Topic: Front brake light requires superhuman squeeze to turn on

[briandk]

I am trying to get my 550 ready for inspection and first thought that the front brake light switch didn’t work, but if you really grip it and squeeze the lever it will turn on.
The front brake feels wooden and weak, but it’s my understanding that is not unusual.
I replaced the brake master with an aftermarket replica, and bled the system but that didn’t really help. It might brake slightly better, but the light still only comes on with a lot of effort.

Can it be the brake light switch itself or should I look at hoses? The lower hose was replaced with a braided at some point, but the upper hose looks original.


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[scottly]

The front brake feels wooden and weak, but it’s my understanding that is not unusual.
I replaced the brake master with an aftermarket replica, and bled the system but that didn’t really help.

What is the piston diameter of the aftermarket "replica"?

[briandk]

What is the piston diameter of the aftermarket "replica"?

I am not sure, but it is this one: https://m.ebay.co.uk/itm/HONDA-CB350-CB400-4-CB450-CB500-CB550-CB750-FOUR-FRONT-BRAKE-MASTER-CYLINDER/352444725183?item=352444725183

The problem was there with the original master also, that is why I tried replacing it.


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[scottly]

The seller doesn't have any info posted on the size of the piston. Was there any difference in the actual braking action with the new MC? Was the old MC an original 14mm part?

[briandk]

The seller doesn't have any info posted on the size of the piston. Was there any difference in the actual braking action with the new MC? Was the old MC an original 14mm part?

Performance of the two masters felt similar, perhaps slightly better with the new one, but may be because the system was bled when I swapped them. The old one at least looked original (right color and cap).

I have a 19mm radial master from an mv augusta f3 I could try and throw on just to see if it made any difference, but I suspected the switch itself or the hoses since the problem was also there with the original master.

[CB_Dan]

In my opinion, most likely is either the front brake switch or the upper rubber hose. Highly probably that there is not enough pressure generated to trip the front brake switch, assuming the switch is in working order, due to the flex in the rubber hosing.

Old rubber hoses, underwhelming MC, or a faulty/dying brake switch would be the only real causes.

4into1 has a reproduction brake switch available. I just picked one up for my 750K1 because the original is always triggering the brake light despite not depressing the front brake.
https://4into1.com/reproduction-front-brake-switch-35350-300-016-honda-cb350f-360-400f-450k-500-550-750/

[scottly]

I would suspect the switch itself; it shouldn't take that much hydraulic pressure to turn the light on.

[PeWe]

What is the piston diameter of the aftermarket "replica"?

I am not sure, but it is this one: https://m.ebay.co.uk/itm/HONDA-CB350-CB400-4-CB450-CB500-CB550-CB750-FOUR-FRONT-BRAKE-MASTER-CYLINDER/352444725183?item=352444725183

The problem was there with the original master also, that is why I tried replacing it.


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Look like the MC my CB750K6 (and K2) got from DSS. Work fine with single as well as dual brakes. https://www.davidsilverspares.co.uk/CB750K6-FOUR-1976/part_123916/
I replaced the ugly cap with a stock looking one   https://www.davidsilverspares.co.uk/CB750K6-FOUR-1976/part_189670/
Light will lit with a soft 2 finger squeeze. Switch is the really old Honda switch from 1976

[robvangulik]

A 19mm master is far too large, will feel rockhard and brake less than putting your feet on the ground!
The original is 14mm.
Its easy enough to take the switch off the bike and see if there is a lot of junk blocking the pressure pad inside. And when you're in there, just replace that upper small piece of brakeline too, won't cost a lot and gives certainty that THAT isn't giving trouble.

[Bankerdanny]

The brake light is controlled by a pressure switch in the splitter mounted on the lower triple. It is unlikely the master was ever the issue.

[Scott S]

 That master cylinder works fine and is the correct size (though there is a similar looking one for Kawasaki's that's 19mm).

 If you need a brake switch, the same switch was used on some Honda cars (can't remember which ones at the moment) and can probably be found at a local auto parts store.