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Floor board/frame rail replacement question


fyanrudger

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Doing Zedd floors/Baddog Rails. I'm doing the prep work and buddy is going to come next friday to officially weld things in. I just pulled out the passenger side pan and want to do the same for the driver side, but I read that it's possibly not advisable. This info came from a how-to/site that had the car on a rotisserie. My car is on stands and completely level front/back and side-to-side. Is the car prone to twisting/sinking without the floors and rails half-hacked off?

 

Thanks!

 

*Sorry for the double post. Should have been in this forum...

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If your drivetrain is still in the car I dont see the problem. All the components will keep the body in check. Make sure your doors are always align during removal and installation of the floors. If you have strut bars it would also help keep everything incheck.

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Are your seat rail supports still there? They will keep things together . If your inner rockers are solid then you should have a lot of movement.

I think I welded a support across the floor from trans tunnel to inner rocker because I was replacing seat supports too. My car was also on jack stands.

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From about 72 on the drivetrain is entirely rubber-mounted.  Rubber donuts on the ends of the transmission cross member, so no precision on alignment.

 

There was a thread a little while ago that mentioned the effect of the floor panels.  Some said they had little effect, but one member said that their body got a little rubbery with the floor panels removed.  Search the internet for monocoque chassis articles and you'll probably find a few references to the effect of every surface of the body on stiffness.  They'll make you wonder if you should even put flat sheet in the floor instead of structured.  It's interesting reading.

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If your drivetrain is still in the car I dont see the problem. All the components will keep the body in check. Make sure your doors are always align during removal and installation of the floors. If you have strut bars it would also help keep everything incheck.

 

Drivetrain and strut bars are in place.

 

Are your seat rail supports still there? They will keep things together . If your inner rockers are solid then you should have a lot of movement.

I think I welded a support across the floor from trans tunnel to inner rocker because I was replacing seat supports too. My car was also on jack stands.

 

Inner rockers are solid...I assume you meant "you 'shouldn't' have a lot of movement", right? Hah.

 

Getting new mounts made so I removed the seat rails on the passenger side, but I suppose I can remove the floors/rails and leave the seat rails on the driver's side until the passenger side is fully welded in and remove them last minute.

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Part of the Factory Service Manual.  Has dimensions for "tramming", which is apparently what straightening a bent chassis is called.  Good general descriptions of what's important on the body also.  You can't go wrong by at least reading the first few pages.

 

I haven't done this kind of work but if I was I would probably tie the strut towers, front and back, together with a tower brace on each, then set the body down on a level surface with pillars supporting the body at the tower tops.  Or at the inner control arm mounts.  No suspension.  That's just a first inclination though, there may be better ways.

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Part of the Factory Service Manual.  Has dimensions for "tramming", which is apparently what straightening a bent chassis is called.  Good general descriptions of what's important on the body also.  You can't go wrong by at least reading the first few pages.

 

I haven't done this kind of work but if I was I would probably tie the strut towers, front and back, together with a tower brace on each, then set the body down on a level surface with pillars supporting the body at the tower tops.  Or at the inner control arm mounts.  No suspension.  That's just a first inclination though, there may be better ways.

 

Ahhh, I will have to read that. Basically where I'm at with the jack stand under the transmission (had to remove the mount to get at portions of the floor) as Morbias brought up below. I'm still torn on pulling the other floor out...I feel better about it now...but I'll have to see how this progresses over the next couple days. There's a lot more "massaging" to be done on the Zedd floorboards than I expected.

 

When I did my floors and framerails I used four jackstands and also a bottle jack under the transmission mount to support the tunnel sheet metal, then did one side at a time to reduce the chance of things moving about.

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  • 2 weeks later...
  • 3 weeks later...

I did some research with the FSM and also talking to some bodymen that I know. They looked over the car with me as well. On a standard body, all they can do is mount the car in a frame rack and then proceed to adjust leveling of the chassis so that the known good datum measurements are correct. Essentially there is a datum line (similar to ground level) that all these location points are measured off of. When these undamaged areas fit the measurements, then the measuring stick of the frame rack becomes the datum line and you can proceed to check and correct the damaged area so datum measurements are correct in that area as well.

In a datsun, it appears that the pinchweld is pretty close to it, but it does not say for sure. The outboard edges of the floorboard (factory chassis is one piece of metal from left floorpan, up and down the trans tunnel and across the other floorpan) where it is spot welded to the rocker is evidently straight at least. I would level the car so that the edge of the floorpan where it terminates with a ~3/4" lip turned upward to spot weld to those rockers is level. If your spot weld lines along the front and back of the floorpans are intact then that pretty much dictates where the pan goes there. That merely leaves the side-to-side level of the floopan when you weld it to the trans tunnel which you can use magnetic levels to determine (as long as you level those floorpan edges from one side of the car to the other).

The distinctive locating points on a Datsun are front strut tops (inclined 13 degrees 45 minutes), engine mount holes (45 degrees) in the front subframe, front differential mount and rear strut top holes (16 degrees 17 minutes).

As a side note, it does not really indicate measurements for the frame rails under the floorpan. The frame rails in the engine bay are evidently supposed to be perfectly parallel with each other (638mm inside measurement)

In my eyes, that pretty much indicates that unless you distort your trans mount (or door openings because the rest of the body is weakened) while welding the stuff in it does not matter. Just get them level and parallel with each other and put them as close as you can with what was there before.

Edited by WizardBlack
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