Replacing Hub Bolts

Anyone eplace these things with a regualr hex head bolt? Im trying to find a hex flanged metric grade 10.9 but cant, would a socket cap screw work? Or just a reagular hex with a washer? Anyone have a source for hexflange metrics?

you talking about the three/side 12-points for the front? I had the same problem, my bonehead buddy tweaked mine but I ended up getting some regular oversize hex heads that should work, also got some black oxide thick washers that I may or may not use. They are m12x90 grade 10.9 mcmaster carr part number: hc1012090-005m2. They don't have the quick start end but should work fine. Of course they only come in packs of 5 so I have 4-extras.

Hope that helps, I could not find the OEM anywhere, never tried the dealer but pretty sure they would want an arm and a leg, if they even had them.
good luck

Stealership or the junk yard.

Ok. I knew there was another place out there other than grainger, fastenal, or msc. thanks. Will take a loook.

actually sorry, that was the manuf. part number that was on the bag, here is the correct mcmasterr carr pn: 91310A740

I could not live without mcmaster carr, they have.......everything, always comes next day by a private white van or pickup truck.

Skullvarian said:

actually sorry, that was the manuf. part number that was on the bag, here is the correct mcmasterr carr pn: 91310A740

I could not live without mcmaster carr, they have.......everything, always comes next day by a private white van or pickup truck.

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were those the flanged ones?

IIRC, the hub bolts aren't 10.9 hard, they're at least one step up. And not simple flanged heads either, there's a distinct profile down the bolt. These are some of the very few parts that I'll keep OEM.

the set I ordered do not have a flange, they are standard hex (19mm socket) but they should work fine.

ChiXJeff said:

IIRC, the hub bolts aren't 10.9 hard, they're at least one step up. And not simple flanged heads either, there's a distinct profile down the bolt. These are some of the very few parts that I'll keep OEM.

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funny, the ones I took off say 10.9 right on the head, albeit they are flanged and do have a weird necking compared to the partially threaded units I ordered with a straight shank, they are stronger if anything due to a straight profile. I'll replace the bats in my camera and snap a pic.

Skull, Are you using hardened washer under the heads? I would think you would need to as the stock ones have the flange. Maybe the stock ones are 12.9?

I do have the .175" thick black oxide washers, can't find the part number but the od is 1" and the id has to be drilled out for clearance, but the head will be the same footprint as the oem, just with a thick washer. Still deciding on whether I really need it but we'll see.
good luck.
pics of bolt I used next to oem, both 10.9....

Thanks for the pictures.

No reason a socket head wouldn't work - SAE socket heads are H&T to SAE8 anyhow, and ISO socket heads to ISO PC10.9 or better (actually, I think they get H&T to 12.9, but I'd have to check.)

Hardened washers (the thick black ones) may be indicated, but I'm not sure. If we're talking about the same screws (retain the hub bearing assembly to the iron knuckle up front,) then they're not really loaded in tension anyhow - they're more going to be loaded in shear, and the pilot going into the bore on the knuckle will take most of that. The only real "tension" load on them will be from installation preload - early hub screws get torqued to 75 pound-feet.

Did they change the size of the screws later? Early screws are M8-1.25 by about 60-70m/m (I'd have to check the UHL,) but you're citing M12 (M12x90? Sounds like it should be M12-1.75x90m/m - unless the thread pitch is weird...) Got any idea when they changed that, or are you going to make me dig it up myself?:helpme:

@Skullvarian - I see what you mean about the "profile" on the screw. I don't know why they do that instead of using a full-diameter grip, but the necking up is to properly locate the screw in the mating part (the knuckle.) I've no farkin' clue why they'd neck it down between there and the threads - easier to just roll a thread on a straight grip (I'm sure there's some engineering reason for doing so, but I don't know what it is. I've seen things done with sound engineering reasons that just didn't apply in that case anyhow - RENIX manifold studs come to mind...) You wouldn't still happen to have one of those screws loose and handy, would you? And a caliper or a mike? I'd be interested in seeing what the OD of that "grip swelling" is relative to A) the necked-down grip section and B) the "straight grip" on the replacement screw.

As far as the flanged head, that's usually done to allow for a reduced wrenching surface (reduced hex, reduced 12-point, E-Torx, et al.) Since you lose bearing area if you go right to a reduced wrenching head, it gets replaced with the flange. Yah, the flange on the OEM screw is wider than the bearing area under the OEM hex head (round part, not the actual hex itself,) but note my comment on tension loading/shear loading above. You see something similar on screws for universal joint straps - they go with a reduced wrenching head to give you tool clearance, but then go to a flange to get bearing area. I've replaced these with socket heads and no washers without incident - you actually get more tool clearance (using a "round end hex key socket" - you get the internal wrenching and provision for 20-30* of tool misalingment!) and the bearing area doesn't need to be great anyhow.

I've been thinking of replacing the goofy 12-point OEM screws with socket heads, but I'm not going to bother until I have to pull a hub assembly for whatever reason again...

Skullvarian said:

actually sorry, that was the manuf. part number that was on the bag, here is the correct mcmasterr carr pn: 91310A740

I could not live without mcmaster carr, they have.......everything, always comes next day by a private white van or pickup truck.

Click to expand...

I believe that mcmaster is owned by the same company that owns fedex or ups (one of the two), which is why they ship so damn fast and cheap!




I have to ask, why ditch the stock bolts?? They work fine, and who doesn't have a 12point 13mm socket?? They thread real easy too with that nipple before the threads. Also, even though you often have to beat the heck outa them bolts, they very rarely break, probably due to the small size socket they require relative to the bolt size (see how big of a socket the regular hex bolt has). I've busted rachets on them before, and bent wrenches.....but as far as I can remember I don't believe I've ever broken one of those bolts!!!

mjma said:

I believe that mcmaster is owned by the same company that owns fedex or ups (one of the two), which is why they ship so damn fast and cheap!




I have to ask, why ditch the stock bolts?? They work fine, and who doesn't have a 12point 13mm socket?? They thread real easy too with that nipple before the threads. Also, even though you often have to beat the heck outa them bolts, they very rarely break, probably due to the small size socket they require relative to the bolt size (see how big of a socket the regular hex bolt has). I've busted rachets on them before, and bent wrenches.....but as far as I can remember I don't believe I've ever broken one of those bolts!!!

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I was thinking for trail repairs. One less socket to remeber to bring/lose, all m trail sockets are hex. That and the hex bolts will take more of a beating when trying to get the hub out. i have wrecked the heads on a couple, had to grind the heads a little so i could get a socket back on.

2000bluexj said:

I was thinking for trail repairs. One less socket to remeber to bring/lose, all m trail sockets are hex. That and the hex bolts will take more of a beating when trying to get the hub out. i have wrecked the heads on a couple, had to grind the heads a little so i could get a socket back on.

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Along those lines, there's a reason that I have a set of sacrificial bolts. I'll beat on the sacrificials, but not on the good set.

mjma said:

? They work fine, and who doesn't have a 12point 13mm socket??

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this might be somewhat of a goofy question and a little off topic, but are they 13mm or 1/2" 12 point??? i used a 1/2" and it fit good and snug. maybe 13mm and 1/2 are close enough. (13mm = .511")


i just noticed that this is my 100 most..... yaay to me

yessir, sorry for the omission, it is indeed 1.75mm thread pitch, not sure when they changed it as the hubs I was working with were from 91, haven't really noticed a difference but my buddy has a 88 I can check out.

I really don't understand the necking either, seems weird to me but maybe it has to do with ease of assembly or something else completely(got a good deal?), again only speculation.

I don't have the bolt handy but I do have it at the shop handy I can take some measurements for you tomorrow. I do know for sure the "grip swelling" is in fact the same diameter as the entire shank of the replacement, I have no idea why they would turn down a finished bolt prior to heat treating etc but it really seems like it was a secondary machining process. I would be more than happy to send you one in the mail if you want to document it or speculate further. Either way I will get some more measurements tomorrow.

5-90 said:

but you're citing M12 (M12x90? Sounds like it should be M12-1.75x90m/m - unless the thread pitch is weird...) Got any idea when they changed that, or are you going to make me dig it up myself?:helpme:

@Skullvarian - I see what you mean about the "profile" on the screw. I don't know why they do that instead of using a full-diameter grip, but the necking up is to properly locate the screw in the mating part (the knuckle.) I've no farkin' clue why they'd neck it down between there and the threads - easier to just roll a thread on a straight grip (I'm sure there's some engineering reason for doing so, but I don't know what it is. I've seen things done with sound engineering reasons that just didn't apply in that case anyhow - RENIX manifold studs come to mind...) You wouldn't still happen to have one of those screws loose and handy, would you? And a caliper or a mike? I'd be interested in seeing what the OD of that "grip swelling" is relative to A) the necked-down grip section and B) the "straight grip" on the replacement screw.

As far as the flanged head, that's usually done to allow for a reduced wrenching surface (reduced hex, reduced 12-point, E-Torx, et al.) Since you lose bearing area if you go right to a reduced wrenching head, it gets replaced with the flange. Yah, the flange on the OEM screw is wider than the bearing area under the OEM hex head (round part, not the actual hex itself,) but note my comment on tension loading/shear loading above. You see something similar on screws for universal joint straps - they go with a reduced wrenching head to give you tool clearance, but then go to a flange to get bearing area. I've replaced these with socket heads and no washers without incident - you actually get more tool clearance (using a "round end hex key socket" - you get the internal wrenching and provision for 20-30* of tool misalingment!) and the bearing area doesn't need to be great anyhow.

I've been thinking of replacing the goofy 12-point OEM screws with socket heads, but I'm not going to bother until I have to pull a hub assembly for whatever reason again...

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Skullvarian said:

yessir, sorry for the omission, it is indeed 1.75mm thread pitch, not sure when they changed it as the hubs I was working with were from 91, haven't really noticed a difference but my buddy has a 88 I can check out.

I really don't understand the necking either, seems weird to me but maybe it has to do with ease of assembly or something else completely(got a good deal?), again only speculation.

I don't have the bolt handy but I do have it at the shop handy I can take some measurements for you tomorrow. I do know for sure the "grip swelling" is in fact the same diameter as the entire shank of the replacement, I have no idea why they would turn down a finished bolt prior to heat treating etc but it really seems like it was a secondary machining process. I would be more than happy to send you one in the mail if you want to document it or speculate further. Either way I will get some more measurements tomorrow.

Click to expand...

I'm sure it's not so much "turned down" as "rolled down" - rolling is cheaper and, in this case, actually a better process (screw threads are rolled because it is cheaper to do so. Since metal isn't removed - merely displaced - and the threads are effectively "cold-forged" into the metal, you get a stronger screw anyhow...) However, roll-forging the "grip" on the screw doesn't make much sense, since it's an extra manufacturing step, requiring extra energy and tooling, and can be made up for simply by selecting a different material or a different H&T process. So, I just don't understand.

I know they're threaded M8-1.25 1987-1989, since I've worked on all three years. I've got that 1990 in the garage that I'm finally going to be able to get to for deconstruction, so I'll check that as well. I may have to dig through the Timken books to see if they list a difference - but the idea of changing the screw thread there doesn't make any sense to me either (an M8-1.25 PC10.9 screw is plenty strong for that application. No need to go larger, methinks. Unless ChryCo got a deal on M12-1.75 screws and tooling, but then the reduced wrenching head should still be a bit larger - like a 15m/m or so.)

I'd appreciate those measurements (as well as OEM application info for hte M12-1.75 screw and the underhead length, so I can add it to the table...) and I'll let you know if I need to examine the screws myself - but I don't expect to need to.

As far as why to replace them - easy. Ever round off a 12-point wrenching head? The first time it happened to me was on a cylinder head screw for a 1980 Honda Accord CVCC engine. Since the screw was down in a pocket in the head casting, it took me three days to get out (at five hours per day. The auto hobby shop at NAS Moffett was only open eight hours a day - the first hour was spent getting everything out, the last hour putting everything back, and I did have to eat. Fortunately, the NCO club was a short walk away.) I finally ended up using some variety of "tap acid" that was designed to knock the carbon bonds out of the steel, which softened the screw greatly (and the broken drill bit and tap extractor from earlier efforts. I'm sure the slot that I managed to cut in the thing also helped, since it broke the plating and allowed the acid easier ingress...)

I felt the socket give on the screw, and dye-checked the socket for cracks (didn't find any.) At that precise moment, I decided to thoroughly hate 12-point wrenching heads... I'd rather deal with spline-wrenching screws or Whitworths...

5-90 said:

If we're talking about the same screws (retain the hub bearing assembly to the iron knuckle up front,)

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You sure about that?