I need to replace some bolts on my upper and lower control arms. Can I use standard Grade 8 bolts from a hardware store - or do I need to order the direct replacements from an Auto Parts store?? What is the difference between them? I also need motor mount bolts and a few others that I want to make sure don't twist or break or rust like crazy.

Suggestions??

Stock bolts were grade 5, black oxide finish if I recall. Grade 8's are just fine to use, most come with a zinc finish. You can also get armor coat finish. They all rust with time, but zinc and armor coat will last longer then black oxide.

Great - thanks! Just what I was looking for!

Totally Stainless has high strength stainless bolts for the suspension in a package. They polish up nice and dont rust. A little pricey though. Try to catch them at a car show and save some bucks.

Stock bolts were grade 5, black oxide finish if I recall. Grade 8's are just fine to use, most come with a zinc finish. You can also get armor coat finish. They all rust with time, but zinc and armor coat will last longer then black oxide.

I'm not positive, but I don't think this is accurate. I think all suspension bolts, particularly those holding the arms on, are grade 8, and I wouldn't use anything less than 8 on these parts.

I would NOT buy them at a hardware store, there's a lot of cheaper stuff finding it's way in, for something that critical I would get from a reputable supplier, like totally stainless, ARP, etc. but I guess you can never really tell where stuff is from.

You need to be aware of the stainless stuff, you must use antiseize compound or the stainless weakens over time due to whatever-the-heck-that-process-is-called. Pete Lohr (wagons moderator) uses armor-coat and really that seems like the best choice if you're starting fresh. Here's Pete's site: www.einstyn.com and here's a link to his discussion on armor-coat suspension bolts (about half-way down the page): http://www.einstyn.com/einstyn-hardtop-04.htm

His "available here" thing doesn't work, but I'm sure if you PM'd him or did a search you could find them.

the factory bolts use a machined shoulder for a more precise fit. grade 8 bolts would be ok but i would use factory style bolts

Right, b/c some are selling 7.5's as 8's!!

I'm either going to RR iron anvil/prick punch ding my 8 nuts so they become self-locking or drill and safety wire/cotter key all of them that are on my A-arms and leaf springs!

pdq67

I use hardware store grade 8s with standard grade nylock nuts in all but the upper A-arms, where I use Grade 8 nuts with threadlocker on them.

The lower A-arms, and all rear arms are mounted in double-shear and all of the forces are in shear, so the grade of the nut does not matter, all it does is hold the bolt in place. The upper A-arms have tensile loads on them, so you need the nut to be as strong as the bolt. My upper arms are adjustable w/o shims, so I don't use the stock knurled bolts in the uppers. :)

im suprised that there is a stainless bolt available for suspension applications. never heard of it before reading this post.

any other options for a long lasting coating on grade 8 bolts? nickel plating? ive heard about some armor plated bolts from mcmaster carr, just not sure how they look.

Tim

I use hardware store grade 8s with standard grade nylock nuts in all but the upper A-arms, where I use Grade 8 nuts with threadlocker on them.

The lower A-arms, and all rear arms are mounted in double-shear and all of the forces are in shear, so the grade of the nut does not matter, all it does is hold the bolt in place. The upper A-arms have tensile loads on them, so you need the nut to be as strong as the bolt. My upper arms are adjustable w/o shims, so I don't use the stock knurled bolts in the uppers. :)

Exactly! :thumbsup:
I've got Grade 8 bolts in all my '70s suspension mounting points... NEVER been any issue. I add a couple drops of Loctite Thread Locker before final assembly.
The gold cad plating on these bolts is more than enough corrosion protection to get you and your Chevelle thru the next 40 years. ;)
And to clarify, the factory used nothing stronger than a Grade 5 bolt.

I replaced all the rear suspension bolts with stainless jobs from Home Depot...cause they look nice primarily. Is this an issue? They are alot heavier than the cad-plated grade 8's from Home Depot, so you would think they are stronger. My Edelbrock no-hops and upper controm arms came with the cad-plated/gold bolts , so I figure were good.

But, I dont wanna "Bob West" into the wall either...

normal stainless bolts(ie everything i have EVER seen, minus the totally stainless stuff) is only as strong as grade 2. if you value your life or those driving next to you, youll pull them and replace with grade 8 +.

Tim

normal stainless bolts(ie everything i have EVER seen, minus the totally stainless stuff) is only as strong as grade 2. if you value your life or those driving next to you, youll pull them and replace with grade 8 +.

Tim

Stainless isn't graded the same, and this is essentially correct - unless you get strengthened stainless, you should certainly NOT use it. The stuff from totally stainless and others is actually stronger than grade 8 per the specs, but it's made specifically for suspension as a grade 8 replacement.

I'd take out anything stainless from a hardware store that's critical.

Thanks guys, will-do!

Stainless has another trait that everyone should be aware of,it has a tendency to "Gall" as in seize.A good anti-seize compound applied to the threads will take care of this problem.

I'm not positive, but I don't think this is accurate. I think all suspension bolts, particularly those holding the arms on, are grade 8, and I wouldn't use anything less than 8 on these parts.

I'm pretty darn sure all the bolts I removed from my '70 were grade 5, even Bill agree's!

Exactly! :thumbsup:
I've got Grade 8 bolts in all my '70s suspension mounting points... NEVER been any issue. I add a couple drops of Loctite Thread Locker before final assembly.
The gold cad plating on these bolts is more than enough corrosion protection to get you and your Chevelle thru the next 40 years. ;)
And to clarify, the factory used nothing stronger than a Grade 5 bolt.

:thumbsup: I've never had a problem with a grade 8 either. Zinc are just fine, but I put the armor coat bolts from McMaster on my Chevelle. Still look great with no rust after 2 years and stronger then he!!

Kyle

Another option is to use a G5 aircraft bolt from Aircraft Spruce. The trick is to get the grip length correct so that the full bolt diameter is in double shear. What I did not like about using the stock-type bolt is that the thread is in shear. With an aircraft G5 in full double shear the overall shear strength is higher than a stock G8 with one thread in shear.

Zinc are just fine, but I put the armor coat bolts from McMaster on my Chevelle. Still look great with no rust after 2 years and stronger then he!!


any pics of these bolts? how do they differ from the zinc coated stuff. ive looked them up at mcmaster before, but their site didnt have a picture.

Tim

This pic is from Pete Lohr's site (www.einstyn.com), our Wagons moderator:
http://www.einstyn.com/einstyn1/hardware.jpg

i think grade 8 is harder and more brittle and would snap sooner. grade 5 is softer and bends more. at least thats the way ive been told. i think factory is grade 5. grade 5 or 8 should be fine. i prefer gold cad plate for antirust. grease um up.

I went with the Grade 5 bolts after looking at the factory specs.

when i did the front suspension of my Nova, i just brought my stock bolts to Mills Fleet farm and got some grade 8 bolts, nuts, and washers that matched the stock grade 5 stuff.
since they sell hardware like that by the pound and i only got like 2 pounds, it only cost about $3 for everything. everything was gold cad plated and contrasted nicely with the semi gloss black of the subframe.
when the time came to actually put the subframe in the car and i needed shorter bolts due to the CE solid aluminum mounts i was using, i went there and bought another 3 pounds or so of grade 8 hardware for about $5.
man, i love that store..

I used grade 8 from the hardware store in 98 when I did my suspension rebuild on my convertible. I just took them off and they are like brand new.

I replaced my front LCA bolts, and the heads had markings that indicate GR 8. Also, the replacement from ground up was GR 8. The nut also is GR 8 and marked differently than this pic:


http://www.ss396.com/mm5/graphics/00000009/BPB-1430.jpg

i think grade 8 is harder and more brittle and would snap sooner.:noway:

The Industrial Fastener Institute (Inch Fastener Standards, 7th ed. 2003. B-2) states that "shear strength is approximately 60% of the minimum tensile strength."

ASSUMING COARSE THREADS (averages):

Proof Load (psi) / Minimum Yield Strength (psi) / Minimum Tensile Strength (psi)
Grade 5-(sizes 1/4" to 1") 85,000 / 92,000 / 120,000 OR 72,000 SHEAR
Grade 8-(sizes 1/4" to 1 1/2") 120,000 / 130,000 / 150,000 OR 90,000 SHEAR

check out: http://www.almabolt.com/pages/catalog/bolts/proofloadtensile.htm- for precise strengths

BOTH the grade 5 and grade 8 bolts will snap, or shear, at a certain point. personally, I will not re-use grade 5 bolts that "could bend". they would just bend until they snap, just like a grade 8 bolt. however, the grade 8 bolt can take the repeated abuse WITHOUT "bending".

did i say reuse? the grade 5 bolts have been in my 71 ss since new. no problems. im getting ready to swap in tubular control arms now. my only concern is upper arms binding w/the poly bushings. they are greasable. i will use new bolts 5 or 8 i dont care.

Another option is to use a G5 aircraft bolt from Aircraft Spruce. The trick is to get the grip length correct so that the full bolt diameter is in double shear. What I did not like about using the stock-type bolt is that the thread is in shear. With an aircraft G5 in full double shear the overall shear strength is higher than a stock G8 with one thread in shear.

This is an AN8 bolt (Army Navy, 8/16, SAE size thread of 1/2-20) such as CarlC is speaking courtesy of aircraftspruce:

http://www.aircraftspruce.com/catalog/graphics/04-00835.jpg

It's rated at min 125,000 PSI so slightly above Grade 5. And here's an example of the same concern I have about threads being in shear: http://www.russellw.com/planes/cruisemaster/maint_landing_gear_bolts.htm Read the paragraph below the bolt pic.

Any experience using these locking nuts?: http://www.aircraftspruce.com/catalog/hapages/an363.php

Could use a hand getting a couple of measurements here:

1.) Using the AN8 sizes listed here: http://www.aircraftspruce.com/catalog/hapages/an8.php what would be the ideal Chevelle 'grip' length for the rear control arms given a washer at the bolt head and one at the nut?

2.) Does a 1/2" bolt fit the OEM frame mounts snugly or is there slop? Does it matter? Several aftermarket RCA companies are using 12mm bolts to cover A & G Bodys. 1/2" = 12.7mm, so an M12 = slop on our cars.

You can use up to three washers on the nut side to tailor the grip length.

Those are the same as I run on my car along with the plastic-type self-locking nuts from Aircraft Spruce. The bolts in the front suspension are not very tight in order to reduce binding (delrin bushings.) Since the thread on the AN bolt is fine the installation torque must be adjusted accordingly if rubber bushings are used.

The car has multiple road course track days with zero fastener problems.

Order a bag of AN washers at the same time. It makes the installation a lot easier.

Minimum shank length = distance of the clamped components + 2x washer thickness. If you found one with this exact length a second washer on the nut side would likely need to be used to avoid running the nut into the unthreaded shank. Since automotive frames and suspension components are thin getting something exact is hit and miss, hence the extra washers. Carroll Smith's "Nuts, Bolts, Fasteners, and Plumbing" is a nice guide for making choices on various fastener and automotive structural connections.

There is no amount of abuse you could dish to a typical grade 8 suspension bolt that would snap it IMO. Even if you jumped it like the Dukes of Hazzard. The only way I can see a grade 5 or grade 8 breaking is maybe in an accident, by then its too late.

I got a stanless bolt kit from Mark @ SC&C when I ordered my rear LCAs...

This is an AN8 bolt (Army Navy, 8/16, SAE size thread of 1/2-20) such as CarlC is speaking courtesy of aircraftspruce:

http://www.aircraftspruce.com/catalog/graphics/04-00835.jpg

It's rated at min 125,000 PSI so slightly above Grade 5. And here's an example of the same concern I have about threads being in shear: http://www.russellw.com/planes/cruisemaster/maint_landing_gear_bolts.htm Read the paragraph below the bolt pic.

Any experience using these locking nuts?: http://www.aircraftspruce.com/catalog/hapages/an363.php

Could use a hand getting a couple of measurements here:

1.) Using the AN8 sizes listed here: http://www.aircraftspruce.com/catalog/hapages/an8.php what would be the ideal Chevelle 'grip' length for the rear control arms given a washer at the bolt head and one at the nut?

2.) Does a 1/2" bolt fit the OEM frame mounts snugly or is there slop? Does it matter? Several aftermarket RCA companies are using 12mm bolts to cover A & G Bodys. 1/2" = 12.7mm, so an M12 = slop on our cars.

I do aircraft structural in the USAF. we use that type of hardware for everything that is bolted. We generally use the MS21042 type locknuts. they use a thread design that is slightly out of round for their locking feature. they can be pretty tight on initial installation. the other nuts are "interrupted thread" design and will lose their locking ability if they are removed and replaced more than a few times. good quality stuff. I can't vouch for this company, but if they are AN or MS spec stuff for real, it is held to pretty high standards.

i got grade 8 stainless from www.boltdepot.com

troposcuba -
Can you comment on these two locknuts: http://www.aircraftspruce.com/catalog/hapages/an363.php and this: http://www.mechanicsupport.com/stop_nut.html

Is there a torque chart available for AN bolts?

From the second link:

The elastic lock nut is more friendly to the threads, locks out moisture and prevents corrosion; and the nylon deforms rather than gouges. Except in areas of high-temperature, the elastic lock nut is generally preferred.

Recommendations for use per FAA AC43.13-1B Acceptable Methods and Practices:
Elastic lock nuts are not to be installed in areas exceeding 250 degrees F.
Do not reuse elastic lock nuts if the nut cannot meet the minimum prevailing torque values shown in the chart
Do not use self-locking nuts on parts subject to rotation
Do not use self-locking nuts where the loose nut, bolt, or washer may fall or be drawn into the engine air intake scoop.
Do not use self-locking nuts to attach access panels, doors, or any parts that are routinely disassembled before or after each flight.

This fits the bill for suspension components. If your suspension components get over 250*F there are other serious problems.

Another factor that hopefully Sean can comment more on is reuse of the bolt if the metal-locking/thread upset type nut is used. I would be very hesitant about wanting to reuse a fastener after the threadform has been damaged by an upset-type nut. I have zero concerns in my appliction about reusing the bolt when nylon locknut is used, but if removed I will use a new nut since the fastener is not tightened to a %yeild point. I just buy a bag at the same time as the washers. If you really needed the super double throwdown some blue Locktite could also be used but care would need to be used so that it does not come in contact with the nylon seating area.