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On rough roads or when there is a lot of vibration, the quick release on my front brake will sometimes pop open. Is there a way to prevent this from happening?

Closeup of front brake

If it helps, the bike is a 1995 Trek 370, which has Shimano 250EX brakes and Shimano Exage 300EX levers (according to BikePedia).

  • Do you have a quick release on the brake lever too? Post a photo if you’re unsure – Swifty Jul 24 '18 at 20:37
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    It’s a design flaw. Try some electrical tape to keep it in place. – Rider_X Jul 24 '18 at 21:12
  • If the level disassembles with a bolt, disassemble it and add a washer or some such to increase the friction. – Daniel R Hicks Jul 24 '18 at 21:15
  • @Swifty No, there is no quick release on the brake lever. – Brent McCarthy Jul 24 '18 at 21:58
  • @Rider_X Would I just tape the quick-release lever to the caliper arm that it's attached to? – Brent McCarthy Jul 24 '18 at 23:14
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That photo shows a pretty filthy bike.

I'd start with a full disassemble of the rear brake caliper, and clean all the metal parts, and especially on the friction areas. Then I'd buff the whole thing with brasso or JIF cleaner. Then reassemble and see if it improves. If not, you could rough up the friction surface under the quick release using some sand paper.

If the main spring in the brake caliper is weak then this may be a losing battle, because sourcing replacement parts is hard. In this case, just explore for some more modern double pivot calipers, and fit them up with new brake cables.

The temp fixes suggested by others are exactly that - temp fixes. I wouldn't even ride this bike if your braking ability is compromised.

  • Okay, it sounds like replacement of the caliper is the way to go. Would a new caliper require a new brake cable, or would that be a preventive measure? – Brent McCarthy Jul 25 '18 at 15:59
  • @BrentMcCarthy purely preventative. Brake cables are consumables and generally last 1-5 years for normal usage. They normally rust on the inside increasing friction which shows as a brake that pulls on but is reluctant to release. A replacement pack of cable parts should be 1/20th the cost of the replacement calipers, and a nice fresh inner cable makes installation easier. The inners will settle over a month, so expect to adjust them after a bit. Totally normal. – Criggie Jul 25 '18 at 21:49
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    To expand on that - if its been dirty a lot, then the grit may have got into the brake making the friction of the QR lower by abrasion. Cleaning will help show that. You could also add some kind of friction washer when reassembling the QR but brakes are not really a place for experimenting, New calipers would be safest. – Criggie Jul 26 '18 at 11:15
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Presumably the QR lever originally had enough friction to stay closed but has worked loose or a plastic washer or bushing that provided the friction has degraded. Obviously keeping a brake functioning is a high priority

Probably the simplest solution is to use a bit of tape to hold the lever closed, but tape may come off. Maybe you could use a small zip tie or the type of wire used to stop bolts coming loose.

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Criggie is right of course, so I’m going to amend this a bit.

You should stop riding the bike until you replace the brake if your braking is compromised. The.QR isn’t really serviceable so if it’s not functioning the unit should be replaced.

If you must ride to the bike shop to have this done, you could choose to bypass the QR by opening it fully and re-fixing (tighten) the cable to take up the slack.

Might be a bit hacky, so proceed at your own risk etc. But I’ve seen people set their bike up like this on accident even, not realising how QR works.

Sometimes bike maintenance just means replacing worn out parts.

  • Going without the QR is a fine temp fix - I'd be worried that the QE mechanism might not take the full strain of braking while in the open position. But good enough for gentle braking. Risk is emergency braking is always unexpected. – Criggie Jul 26 '18 at 11:22
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    @Criggie mm, but it would still be the same mechanism, just in the open position. Brake designers must have thought about us using brakes without closing the QR, Shirley? – Swifty Jul 26 '18 at 11:37
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    It'll vary, but I think that when the QR is closed, the cable is pulling more on the main arm and pulling the QR onto the arm... some(?) force will be through the QR's mount but not all of it. When the QR is open its a simple link in the chain and 100% of the braking forces are being pulled straight up through it. So the QR cam's axle has to take more of the forces. I don't have the maths to guess how much strain would go through that tiny axle when its closed normally, but when open it will be taking "more" force. – Criggie Jul 26 '18 at 11:41
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One other idea: I guess for the quick release to come loose the cable temporarily has to be unloaded by vibrations (try releasing the QR while pulling the brake, it shouldn’t be possible).

Maybe the springs are too weak or the cable is too dirty? Is brake action smooth and easy? If not, you might want to replace your cables and housing first.

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    I think this is good, I just handled a boxed Sora 3500 brake and it has nearly no friction in the QR. The mechanism would be held closed by the tension in the cable vs caliper return spring. If the spring isn't functioning fully then reduced tension could be not enough to hold the QR shut – Swifty Jul 26 '18 at 12:07
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Adjusting the brake.1. Release the cable on the brakes. 2.Otkruchivaem almost to the end regulator of a tension of a rope on a handle of a brake. 3.Prezhimaem pads to the rim of the wheel and in this position we pin the cable .4.Turn back (until the stop) regulator cable tension on the handle brake.

  • Otkruchivaem ? Prezhimaem ? Are you using google translate from Russian ? Do note that the question has nothing to do with brake adjustment, and is just about how to stop the QR from opening under vibrations. – Criggie Jul 26 '18 at 11:18

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