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Mafac racer bushing upgrade

Old 04-12-11, 04:39 PM
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PDXaero
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Mafac racer bushing upgrade

CAN IT BE DONE



Apparently the bronze sleeve bearing is supposed to be 10mmOD 8mmID and 9.8mm length
the plastic thrust washer is supposed to be 15mmOD 8mmID and 1/16in thick

Mcmaster has the bearing for $2.17 ea and the washer $0.40 in bronze, over 1$ in plastic.

A. Should I go for it?
B. Is it worth it or only appreciable to the snooty retrogrouch?
C. Plastic or Bronze on the thrust washer?

And before you tell me to spend $12 on better brakes.... NO.
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Old 04-12-11, 04:44 PM
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Its only money....go for it.

I have 4 sets of titanium crank bolts and titanium Campy threaded axles sitting in a box.....it was only money.
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Old 04-12-11, 04:47 PM
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I would just make sure it's not the bore that is worn. I say go for it. If the parts don't work, send them to me. I have a huge stash of odd bearings/bushings.
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Old 04-12-11, 04:52 PM
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I say try it and while your at it order me a set too.
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Old 04-12-11, 05:03 PM
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Put it all in a bag and remarket it on ebay for $40 bucks a set.
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Old 04-12-11, 05:28 PM
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Originally Posted by triplebutted View Post
Put it all in a bag and remarket it on ebay for $40 bucks a set.
Now that's clever!

I'm curious to hear how they work in your brakes. I'm glad we have so many Mafac fans here!
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Old 04-12-11, 06:17 PM
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I just pulled the pair that I had apart that looked like they were on Davy Jones' bike(no not the Monkees' Davy Jones either). Got some aluminum polish and steel wood and went to town. Then just lightly sanded and greased the studs and bushings and they were smooth as butter. What about trying delrin instead of brass bushings?
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Old 04-12-11, 06:36 PM
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Do the Racers have the same dimensions as the Competitions?

Bookmarking this thread in case I have a need when I get to that point.
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Old 04-12-11, 07:23 PM
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Originally Posted by Henry III View Post
I just pulled the pair that I had apart that looked like they were on Davy Jones' bike(no not the Monkees' Davy Jones either). Got some aluminum polish and steel wood and went to town. Then just lightly sanded and greased the studs and bushings and they were smooth as butter. What about trying delrin instead of brass bushings?
Yeah, I rebuilt mine pretty much the same way-- polished up the aluminum parts and studs, degreased the plastic bushings, applied fresh grease, and they're smooth as anything... but honestly, they're not very powerful centerpulls to begin with... what's all the hubbub about them?
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Old 04-12-11, 08:25 PM
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I thought that racers had a plastic bushing?
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Old 04-12-11, 09:05 PM
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Originally Posted by unterhausen View Post
I thought that racers had a plastic bushing?
Correct. I was under the assumption the OP wanted to "upgrade" to brass. But I guess now that you mention it, a bushing of 2mm thick brass won't fit.
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Old 04-12-11, 10:08 PM
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the bronze bushings are not a bad idea. I think I might go for a flanged bearing. 5448T3 has a 16mm flange, although the outside of the bushing area is 12mm. You could cut that down on a lathe or ream the arms.
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Old 04-13-11, 12:21 AM
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Some racers had bronze bushings. There are a lot of racers out there in a lot of iterations.
To clarify, the brakes I have are the red plastic sleeve.
I pulled them and cleaned them but just got to thinking about how much of a difference bronze would make. Target bike is a 69 PX10 and that predates the mafac competition brakes, but still, Racers were some of the best brakes anywhere in the 60s.
Also brazed pivots (a la PY10) are not out of the question but I can't find them for the life of me.
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Old 04-13-11, 07:33 AM
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I never saw a Peugeot with brazed pivots before. There was a framebuilder making them a while back, I don't think he has them any more. I am part way through making some, but I'm a little conflicted about permanently sticking racers on a frame; they are unique and you are stuck with them once you put the bosses on.

The ones on the PY10 pictures I saw look very much like Mafac cantilever bosses. The issue with using cantilever bosses is that they are longer, but it seems like they could be modified.

Last edited by unterhausen; 04-13-11 at 08:18 AM.
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Old 04-13-11, 10:02 AM
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Originally Posted by southpawboston View Post
... but honestly, they're not very powerful centerpulls to begin with... what's all the hubbub about them?
??? IME, MAFACs are the most powerful centerpulls out there, smooth and great modulation to boot. Is your straddle cable too long maybe? Then again, maybe they are junk. Send 'em to me and I'll dispose of them for you.

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Old 04-13-11, 10:15 AM
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Originally Posted by bobbycorno View Post
??? IME, MAFACs are the most powerful centerpulls out there, smooth and great modulation to boot. Is your straddle cable too long maybe? Then again, maybe they are junk. Send 'em to me and I'll dispose of them for you.

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Ha! You know, maybe I have them set up totally wrong. Also, maybe the problem is with the brake levers (Tektro inverted). Lastly, maybe the problem is with the pads (VO salmon). They just feel very mushy, and don't have the best stopping power. They're also prone to squealing. I can try shortening the straddle wire to decrease the mechanical advantage.
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Old 04-13-11, 10:22 AM
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I've posted this before but I'll say it again. The MAFACs on my UO8 will stop a freight train. They are better than the Weinmanns on my Raleigh. But then, I don't usually go as fast as a freight train.
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Old 04-13-11, 10:28 AM
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If they're mushy, the straddle cable is likely to be too short, from too much leverage. If they're stiff but don't stop, the straddle cable is too long.

Set them up right and you'll love them. It takes time and patience, but they're easier than cantilevers to set up.
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Old 04-13-11, 10:34 AM
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Originally Posted by noglider View Post
If they're mushy, the straddle cable is likely to be too short, from too much leverage. If they're stiff but don't stop, the straddle cable is too long.

Set them up right and you'll love them. It takes time and patience, but they're easier than cantilevers to set up.
Funny, because I've never had problems getting cantis "just right".

Really? too short? I thought it's when the straddle cable is too long (yoke is high) that you get mushiness, and when the cable is too short (yoke is low) they feel stiff. Do I have it backwards? Mine are definitely mushy, like something is flexing a lot.

Here are pics, tell me if you think they're too long/short:




Last edited by southpawboston; 04-13-11 at 10:39 AM.
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Old 04-13-11, 11:32 AM
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I always imagined an equilateral triangle formed by the straddle cable and the anchor points was the ideal.
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Old 04-13-11, 01:44 PM
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Originally Posted by unterhausen View Post
The ones on the PY10 pictures I saw look very much like Mafac cantilever bosses. The issue with using cantilever bosses is that they are longer, but it seems like they could be modified.
unfortunatly not. Here in the right frame is the Racer hanger on a fork to give you appropriate location and the MAFAC canti bosses, they are made to sit out side of the fork blade to give a better angle for the canti brake.
In the left frame you can see the actual centerpull bosses, almost straight bosses for the front and slightly inside for the rear, also as you mentioned, shorter.


Originally Posted by southpawboston View Post
Correct. I was under the assumption the OP wanted to "upgrade" to brass. But I guess now that you mention it, a bushing of 2mm thick brass won't fit.
But it will!
the plastic (delrin) bushings are the same size as the bornze bushings that were in some models.


Originally Posted by unterhausen View Post
the bronze bushings are not a bad idea. I think I might go for a flanged bearing. 5448T3 has a 16mm flange, although the outside of the bushing area is 12mm. You could cut that down on a lathe or ream the arms.
Too much machining for me. I no longer have a lathe other wise I would try to make the CP boss braze-ons.
The flanged bushing you mention would require me to thin the OD, flange thickness, and flange width.
The ones I have found thus far would only require me to overbore the ID of the thrust bearing, easy enough to do with a drill press.

I really need to get some parts shipped out today but assuming I order parts this week I will buy two full sets, firstly in case of some failure of adaptation, but also, if it works I will send the second set to another member (bianchiGirl already voiced interest) for an impartial review.
Hopefully its not just hype. There has to be some reason that bronze bushings were installed on nicer models.
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Old 04-13-11, 02:30 PM
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Originally Posted by PDXaero View Post
But it will!
the plastic (delrin) bushings are the same size as the bornze bushings that were in some models.
I stand corrected! It does look like it would work.

But is the canti stud that you have propped on the fork leg inverted 180 degrees? The spring retainer hole should be facing in. Would flipping it change the position of the post?
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Old 04-13-11, 02:34 PM
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Originally Posted by southpawboston View Post
I stand corrected! It does look like it would work.

But is the canti stud that you have propped on the fork leg inverted 180 degrees? The spring retainer hole should be facing in. Would flipping it change the position of the post?
It is flipped around, that was my trying to position it as closely to the racer pivot as I could by mounting it backwards.
Not mounted, just balanced with the use of one of the rear pivots underneath... :sneaky:
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Old 04-13-11, 04:54 PM
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I'm not sure what's ideal. I could be wrong but I'm pretty sure longer decreases leverage. When I shortened mine. I got more stopping power.
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Old 04-13-11, 05:30 PM
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If the straddle wire is too short, the caliper arm will flex first. If the straddle wire is too long, the brake wire will flex first. You are correct Tom.

Another thing to consider is the amount of cable movement for blade movement. If it pulls less wire, it pulls with greater force.

Last edited by ftwelder; 04-13-11 at 06:02 PM.
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