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Center pull spring tension: MAFAC vs. Dia-Compe

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Center pull spring tension: MAFAC vs. Dia-Compe

Old 09-12-20, 05:52 PM
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Center pull spring tension: MAFAC vs. Dia-Compe

I think I've asked this before, but the question may have been buried in another thread and I don't think many saw it. I have a pair of MAFACs on my '70 Peugeot with modern silver Shimano short-pull brake levers (BL-R550s). The braking action is very light -- level pull is very easy and smooth -- they're generally just very nice-feeling brakes. I've had these same levers (the actual two brake levers...not just two more of the same model) on another bike that I used to own with Dia-Compe center pulls (both were 650s). The return springs felt about twice as firm on the DCs vs. the MAFACs. Brake action was still good from a friction standpoint, but they were more tiring to use. I took the calipers apart and greased everything, but that didn't have much effect. Cables and housings are/were fresh on both bikes. I think I had both adjusted about the same regarding how close the pads rode to the rims when not actuated.

Is this just the nature of the two types of brakes? Are MAFACs known to have lighter return springs? Dia-Compes seem a little easier to come by, but I wasn't very satisfied with how stiff they were. The return springs visually looked much more stout on the DCs, which seems to match their operation. Are they all that way, or did I just happen to find some DCs that might have had heavier springs than usual?
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Old 09-12-20, 10:38 PM
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The return spring force acting at the cable is dependent on the caliper, it's leverage and it's spring torque.

Different levers will have different leverage. Mafac levers pull a lot of cable so seem to have less leverage acting on the cable. Shimano has gone in this direction of late, in order to reduce the effect of the cabling's elasticity on the braking feel as felt at the lever. I'm assuming that the Mafac calipers utilize lower spring tension applied to the cable, so work best with such levers that have less leverage.
I think that Universal brakes similarly have lower leverage at the levers and more leverage at the caliper.
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Old 09-13-20, 08:15 AM
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Thanks for your reply. If I understand your reply, you're saying that the MAFAC levers had a longer pull (and thus had lighter springs at the calipers), whereas the DC brakes might have been designed for a shorter pull lever and had stronger springs...for a similar "feel" at the lever?

I like the idea of the DC calipers (it seems they're more plentiful and perhaps easier to setup), but I do wish they had lighter return springs to make them a little more enjoyable to use with a variety of levers. I wonder if I could swap the springs with something from a different model of brake.
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Old 09-13-20, 08:19 AM
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As stated
Originally Posted by dddd View Post
The return spring force acting at the cable is dependent on the caliper, it's leverage and it's spring torque.
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Old 09-13-20, 08:43 AM
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Even though the leverage of the Dia-Compes will differ from the Mafacs, I'd venture to say what you're feeling is primarily a difference in spring torque.

Early Weinmann 999's (Dia-Compe 650's are clones) made before December 1962 had a single spring spanning both arms, with a single loop at each end. These springs provide a noticeably lighter feel - including when you simply squeeze the caliper with your hands, rather than adding the mechanical advantage of a lever into the mix - than the later, separate springs.

Also, if I'm not mistaken, the 650 springs have two coils, while the Weinmann springs (at least the earlier separate-spring variants) have a single coil.

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Old 09-13-20, 09:48 AM
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We have two bikes with the same levers (a Tektro flat-bar model), but one bike has vintage (prob. later than 1962) Weinmann 610 on the front, and the other a Mafac Competition. When I squeeze the front brake of each (to take the difference rear brake cabling might make out of the picture), the Mafac-equipped bike feels noticeably "gentler", even though the Weinmann brake's spring is a single coil, and the Mafac's is a double.
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Old 09-13-20, 11:33 AM
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Perhaps it should be pointed out that once upon a time, a nice stiff return spring was interpreted as a sign of a quality brake. Light feel wasn't a thing till the ~ 90s.

I don't remember any big difference between MAFAC and Dia Compe or Weinmann calipers. Maybe a little. The levers are more different IMO.

It'd be easy enough to check spring pull with a fishing scale on the straddle wire. I'd check but have neither type set up at the moment.
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Old 09-13-20, 12:44 PM
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Isn't it possible to weaken the spring by bending it in the "wrong" direction? I've done this with single pivot side pull brakes.
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Old 09-13-20, 03:07 PM
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Thanks, all. I have two DC-style calipers in my bin at the moment, not used on a bike. I think both are 610s and both use separate springs, one for each post (vs. one transverse spring). One is a Peugeot-branded one with noticeably stiffer springs than the other one. The spring is single-wound and the wire is relatively thick. The more compliant one is a Schwinn Approved-branded one with double-wound springs with a thinner wire. I guess that would make sense that these are more compliant -- thinner wire AND a longer wire. Again, these are not mounted on bikes and spring torque is perceptably different when compressing by hand. That Peugeot one would be a real workaround, like a firm stress ball. The motion is smooth...the springs are just pretty stiff.

I was hoping there was a chart or "crib sheet" out there that offered a matrix of different DC center pulls and their various springs fitted to them over the years, especially as some may want to try to match brake levers to different brake types. But maybe there wasn't a lot of consistency with these. Or maybe it's as simple as the single-wound ones are "stiff" and the double-wound ones are "less stuff" and that's all there is to it.
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Old 09-13-20, 03:11 PM
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I just checked the MAFACs on my Peugeot and the springs are thinner and double-wound, and more resemble the Schwinn-branded DCs. It's hard to tell with them on the bike, but I guess the MAFACs feel about the same as the Schwinn DCs...so maybe it's just as simple as two spring options -- the thicker single-wound vs. the thinner double-wound.
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Old 09-13-20, 04:43 PM
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Originally Posted by noglider View Post
Isn't it possible to weaken the spring by bending it in the "wrong" direction? I've done this with single pivot side pull brakes.
Practically, no.

Go grab a paper clip. Bend it just a bit, it springs right back. That's elastic deformation.
Take that same paper clip, Bend it until it straightens out a bit and doesn't spring back all the way. That's plastic deformation, the bit that springs back at the end is elastic deformation.
Plastic = permanent
Elastic = temporary

Now go unfold that paper clip until it's straight. Bend it back and forth until it breaks, and count how many bends it takes. Note how far you bend it each time. Probably several bends of 180 degrees.

So, yeah, you can weaken a brake return spring until it brakes, but theoretically only.

If what you mean by "weaken" the spring is does it loose elasticity? Answer is also no.
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Old 09-13-20, 04:52 PM
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I trust you, @gugie, but how is it that I've done it successfully on side pulls and V brakes?
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Old 09-13-20, 05:47 PM
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noglider I think one of the possible differences, at least with linear pull brakes, is you're really bending the lever arm on the end of the return spring. The spring force itself is not changed...you're just changing the position of the end of the lever that actuates that spring, to either preload it more or less.

The springs on the DC center pulls don't really have a lever arm to reposition. Although, now that you mention this, MAFACs do...so it could be possible to do this with those brakes.
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Old 09-13-20, 07:40 PM
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Aha, thank you, @hokiefyd. That explains it.
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Old 09-13-20, 07:46 PM
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Originally Posted by noglider View Post
I trust you, @gugie, but how is it that I've done it successfully on side pulls and V brakes?
Confused.
You were successful...
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Old 09-13-20, 08:19 PM
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Note that it is also possible to reduce the spring's linear pre-load force simplyh by using thicker pads or by adding a pad spacer (threaded length permitting, I've sometimes had to then put the pad nut's washer on the wrong side of the arm).

@hokeyfyd: It's always interesting to learn of how many "Schwinn-Approved" modifications (of the conscientious, intelligent sort) that Schwinn demanded on their very large parts orders from overseas.
Countless how many!
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Old 09-14-20, 02:26 AM
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Originally Posted by gugie View Post
So, yeah, you can weaken a brake return spring until it brakes, but theoretically only.
I see what you did there. Will theoretical brakes replace discs?
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Old 09-14-20, 05:52 AM
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Originally Posted by dddd View Post
Note that it is also possible to reduce the spring's linear pre-load force simplyh by using thicker pads or by adding a pad spacer (threaded length permitting, I've sometimes had to then put the pad nut's washer on the wrong side of the arm).
Yes, good point. I seem to always find myself running tires sufficiently wider than the rim width that I need to run my brakes with some preload on the springs just to get the pads close enough to the rim surface that I don't run out of brake lever (so the brake opens wide enough to let the tire out). The certain downside to that is the cable pulling force (regardless of lever) will be higher than if the brakes were able to be run more or less wide open.

Originally Posted by dddd View Post
It's always interesting to learn of how many "Schwinn-Approved" modifications (of the conscientious, intelligent sort) that Schwinn demanded on their very large parts orders from overseas.
Maybe that's the ticket...maybe the Schwinn-branded DCs are the center pulls to get for people like me who prefer a lighter brake feel vs. a heavier one. I don't ride drop bars, so my lever choice is essentially limited to short- or long-pull flat bar brake levers. I'm already running short-pull levers and, if I understand mechanical advantage correctly, running long-pull levers will just make the felt return spring tension even higher (to say nothing of probably not pulling hard enough on the brake calipers themselves to get good braking).

(I already remove the return springs from the levers themselves, to get the lighest feel reasonably possible.)
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Old 09-14-20, 12:28 PM
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Yet one more thing that will help reduce the spring pre-load force is to use wider rims.
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Old 09-14-20, 12:40 PM
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It's possible to remove the springs and create a test fixture .. standardize the lever length

and a weight you can add to, and a scale to measure how far it moves for a given weight

and do actual science... If you really want to know..


by the way there are springs that are wound up, cold, on a machine efficiently.. fast &

then there is a spring that is wound then heat treated .. spring tempered..




...

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Old 09-14-20, 02:06 PM
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Originally Posted by hokiefyd View Post
I think one of the possible differences, at least with linear pull brakes, is you're really bending the lever arm on the end of the return spring. The spring force itself is not changed...you're just changing the position of the end of the lever that actuates that spring, to either preload it more or less.
Yeah, partly that. Even if just the bent ends deform a bit, that can be enough. Regardless, overbending springs was the only way to correct early cantilevers if they were unbalanced, and it worked.

I suspect also that the springs are not perfectly tempered steel springs. Mild steel is still springy. If you push it past it's elastic limit, then it bends. I'd guess the temper on production brake springs would be somewhere in between spring steel and a more typical temper.

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Old 09-15-20, 05:12 AM
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Originally Posted by Charles Wahl View Post
I see what you did there. Will theoretical brakes replace discs?
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Old 09-15-20, 07:07 AM
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Originally Posted by gugie View Post
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Old 09-15-20, 07:33 AM
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What a strange conversation. I guess this is what happens when all of you grey heads get together?

On topic: I'd suggest a shortcut to determining spring resistance would be to measure the spring wire diameter. Assuming all other things are functionally equal, a larger diameter wire would provide greater resistance. My personal preference is a strong return action, either from the brake calipers or the levers themselves, but then again, I don't have arthritis, and I'm allegedly in my prime.
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Old 09-15-20, 07:59 AM
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OP here -- I disassembled both pairs of center pull brakes I have and confirmed the spring wire diameters are actually the same: about 2.3 or 2.4mm in diameter. The stiffer springs appeared to be larger in wire diameter, but I think that was just some confirmation bias on my part. I think it's the different length that matters here. The stiffer springs are wound about 1.5x around the post in the backing plate and the more relaxed springs are wound about 2.5x around the post. Essentially, the more relaxed spring is about twice as long. Given the same wire diameter...that probably makes sense -- a coil spring is really just a torsion bar in a coil (right?), and a longer bar should equate to a lower spring rate (or perhaps lower "total resistance" is a better term, if "rate" is a measurement of resistance x length).

I did swap the springs -- I moved the "double wound" springs from the Schwinn brake to the Peugeot brake and the Peugeot brake now feels softer. Interestingly, the Schwinn brake also had red nylon bushings on what appear to be bronze barrels, whereas the Peugeot brakes had black nylon bushings on what appear to be steel barrels. I tried different bushing combinations also, but that didn't change perceived feel -- it's all in the return springs.

Obvious conclusion: there appears to be at least two return springs for DC/Weinmann brakes: "single wound" and "double wound". The single wound springs, probably as expected, provide a higher return force to the brake. There may be other springs installed on these brakes also...I don't know. Observing photos of these brakes for sale on eBay, there doesn't seem to be a trend with regards to arm length or branding or anything like that...some brakes have the single wound springs and some brakes have the double wound springs. Both styles are interchangeable, and both appear to be available in the aftermarket as replacement parts, so one could customize any on-hand as desired with different springs.
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