hokiefyd 

I haven't seen as much information on setting straddle wire height for Racers as I have for cantilevers. Does one typically want the straddle wire to intersect the brake arm at about a right (90 degree) angle to the pivot? In other words, draw a straight line between each arm's cable attachment point and the pivot (line AP)...and then draw a line from that from the attachment point up towards the straddle wire hanger (line AH). Should that included angle be about 90 degrees?

I imagine if you set the straddle wire too low (the included angle is less than 90 degrees), some of your pulling force will be directed toward the pivot itself, and the arm would move with more speed and less force (less mechanical advantage)? Then, as you pull the arm further, the speed would slow and you'd get more mechanical advantage as the included angle approaches 90 degrees. Is that about right? Or totally off?

tiger1964 

Thanks, good info but
(a) Yeah, no Competition with ball and socket,
(b) you'd think a product called "Tiger" would be permanently etched in my mind, and this is the first I'd heard of it,
(c) looking at the B&S attachment, I'd see it's fine for alignment up and down but not for toe-in, so why design it that way?
(d) no idea on reach so perhaps not useful to the OP
(e) now I need to locate a set of Tiger brakes just due to the name?

El Chaba

Brace yourself$$$$$$$$$$$$

sovende

I have a pair of MAFAC "Racer" center pulls that were "harvested" from an older Peugeot and are destined for a bit newer Peugeot "custom" (but entry level) build up. I definitely concur with the mention that the red plastic spacers are likely to be somewhat brittle and one needs to be very careful in the disassembly process so as NOT to damage them. The suggestion that the straddle cable and yoke interface be free of kinks (in the former) and free of corrosion (in the latter) is important. Another potential issue is corrosion on the arm of the spring that "pushes" the caliper out (and the pad away from the rim)! It needs to be able to slide in the notch of the little nipple on the back side of the caliper arm. Friction at that interface "may" prevent the self-centering of the caliper. Movement at this interface may be miniscule but could add to the problem. Friction at the caliper arm pivots is prolly most critical but the other areas may have impact also. If the assembly is to be taken apart, one might as well ensure that friction at every interface is minimized. Just sayin' !

79pmooney

For years (decades?) the Racers did too. I used nothing else between 1967 and mid to late '80s when I purchased a pair with plastic.

microcord

Well, this is interesting. My problem turns out to have nothing to do with the straddle cable. When I take off the straddle cable (from one side, anyway), remove the nut and curious contoured giant washer from the back, pull the brake out the front, hold it in my hand from one brake shoe to the other -- like a curiously uncomfortable version of



-- and squeeze, the result is utterly asymmetrical. The arm for the left brake shoe pivots as it should; the arm for the right one doesn't seem to pivot at all. For what little looking at the non-disassembled brake is worth, nothing seems amiss. As for disassembling it, of course I'd want to do that on a table rather than with it kind-of resting on the front tyre. Both wires are cut short and soldered: if I cut off the soldered section the result might be hard to re-thread. I could sacrifice the brake cable, or I could try to unhook the straddle cable from the, uh



without removing the brake cable from the latter: I'd guess that this would be possible but that reversing the procedure would not. So I think that I'll limp to LFBS (local frame-builder shop) and ask him (the last time we talked, before there was any trouble with the brake or indeed anything else, he seemed keen to give the bike a look-over), and if he's not keen to look into the brake I'll buy a spare brake cable or two (always good to have around) and take a look myself.

Unfortunately for me, your area of the Pacific rim and mine have very different pricing. Though a couple of years ago I did pick up a very spiffy example of a Shimano 600 centre-pull brake, because it was $10 or so (probably because it had lost its twin) and I had a vague feeling that it might be useful some day.

microcord

Sorry, somehow I missed this message. You're right, they do indeed! Here. I hadn't even noticed that they sold bits of brakes and the like; many thanks for the tip.

oneclick 

This is simple to fix.

One of the pivots doesn't.

You need to undo the screw that holds that arm on. This can be done on the bike; depending on what tool you use you may want to remove the wheel to get access.

One of the best tools for this is one of those flat steel stamped multi-size ones. The flats are very thin, so sockets are NOT good *unless* you grind the ends flat. You want a good-fitting tool especially if you also know the pivot's stuck - the screw may have some corrosion.

Unhook the straddle cable and as mentioned above release the spring. Undo the screw, remove the arm (here you can determine how bad the pivot is by how hard you have to wiggle it to get it off), lubricate it and re-assemble.

Then do the other one, you need the practice.

microcord

Amazing. Here I am, discovering new dimensions of my own ignorance. One thing I thought I did know was never to use one of those tools, unless of course one was on the road and there was nothing better at hand, And that's one reason why I don't have one. I do have a 12mm what-I-thought-was-a-cone-spanner; when I read Sheldon Brown on the matter, I realize that what I have is intermediate between a cone wrench/spanner and a regular wrench/spanner. I'll try it tomorrow morning, carefully.

gugie 

MAFAC centerpulls are made to disassemble easily.
As @oneclick mentions, this is readily done on the bike.
Before you start to do any disassembly, disconnect the springs first, this will make disassembly much easier.

Here's a blow up diagram of a MAFAC Racer.

ehcoplex 

It may take a little bit of finagling, but you ought to pretty easily be able to get the straddle cable off the hanger (and back on again) without undoing either the straddle hanger bolt or the bolted end of the straddle cable. It's really just wedged behind (or in front of, depending on perspective...) the brake cable in the hanger. Then you'll have the calipers free of the bike and can work on a table.

bear_a_bug 

This should help. If the pull is still uneven distributed between calipers, consider carefully bending either of the springs themselves to adjust tension using two pliers. This solved an uneven pull for me (turns out one of my springs had somehow been just slightly bent out of shape).

leftthread

For reference.

gthomson

On the subject of Mafac Racers, what's the solution for replacing the brake pads? Are there specific pads you would buy or can you get mountain bike brake pads that would work?

El Chaba

Koolstop makes replacements that fit perfectly…Available in both black and salmon compounds. I prefer the black for both appearance and performance, but people who ride in the rain a lot seem to prefer the salmon. Replacing the original pads with these should be the first step in living with a bike with Mafacs that gets ridden.

markk900

I had trouble finding the koolstop pads here in Canada the last time I looked a number of years back (probably all over the place now) so used the regular Kool Stop post mount pads made for something else - they have worked fine ever since.....

microcord

Friends don't let are hesitant about recommending that friends buy from immense oligopolists named after rivers, but the last time I looked Amazon Japan (where I happen to be) was selling Koolstop pads for Mafac shoes: black for a palatable price; salmon for an impalatable one.

OP speaking. I was suddenly hit with a pile of (salaried) work, so I had to hold back for a couple of days; but I have looked at my front Mafac "Racer". If I may steal gugie 's photo (and demonstrate my utter incompetence with Gimp):





After unhooking the straddle cable and dislodging the lower end of each of the two springs, I undid bolt "C". It came out very smoothly and is in excellent condition. I assumed that the outermost plate (the one stamped 'MAFAC "RACER"') would come off easily. However, it won't. It won't even start to come off.

When anything's stuck, I reach for the can of WD-40. (I don't know any better.) I liberally sprayed it onto any relevant-looking bits and left the brake for a couple of days.

My hands aren't particularly strong. OK, they're weak. Pushing and pulling on "A" doesn't trigger any pivoting around "C" Neither does pushing and pulling on "B". But with "A" between one thumb and forefinger and "B" between the other thumb and forefinger, I can get it to pivot, reluctantly. (There's far too much friction.)

If I used inserted the business end of a wide-bladed T-handle screwdriver under the "M" of "MAFAC" and twisted, this might move the plate off. Or it might just deform or break something (but not the screwdriver). No, it seems a stupid approach. But what's a more intelligent approach?

ehcoplex 

No, don't start wedging screwdrivers in yet! So you can get the arm to pivot at least a little at point C? There isn't (or shouldn't be...) any metal-to-metal contact in the pivot, so it shouldn't be corroded together, it's just the plastic bushings. Soak the pivot-point with more WD40, work the arm back and forth on the pivot as much as it will move. Keep doing that.... and doing that.... It will eventually come off. It may require the assistance of some stronger hands. It's likely just very gummed up/solidified old grease or oil that's stuck. You could try soaking the whole caliper in some mineral spirits, which might dissolve the grease more effectively than the WD40.

microcord

Thank you, ehcoplex . I'm a bit sleepy now, but I'll give it a go tomorrow morning.

ehcoplex 

And if that arm isn't more-or-less freely rotating it indicates the source of your original issue.

microcord

OP speaking. Quick version: What should I bear in mind when attempting to ream out a slightly greater internal diameter of a plastic bushing?

Blow-by-blow version: Wiggle-wiggle-wiggle worked: the right/outer arm (the troublesome one) of my Mafac "Racer" came off; and then the left/inner arm (easily) came off too. Nothing looked odd about the right boss. The red plastic bushing that goes on it looked as if it was very slightly dirty, or perhaps just stained: I cleaned it up but this didn't bring any improvement in pivoting. I guessed that either the boss was too big or the internal diameter of the bushing was too small. So I tried each arm, back to front, on the "wrong" boss. (Of course the brake shoe pointed outwards, but all I wanted to check was the ease of pivoting.) The left arm pivoted easily on the right boss; the right arm didn't pivot at all easily on the left boss. I infer that the right boss is OK but the bushing of the right arm is too tight. So I'd like to increase its internal diameter very slightly. My limited understanding of Wikipedia articles on related matters suggests that I should use a burr mounted on a milling machine, but I'm just a regular ignoramus with a cheap set of hand files. (I don't even have a vise.) I could just go ahead and try; but I wonder if there's any advice I might benefit from.

ehcoplex 

Those plastic bushings are so thin I doubt you'd have any luck trying to make it any thinner... It also seems unlikely that's the problem. Were these brakes ever working properly? If they were, than it seems it ought to just be a matter of cleaning things up and lightly greasing the pivot points. Have you pushed the bushings out of the arms?

repechage

sheldon brown had written one.
from my experience- shorter the straddle wire, more power. There is a trade off for "touchiness" but I live 600' up a road with two stop signs and a signal light at the bottom, at a 14% grade some segments just prior to the stops, give me power.

repechage

cheapest solution- different caliper as you don't have the tools.

CV-6 

Amir Avitzur, previously mentioned by Gugie, used to offer rebuild kits with brass bearings. I recall them being about $20, probably more now. He included an ingenious little press to install and remove the bushings. He may still have some.