Re: Trailing Arm Bolts - Engineering

[jtrealty@xxxx]

I can't speak for all of the venders. I know that Rob Grady has a 
higher tensile strength bolt and nut he recomends. Also way back in 
old Delorean Worlds there was a vender pushing a bracket that he 
claimed "improved" the system and prevented bending or breaking the 
TAB. I have to agree with a post that mentioned getting a harder and 
stronger bolt may mean that instead of a gradual failure it would just 
shear off when pushed to it's limit. (Being harder it also means 
brittler). Replacing the rubber pivot bushing with a less compliant 
ureathane may help improve handling but at the cost of more noise and 
vibration being transmitted into the frame. If this is a way to go 
then you must make the metal tube (spacer) inside strong enough (thick 
enough) to withstand the higher compressive stresses. You will also 
need hardened shims (washers) so they aren't squished. A heim joint 
would have the advantage of no preload so when you twist the joint it 
isn't trying so hard to return to it's neutral position. A ureathane 
joint made so the ureathane can swivel around the metal spacer could 
do the same thing. On many older cars there are venders that sell 
urathane bushings to upgrade the suspension (take alot of the 
looseness and compiance out) to improve handling and stiffen up the 
steering and suspension. Ureathane is also less prone to aging and 
damage from oil and gas. In all cases it makes the ride harsher 
(stiffer) but more responsive. BTW the workshop manual calls for 55 
ft/lbs see K:08:02-K:09:01. In some cases torque values are not 
created so much for the fastener as for the components you are trying 
to fasten together. I think in this case the limiting factor is the 
metal spacer tube in the pivot bushing. In most cases unless 
specifically called out torque values are for CLEAN, DRY threads. When 
using bolts and nuts close to their yield point or a critical fastener 
it is never a good idea to reuse (retorque) more than a minimum # of 
times. Every time you torque a bolt and nut you stretch them a little. 
After too many cycles you will just pull it apart or rip the threads 
out of the nut. On many of the newer cars where many bolts and nuts 
are tightened to high levels the manuals warn you not to reuse the 
fastener. (Another reason to refer to the manual for the specific car 
you work on!)BTW how often have you ever seen mechanics use a 
CALIBRATED (in the last 10 years at least) torque wrench on suspension 
fasteners outside of wheel lugs! There is much more variation in 
torque then you think!
David Teitelbaum
vin 10757