Suicide mount question... AM I gunna die?

OK, so my front suspension is just about finalaized on my project T. The frame is hand built, but not totally by me. (I know, BOOOOO...) It was originally built in the 60s as far as I can tell, and whoever did it mounted the spring on top of the perch, using a plate and two U-bolts to locate it. The perch is built nice and strong, but most rods I see have the spring mounted below the perch. Am I in danger of having the bolts snap and send me straight into the guard rail? The hardware is all grade 8. The bolts are 3/8.

 

i have seen some old t's done that way but i would feel much safer with 1/2 hardware

 

If it breaks just change your name to "Braininabucket".

JH

 

Answers to the same question.

 

[ QUOTE ]
...using a plate and two U-bolts to locate it...
The hardware is all grade 8. The bolts are 3/8.


[/ QUOTE ]
Grade 8 U-bolts ? ? ?






Some people contend that Grade 8,at 150,000 psi tensile strength is too brittle for suspension use.
Grade 5,with 120,000 psi tensile strength,is less brittle.

If your U-bolts were 3/8-NC,
the minor diameter of the thread would be about .156",
which gives us an area of 0.02433 square inches,
multiply by 120,000 psi tensile strength,
and you get 2920 lbs tensile strength.

If the front of the car weighs 1200 lbs,
and that weight is supported by 4 bolts in tension,
then each bolt has to be able to handle 300 lbs, multiplied by a safety factor.

2920 divided by 300,gives a safety factor of about 10
More than enough.

 

Ian, that is way too much math, but I appreciate the input. I am going to use regular grade 5 bolts instead of U-bolts.
I forgot to mention that I had switched to regular bolts in place of the U bolts that came with the ch***is.
After looking at it, I think I can add another pair of bolts to the center of the perch with room to spare, and with six total I wont have to worry.

BTW, the metshapers.org website it cool stuff. I'm just getting started with this stuff and I think it will come in handy.

--Jess

 

In my 50 plus years of Hot Rodding I've seen countless numbers of T's done like this. I've never heard of all 4 bolts breaking at once, grade 5 or grade 8. Just make sure you torque properly for the grade you chose, don't worry so much! And "Yes" your gonna Die. I doubt it will be from the front of your T falling off. Lets just hope your verry old when it happens.
The Wizzard