barkersoldbean

We have a 1970's vintage Bill Phillbrook Tandem fitted with Mafac Cantilever brakes. The front brake is very good - albeit with a lot of squeal type noises. The rear brake is about as useful as a chocolate fireguard - it delivers a discernible but totally inadequate braking performance.

We have no rear drum brake.

I have tried, new brake blocks (Kool stop salmon), lubricated the cross wire to ensure the hanger doesn't stick etc.

I think that i have the angles ok (see pics) of the brake levers - i.e. pulling from horizontal.

On the basis that this is in my opinion dangerous - i ordered a set of Jones cantilever brakes (en-route from the US as we speak), but in the meantime does anyone have any wisdom on improving rear brake performance as i am nervous about using the tandem in anything other than 100% dry conditions.

Rims are pretty standard Mavic 36 hole. Braking surface area looks ok - not covered in grease, oil etc.

Dean V

Be aware that most modern cantilevers are designed for 80mm pivot centres. Older bikes like yours are usually closer to 65mm. Depending on the particular brake design and adjustability this may make them difficult to fit. When I fitted some Avid Shortys to our Bob Jackson some machining of the arms and brake block grinding was required to get them to fit.

MNBikeCommuter

I haven't had experience with Mafac brakes, but to me it looks like the angle of the straddle cable isn't set up for ideal mechanical advantage. It looks like you have a little "extra" rear brake cable remaining, so I'd suggest try shortening the straddle cable and see if that helps. (If not, it was a cheap attempt at fixing the problem. :-)

austex

I think your straddle cables (front, too) are much too short. For maximum braking power, each side of the straddle cable should form a 90-degree angle with the brake arm to which it attaches just as the respective brake pad comes in contact with the rim. This often means making the straddle cable as long as possible, so long as the straddle hanger does not come too close to the housing stop.

Tom

barkersoldbean

Thanks for this - i will be doing some experimentation this week on straddle cables - there seems to be conflicting advice on this - shorten and lengthen are being proposed as solutions!.

One thing that was also mentioned to me (outside of this forum) as a possible cause of poor rear braking performance was the cable age - i.e. it is too stretchy (old inner cable, old outer sheath). Does anyone have experience of performance improvement from moving to pre-stretched inner cables and more modern outer (eg jagwire) sheath?

Tony

TandemGeek

New cables & housing will always help, especially if the current ones are of unknown vintage. The old Mafac brakes are perhaps some of the least powerful cantilevers out there.

You might want to consider adding an in-line brake booster between your brake lever and the downtube cable stop (something like a Brake Power Booster, aka BPB or an in-line Travel Agent) as I'm not sure if the Shimano brake levers on your bike have enough leverage to get the amount of braking power you'd want, even with new cables, etc.

More info on cantilevers that may be of interest if you haven't seen it: https://sheldonbrown.com/cantilever-geometry.html

waynesulak

Another vote for Sheldon's explanation. As explained by Sheldon, the reason for apparent conflicting advice is that what feels powerful does not always give the most stopping power. I think the Mavics should work ok if properly installed and adjusted.

Wayne

Wayne

TandemGeek

Hmmm... maybe or maybe not.

That model of Mafac caliper brake will always be marginal on a tandem, even with a proper, higher-leverage brake lever like a DiaCompe 287v or a Cane Creek SCR-5V.

The levers on that bike look to be an 80's model Shimano 600 Ultegra designed to work with SLR dual-pivot calipers.

barkersoldbean

Good advice - sheldon b article excellent. Understand the shorter straddle cable now. Hopefully, shorter straddle cable, new cables, jones cantilevers (still awaiting customs clearance in the UK!!) will sort things.
Thanks for all the excellent advice.
Tony

barkersoldbean

Just got the Paul cantilever brakes from the US. Great quality, but your point above is correct. Tricky. Need to do some clever shimming to get them to work.........

aixaix 

I know you have already dealt with the issue, but I'm curious what those with more experience with cantis than I have to say. The mounting bosses look to me to be way too close together for the MAFAC cantis. I've seen them installed and working OK, but the angle at rest of a line drawn through the pivot bolt and pad anchor bolt was nearly vertical, while yours is quite far from that. Seems to me you'd need an impossibly long straddle cable to make them work the way they were designed to.

waynesulak

Let us know how it works out.

Leisesturm

Ok, this: (from the o.p.) "The rear brake is about as useful as a chocolate fireguard - it delivers a discernible but totally inadequate braking performance." Sounds about right... even on our disk equipped tandem. Anyone here have a different experience?

H

waynesulak

Are you saying your tandem with disk has inadequate rear braking?

We use V-Brakes front and rear. Braking is great. Rear works well.

barkersoldbean

For those of you interested - see pic of Paul canti's now installed on rear of our tandem. Huge struggle because of the 65mm spacing (had to machine 4 customs 40 degree shims to get the right contact angle) but now sorted. Quality is just superb.
We have a 100km ride Friday up and down dale so will be able to report on whether the brakes are any better.
Decided that the best route forward is over the winter to get the frame sorted with brake disc mounting lugs added and a phil wood 130mm disc hub.
T

Leisesturm

We have two tandems, one equipped with V-brakes the other 160mm disks. Both stop very well and I spent a lot of time getting the adjustments 'just so'. Perfect amount of lever pull and as equal a feel between front and rear as possible. On neither tandem nor on any bike I have ever ridden, has the rear brake used alone been 'overwhelming'. Far from it. For a time, on our cargo tandem we had no rear brake at all. The boss insisted we make a food run before I had it sorted. Refusal was not an option... well it was, but... anyway, long story short, the front brake alone (v-brake) was well up to stopping a ~340lb team, plus ~80lbs of groceries, even from a high speed descent. Would I have dared pull that stunt with only the rear brake operational???? Never!

H

Leisesturm

Hmmmmm.... you do know that the way you have those canti's set up, flies in the face of accepted adjustment right? I don't run canti's so I am just saying. I am no fan of dogma or traditionalism but usually when there is a consensus about a thing like brake setup, there is a reason. It couldn't hurt for you to read what Sheldon Brown has to say about cantilever setup to get some insights.

H

EDIT: from reading earlier posts, it appears others have sussed this. Those calipers were intended to be much further apart at rest so the ends of the levers would form a much less acute angle with the straddle cable. Different levers indeed would help as the TandemGeek noted, so would some modern calipers. Sacrilege? Not really, in silver, some Tektro calipers would look really cool on that frame. Have a look at the Velo Orange website to see how easily it is possible to have 21st Century performance while keeping hold of 19th Century classic style.

barkersoldbean

The Mafac and Paul cantilevers are Wide Angle - i.e. Cantilever angle is >90. The Paul version with its shallow brake pads is similar to the Mafac with its deeper section pads.

My focus has been as per Sheldon;

A larger contribution to the mechanical advantage of a well-adjusted cantilever brake, especially a low-profile one, comes from the transverse cable. The mechanical advantage is strictly determined by the "yoke angle ". The formula is:
Mechanical Advantage = 1/sin yoke angle
For readers without slide rules I have calculated a few examples: [How quaint :-) John Allen]
Yoke Angle
(Degrees) Mechanical
Advantage
90° 1
80° 1.015
70° 1.063
60° 1.15
50° 1.31
40° 1.55
30° 2
20° 2.92
10° 5.76
5° 11.47
0° Infinity!
A 90 degree yoke angle would result from an infinitely long transverse cable, such that each side of the cable was running vertically down from the cable yoke.
A 0 degree yoke angle would represent the shortest possible transverse cable, running in a perfect straight line along the top of the cable yoke.

As you can see from the table, the shorter and straighter the transverse cable, the more difference it makes. This effect is what makes it possible to make a low-profile brake with good stopping power.

I have now found that the Paul cantis, with longer brake shoes and shortening the straddle cable as much as possible = optimised braking- although the shorter straddle cable makes the brakes feel "spongy" at the brake lever.

That said, i am still not happy and think that my only real option is to build a new rear wheel (Phil Wood 130mm disc hub, Velocity offset rims) and get some calliper mounts brazed onto the frame during the winter - and just live with it as is and be cautious down big hills/take a break mid-downhill to rest the wheels so they don't overheat.

Thoughts?

T

waynesulak

Not sure what you mean by "optimized braking." Do they provide reasonable stopping power? A small amount of Spongy feeling is not always a bad feel in a brake. Stopping distance is what matters.

I noticed from your pictures that the ell brake bridge is low enough to be drilled for dual pivot caliper brakes. I can't determine if it has adequate diameter.
This would be much less costly than a new rear hub and not damage the paint job. Have you considered that option?

Of course disks excel in wet conditions so that may be the best for your bike.

Wayne

barkersoldbean

Interesting comment.
I have measured the width of the brake bridge and it is around 10mm diameter.
I have also grabbed an old shimano 105 dual pivot brake (normal reach ) and it looks like the clearance is ok - it would fit.
The mounting bolt of the dual pivot lever is about 4-5mm.
Anyone know whether this would have sufficient structural strength to give it a whirl?
Tony
(ps - thanks to TandemGeek for the Velo Orange link - brilliant site)