Single or double shear shock mount

[Alex]

I'm trying to understand if my front shock mount is in single or double shear and if this is okay (i think it is, but never seen a design like this)

Two tabs are welded onto the lower control arm

One of the tabs has a 1/2'' hole, the other side has a 1'' hole

The side w/ the 1'' hole has a spacer that gets hand-pressed into the hole.

The spacer sits a smidge past flush on the inside of the hole

The shock is a very tight fit - I drop the shock from the top down, then slide the spacer in and tighten everything up.

I'd thought about welding the spacer to the mounting tab but the problem is it's a very tight fit to get the shock in and if welded and tightened the only way to get the shock out would be to hammer it out and/or bend the mounting ears a bit. As is the way i remove it is to undo the bolt and then wiggle the spacer out of the mounting hole which creates juuust enough clearance to wiggle the shock out (i.e., the spacer has to come out to create enough room to let the shock wiggle out freely without any force).

 

[Howard Jones]

That would be double shear. I think the "collars" being used is a good idea and IMHO is superior to just a hole through the tab. The collars will spread the load by increasing the material thickness of the tab at the through hole. In your case one of the collars is left loose. This is probably done to allow for use with different shock eye widths.

Nothing wrong with the design as far as I can see as long as the collar is a nice tight fit into the tab material. You could just weld the adjustable collar on the tab to suit your shock eye width and that may well be the intention in the first place.

 

[Alex]

one collar is welded in, the other is loose. I guess where my concern/question is is leaving it loose okay, or asking for a failure down the rod. It's a tight fit but I can wiggle it in/out by hand with a bit of effort.

I've just never seen a design where a collar is loose before.

i am tempted to weld it in, but my concern is how to get the shock in/out - I painted the spacer and while drying left it in the mount and tightened it together (to simulate welding it so it can't pop out). when it dried i tried to remove the rod end and couldn't because of how tight it was - I need to hammer the rod end out and/or wiggle the collar out of the hole - so if welded I'm not sure how I'd ever get the shock out

 

[Terry Oxandale]

If welded, how is this any different that a normal rod-end clevis (sheet clevis) that only has two holes in it. Slip the rod end into it (or shock end), pass the bolt through both pieces, tighten nut. Reverse for taking the shock out. I used a common rod-end clevis for mine without issue. For example, I use a similar one (link) with 3/8" holes for my sway bar mounts welded to my arms:

https://www.aa-mfg.com/clevis-for-1-2-heim

 

[Alex]

If welded, how is this any different that a normal rod-end clevis (sheet clevis) that only has two holes in it. Slip the rod end into it (or shock end), pass the bolt through both pieces, tighten nut. Reverse for taking the shock out. I used a common rod-end clevis for mine without issue. For example, I use a similar one (link) with 3/8" holes for my sway bar mounts welded to my arms:

https://www.aa-mfg.com/clevis-for-1-2-heim

that's what I've spent the last day wondering ... and then I figured it out now.

I poweredcoated the spacer and ground off the coating on the side but not the lip. So the rod end, when tightened, dug into the powdercoat to the metal and created a ridge of powdercoat so when i undid the bolt and tried to remove the rod end i couldn't because the ridge of powerdercoat blocked it. Wire wheeled it off and bam, works perfectly.

Okay, I r special, i admit it

 

[Alex]

all welded up and works fine .... can't believe I wasted so much time because of a ride of powdercoat, lol

 

[Terry Oxandale]

In all honesty, I never understood the design of these types of shock mounts. Thanks to this thread, I have a better understanding of the design and use.

 

[Howard Jones]

A word of caution about powder coating suspension pieces. Most race designers will not powdercoat or for that matter even chrome plate suspension parts, especially A-Arms.

We should remember that these prototype cars we all love are really race cars being driven on the street. I would argue that street use is a MORE extreme environment than a nice smooth race track.

These pieces need to be inspected on a scheduled basis for cracks and plating. Powdercoating, plating, or even too much paint will cover the crack to the point that you can't see it until it's too late.

I put ONE light coat of paint on the pieces I make and use a light shade of flat grey so I can see the crack as easily as possible.

I'm just sayin..............

 

[Mark Winton]

A few observations:-
1> Yes, bolt is in Double Shear, but ...
2> To be effective as such, the bolt thread should not take bearing load - that's what the bolt shank is for. (Thread O.D. is under-size to bolt shank O.D. so will slop around in a hole). Thread is only to hold the nut that holds it all together.
3> Do not weld - Coil-over mounts operate in a fatigue environment; weld (even good welds) are about the the best crack initiators that you could create.

 

[Mark Winton]

A few observations:-
1> Yes, bolt is in Double Shear, but ...
2> To be effective as such, the bolt thread should not take bearing load - that's what the bolt shank is for. (Thread O.D. is under-size to bolt shank O.D. so will slop around in a hole). Thread is only to hold the nut that holds it all together.
3> Do not weld - Coil-over mounts operate in a fatigue environment; weld (even good welds) are about the the best crack initiators that you could create.

 

[Mark Winton]

Double or Single Shear refers to the number of shear planes for a bolt or rivet. A single lug relates to Single Shear and a lug either side of the rod-end or whatever puts the fastener in Double Shear. Bolts mounted in this way (ie. not axial load) fail by either bending or shear. Double shear doubles the shear capacity, and typically reduces the bending, but how much is geometric specific. Never let bolt threads act in bearing on the lug or what looks like is Double Shear is in reality only be Single Shear !

 

[Terry Oxandale]

Thanks Mark. From my observations, 95% of our shock mounting is done via a welded bracket or clevis on one end or both. I suppose the success of this has been the orientation of the welded bracket and quality of the weld. In regards to the bolts, I've always sized a bolt in which the shank resides across both sides of the clevis (sometimes a washer is required to ensure this, and then the excess threads are removed as needed. I do powerdercoat mine, but the request is for a light dusting (they look at me oddly when I request that) to keep the thickness to a minimum, but still protect the pieces.