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I'm using C5 Corvette subframes and suspension for my build, and the rear subframe is crooked. I've known this since I first got it, and after a lot of thinking I decided that it would probably be okay. But, now that I've built a lot of stuff around this subframe I'm thinking about it again and I'd like to get some feedback from others.

Specifically, the subframe mounts the lower A arms and both of them fit and move as you would expect, however the right side angles up from front to rear more than the left side. The rear bolts for the A arms are level, but the very front of the right side ends up about .25" higher than the left side. Back of the back mount to the front of the front mount is about 18".

I do not believe that the car from which this subframe came was ever wrecked. I would not want to try to twist it back into shape as it's an aluminum subframe.

Are (were) GM's tolerances that wide for these things? The front subframe is pretty good.

I am building the mounts for the upper A arms, so I can make some small corrections. Also, I can put shims between the subframe and the chassis to make other small changes. I'd rather not shim very much.

-Omaha

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Aedifico ergo sum.

If it is bad enough that you have noticed it now I would try to find a solution. Have you thought about not using the subframe and making your own, it is more work but lighter, stronger and much more satisfying.

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2015 & 2016 EMod Florida State Autocross Champion
2013 & 2014 DSP Florida State Autocross Champion

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The vertical mounting surfaces for both front and rear sub-frames is 3mm. [relativaiy to each other] 98% where built within 2.3mm variation. Dave W

Thank you for the replies.

I'm not sure my fabrication would be lighter or stronger than the factory aluminum subframe, and I've kid of designed around it. But, yes, I've now been considering what it would take to build my own mounts. Because of how much I've built around the factory subframes, I would basically have to start over. I'm trying to decide if it's worth it.

I do have the specs for the vertical mounting surfaces, but the specs are for the chassis to which the subframes bolt. Basically, I used my level garage floor and alignment strings to orient the vertical mounting surfaces in relation to each other according to the chassis specs. Height was the only thing I really had to worry about; every thing else was just about being straight and symmetrical. Putting the front subframe on level blocks of wood made the vertical mounting surfaces match up perfectly front to back and left to right. No shimming necessary. The rear subframe was a different story, as it was not possible to get the heights of the pads to relate to each other correctly. The subframe seemed to be twisted.

The rear subframe is not super stiff on its own (though it does become very stiff when bolted to the chassis), so it might be more or less pulled into spec by a being bolted to a factory chassis with that met specs. I could simulate this by using shims at the mounting points. As an alternative, I could buy another used subframe to bolt on. As my fabricated chassis is built around the twisted subframe, I would need to use shims to match a new one that was straight. At worst it would add a 1/4 inch to my ride height, so maybe that's my best solution.

-Graveyard

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Aedifico ergo sum.

"The rear subframe is not super stiff on its own"
If it's any constellation, Pratt-Miller who makes the GM racing Vettes, does not use either of the cast sub-frames. They make thiers sub-frames out of 1" sq steel tubing. Dave W

Interesting. I was not aware that the C5R had a steel subframe. I wonder if that's because they're looking to gain some stiffness or if they've changed the geometry/wheelbase. Maybe both.

This race car uses the GM subframes:
http://aviracing.com/

From what I've heard, that chassis is extremely stiff, though I haven't seen any specific numbers.

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Aedifico ergo sum.

The Pratt-Miller Vettes are built for the Lemans series. I believe the series has several restictions on the frame. At the time Dana made the aluminum ZO6 space frame, but they [Pratt-Miller] where not allowed to use it in the racing series, but could used the aluminum rear balkhead and yes they did alter suspension but I can not remember the details other then they had more anti-squat in the rear and very little ackermann in the front suspension.
But did remember that just the air wrench and the titanium socket to remove the wheels, cost more then my complete car!!!
Dave W

loaded subframe was probably left hanging by that bolt when the disassembly took place