Bolt grade question. . . . - The 1947 - Present Chevrolet & GMC Truck Message Board Network

*racedvl* · 06-27-2004, 11:24 AM

I am getting ready to finish hanging new brakes on the 72 rear end I have for my truck, but I seem to be having a problem. I cannot find a Grade 8 bolt in 5/16ths in a 1/2" length, for the rear wheel cylinders. Will a grade 5 work OK in place of a grade 8? I really want to replace the old bolts. Thanks for any help. Jason.

dave-68 · 06-27-2004, 02:04 PM

Grade 5 Bolts have a tensile strength of 120,000 psi (under 1" dia.) whereas grade 8 is 150,000 psi. May not seem like much of a difference, but I wouldn't skimp on brake components. I looked in a McMaster Carr catalog fo 5/16-18 screws and I didn't find a hex hed cap in 1/2" length either. But I did find Socket Head cap in 1/2" long in alloy steel (180,000 psi), which is stronger than Grade 8. If you want to use Hex head cap you can always cut a longer one to length.

Dave

**kwmech** · 06-27-2004, 02:12 PM

Use the grade 5s and don't worry about it.

1971 Cheyenne · 06-27-2004, 02:50 PM

I found grade 8's at NAPA for those. Keep looking, they arn't too hard to find.

Gordo · 06-27-2004, 09:11 PM

I would think the large hole in the backing plate in which the backside of the wheel cylinder fits snuggly is to take the side to side stress, leaving the bolts to keep the cylinder in place up against the backing plate. Use the grade five and get some sleep.

krue · 06-27-2004, 09:38 PM

Go with the grade 5. It's plenty strong for that application.

chevroletrucks · 06-27-2004, 10:36 PM

Over the years here in the rust capitol of the earth Northwest Indiana, I've replaced at least hundreds of those bolts all with grade 5 bolts. Mainly because thats all we have in stock in our bolt bin at work. I have never had one fail yet. I think you'll be o.k.

*Shane* · 06-28-2004, 12:29 AM

Grade 5 will be fine for wheel cylinders ... these bolts won't be under any under any Axial (radial/rotational/torsional) or Lateral (sideways) load, so you will be fine. They are only holding the cyclinder against the backing plate.

Heck, even wheel lugs and lug nuts aren't grade 8 ... same principle.

*racedvl* · 06-28-2004, 05:34 PM

Well, the vote seems to be grade 5. Thanks folks.

06-27-2004, 11:24 AM	#1
racedvl Account Suspended Join Date: Jan 2000 Location: Woodstock, IL Posts: 7,020	Bolt grade question. . . . I am getting ready to finish hanging new brakes on the 72 rear end I have for my truck, but I seem to be having a problem. I cannot find a Grade 8 bolt in 5/16ths in a 1/2" length, for the rear wheel cylinders. Will a grade 5 work OK in place of a grade 8? I really want to replace the old bolts. Thanks for any help. Jason.

06-27-2004, 02:50 PM	#4
1971 Cheyenne Registered User Join Date: Nov 2002 Location: Bellevue, WA Posts: 1,480	I found grade 8's at NAPA for those. Keep looking, they arn't too hard to find. __________________ Brian Pal 1971 Cheyenne 10 454/th400-Undergoing a full frame off resto. 1972 Chevy short/step 2wd, 350/th350 1983 M1009 CUCV Military K5 Blazer 1981 Dodge 1 ton 4x4 dually flatbed

06-27-2004, 09:11 PM	#5
Gordo Registered User Join Date: Jan 2001 Location: Killingworth, CT. USA Posts: 3,378	I would think the large hole in the backing plate in which the backside of the wheel cylinder fits snuggly is to take the side to side stress, leaving the bolts to keep the cylinder in place up against the backing plate. Use the grade five and get some sleep. __________________ 1971 C10 swb stepside 350/700R4/3.73posi (retired as of 4/22/03) 1998 S10 short bed 2002 S10 Blazer 1942 Oldsmobile 1958 Massey Harris Pony 1951 Wife Killingworth, Connecticut May those who love us, love us, any of those who do not love us, may God turn their hearts. And if God is unable to turn their hearts, may he turn their ankles so we may know them by their limping. A man who works with his hands is a laborer; a man who works with his hands and his brain is a craftsman; but a man who works with his hands and his brain and his heart is an artist.

06-27-2004, 09:38 PM	#6
krue Designated A-hole! Join Date: Mar 2003 Location: South Mississippi Posts: 36,448	Go with the grade 5. It's plenty strong for that application. __________________ "If it ain't broke, fix it 'til it is!" Being stupid ain't illegal. We're Still Debt Free Except for the House!!! www.daveramsey.com 70 GMC SWB Stepside project "Green Booger" soon to be 6.0l/4l80e 93 S-10 "Poppaw's Truck"

06-27-2004, 10:36 PM	#7
chevroletrucks Registered User Join Date: Sep 2002 Location: Northwest,Indiana Posts: 128	Over the years here in the rust capitol of the earth Northwest Indiana, I've replaced at least hundreds of those bolts all with grade 5 bolts. Mainly because thats all we have in stock in our bolt bin at work. I have never had one fail yet. I think you'll be o.k. __________________ 67' Chevy C10 Lwb small rear window 71' Gmc 1500 custom 4x4 72' Gmc Grande Sierra

06-27-2004, 02:04 PM	#2
dave-68 Registered User Join Date: Oct 2003 Location: Palm Bay, Florida Posts: 75	Grade 5 Bolts have a tensile strength of 120,000 psi (under 1" dia.) whereas grade 8 is 150,000 psi. May not seem like much of a difference, but I wouldn't skimp on brake components. I looked in a McMaster Carr catalog fo 5/16-18 screws and I didn't find a hex hed cap in 1/2" length either. But I did find Socket Head cap in 1/2" long in alloy steel (180,000 psi), which is stronger than Grade 8. If you want to use Hex head cap you can always cut a longer one to length. Dave

06-27-2004, 02:12 PM	#3
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,717	Use the grade 5s and don't worry about it.

06-28-2004, 12:29 AM	#8
Shane Account Suspended Join Date: Jun 2000 Location: over yonder Posts: 14,270	Grade 5 will be fine for wheel cylinders ... these bolts won't be under any under any Axial (radial/rotational/torsional) or Lateral (sideways) load, so you will be fine. They are only holding the cyclinder against the backing plate. Heck, even wheel lugs and lug nuts aren't grade 8 ... same principle.

06-28-2004, 05:34 PM	#9
racedvl Account Suspended Join Date: Jan 2000 Location: Woodstock, IL Posts: 7,020	Well, the vote seems to be grade 5. Thanks folks.



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