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Replacing cap bolts- bolt strength? #4107201 05/26/16 12:49 PM
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ford46guy Offline OP
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I posted a thread about a tractor transmission that failed because all the cap bolts broke.

The original bolts are around 5/16ish, medium thread (didn't get to the store to measure them). They don't have any strength markings on them. They may have failed because things loosened up. It is cast aluminum case. I'm using locktite when I reassemble.

I want to replace with grade 8 (8.8) but I worry that is too much for the case. Any opinions on this?
There is no service manual for this product (it is throwaway). I'm wondering what the torque would be on these bolts. I know for a car diff it is very high, and I know some diffs (like the mark 8) are made from aluminum. From the poking around I see 15-20ft/lbs for similar tractor units.

http://www.bobistheoilguy.com/forums/ubb...24c#Post4106576


95 Tbird V8 240K PP SYNTH ULTRA 5W30
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Re: Replacing cap bolts- bolt strength? [Re: ford46guy] #4107208 05/26/16 01:03 PM
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A_Harman Online Content
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Watch out, you're terminology is contradictory. Bolts with head markings reading "8.8" are metric bolts that have the equivalent strength of SAE grade 5. Are you working with metric or English bolts?

"10.9" is the metric bolt strength class equivalent to SAE grade 8.

Last edited by A_Harman; 05/26/16 01:04 PM.

1985 Z51 Corvette track car
2002 Camaro Z28 LS1/6-speed
2001 Dodge Ram 2500 diesel
1972 GMC 1500 shortbed project truck
Re: Replacing cap bolts- bolt strength? [Re: ford46guy] #4107209 05/26/16 01:04 PM
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440Magnum Offline
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Grade 5 should easily suffice. Grade 8 will work, but its overkill in an aluminum case like that. The case will fail before the bolts will, probably even at grade 5 bolts. Its not a question of "being too much for the case" unless you overtorque them.

The torque spec won't be nearly as high as a car differential, but without looking it up I'd assume your 20 ft-lb guess is pretty good. I'd probably throw some loctite on there for good measure.

Two different oils? Is this a hydro unit? Most Peerless tractor transaxles I know of are packed full of Bentonite grease.


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Re: Replacing cap bolts- bolt strength? [Re: ford46guy] #4107217 05/26/16 01:10 PM
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Yah-Tah-Hey Offline
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There are bolts and then there are bolts. The grade 8 SAE bolts will have five slash marks on the head. Bolt torque values can be found with a Google search.Keep in mind that there is a lot of fastener junk around so do some fastener due diligence. I would think grade five(three slash marks) would be adequate in that application.

Re: Replacing cap bolts- bolt strength? [Re: A_Harman] #4107219 05/26/16 01:10 PM
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ford46guy Offline OP
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I believe it is an M8 bolt but I didn't measure it yet. It is 7.76 mm Diameter. It has no markings whatsoever, so that implies it is made to assemble a table.

Thanks for clarifying, I did misuse the strength spec.


95 Tbird V8 240K PP SYNTH ULTRA 5W30
98 MGM 160K M1 HM 5W20
96 Explorer EB V6 159K PP SYNTH HM 5W30
95 Conti 155K MC 5W20
11 GS350 90K PP HM 5W30
Re: Replacing cap bolts- bolt strength? [Re: 440Magnum] #4107222 05/26/16 01:11 PM
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ford46guy Offline OP
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Originally Posted By: 440Magnum
Grade 5 should easily suffice. Grade 8 will work, but its overkill in an aluminum case like that. The case will fail before the bolts will, probably even at grade 5 bolts. Its not a question of "being too much for the case" unless you overtorque them.

The torque spec won't be nearly as high as a car differential, but without looking it up I'd assume your 20 ft-lb guess is pretty good. I'd probably throw some loctite on there for good measure.

Two different oils? Is this a hydro unit? Most Peerless tractor transaxles I know of are packed full of Bentonite grease.

Yes, 80w90 + some expensive peerless mystery oil in a quart bottle. A smelly gear oil came out, but they likely mixed when I split the case.

In another thread xW-50 was suggested for the pump.


95 Tbird V8 240K PP SYNTH ULTRA 5W30
98 MGM 160K M1 HM 5W20
96 Explorer EB V6 159K PP SYNTH HM 5W30
95 Conti 155K MC 5W20
11 GS350 90K PP HM 5W30
Re: Replacing cap bolts- bolt strength? [Re: ford46guy] #4107436 05/26/16 06:19 PM
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Merkava_4 Offline
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Get automotive grade bolts. Rockford or Auveco.

Re: Replacing cap bolts- bolt strength? [Re: Merkava_4] #4107902 05/27/16 09:35 AM
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Oldmoparguy1 Offline
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Originally Posted By: Merkava_4
Get automotive grade bolts. Rockford or Auveco.


+1


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If Noah had used Zip, he could have used a smaller boat.
Re: Replacing cap bolts- bolt strength? [Re: ford46guy] #4108831 05/28/16 10:34 AM
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zeng Offline
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Originally Posted By: ford46guy
I believe it is an M8 bolt but I didn't measure it yet. It is 7.76 mm Diameter. It has no markings whatsoever, so that implies it is made to assemble a table.

Thanks for clarifying, I did misuse the strength spec.


Heck, since Peerless is American.. it can't be M8.
7.76 mm should then be 5/16 inch. Pitch isn't the same.

Edit:
http://www.americanfastener.com/astm-sae-and-iso-grade-markings-for-steel-fasteners/

Last edited by zeng; 05/28/16 10:39 AM.
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