Diff Cover Bolts

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JimG
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Diff Cover Bolts

Post by JimG »

Has anyone replace the stock cover Torx bolts with something easier to work with? If so what did you use and what size were they?
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john keefe
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Re: Diff Cover Bolts

Post by john keefe »

Best solution might be socket-head (allen) bolts, no worries about clearances with a hex socket. But, socket-heads have a thin shoulder, so you would need washers specifically sized for socket-heads. Tempered/hardened not necessary, but I'd think stainless would be a requirement. If I get the chance, I'll see if I have spares to size for you.
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Re: Diff Cover Bolts

Post by john keefe »

10mm x 1.50mm pitch
Thread length = 30mm
Head to tip length (shank + thread) = 35mm

Looking at other socket-head bolts of approx. same size, the heads are pretty tall. If you're concerned about "cosmetics," you'd probably have to grind down the tops. There's usually enough depth in the socket, and as long as you use anti-seize it shouldn't be a problem to unbolt them later. If you're going that route, I'd stick with stainless to avoid rust after grinding.
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Re: Diff Cover Bolts

Post by my8950 »

I just did this a few weeks ago.
I didn't have to grind any of the heads.
I'll try to find a photo and post it up here.
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Re: Diff Cover Bolts

Post by my8950 »

It was a little challenging to get the bit up in the bolts close to the spare tire well, I had to pull the sway bar down. I ended up loosening one bracket and removing the sway bar on one side to get it out of the way. Like I should have but did not do is document the bolt sizes, but I believe the one listed above is the proper size.
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andyofcolumbusmerkur
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Re: Diff Cover Bolts

Post by andyofcolumbusmerkur »

This place has some for 11 bucks for a ten pack. They look a little long though, they really need to be 30mm?
https://www.fastenere.com/m10-150-x-30m ... OvEALw_wcB
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andyofcolumbusmerkur
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Re: Diff Cover Bolts

Post by andyofcolumbusmerkur »

They also have them in 16mm, 20mm, 25mm.
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Re: Diff Cover Bolts

Post by john keefe »

Technically, you need at least 3 full thread engagement, but that puts a lot of stress on the female threads if the threaded hole is much deeper than the bolt length. Depends on what kind of tension/compression loading loads will be encountered. General rule for low/moderately stressed clamping, with margin of safety usually works out to a minimum 6 threads engagement.

Don't forget to use one with a shank. The stock shank is roughly the thickness of the cover, which allows the bolt to fit more snugly in the cover holes. Prevents scoring of the cover holes, but it also makes for a much stronger bolt vs. running threads all the way up to the root of the cap/head. Those kind of bolts work for residential/commercial construction, but you don't have the stresses or relative movement you have with machines.

I wouldn't go much less than 25mm on the thread length. The loads on a diff cover aren't huge, but diffs get REALLY hot, and the case expands, which is one reason why you have to rebuild these diffs with tighter tolerances, so they still work when the different metals expand. So, you have 8/9 diff-cover bolts to ensure the cover expands more uniformly with the case to maintain a seal. IIRC, aren't some of the bolt holes in the case are open-ended... maybe that length was simply spec'd to fill the hole so it doesn't get gunked up with road grime, oil, etc., or start rusting deeper inside the hole?
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Re: Diff Cover Bolts

Post by JimG »

Thanks all for the info! John where did you find the socket head bolts with a shank?
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john keefe
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Re: Diff Cover Bolts

Post by john keefe »

Jim, I haven't converted mine, that was my8950. But yeah, metric socket-head bolts with the exact length shank you should have might be a hard-to-find item. If/when I do need top quality, or specialty bolts, I go to Olander out here, but I don't know if that's a national chain.

Last resort would be to go to a small local airport, and ask one of the mechanics where they get their stuff from. Aircraft service parts are probably the best, most tested stuff you can find, and have to meet strict FAA standards. There's all sorts of unique design items for even the lowliest single seaters that are required for the stringent FAA standards. Once you're up in the air, ain't no place to pull over if something works its way loose. :shock:

Or, you could hacksaw a deep cross pattern on your stock bolts, so you could use either a flat, or Phillips head bit. :lol:
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Re: Diff Cover Bolts

Post by salukixr4ti »

Aircraft hardware is rarely metric. Unless it is a truly serious corrosion issue, try a penetrating oil called AeroKroil made by Kano. Make sure it gets under the head, and you don’t need to drown it. Let it work, and before attempting to break the torque on the fastener, give them a couple taps. The tough to get to fasteners can be tapped lightly on the sides with an extension. Once the fastener begins to loosen add a little more Aero kroil. I’ve used it over 20 years on turbine bolts that were stubborn-great stuff.
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john keefe
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Re: Diff Cover Bolts

Post by john keefe »

salukixr4ti wrote: Sun Aug 16, 2020 2:23 pm Aircraft hardware is rarely metric.
True, in the U.S. But, it's locating the source/manufacturer of the hardware that's the goal. If they're making aircraft hardware, they're probably also making quality Metric stuff. Who knows who Ford was/is using for their high spec hardware, but there's somebody out there with a connection to somebody, and talking to an aircraft mech is probably a good start.
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Re: Diff Cover Bolts

Post by my8950 »

If you guys get to the point of wanting a set of bolts like I got but can't find them local, let me know and I can send you a set.
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Re: Diff Cover Bolts

Post by salukixr4ti »

I am an A & P, IA, and director of maintenance for an aircraft maintenance and modification shop in Wichita, KS with 25 + years in military and civilian aircraft. There is nothing particularly exotic about what was used in any of these cars.
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john keefe
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Re: Diff Cover Bolts

Post by john keefe »

Great background. Love to hear about some of the military craft you saw/got to work on. Anything from WWII vintage?

Agreed, nothing exotic in these cars. Just a question of finding a metric socket-head bolt with the appropriate shank length. If you've got a source for really good hardware, maybe a national chain, I'd appreciate having it in my file and future ref.
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