Hot Rods Double Shear or Single Shear

Mounting up my rearend, I have set it up to be in double shear, but it has become apparent that it will be be hard to remove unless it is in single shear. Is double overkill ( I like it best ), or am I over thinking this?

 

Single shear is easier to fab, but Double shear where practical is the way to go. Just spend the time to lay it out properly to allow for maintenance later

 

Double is the way to go. Single induces bending load in the bolt, in addition to the shear.

 

If you have to ask....

 

You are looking for better expertice...........Thank you all.

 

Always double shear on a critical component.

 

Double-shear is of course better...but...single shear CAN work, given the right selection of materials and fasteners.

Of course, IMO that'd mean starting over with thicker brackets, larger bolts, and close-tolerance bolt holes...

 

the double shear , is hands down the strongest.
on the flip side, if you put too much power to the wishbones, you will run over them...at the very least, bend them.
(with lots of traction) but they do look so cool.

 

Thanks Gimpy......I hope you don't think I was being an a$$ hold on...

 

Nope. I do my best not to judge character. Safety, on the other hand....

 

Are those model A wishbones?

 

Double shear could destroy those wish bones under heavy acceleration.

 

In your case the double shear is not for the bolt junction but to increase the surface area of the axle connection and add rigidity to a light bracket.
Biggest issue is with too concentrated contact area of the thin bracket mount to the thin axle housing that causes the bracket or the axle tube to fatigue crack. Doubling the area reduces the stress on the housing mount. You might find that just making a thicker axle mount will accomplish the same result. My other issue is with the use of the Model A radius rods as they really arent designed to be used in this fashion due to their thin wall construction. They really are just triangulation rods for the torque tube. Looks neat but could bend under severe acceleration or braking.

 

Search: torque arm.

 

A couple of observations in hopes of helping answer the question:

Only photos 2 & 3 are in double shear from what I can see

As has been said, the weak point in your double shear connection is the radius rod.

Allowable shear for a pin (bolt) is generally in the range of 40% of the Yield Strength of the steel. Let's assume the bolts and the radius rods are both 36000 psi steel (typical carbon steel - although the bolts are most likely much stronger...but for the sake of discussion).

40% of 36,000 psi = 14,400 psi. If that's a 1/2" diameter bolt, the cross section area ~ 0.2 square inches. 14,400 x 0.2 = 2880 pounds of force that that bolt can take in shear - double that for your double shear to 5760 pounds for the connection

Now, if you look at the rod (which would have to transfer that load to the connection) - I don't know the size but I'm looking at the pictures and assuming it's about 1 inch x 1/8 inch give or take. Subtracting out the hole diameter for the bolt to go through, you have about 1/2 inch x 1/8 inch of cross section left inside that connection. That 1/2 x 1/8 is 0.0625 square inches. If you apply that 5760 pounds to that cross section you get 5760/0.0625 = 92,160 psi of stress - which far exceeds the 'allowable' stress of 14,400 psi or even the 36,000 psi yield stress.

So, in the end, I'd be more concerned about the connected part in this case than the connection.

If you really want to use that rod, you'll have to beef up the end by welding plates to it and then widening the opening of your connection to accept it.

Just the observations of a registered PE - the acutal numbers will vary based on the materials and dimensions actually used - hope it points you in the right direction

Also, as pointed out, single shear does induce bending into both the bolt and the connection - anything can be accounted for in design. If anyone has any idea of the actual loads taken by these components it would make a design check very easy -

 

The locator arms from the rearend to the cross member are made from thick wall front wishbone stock of unknown origin, not the folded sheet metal stock type.

 

They definately are thicker than I thought - I'm not familiar with those at all as I'm more of a 50s GM guy.

I guess at this point, you have to rely on input from someone who's used these in your application and if they've had any problems - if you measure the thickness and height minus the hole diameter and get an area, you can at least get an idea of what it can take compared to the bolts - in actuality, whatever force comes in will be divided by the two arms of the wishbone - still likely the weak point compared to the connection, but all engineering has a weak point - the idea is to make that weak point strong enough to do what it needs to do -

 

Soapman if you used the front wishbone section its tough enough for narrow tires so your arms should be ok as long as you arent drag racing with super wide tires. Olddad I followed the math but the way I approach it there are two bolts connecting the bracket to the axle not one like your figures compute so that would be double the strength. I'd be more concerned with the torque generated by the tire then apply that to the bolt yield point.

 

2880 was the value for one bolt - I doubled it to 5760 for the double shear

 

Can you explain your line of thought?

 

...and I agree completely that the torque generated at the tire is the source of the load to that connection - if you had an idea what that torque number was and a decent amount of geometry info for the whole setup, that value of torque could be resolved into an actual load / force in each of the components - I'm 100% positive that someone out there has done this math and has an order-of-magnitude value for what you should design these components for - I just don't know what that number is

 

I dont care what you did to the actual rod....its the ends that scare me....Little dinky toys...barely good enough for 40 hp...let alone a hot rod...

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Yep... What he says... I don't understand why more of you guys aren't freaking out... Your concern is double and single shear, but just look at the pic of the little forging compared to the brackets you made on the rear... What looks like the weak link?... I think it's Time to go back to the drawing board on that design ..

I have warned people on radius rods before .... Some listen... Some don't ...... Just think of 80 mph on the freeway and your rear axle wants to leave your little party.... You might get lucky and live through it... Or you may kill an innocent bystander

 

I dont know what you two girls are freaking out about, the mounts appear to be at least 1/4" plate doubled that's 1/2" total plenty heavy enough and the wishbone fork is at least 3/8" x 1" with two point mount. Its probably stronger than the normal 7/16" clevis pin style units. What is the "not built like a tank" weight approach that has you guys all fired up? Most of the torsional load stress on the radius rod is eliminated or is lessened by the tie rod end mount of the radius rod so the link isnt overly twist stressed at the bolt mounts.

Olddad yes this is an issue, weight of the vehicle,engine torque of the drive line, the tire composition factor, the tire contact patch area, the surface area coefficient of friction between the tire and the roadway would be necessary, tooo many unknowns for accuracy, just go with the fact that the tire will probably spin before the metal breaks.

 

Dick , I have read a lot of your posts and you are a very knowledgable individual ... I respectfully disagree ... The brackets that were made on the rear are not my concern its the dinky little old model A forging that is connecting the wishbone to the brackets on the axle ... That is the recipe for disaster in this equation ... If my car had that setup on it I would never drive more than to the corner store

I WOULD NOT EVER LET SoMETHING LIKE THAT LEAVE MY SHOP

 

Do I really need to explain this to the great DICK.

My problem is not with his axle mounts. I think they look plenty strong.

Its with the flimsy model A wishbone end....if you think that thing is strong enough to provide enough strength to not bend under the torque of even a moderate engine you're a fool. I don't care what you think that tie rod end is going to do to reduce stress. Its going to fail. Not if, but when.


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So you guys are telling me that the Model A forged section is weaker than 36" long 1/2" tubing hairpin wishbones. Now explain just why you think that it flimsy other than it looks like it.

 

It's the way the forging is shaped...you have two ears that are 1" wide and about .125 -.186 thick and they are about 5" long .. It's a pretty basic concept ...

I shouldn't have to explain... Just look at it... Am I seeing a different picture than everyone else? I have physically had those type ends in my hands before.. I wouldn't use them ... Always error to the overbuilt... Your life or someone else's could depend on it

The ladder bars I buy and make are 7/8 Dom tubing with gussets inbetween the tubes the axle plates are 1/2 cold rolled with 2 1/2 grade 5 bolts

I have seen speedway hairpins twisted like pretzels

 

I have heard of those hairpin style failing... i'm not a big fan of them either.. ..I'm honestly just not a big fan of open drive rears in early Ford Hot rods without significant additional changes to the rear. Period.

what is going to prevent that from moving side to side and bending as I slide the car around a corner at speed? Or what's gonna stop it from bending/taco-ing when I drop the clutch at 5k on my small block chevy powered hot rod with slicks.

For thought...here is what is considered stronger.

http://www.jalopyjournal.com/forum/showthread.php?t=293274

http://www.jalopyjournal.com/forum/showthread.php?t=663784&highlight=bent+wishbones

Now I am just guessing here. But the reason he split his rear bones is that he probably went to a open drive transmission or different rear end. Anyways, now that the torque tube is gone... It's asking a lot of those little forgings. I'm sure you understand that the TT is a pretty significant piece of the rear suspension as these were designed. I personally would not ride in that car. I think he would be better off using a 35-36 rear bone there.

Are you honestly saying you would use a Model A rear wishbone forging in that manor in a hot rod? and drive it like a Hot Rod?

I bet I can break that in 15 minutes or less.

Some hot rod savvy lawyer is going to have a field day with something like this one day and WHOOPS!!!! there goes hot rodding as we know it.

Or maybe I am wrong. I'm just a backyard engineer. Maybe everyone has been missing out on using cheap, readily available model A bones over the last 80 years.

 

I see it....there are at least 2 of us that are apparently crazy over engineering things.