TOBY-TAB update

["Toby Peterson" <tobyp@xxxx>]

Hello List - I have some important information that I want to pass 
along for all interested parties regarding a bent bolt that was found 
at a tech session in the midwest last spring. The bolt was one of my 
bolts, and had been installed by the owner. If the owner wishes to 
add anything to this post, he is welcome to (he is a highly regarded 
member of this list). The information that I was given was that the 
installation was done with new "large" flat washers obtained from one 
of the DeLorean vendors, and that he had put something close to 
20,000 miles on the bolts, including hitting some rather significant 
potholes. The car's owner noted that the new flat washers were worn 
nearly half way through the thickness where the sleeves through the 
trailing arm and bushings contact them. The bent bolt was eventually 
sent back to me for evaluation. I sent it to the original 
manufacturer in order to verify that there was nothing defective 
about the bolt, or the materials used to make it. I received the 
manufacturer's formal written report yesterday. The bolt was sent to 
an independent testing laboratory, where it was tested to ultimate 
tensile failure to verify material tensile properties, tested in 
double shear to verify ultimate shear strength properties, and tested 
for Rockwell hardness to see if there were any variations in hardness 
in the bent area of the bolt. The bolt failed at a tensile load of 
31,603 lbs, which translates to a tensile strength of 245,360 PSI. 
The shear strength (using standard double shear tests) of the bolt 
was 265,580 PSI, with a peak load at the breaking point of 45,489 
lbf. To get the single shear stress values, you divide the double 
shear stress values by two, giving you a shear strength value of 
132,790 PSI in single shear. The minimum values for this grade of 
inconel are 220,000 PSI (tensile) and 125,000 PSI (shear), so the 
material was well above the minimums. The Rockwell hardness values 
were all in the range of 47.15 - 47.97 Rc in the deformed area of the 
bolt.

What the heck does all of this mean? The TOBY-TAB bolt is incredibly 
strong, but even it can't survive in a loose joint where the washers 
have worn significantly. The impact loads and general pounding that 
the parts of the trailing arm connection take on rough roads and 
during performance driving will eventually bend any bolt that is 
installed there, even mine. The stock, or even "improved" bolts 
don't stand a chance in this environment. Bottomline - The TOBY-TAB 
is the best that can be had, but you must still ensure that all of 
the parts in the joint, including washers and sleeves, must be hard 
enough to resist wear, and the tightness of the joint must be 
maintained through normal maintenance. I am looking into a new flat 
washer material that I think will solve this wear problem, but the 
cost may be nasty. I will keep the List apprised of any further 
developments. As always, I welcome all of your input into this 
issue. Thank you for your support of the launch of this new company. 

Toby Peterson VIN 2248
DeLorean Parts Northwest, LLC
Winged1