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Custom S30 X-member. If you were starting from scratch...


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An 18-year-long story short: '72 510 with bored and stroked 4.4L Buick 215 project started by an ignorant 20-something me, back in the mid-'90s. Lots of bad advice from a SoCal-based race shop (RIP). The front-steer 240 rack that was added to the 510 x-member is horrible, done with little knowledge of bump steer or Ackermann. The car has never been functional and I just got it back after 15 years away. The goal is a canyon-carver and autocross/track day car. The front end needs revision, and going back to the original steering box doesn't work with the exhaust and oil pan. I need an S30-like X-member.

 

I spent a few hours searching archives, so if I just missed the info and you can direct me to it, please do. I try to bother others only when I can't find the info I seek.

 

I TIG weld. I fab bicycle frames for a living. I have basic engineering knowledge. I'm going to make a custom front X-member that utilizes the basics from the S30, but everyone modifies the set-up in one way or another to improve it. What I'm hoping to learn is the best possible way to modify the design, since I'm not constricted by stock, existing parts.

 

Are higher, more outboard LCA points superior to bump-steer spacers? Is the stock rack mounting height optimal? Are the knuckles the right shape and length? (I'll probaby be making custom  or modifying stock S30 since I have to mate to ZX struts) Is there some reason why another rack should be chosen, before all this time and effort is undertaken? Anything and everything else I'm not thinking of? I know that I'll need to relocate the T/C rods/fab creative T/Cs that work in the stock location/ develop A-arms to work with the new, custom X-member.

 

Any and all help you can offer will be greatly appreciated. I'll get some pics up if people are interested.

 

Thanks!

Edited by ByStickel
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Why not just swap an S30 cross member?  It's a pretty light weight and complex piece. It would be difficult to match it's strength to weight ratio. The hardest part is changing the tension rods to compression rods. That and the S30 struts are about 2" shorter. When I did my L24 510 swap I used the S30 X-member and made compression rod mounts and lowered the strut top mounts. But depending if you are lowering anyway the 2" higher mounts might work.

 

If doing it from scratch the choice of material size would be the question. Probably an unusual tubing size, like 1"x3"x .095" or even .078". Or 1"x4" or 2"x4"x .078". Actually 2"x3" would be closest to the S30.

 

The S30 X-member is .075" but it's made of two pieces that are flanged together so the flanges are .150" and it has doubler plates on the motor mounts, chassis mounts, and inner lower arm mounts.

 

If you know Solidworks or a 3D modeling program it would be helpful, you could work out all the geometry and clearances much quicker that way.

 

I would keep the S30 rack, it's a pretty nice piece, light weight, very durable and a quick ratio. The 240 had an aluminum gear housing and lower pinion shaft bushing, the 280 went to a cast iron housing with a roller bearing on the lower pinion. I prefer the earlier one since it's lighter and I've never seen any problem with the bushing.

Edited by Chris Duncan
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I'm not sure what you are asking really.  This is going on a 510 or a 240?  for a 5 inch travel suspension you can get away with a 15 inch lower arm and a 7 inch upper if you're looking to make a double a-arm setup.  If you're looking to fab up a replacement 240Z cross member or something for a 510 I'd look at making something similar to the Mustang K-members.  Set your ride height and mount the arms level and if you want some anti-dive make the lower rear pickup adjustable.

 

Stock S30 Z suspension is designed with bumpsteer.  You either need to bend the knuckles or shim them down at the outer tie rod connection.  Many people raise the inner to match the rack so if you build from scratch take a look at aligning the inner pivots.

 

Hope that helps,

Cary

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Thanks, guys.

 

It's going in a 510 to clear the rear-sump Buick 215. I do have the early 240 rack. If I use the S30 X-member, I lose critical space for the exhaust to run between the x-member and starter on the passenger side. There is X-member structure behind the arm on the S30, whereas the 510 has the arm behind the member, in single shear. Also, I'd need to recess the sheetmetal and move or duplicate the formed doubler plate that's on the outside of the chassis, since the 510 needs an extra pair of holes to put the S30 piece in the right spot. The doubler plates provide extra space for the X-member bolt heads. I keep thinking that I'm going to end up wanting to convert this car back to stock sheetmetal when I'm too old to work and it's the only thing of value I have left, so the fewer sheetmetal mods the better.

 

The whole thing is a mess and I wouldn't go this route if I had it to do over again, but here I am, with a valuable engine that should do what I'm hoping for (torquey, with linear throttle response).

 

Cary,  guess I'm most curious about relocating the LCA inner pivots out and up (how much?) This should act similarly to bumpsteer spacers, but I wonder if those original locations are always off, compared to rack width, or if it's only a problem on lowered cars.

 

I'll be using 280zx struts which do not share the S30's strut angle (510/ZX are more vertical), so what works for Z will probably not work for my set-up, but the info on LCA location should help me.

 

Thanks.

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I've had a few 510s.  I had one with a rack and a VG30DE conversion in it so I know what you're looking at.  On mine I used the 240 rack and crossmember and made custom rear TC pickups.  If you go here http://datsuns.com/projects/510-TwinTurbo/fvs_N.html this car was built the same as mine.  If I were to do this again I would build a k-member to use as the rear attachments.  On the car I would use epoxy and rivets to hold the bracket, which could be removed.

 

The S30 crossmember mods needed for bumpsteer are in the stickies.  They contain a lot of good info that will help you with this project.  I have to admit that way back then I was very into 510s and was so looking forward to my new V6 car.  Dave from Datsuns.com gave me a ride in his and it was fast.  Then I got a ride in Charlie Barmissa's 302 powered V8 Z and I never worked on the 510 again.  It still sits in my garage.  I have a friend with a 510 very much like yours he calls Beefy.  It sounds nice.

 

Good luck with the project!

 

Cary

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Thanks again, Cary. I like the idea for the rear T/C mounts.

 

I'd love a Z, but have to wait until one falls into my lap. They're getting pricey. I had thoughts of doing the 215/Rover swap into a Z, and maybe that's what will become of this engine if I don't end up happy with the 510. I appreciate the link and your time and input!

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I was talking with a guy earlier this week that has the Buick 215 in an Austin Heally bugeye Sprite. Somehow he made it work cause he's been driving it for years now. Where there is a will -there's a way. Good luck.

Edited by Phantom
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