.