[Mgs] 80 MGB - Cross member to Body bolt

[Matt Trebelhorn]

While I'm not going to argue that weaker fasteners are necessarily  
better than a nice Grade 5, the load on these isn't ever going to be  
all that high.  I'll explain why I think that, and you can tell me if  
it sounds crazy.

The way I see it, those nuts carry a vertical load -- they hold the  
crossmember on when the car is jacked up, or if you pick the car up  
and hold it upside down by the crossmember, they hold the car up.   
Now, that second scenario is unlikely, so we're looking at other ways  
in which a vertical load is carried by the nuts and washers.

That boils down to loads put on the suspension by an anti-roll bar,  
or momentary loads that involve similar issues -- a pothole, say, or  
braking loads that would pull the crossmember rearwards -- some of  
this turns into a vertical load, pulling the crossmember down.

In both of these scenarios, though, the load is leveraged against the  
nuts, and the weak point in the system isn't the hardware, but the  
rubber mounting pads.  If you have an anti-roll bar that puts enough  
vertical load on the crossmember to break even a grade 2 fastener of  
that size, you would long ago have crushed the rubber pad, and  
probably broken some other suspension bits, too.  If you hit a  
pothole hard enough to pop those fasteners, you would also destroy  
the rubber pads first; at any rate, your suspension would be in bad  
shape.

I was in an accident a few years ago that pushed the front wheel back  
a tiny bit -- and the only suspension bit destroyed was the rubber  
pad on the hit side; when it came back from the bodyshop, the car  
drove like hell until that got replaced.

Yes, a really weak fastener in that application might have broken.   
But it would have been the difference between a broken suspension in  
a badly broken car and a badly broken suspension in a badly broken car.

So that's my story -- that they're not loaded in such a way that you  
would ever put enough of a load on them to break the nuts without  
breaking lots of other things first.

Crazy or no?
Matt


>
> on 7/17/07 8:03 PM, WJHS1960 at WJHS1960 at comcast.net wrote:
>
>> <<BTW,  if you get stainless locknuts and washers from
>> the hardware store, they polish up nicely.....>>
>>
>> You must have a Death Wish, Bob.  Just what I want on any  
>> automobile is Grade
>> 2 fasteners.
>>
>> N    O    T    !!!
>>
>> Suicide comes to mind!!
>>
>> ONLY Grade 5 fasteners are used on any/all LBCs!!!
>> _______________________________________________