SHORT COMINGS OF THE STOCK FRAME DESIGN
Original Frame Cross Section
RATCO Frame Cross Section with Foam Fill
Everyone who owns a Triumph for any length of time soon learns of the failures and shortcomings of the cars design with the frame right at the top of the list. It must be said that these frames have stood up surprisingly well for having been made so long ago with less than quality materials and no attempt at rust proofing. Still many have endured for 40 + years and some will go on for much longer in faithful service to there loving owners. Still others will not make it much longer and many should not be in service at all.
The original frame was made of sheet metal bent into “C” channels. Two sizes were made. One was deep drawn measuring 3 inches tall and 2.75 inches deep (approximately!!) and the other was 2.875 inches tall and .75 inches deep. The smaller channel was placed into the larger and the resulting lip was spot welded every 1/2 inch (or so!) along its length. The resulting box was cut to length and, if necessary the pieces were bent to shape before being welded together to form the final base frame assembly. The towers, brackets and mountings were all stamped from 12 gauge (.090) steel then assembled and mounted on the base frame using electric spot welds or full pass arc welds. The RATCO sample above is made from 11ga Steel (0.119 nearly 1/8" thick). Also shown is the internal foam filling to eliminate water intrusion and reduce harmonic noise from road vibration.
The result was an impressively strong chassis that caused some journalists of the day to say that the car seemed to be machined out of one solid piece of metal and others to say that it was the most rigid sports car available. It was all that, but time has a way of sapping the strength out of most everything.
The real problem with the design was the fact that the spot welding created openings in addition to the openings at the ends of the chassis which allowed the ingress of water into the frame rails. The frame literally rots from the inside out. You can see from the image above that the steel at the bottom of the frame is significantly thinner than at the top. We see many older frames which look to be in good condition from the outside, but have slimmed down over the years and are of questionable strength. Investigation with a pick hammer will often uncover numerous areas of rust penetration on seemingly solid frames. The assembly technique of using sandwiched steel channels might have been economical and expedient but it did nothing for the frame's longevity.
The Triumph engineers failed to place weep holes in the correct spots on the chassis which would have allowed water to exit. There was no rust-proofing applied and many areas of extreme stress were not properly reinforced, if at all. Add forty or fifty years of exposure to the elements to these design flaws and eventually, serious problems will occur in many critical locations; with the rear swing arm and the lower front wishbone mounts being the most prone to rust and failure. Bodies sag on weakened frames and doors began not to close. Bumper brackets lose their mounting points to rust and A and B posts break from their mounts due the flex in the chassis. Hang around these cars long enough and you will see all the failures in due time.
We recently worked with a friend who was looking to restore an original frame. The frame had been undercoated at some point in it's life which made it look fairly good, and a thorough probing with a pick hammer did not reveal any significant rust. We sent the frame out for sandblasting and were quite shocked with the results. You can see in the photos, there are many holes clear through the steel, but what really surprised us was the poor quality of the original welds, many of which had cracked, but were all obscured by the thick coating. Most of these photos are of the front and rear spring towers mounted to the frame. A critically important junction. Original frames often look much better than they actually are. The cost to patch up this frame and re-weld the defective joints could easily exceed the cost of a new frame, and the result is a 50 year old patchwork quilt. Would you really want to take this frame through some twisty curves?