Folks,

So I started this project 6 months ago with the help of some great folks on the forum with the goal of upgrading the top-end of my motor and installing my TKO600. One thing led to another and as of last Saturday, here is where I have ended up



The powertrain upgrades are done, but in looking at the body mounts, I figured I was so far into the car that I wanted to be completely done when it goes back together. Atleast it was easy getting the tranny installed without a body on the car .

While I'm at it....

I am interested in lowering the rear differential. I've seen this done in the past by several forum members and it strikes me as the best way of keeping the half-shaft geometry correct while lowering the car itself. There are two ways of accomplishing this from what I have read; eliminating the rubber mounting cushions and welding discs to the crossmember, essentially hard mounting it to the frame, or notching the cross member and recessing the differential mounting point into the cross member.

I'd like to go with the second option of recessing the cross member and have obtained a second crossmember from a forum member (I like to keep the original stuff just in case).

I've searched but cannot find a thread on this procedure. It seems fairly straightforward but I am looking for some of the gotchas in the process. I know the following will have to be accounted for:

• Ensuring upper shock mounting holes are moved to allow for full shock compression
• Relocating or shimming of the front differential mount
• Making sure the differential does not contact the body when it is back in place

So I have a few questions that I would appreciate help on from forum members who have done this in the past.

1. How far can the diff be recessed in the crossmember without interfering with the body?
2. I have heard that Billstein Sport shocks are already a bit shorter than normal shocks as they are often used in lowered applications. Is this true? If so, does anyone know by how much?
3. How have folks tackled the front diff mount? Have you ground it off the frame and relocated, or is using an appropriately sized shim spacer adequate?

If there is anything else I am missing (probably), please feel free to fill me in.

I'm sure this will be an odyssey, so I'll keep posting progress pics as I go, but I only get to work on the car on the weekends, so this is gonna be a while.

Thanks in Advance
-Fred

 

buy a Chevy Power book (get the one with the Corvette section)

 

Thanks for the quick reply.

I have one and will be using it as a guide to stiffen the chassis, but the Chevy Power Book recommends the steel disc method and elimination of the rubber bushings on the crossmember. I know its a matter of preference, but I would rather keep the rubber bushings and notch the crossmember.

 

Eliminating the rubber mounts and welding the discs in tackles three issues at once. First raising (not lowering) the differential for better half shaft geometry on a lowered car. Second, making the frame stiffer by the differentials three mounting points being bolted solid. And third, it helps address wheel hop.

 

I've decided to go with the steel disc route and hard mount the cross-member to raise the differential.

Thanks for the advice.

 

I am also interested in mounting the diff crossmember solidly. Does anyone have any pics of this mod done with solid discs replacing the rubber bushings?

 

cut out the steel "hat" (or "cups") from the original rubber mount (drill holes, torch). steel plate top, bottom adapters ID sized for steel hat. jigged to frame to get right depth, placement before tack-welding in-place. excuse the welds, this is one of my first learn-to-MIG projects 20 yrs ago.

i've found that since the C3 body is insulated from the frame with rubber bushings, you can barely hear the gear whine, only if you listen closely and everything else is kinda quiet. of course front diff mounting bushing is solid aluminum biscuit.

i've done this for 2 C3's now.