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Heavy Duty frame rails and connectors

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Orginially I was thought I could get away with repairing the frame rails.  But after cutting open the frame rails, corrosion made them unrepairable.   So rail replacement was  necessary.    After checking out the replacement floor pans and frame rails available, I decided to construct my own.   Normally one can get away without bracing the body to do the replacement.  But I

found some corrosion on the front of driver side rocket panel.   Could not determine how strong the rockers were without cutting them open.  I constructed body bracing inside the car just above the floor pan.   The bracing was mounted to the two lower door hinges mounts.  The outer seat belt mounts were used for the other side of the body brace.  1" square steel tubing was used in a crossing pattern to provide support for the floor pan.  I want to make it bolted in instead of just welding it .Construction took about

two days with all the fitting that necessary.


  floor panel corossion


   pics of removed rusted areas


   lower door hinge mount


    top view of the body bracing above the floor pan


    close up view of door hinge mount


   picture of repaired crack in rear transmission tunnel


   frame rail rust









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I guess shipping is the real killer when bringing in stuff to the islands?  I would just warn you to only do one side at a time then just do the floor pan then when that is completed do the rocker, you could also bolt up the transmission mount to add a bit more stability.

Are you going to extend the floor pan rail so that it connects up with the sub frame in the back? Like the rail extensions that BadDog sells.

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Shipping stuff here is a killer!!   Replacement floor set (both sides) without the rail upgrade shipped here by Post was over $400.   I still plan to do only one side floor panel at a time even with the body brace.   You never know if you might need some additional measurements.   Can't get it if you cut up both sides.

My old transmission mount was removed when I first put Chevy 327 with Turbo 400 about 1974 or so.   I do plan to connect the front frame rails to the rear

ones.   I will beef up the front side of the rear frame rails as I was thinking about putting a whole independent suspension and narrow it.   But for now, I'll

leave the R200 differential in.  Also. I plan to upgrade the front frame rails for the LS3 motor.


floor panel cutout 2

floor panel cutout

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Found additional rust in front left side rocket panel.   So I constructed additional bracing for the engine compartment.   The bracing of 1" x 1" steel square tubing connects the firewall with the two strut towers.  The bracing is necessary if corrosion is found in the engine compartment frame rails. 



  rocker panel rust


  firewall bracing


  firewall bracing

floor panel cutout

  floor pan cutout





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  • 3 weeks later...


     I used a Sunex Toon #SX278C punch and flange air tooll.    There are various brand air punch and flange on the
market.  They are all basically the same.  The cut line must be straight as the guide depends on the cut line for straightness.  The resulting flange does provide
additional strength and leaves a flat surface when finished.


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exterior view of firewall and rocker panel


  interior view of firewall


   Put a cardboard on a floor jack under the hole in the floor.
 This is used to create a template for sheet metal replacement floor pan.  The hole was traced with a flet pen.   Notes and measurements were written on the cardboard for reference.  Always add additional sheet metal as you can always cut the extra material off.  Adding material later is more difficult.   I replaced the floor pan with 20 gauge sheet metal( the original was 22 gauge stuff).  The pan consists of
both straight bends but have curved edges too.
sharedmedia=gallery:images:35465]  fitting and cutting the pan


  aligning the pan






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  corner opening left front of floor pan


  using a bench vise slowly pound in circular pattern from inside to out.   Open jaws as you increase pounded area.


  used the vise jaws to bend the top edge of pan


  after matching the patch, tack weld patch to pan


  check pan alignment then final weld patch






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Thongs are acceptable wear except when welding.


P1030508 (1)

   Hammer welding was used when both sides are accessible.  Must use a dolly on backside to hammer weld flat after welding with steel rod.  The advantage is the weld is flat on both sides.  Any welding on the Datsun 25 gauge metal requires a lot of patience.


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glue gun

  New method of attaching replacement floor pan to car body-two part structural adhesive.



  After applying adhesive to both sides, the replacement floor pan and body must be held together for 4 hours to cure.


  Cleco clips and metal screws can be used to hold panels together.


Bottom view of floor pan showing screws and cleco clips


  Using the structural adhesive to repair a small rusted area.
Tomorrow, the cleco clips and screwscan removed after welding the seams together.  The screw holes will
patched using the adhesive with a tooth pick and acid brush.





Edited by toolman
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Bottom view of floor after welding and removal or cleco clips and screws.   As far as verdict on using

structural adhesive is still pending.  It works fine for small metal patches without welding.  However,

using it on parts that will be welded afterwards, there is some burning and smoke when welding.  So

although they say you weld after it dries, I think there is contamination of the welding with the smoke.

I have not had a chance to test the adhesive by prying a glued portion yet.  Will get back on that evaluation.

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  corrosion on old frame rails


  replacement frame rails


  using magnets to support frame rail


  aligning rail


  rear frame reinforcement
   I decided to replaced the corroded  frame rails with 2 1/2" X 1" X 1/8" steel tubing.  These rails will run from the firewall to
the rear frame member.   They will add additional structural strength to the body.   Transmision mounts can easily fabricated
by attaching  crossmember to them.

   A 3/16" steel plate was welded to the rear frame to provide a strong location for jack stands.





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  frame rail-rear crossmember to firewall


  close up view


The frame rail extends from rear crossmember to engine firewall.  Checking out the front section of frame rail from firewall

to core support.   Wire brushing the area for close inspection-looking for signs of corrosion.  if I decide to go all the way, have to

add additional supports from strut towers to bumpers mounts and one between the bumper mounts.

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