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Cross Member Mounting Points


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Gday, 

 

I have a very low quality chassis diagram for my dimensions as I have been working on my 78 280z, I would like to confirm the measurements I have before I attach my cross member finally into my new frame rails. 

 

Can one of you blokes please fire-off to me your measurements from the firewall to the first mount as indicated in my attached photo?

 

post-28059-0-21172900-1385509032_thumb.jpg

Edited by TieFighter88
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When I built my front frame rails about ten years ago, I went by the 260Z frame drawing for placement of the TC buckets and the crossmember placement.  After welding everything up, I discovered that the 260Z FSM had some significant errors.  I believe that these errors were corrected in the 280Z FSM but I am not sure.

 

If it were me, I would clamp the crossmember in place and assembly the suspension to make sure everything is correct.  You may even want to move the crossmember slightly forward of the stock location to gain a little caster.  If you do, make sure that the wheels clear the fenders and air dam.  Also if you go too far forward, the steering shaft will not reach.

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When I built my front frame rails about ten years ago, I went by the 260Z frame drawing for placement of the TC buckets and the crossmember placement.  After welding everything up, I discovered that the 260Z FSM had some significant errors.  I believe that these errors were corrected in the 280Z FSM but I am not sure.

 

If it were me, I would clamp the crossmember in place and assembly the suspension to make sure everything is correct.  You may even want to move the crossmember slightly forward of the stock location to gain a little caster.  If you do, make sure that the wheels clear the fenders and air dam.  Also if you go too far forward, the steering shaft will not reach.

I have heard this story before from another bloke, thats why I wanted to make sure before I start drilling holes in my fresh rails. Yep , I think after I got my ballpark measurement, I will dummy-bolt everything and see how far the steering shaft will give me... will have to check for the header clearance to, I have the 6-to-1, knowing my luck they would get in the way... 

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TieFighter,

 

I just noticed that you are only about 45 minutes from me.  If you want, you can come over and take some measurements after the Thanksgiving holiday.

 

Do you plan to autocross when complete?  The season starts in January.

Edited by 74_5.0L_Z
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TieFighter,

 

I just noticed that you are only about 45 minutes from me.  If you want, you can come over and take some measurements after the Thanksgiving holiday.

 

Do you plan to autocross when complete?  The season starts in January.

I might take you up on that, my in-laws are in Melbourne and I and back and forth all the time with the missus. 

 

I definitely want to autocross, how do the inspections/waivers work? Because the whole front end of my chassis is a garage job, and not official SCCA stuff, not saying I am incompetent, worried it might scare them to let me on the track with my creation...

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The FSM doesn't even call out the dimension to the firewall, from anywhere, that I can see.  Doesn't look like a good reference point.

 

Why trust somebody's shaky tape measure hand when there are several ways to cross-check the FSM numbers, and/or back out a super-simple dimension like to the top of the front strut?

post-8864-0-73594200-1386270902_thumb.jpg

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I think the sway bar mounting holes would be the easiest and most reliable reference point.  When I made my frame rails, I used the dimension of the sway bar mounting holes that were published in the FSM and had no problem.  I did have issues with the published fore/aft position of the TC mount and the position of "Point B."

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OK,  I went back and tried to reconstruct what the error was with the 260Z FSM frame drawing, and I believe that I have found the error.  I am posting the 260Z FSM drawing below so that I can point out the error.

 

 

 

Frame.bmp

 

 

 

 

The dimension between the TC mount and Point B is too short on the 260Z drawing.  The listed value is 11.3 inches.

If you look at the frame drawing posted by NewZed, that drawing shows the dimension as 12.88.  That number is correct.  Unfortunately, that dimension is to the engine mount on the crossmember.  You can however measure the crossmember and calculate the additional distance you will need to the frame mounting holes.

 

I hope this helps.

Edited by 74_5.0L_Z
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OK,  I went back and tried to reconstruct what the error was with the 260Z FSM frame drawing, and I believe that I have found the error.  I am posting the 260Z FSM drawing below so that I can point out the error.

 

 

 

attachicon.gifFrame.bmp

 

 

 

 

The dimension between the TC mount and Point B is too short on the 260Z drawing.  The listed value is 11.3 inches.

If you look at the frame drawing posted by NewZed, that drawing shows the dimension as 12.88.  That number is correct.  Unfortunately, that dimension is to the engine mount on the crossmember.  You can however measure the crossmember and calculate the additional distance you will need to the frame mounting holes.

 

I hope this helps.

So I gather that the diagram implies, the crossmember mounts and engine mounts are along the same plane/axis, spaced equally from the middle of the strut tower? So I could rely on putting the midpoint of my cross member mounts along the line straight down from the center of the strut towers to the rails? 

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