cudak888 

Some time ago, I came across a fascinating 2011 discussion with PDXaero, Dawes-man and gugie about installing brass bushings in Mafac centerpulls (yes, even before Jan Heine invented them) as a way to either overcome wear from factory Delrin bushings or just to get excess play out of the arms.

I filed this away (in a deep dark hole) in my brain until about a year ago, when I wound up with a Union-badged Polycarbonex aluminum-and-plastic city bicycle. I chucked the frame in nlerner's general direction and harvested it for parts for my 1980 Sports build, but I took particular interest in the brakes.



The bike came with late-model Altenburger Synchron brake calipers, the ones photographed above. These are generally considered to be the first commercial attempt at a dual pivot brake, and they have the distinction of performing barely better than the average comparable Weinmann sidepull of the time. After all, nothing can go wrong when your product has a form of "Synchro" in the name, eh?

I took the Altenburgers apart sometime ago and realized some of the sloppiness came from play at the arms. They pivot directly on an unthreaded section of the mounting bolt with no bushing, resulting in a fair bit of flex on application. Having seen the discussion threads about using brass bushings on Mafacs, an ill-conceived, over-complicated, probably-not-going-to-work-or-at-least-be-mediocre-at-best idea sprang to mind: Could the Altenburger arms be bored out for Oilite bushings?

So, a few weeks later, an order from McMaster Carr brought forth a bag of Oilite bearings, part #6658K732, 8.01mm ID and an 11.03mm OD. And they sat for nearly a year until I decided to get off my duff and try this today - at which point, I discovered that in all that time, I still hadn't bought an 11mm drill bit. So I decided to do what any self-respecting machinist would not do: I grabbed a 7/16" (11.113mm) bit, shoved it in the drill press, and said no prayers because this was going down (literally), regardless:



Much to my surprise...nearly perfect fit. Not too tight, not too loose.

Yes, I have my doubts about cutting that much material off the lever at the pivot point. Lots of force there. Maybe they'll break, maybe they won't. There are a gazillion Altenburger Synchrons rotting away out there and the loss of this set for some science du jardin buffoon isn't going to matter much.





I knocked off some of the displaced aluminum on the belt sander and - to be on the safe side - set the bushings in permanently with Loctite 603. Strong stuff that sets VERY quickly, and though it's filling the gaps, it's not expanding to fit the gaps, so I don't expect it to snap the aluminum around it from pressure either.



The assembly of the caliper itself was uneventful, but it did feel extremely tight initially. A bit of silicone lubricant on the plastic-covered pin that the outer lever rides on fixed that. The return spring is nice and strong, stronger than what you'd expect out of a Weinmann centerpull.

Now, part of what rekindled an interest in this experiment is the test bed itself: The Motobecane Nobly I've had kicking about (from the Saturday's Haul thread), which I've been meaning to build up and kick out the door. I gave up any idea of doing a fancy build on it and - based on a bit of brainstorming last night - decided to throw a hodgepodge of parts on it just to make it work, which led to the rediscovery of this experiment I never carried out. Curiously, most of the bits that I threw on the bike to get it to work - wheels included - are leftovers from the Polycarbonex.



And yes, it's fitted with the Polycarbonex's front fender, as I think I might want to keep the Moto's original chromed steel fenders. Yes, the gray fender makes it even uglier, but hoarding spares for some ambiguous build 10 years in the future is important, dammit.

Or I could beat these grey fenders out with a hammer and start a troll thread that'll piss off everyone here. (Hi, Rob! Would you like to borrow my measuring tape?)

Speaking of which, another tech tip when you're running out of parts: I had no 68mm bottom brackets left, not any that I'm indifferent to anyway. However, I discovered that the Shimano-style (but knockoff all the same) 73mm cartridge BBs kicking around in my spares bins will fit English-thread 68mm shells just fine - provided the left-hand cup is thin enough to bottom out at the shell edge. Based on what I saw, it seems as if the only difference between the 68s and 73's are the thickness of the cup on this side and a fair amount of extra spindle offset to the left. Hey, so the Q-factor is off. It's a city bicycle built in the spirit of the Box O'Crap. It ain't a Confente

I've hooked up the caliper with Teflon-lined brake housing, nothing-special galvanized brake cable, and the Moto's original loosy-goosy Weinmann brake lever. One might dismiss the levers for being cheap, but I've had them perform well when hooked up to Nuovo Record sidepulls. I figured poor performance would be a reflection of the caliper more than the lever, based on my prior experiences. Also, I ditched the strange, plastic Altenburger adjuster barrel for the adjuster off the Moto's factory Weinmann caliper.

Paired with the caliper are a pair of no-name red compound "soft" pads off Amazon that I previously used on a pair of Deore LX arms on "Peaches & Cream," my PAS-converted, EA3-wheeled ex-Spin sharebike. Both were run quickly on the belt sander to knock off any high spots from the previous rims. These work pretty well, though I wouldn't call them Kool-Stops. Basically, they should work well - well enough to do their job, but not enough that they'll compensate for a lousy caliper:



More in the next post - I'm exceeding the photo count limit per post.

cudak888 

And the performance out of this prize package?

Acceptable, but not earth shattering - and I dare say the pads are helping, as I don't think this would stop at all with a pair of period brake blocks. While the bushings definitely prevent the arms from bending on the pivots - which, all in all, is an impressive improvement over factory - it doesn't stop flex at the cable attachment points. For instance:



Eyeball the amount of left hex nut (right one in the picture) is showing from under the forward lever arm. The caliper is currently under heavy force in this picture, with a very hard lever application. The right arm has twisted upwards a good 2mm with this extra force applied to the lever - force that would otherwise be applied to the pads and help with clamping the rim.

So - with light receding at the end of the day, I pulled the Weinmann lever off and installed a Shimano Nexus upright lever. These are exceptionally stiff and as a three-to-four finger lever, you can put a lot of force on them over a nice amount of lever pull. In fact, they have so much reach that I've reduced reach with the adjuster screw - even though my hands aren't small by any means.

Also, these can be adjusted for either linear pull (V brakes) or traditional pull. They're set up traditional, of course:





...and the performance was about the same. I didn't really expect an increase in mechanical advantage, but wanted to confirm it with a lever that I know will perform at its best regardless of the caliper.

I also pulled the adjuster out until the pads were literally skimming the rim, just to see if it would improve matters:





It didn't do much of anything; bringing the lever arms felt as if it reduced some of the mechanical advantage. I could squeeze the lever with all the force I could muster and come to a controlled stop, but I could do the same with less force in the previous config and still come to a controlled - if lazy - stop. I don't accept a lazy stop with panic stop force, and these calipers just won't do that, regardless of config.

So...success? Depends on how you look at it. It was a success from the standpoint that you can only squeeze (pun not intended) so much force out of a caliper which just doesn't have that much of a mechanical advantage inherently built into it. The geometry of the arms will always be an issue which can't be overcome. Though the bushings may provide a slight advantage by preserving some braking force that would otherwise be lost to a bit of flex, they really don't seem to do much in this respect. If anything, the bushings do a lot more towards removing the slop that psychologically makes the calipers feel cheap on application; they definitely feel as if they're a better product now.

Case in point, despite the vertical flexing under a heavy application at the lever, the arms feel a lot more solidly connected to the bridge, and thus, the frame. Looking down upon application, the pad mounting slots aren't shifting at all. It's uncanny, and a feeling I don't usually associate with brake calipers of this era with thin forged arms. Think of it like this: It's as if someone managed to make a brake caliper with the feel of a Nuovo/Super Record sidepull - right down to that very heavy return spring - but managed to make it operate less effectively.

Read into that however you wish.

-Kurt

repechage

Way back we looked at these brakes at the shop and speculated that with bushings and spot facing that these could be good stoppers.

the " mod " dual pivots have a bit better geometry. Be interesting with Kool stop pads.

there was a brake that was advertised in the bike magazines of the early 70's, called a power brake, an interesting design kind of a cross between a power cam brake, Shimano Aero centerpull. Did not have enough extra cash to experiment

stardognine

Well, now I won't have to try it. 😁😉 Thanks for the, umm, education (?). 😁

I actually enjoyed reading that though, and I appreciate your perseverance in these matters. ✌️

cudak888 

I think some form of alternate geometry might get them to stop well, though it's beyond my pay grade.

I could install a pair of black Kool-Stops on it to find out. Still want to tinker a bit with them.

Got a pic of the Power Brake by chance? I swear I've seen something to that description at one time, but can't seem to Google it.

LOL

It was worth a shot. Might still see what can be done. Don't know why I'm fixated on these Altenburgers, but hey - why not?

-Kurt

oneclick 

I've got a pair of the Weinmann-branded Synchrons with Kool-Stop pads and they work with either of these two arrangements.
The first is with a pair of Shimano BL-M700 levers and the second (current) is with bog-standard Weinmann levers.
They feel better - less flex - than Universal centre-pulls, but not as nice as any of the Mafac centre-pull varieties.
Part of any difference in feel is not the brake but all before, the Universals have their levers as the Mafacs etc do - and the bit "after", the pad.
I do like the combination of grip and compressibility that Mafac pads have.

These particular Kool-Stops have nice posts with cup-washers for angle adjustment and that must help compared with normal shoes.

cudak888 

I finished the second Synchron today, and - much to my surprise, with a pair of slightly longer-reach Weinmann levers, the combination works surprisingly well. It's not modern dual-pivot territory, but with both front and rear in action, braking is at least confidence-inspiring.









Please excuse the absolute bottom-of-the-barrel parts bin build and that hateful RD (at least it worked better than the other low-end Shimano RD that was on it). Just trying to get this one done and out now that the experiment is over.

-Kurt