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MAFAC 378E Vertical-Mount Rear Brake Adapter Bolt

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MAFAC 378E Vertical-Mount Rear Brake Adapter Bolt

Old 07-28-20, 06:14 AM
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MAFAC 478E Vertical-Mount Rear Brake Adapter Bolt

Does anyone have a lead on procuring the bolt in the supplied exploded diagram?
The bolt that was delivered with the adapter is too long, and the hex-head is too deep.




Last edited by 1989Pre; 07-28-20 at 06:49 AM.
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Old 07-28-20, 08:21 AM
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Are you sure you have that installed the correct way? That doesn't look right to me.

I have the part you're referencing above. The way you've installed it doesn't jibe with how I remember it.
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Old 07-28-20, 08:25 AM
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See post # 24 here: Mafac Racer brake rear mount

Meanwhile, I should still have that part, but it could take me days to find it if I'm being honest. Still, I'm willing to look.

But short story long, how it's shown in post # 24 is how it should be installed. And that bolt used to mount the caliper to the bracket, you can technically purchase any length at your local hardware store. I swear it was an M5 or M6, but can't remember. I can get a measure on the length if you need it.
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Old 07-28-20, 08:53 AM
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Yes, the way I have it mounted is the same as in the photos on the thread you sent me.
I wasn't sure I could get a bolt at the hardware store, because I thought that the hole might be
French-threaded. I am not too familiar with designation M5 or M6, but the shaft length I need is
about 12mm.
The one I was supplied with is about 22mm length.
If the threads can be matched in the U.S., then I should be alright as soon as I get to the
hardware store, but you know how things are right now; if the salesperson is not wearing a mask,
then we could easily jeapordize eachother over a ten-cent item.
Anyway, thanks for your help, Franco. You are always kind. Don't bother turning your store-room
upside down if I can get a bolt with a thin head somewhere else. Toodles.

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Last edited by 1989Pre; 07-28-20 at 08:57 AM.
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Old 07-28-20, 09:40 AM
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Jebus 22mm is way too long.

M3, M4, M5, M6 are all metric (hence M) sized bolts. If you have a flat screen TV mounting kit or IKEA furniture and kept the bolts off them, the hardware from either is usually in M sizes, but won't always have a hex head. I'm one of those lunatics who keeps coffee cans full of unsorted hardware around for cases just like this.

Another forum member had me hunting stuff down in the shop today, I'll head back over at lunch and look in my 'misc unobtanium bits' tray. I'm hoping the part in question is there. I can confirm threading and length for you then, maybe you can order on AMZN or something. Curious though - why not just cut the bolt to length and hand-file to clean up the entry thread?

Believe me, you don't need to explain the risk situation. I'm happy to see you're being careful, I could share my story but won't ... last thing we need is another overly depressing story to read.

BTW - YMMV but my local ACE hardware has curbside pickup - order online for pickup at door, or you can order by phone/pay by phone/pickup at curb with one of our local locs. Had to fix a cracked P-trap under the sink in June (perfect timing, right?) and used the online-order-curb-pickup. Was seamless..
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Old 07-28-20, 10:21 AM
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OP, is it possible you're not seeing the install correctly? I dug up one I had in the basement and it is more than 22mm. Seen from the side here, 12 mm wouldn't pass all the way through.

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Old 07-28-20, 10:42 AM
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@clubman, I had the same thought until I noticed in his pic, I saw the long bolt for mounting the adapter to the brake bridge and also the fender is in the left-hand of his pic.

Now note the thickness of the bolt head holding the caliper to the adapter - it's 2x-3x thicker than it should be. Wherever he got that adapter from, that bolt is not the original. The original has a low-profile, 2mm concave head.

1989Pre Here's the adapter. It's different than yours, yours isn't original. Maybe it's from another bike to solve a similar situation.

I took caliper measurements. You basically need a M6 x 1.0 threaded stud with an 8mm-10mm shaft. The head thickness is 3mm at the top of the dome and 2mm at the edge. Here are some pictures with digital caliper (finally fixed it) showing the 6mm diameter post, and a metric thread gauge showing 1.0. And some extra pics - notice, your adapter part may not have the nub here either, I'm not sure if that's important or not.






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Old 07-28-20, 10:46 AM
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PS - 1989Pre if this was me, here's what I'd do:

Get an alloy or stainless M6x1.0 thread bolt with a ~9mm shaft on it and a hex head OR see if you can find a "shallow head" hex bolt that's M6x1.0

If all you can find is standard hex head, take that M6x1.0 bolt ~9mm shaft with a standard hex head to a bench grinder and make the head "low profile". Note that alloy bolts can load up a grinding wheel if done excessively (one bolt head won't do it).
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Old 07-28-20, 10:46 AM
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I'd like to see the pics so I can sort it out in my head. I understand what your saying.
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Old 07-28-20, 11:00 AM
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Ah, I see, I didn't scroll down and look!
Sorry OP, you're right, you've got the wrong bolt.
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Old 07-28-20, 11:01 AM
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I suspect this button-head would work perfectly: https://www.amazon.com/dp/B07H14B48J/
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Old 07-28-20, 11:01 AM
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Clubman, I think you are talking about the bolt that secures the adapter to the brake bridge. I have that one.
I am talking about the shorter bolt that secures calipers to adapter. Thanks.
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Old 07-28-20, 11:04 AM
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This could be a good even-shallower solution: https://www.amazon.com/dp/B07TYRGSXG/

Bittersweet part about going button-head is you don't need a cone wrench to tighten it down. Downside is you'll need to engage the caliper to initially get the allen wrench or T-handle to tighten the bolt.
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Old 07-28-20, 11:07 AM
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Francophile, yes, what you are calling the nub is absent on mine. It seems like yours might be the original spec, because
I measured the mounting hole on the back of my MAFAC Racer rear caliper, and it seemed to be about 8mm in width, which would
accomodate the integral sleeve on brake side your adapter.
Eh.., feh...I spent over 50 dollars for this part (with the shipping from Greece) and waited a month for it.
Well, hopefully it will still work, and with your help, I seem to be on my way to owning a new bolt.
That bolt with the allen head is perfectly fine. Thanks so much for finding and sending that.
I am just curious: Is the end of that bolt supposed to come into contact with the brake bridge,
there-by supplying a point-of-tension?


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Old 07-28-20, 11:20 AM
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Just a quick warning: I realized something.

Obviously that's not the stock MAFAC part. That means the bolt may not have the same specs as the MAFAC part. So just be aware, while I can tell you what the MAFAC part uses, you don't have the MAFAC part. Because the part was from Greece, was can be 95% sure it'll be Metric, so it'll use a metric bolt. We can hope it's 6mm and same thread pitch. But ... you may get the bolts from Amazon and they don't fit. Fortunately, Amazon offers easy returns.

And no - that bolt is not supposed to contact the bridge. Think about it - the top-down longer bolt goes straight through the bridge. Ain't moving anywhere with that config.
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Old 07-28-20, 11:22 AM
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PS - $50 is overkill. I would've sold you my last remaining one for that all day long! You should file a claim on eBay over that if it was advertised as MAFAC - it's not! Total BS.
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Old 07-28-20, 11:45 AM
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I personally would probably just take the bolt I have to the grinder and thin the head down to what I need. Or chuck it in the vise and take the angle grinder with a cut off wheel.
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Old 07-28-20, 12:01 PM
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Originally Posted by dedhed View Post
I personally would probably just take the bolt I have to the grinder and thin the head down to what I need. Or chuck it in the vise and take the angle grinder with a cut off wheel.
I won't lie: That's my general M.O. Then cut-to-length and bevel the thread edge, file the entry thread, and bingo.

The reality is this: We can be fairly certain this isn't a 40+ year old bolt, so once you get it ground down, post-pandemic, you can carry it into an Ace Hardware or similar (I prefer Ace, even though they don't own their hardware bins) and use the newly-sized bolt to find a good comparison.

If it were me, I would measure the thickness of the threaded hole to see your max depth, since you don't want to bottom out into the bridge and dent or knock off paint. Subtract 2mm from that measure, then mark the threads that distance from the case of the head. Hacksaw or cutting wheel, some filing, bingo blammo.

Be sure to treat the bolt head with fingernail polish or something after grinding so it doesn't rust.
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Old 07-28-20, 12:13 PM
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Hey 1989Pre gimme a sec, let me blow your mind. DON'T BUY ANYTHING.

I just popped off one of the pivot bolts from a crappy old pair of MAFAC Racers. Guess what? IT'S THE SAME BOLT!

Pop one of yours off and see if it fits. If it does and you don't have a spare, PM me with an address. Will only cost me a buck to get one out to you. I have MAFAC stuff coming out my ears. Won't be the prettiest but it'll clean up.

The only thing that bothers me is the absence of the 'nub' on your adapter which I think acts as a pivot bushing of sorts for the caliper. You could probably find a ferrule or bushing to mimic that, though.


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Old 07-28-20, 12:55 PM
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Thanks, both Ded and Franco. I guess I'm going to have to make a call on this, and the "nub" on the original MAFAC adapter seems to me to be too significant to dismiss. Franco, if you have one of these adapters for sale, I'll pay you what I paid the other seller.
It was my mistake, but I didn't know that there were different types of vertical-mount brake bridge adapters. Hey, I learnt something today, and I wish I could say that every day.
I did notice a slot on the surface of my adapter on the brake caliper-facing side. Something on the body of the appropriate brake caliper set apparently would fit into that, to relieve the mounting bolt of torque and direct stress, kind of what the sleeve does on the other version.
I'll send you a P.M. Franco, and thanks everybody.
Oh.., one more thing: The seller did not specify nor refer to MAFAC in the ad.
So far the building of the Manufrance has gone without a hitch, and this was the only burp.

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Old 07-28-20, 01:47 PM
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If there is room to reach the head with a hex key when the caliper is squeezed you could probably run a wafer head screw in there.

https://www.amazon.com/Ochoos-50pcs-.../dp/B07R68C56G
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