How To Retain Your Classic Car’s Original Frame

Hot Rod Specialties Repair This 1934 Chrysler Frame

By Gerry Burger

It seems doing a complete chassis swap has become SOP (standard operating procedure) for many shops. And while there is something to be said for a completely re-engineered chassis for your vintage car, in many cases it simply isn’t needed, not in the budget, not available, or all the above. In that case it may be time to rescue that old frame.

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02 frame rail being prepared for the installation of a Fatman Fabrication subframe
The frame rail is being repaired in preparation for the installation of this Fatman Fabrication subframe.

Read More: How To Rebuild An 8 3/4 Chrysler Rearend

Before any rescue and repair can be done to that original chassis you must first determine if the chassis is in fact repairable. Extensive rust, damage from a prior collision, or excessive cutting from previous modifications may make the frame beyond repair. The team at Hot Rod Specialties determined the frame under Terry Thompson’s 1934 Chrysler was in overall good condition except for the passenger side lower frame rail. A section of that rail had received rust repair some time in this old car’s storied past. While the repair appeared to be structurally sound it was not up to contemporary standards.

03 the earlier repair of a rusted frame rail marked with soapstone lines
This was an earlier repair of the frame rail. It appeared the lower ’rail had serious rust in this one area. The repair appeared to be structurally sound, but not up to the standard of Hot Rod Specialties. Soapstone lines mark the cuts.

Read More: Dual Master Cylinder Conversion For Your Classic Car

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Since the car was in the shop for a Fatman Fabrications front clip (more on that in a future issue), this was the perfect time for a proper frame rail repair. This is a task well within the reach of many homebuilders who possess a reasonable amount of skill and know-how, including structural fabricating and welding skills. This is no place for “pretty good” welding, it must be professional-grade welding that includes internal fishplates for structural frame rail repair. With that in mind, let’s follow along as the team at Hot Rod Specialties show us how the pros go about properly repairing a damaged frame rail. MR

04 chassis and engine safely supported by jack stands during the repair process
The chassis and engine must be safely supported by jack stands to ensure nothing moves during the repair process. The huge front crossmember will be removed later.
05 frame rail being cut and supported on either side during the repair process
With the frame rail supported on either side of the cuts, the old frame rail section is removed. Pick your weapon of choice; the die grinder, Sawzall, or pneumatic saw all make clean cuts.
06 repaired section of the frame rail with fender mounts on the floor
Here is the old, repaired section out and on the floor. Those two studs are fender mounts so you will need those measurements for the new studs that will be included in the repair.
07 replacement section formed from 1 8 inch cold roll steel with internal fishplates
The replacement section is formed from 1/8-inch cold-roll steel. Internal fishplates are plug welded to the inside of the new ’rail and extend into the old ’rail.
08 showing the fishplate being plug welded to the outer side rail to prevent stress cracks
Here we can see the fishplate is plug welded to the outer side ’rail. Note the ends on the fishplate and the shape of the new outer frame rail are not straight vertical cuts. By using angle cuts you eliminate stress caused when welding. Single line vertical seams can often lead to stress cracks.
09 the final fabricating welding and metal finishing process on a welding table
The final fabricating, welding, and metal finishing were done on the welding table. Here we see the piece back in place. The back side has not been boxed yet to allow welding of the fishplates and welding nuts in place for the fender mount studs.
10 the new piece being tack welded in place with a slightly beveled welding root gap
Satisfied with the fit of the new piece it is tack welded in place. Note the slightly beveled welding root gap on the panel fit. This gap ensures good weld penetration to both outer ’rails and the internal fishplate.
11 the metal finished seams of the frame rail appearing to be original from the outside
After welding the seams they were metal finished, so the frame rail appears to be original from the outside. Inside the frame rail the fishplate is welded and those welds are left unfinished.
12 the inside of the frame rail being boxed after welding nuts for the fender mount studs
Two nuts were welded inside the rail to accept 3/8-16 studs. Then the inside of the frame rail was boxed, completing one very strong rail repair. The front seam is not welded as it will be cut there to accept the Fatman Fabrications subframe.


Fatman Fabrications
(704) 545-0369

Hot Rod Specialties
(317) 802-7762

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Click on this issue’s cover to see the enhanced digital version of Frame Fixin’.

mr february 2024

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