v2racing

I'm coming to the close of the body off chassis restoration on my 75 Vert ( https://www.corvetteforum.com/forums...-my-frame.html ). I have new trailing arms and 2 new bolt and shim kits. Both kits came with grade 8 bolt, but the castle nuts appear to be grade five and the affective nut area of the bolt is only about have of a normal 7/16 x 20 nut. I don't believe these nuts are even remotely capable of standing up to a grade 8 spec of 90 ft lbs of torque. I haven't been able to find anything stronger than a grade 5 in a castle nut.

I can get grade 8 nylock nuts. They can handle the torque. I've never had any problems with nylocks backing off. I'm leaning towards the stronger nylock nut.

What do you think?

Mike

cv67

Either one will do just fine, replaced a lot of stuff underneath with the grade 8 locking stuff too, ocd. Osh love$ me.

Greg

The burden of torque/strength is on the grade 8 bolt supplied. Not on the nut. The castle nut is only there to keep the bolt from rotating out of place. And, as Alan said the spec is only 45-50 lbs. The castle nut will be fine.

DUB

Actually.... the trailing arm bolts originally were a Grade 5. And a slotted nut or castle nut will do the same thing.

The only difference is between the two (slotted or castle) is whatever company you look at on the inter net and what they seem to want call it.

I prefer the nut that has not been shaped or tapered in any way where the cotter pin goes though. I want the nut to be as stout as possible...and that type of nut is what GM used.

And not that this may matters at all....but something to possibly consider.

As I was told by some people who know way more than me in specific areas of a car. They told me that having a Grade 5 bolt is just fine and may actually be better than a grade 8 due to a grade 8 can shear due to its tensile strength. And even though it is stout when being pulled on and tightened...it is brittle when a sideward load is applied to it...much like a drill bit when you put it in a vise and hit it with a hammer.

And knowing that the lower shock bolts for these cars are soft...in order to take all the abuse...if it were like a Grade 8...it could shear.

I am not saying it would...I am just saying. I am also under the assumption that going stouter such as a Grade 8 is better...because I am also striving to provide the best I can for people...but sometimes the people I know let me know that even though that is a good way to think..sometimes... in certain areas it may not be the best way.

DUB

bobs77vet

i like the castle nuts its almost like racing wire wire by tying things to stop them from disassembling

derekderek

that trailing arm bolt is not a bolt. it is a pivot point. it happens to have threads on the end to hold it in place. you put 65 ft lbs on that same bolt in a cylinder head, it is exerting clamping force to seal the gasket. on the trailing arm, it is just making sure the bolt doesn't leave. the shims set the side play, not torque.

v2racing

Well my thinking here is that it actually does squeez the frame together on the shims and trailing arm bushing. I was checking it and it doesn't take much force to move the two outside walls of that pocket towards each other. The flexy frame thing again. At even the 45 pounds torque, I garranty that they are squeezing together.

Mike

v2racing

A grade 5 bolt has 120,000 PSI tensile strength. A grade 8 has 150,000 PSI tensile strength. Shear strength is approximately 60% of tensile strength. A grade 5 bolt would have a shear strength of 72,000 PSI. A grade 8 would have a shear strength of 90,000 PSI, that gives the grade 8 a 18,000 PSI advantage over the grade 5.

Shear strength is what is required for a trailing arm pivot bolt to take loads to the side of the bolt's shank.

Also any bolt below 180,000 PSI tensile strength is considered ductile, not brittle.

Edit: I want to add that the clamping force is extremely important in keeping the trailing arm and shims tight between the sides of the frame. If the pivot bolt is left loose, the bolt will be banging around in the hole in the frame they are riding in. It will tear up those holes if left to run this way

Mike

derekderek

Yes, and one uses enough shims that the frame doesn't have to be squeezed in much at all. Just enough to the 3-sided sheet metal U into a closed box. You need the hard strong bolt to take the side stresses of being a suspension member, not the clamping stress of a fastener. I think a grade 5 with a cotter pin is better insurance.

v2racing

I don't understand your logic. A grade 5 bolt has a 72,000 PSI shear strength and a grade 8 has a 90,000 PSI shear strength. The grade 8 can take 18,000 PSI more side load than the grade 5.

When these cars were designed, the engineers probably didn't foresee the loads modern tires could produce, not to mention the horsepower levels being put in them.

Mike

derekderek

The nut doesn't do much. The bolt and the frame hold the trailing arm in place. The nut clamps down a bit on the frame box, but it is mainly there to keep the bolt from leaving. Look at a reese hitch. 6000 lbs. That little pin that retains the hitch pin sure as hell can't hold 6000 lbs.

DUB

Whatever grade of bolt you choose to use for your application is fine by me. I was just passing along the information I was told by the guys I know who really know stuff.

And YES..I can confirm that there are many Corvettes that when I set the shims in the trailing arm area for the alignment....the shim packs were loose UNTIL the trialing arm bolt was tightened..and then the shims were stationary and would not move.

DUB

'75

When the car accelerates, the trailing arm bolts are what pushes the car, higher shear strength is better.