Tandem Tom

I am hoping you guys can help me out. We ride a Co-Motion Speedster and the rear brake makes an intermittent squeak. Last night we went on a 32 mile ride and I really tried to take notice as to what was happening. The squeak would often disappear when we pedaled and if it started again if I just tapped the brake lever lightly it would stop for a while.
We are getting ready for a month long tour in Denmark and I with it being flat I know I could open up the caliper a bit more but I really like a quick responsive brake.
Thanks in advance for your help!

twocicle

If I understand correctly, your brake is making noise while you are riding but not applying the brake?

That would mean the pads are in contact with the disc due to the pads being too close to the rotor. Either your brake caliper pad adjustment is dialed too closed, or (assuming you have a cable actuated caliper) your cable/wire may be sticking. For the first, that is simple enough to open up the pad adjustment; for the second, I would disconnect the cable from the caliper to check by feel whether or not the brake wire is binding somewhere between the brake levers and the caliper end.

StephenH

Figure out which pad is rubbing, back that off a bit. That may involve recentering the caliper. It may help to pull the pads out, and try to clean out the caliper with air.

Bent In El Paso

Sorry, this post applies to the front disc brake. I should have read the OP's post more closely...

What year is your Speedster? When we purchased ours in 2010 with the Rolf wheels and the Wound-up carbon fork, there was a design issue with the fork that the caliper could not be centered properly over the rotor. This issue was discovered on our bike when the bike shop building the tandem had Co-Motion send a replacement fork thinking the first one was defective. The second fork had the same issue. The bike shop fixed ours by milling off some of the aluminum on the caliper mount. This fixed our issue and we are still riding it that way.

If you have the same setup, this could be the root cause. FYI

joe@vwvortex

Interesting - our Wound up was the same way. Wound up denied any wrong doing in the design so rather than hassle trying to return it where I bought it I used a dremel on the caliper mount rather than the fork.

twocicle

^^^ Except he specifically mentions the issue is with the rear brake. Perhaps CoMo makes a "pushmepullyou" tandem?

Bent In El Paso

You are correct. I read it during lunch while multi-tasking on other things. Oh well.

Bent In El Paso

Now that you mention it, they did mill off the caliper mount and not the fork itself.

joe@vwvortex

Yeah - makes more sense and if you mess up - well - they are easily replaceable.

joe@vwvortex

I read that - could also be a bent disc as well.......

akexpress 

I agree with Joe in that a disc that is warped out of true make the intermittent noises. The OP might consider a riveted two piece disc as they tend to be less prone to warping.

twocicle

^^^ Tapping the brake lever stops the noise, so this suggests that action is resetting the pad/cable position. My bet is on either too much stiction in the cable wire that the caliper return spring cannot overcome, or that the pads are simply dialed in too close to the rotor and need maximum reset to keep clear.

Tandem Tom

I took the wheels into the LBS ,where I work PT, and put them in the truing stand. The discs and rims are perfect. No warp on the discs. I did say that the noise goes away "when" we are pedaling. I think I will look at realigning the caliper and see how it goes.

mkane77g

'Noise goes away when pedaling' doesn't sound like a brake problem.

Tandem Tom

OK? So any thoughts as to what I might be hearing?

TandemGeek

Could be rear hub issue: what brand of hub is it?

Here's my hit list based on the rear rotor being true:
- Is caliper aligned correctly or has it been "torqued" out of plumb with the rotor? Avid BB7's will sometimes rotate when you tighten the attachment bolts, even if the caliper is closed tightly against the rotor as you tighten the bolts.
- If the rear hub is a White Ind or some other type that uses an adjusting or pre-load collar vs. a DT/Hugi or Phil Wood that are press-fit or used screw-on end caps for preloading make sure they have been adjusted to remove any slop from the rear axle/bearings.
- When's the last time and how many miles have been put on the rear hubs since the freehub internals have been cleaned and relubricated? If it's in the 1,000's of miles then that should be done regardless.
- If you haven't done so, a helper spring placed between the caliper's actuation arm and cable stop housing will allow you to increase the rear disc cable pre-load to improve caliper pad retraction and lever feel by removing slop from the brake cable.

Tom Spohn

We had a similar problem with our Cannondale's BB7 rear brake. I thought it might be due to the metallic pad so I bought the non-metallic replacements. What I found when installing them is that the pads can become very slightly misaligned in the carrier causing a squeak--something like a rim brake that has the pads toed out instead of in. Very carefully seating the pads did away with the squeak. I don't know how they became misaligned or why the carrier allowed them to be so. Try taking the pads out, examine them closely for uneven wear, and if OK reinstall them.

PMK

For us, I have found the spherical Avid mounts can also creep, allowing the caliper to reposition itself. Yes they are torqued and then some and still creep from brake use.

Also, as the pads wear, the pad spring has alerts that will be difficult to silence, since they are a wear indicator. Problem is, they sound off before the pad is dimensionally at it's limit.

PK

Tandem Tom

I had the bike up on the bench yesterday and "re-installed" the caliper. As I was sighting through and looking at the pads the inner pad looks to me to be angle a bit. Maybe wear? as I plan install new pads prior to the trip maybe this will correct the issue.
As for the rear hub, I re-did those in the Spring with the "special" lube.

barkersoldbean

We had the same problem on our IBIs with a BB7. I was forever flicking the brake lever to shut it up. Fixed it a la Tandem Geek solution #4 - fit a "helper" spring. Not had a problem since.

twocicle

I came up with that solution because of a couple problems:
1) indirect cable routing caused more wire friction, and
2) the earlier BB7 calipers had lower spring tension.

The initial implementation back in 2003 was posted here: https://www.precisiontandems.com/avidconversion.htm



Mark's similar install (discussed here: https://www.thetandemlink.com/calfee_tandem_12.html) uses a slightly larger helper spring that sits over both ends of the inner caliper points):



More recently (2012) I installed a new BB7 which seemed to have a higher spring tension and does not require the helper (BASTARD) solution and provides very good lever feel.

The advent of the new TRP dual piston calipers looks interesting. Once more feedback is given about it's comparative performance (stopping power, lever feel, etc), it could be a better solution for tandems as those do not have plastic parts than can melt (I have never experienced that aspect). However, easy sourcing of replacement parts for a TRP is a bit unclear, no User/Install Manuals posted on their website, etc.

joe@vwvortex

Yup - the newer versions have much better spring tension. A company used to sell a longer screw to increase tension on the older versions and I ran that after messing with the spring setups. When I bought my front caliper - I could tell there was much more spring tension - so I bought a new one for the back as well - neither of which require the spring.

As for the new TRP's - I'm in the same "wait and see" position. Everything so far looks promising and having a dual piston caliper would be great - whether its hydraulic or not. I just switched to the ICE rotors which are a big improvement as well. With the reduced amount of deflection - they are less prone to bending and much stiffer leading to better brake feel as well.