Re: Trailing Arm Bolts - Engineering

[tobyp@xxxx]

David - You are quite correct in your assessment that the tubes and 
sleeves will collapse if the torque is increased significantly. I 
installed the new bolts at a torque level of 50 ft-lbs, with a 
copper-based anti-seize compound applied to the shank and threads. 
That is the same value as the "stock bolts" as I recall. Forgive me, 
but I ran some numbers today on the preload in the bolts caused by the 
installation torque. I wanted to see how much tensile stress we put 
on the bolts by torqueing to that level. It revealed some interesting 
information ... without going into the calculations in detail, a 
torque of 50 ft-lbs on the TAB with grease on the threads and shank 
would create a tensile (tension) stress of about 116 KSI. (Remember 
that 1 KSI = 1,000 PSI). If the threads on the bolt and nut are 
perfectly clean and dry, the tensile stress value at 50 ft-lbs of 
torque is 48.3 KSI. Trust me on this ... it just works out that way. 
The actual preload is probably somewhere in between those two 
extremes, but it varies depending on the cleanliness of the hardware. 
The average of the two is about 82 KSI. If you are brave enough to 
muscle through a previous post of mine, the maximum allowable tensile 
yield stress on the stock bolts is 103 KSI. We are probably coming 
close to yielding, or stretching, the TAB every time it is torqued. 
The variation could also explain why some people have a problem with 
their TAB's , and others do not. My custom bolts have an allowable 
tensile yield stress of 200 KSI, so they would only get to about 1/2 
of their capability at maximum torque. Okay ... I'm done. I just 
thought that you'd like to know.

BTW - What are some of these other solutions that vendors have come up 
with? I haven't seen "The Fix" for this area yet ... just a lot of 
hand-wringing, and guessing. Please advise. 


--- In dmcnews@xxxx, jtrealty@xxxx wrote:
> All of what you wrote was interesting but it comes down to putting 
> more stress on the bolt then it will see in service by torquing it 
> above that level. If you go overboard you will collapse the metal 
> spacer in the radius arm bushing pn 106716. As is usually the case 
you 
> cannot improve an entire system by changing one part. It usually 
takes 
> a reengineering of the entire system or you just move the weak point 
> to somewhere else in the system. Before you continue you should 
> discuss this with a Delorean vender as they have all "been 
there-done 
> that" and now have a good way to fix this weak area. There is no 
> substitute for experience so before starting on a new project like 
> this you should get all of the history that you can.
> David Teitelbaum
> vin 10757