Which is better 1/2" bolt or 3/8" with spacer?

So which is better to use a 1/2" bolt or a 3/8" with a spacer?

I am working on a chassis I didn't build and therefore there are things I wouldn't have done that way.

On the inboard shocks they used 1/2" on the outboard connection but 3/8" with the spacer on the inboard connections including the shocks themselves & pivot points.  I changed all the easy to get to spots to 1/2" but there are a couple of spots that would be a bear to get to to ream so dare I stay with the 3/8"?

It's basically just the bottom shock mounts and one pivot point left.

I would not have a problem with 3/8 ths. Of course it would depend on the loads expected but if it's just a shock and no other loads then I don't see a problem.

Is the 3/8ths bolt in single or double shear?

Short term ok if its a tight fit use some anti seize on metal to metal remove all slop.

were it extended away from mount I would up size.

won't the correct bolts work, put a paint color on the head that tells you right away it is a different size.

If it is in double shear, the 3/8 with spacer will be far better. With the 1/2, it cannot be tightened, which will let the bolt wear the mounting holes. 

In reply to DeadSkunk :

It's in double shear.

Streetwiseguy, what do you mean the 1/2" can't be tightened?  Do you mean the 3/8" tightens on the sleeve rather than the base of the shock which is better?

The spacer is probably there to allow for pivoting in the connection, a pinned connection. 

Otherwise if  tight its transferring a moment through the connection.

Overcoming the moment would be seen as binding which may be uneven depending upon the instantaneous force applied.  

If tight enough I guess its possible the moment will be absorbed by the rubber grommet in the shock connection and this could rupture the rubber from the twisting.   Depends upon how much rotation is happening and the toughness of the rubber. 

1/2" bolt will have 1.77 times the shear strength of the 3/8" based upon cross sectional area  and equal material.  

carguy123 said:

Streetwiseguy, what do you mean the 1/2" can't be tightened?  Do you mean the 3/8" tightens on the sleeve rather than the base of the shock which is better?

 

If the shock has a steel sleeve in it of a 1/2 inch diameter, its fine.  If its just a rubber bushing, no good.  You must tighten something down solid, or the bolt will wear in the holes.

Shock mounts should look like this one in the link where there is a floating bushing that pushes the shock to one side, not just pinched by the bracket sides.  A&A make bracket cheaper then you can, and there off the shelf in many designs.

If the current set up is a shock only 3/8 is likely fine but if a coil over spring is used go 1/2.

AA-MFG shock mount