Topic: Cb550 front disc brake

[Anthub]

Hi ... wondering if someone can give me some advice.. I’ve recently bought a 1979 cb550 and think that the front disc brake isn’t up to much.
When I sit on the bike and fully apply the front brake, I am able to rock the bike forwards.. is this the norm?


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[CBGhia]

well, 2 things.
1.  They didn't make the CB550 in 79.  It went to the CB650 that year. (in the US anyway, not sure about europe)

2.  When you say rock it forward, is that just the suspension moving is is the tire rolling, as well?  Because the tire should not roll with the brake pulled.
Have you bled the brakes?

[Anthub]

Thanks for the quick reply... Yeah, it’s a UK bike, registered in 1979 so it would have been manufactured in 78 I assume.
Brake has been bled and yes, the the wheel moves when you rock the bike forwards just with body weight alone


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[CBGhia]

Yeah, that sounds like there is an issue with either the caliper, the pads or the master cylinder. 

I wold inspect each component and probably rebuild the master and the caliper.
Do you see any fluid leaking out?

Oh, and there isn't any grease or anything on the brake rotor is there?

I think you probably have a 78 bike.  you can compare VINs here.
http://www.sohc4.net/cb550-model-guide/

[Anthub]

I’ll take the Caliper off and have a look.. For some reason, the previous owner/s have put the forks the other way round so that the Caliper is behind the fork!! Don’t know if that was for a reason or just a mistake..Thanks for taking the time to reply ... really appreciated


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[Deltarider]

Honda marketed their models to all parts of the world over various years so 'Year' is not a very useful way of communicating what model you actually have. Here are the CB550s listed:
CB550K
CB550K1
CB550K2 ('76)
CB550K3
CB550K4
CB550F
CB550F1
CB550F2
When you know your engine- and framenumber, you can determine what model bike you have, including the area code. They're listed in he first few pages of the Parts Lists. And those lists are all here: http://www.honda4fun.com/materiale-documentazione-tecnica/parts-list/parts-list-cb550
Also handy to find and compare the carb numbers.

[Anthub]

Mine will be a K3 then (2027295) ... it must have sat around for a while before it was registered!!


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[scottly]

Do you feel any resistance when pulling the brake lever, or does it go all the way to the handlebar? When a caliper is relocated behind the forks, the bleeder is no longer at the top of the caliper bore, and is impossible to bleed when mounted. Remove the caliper, place something 7mm or more thick between the pads to prevent the piston from being pumped out, and bleed the caliper with the bleeder positioned at the top.

[Anthub]

Yeah ... there is resistance and it stops about 1” away from the grip.. I see what you mean about the position of the bleed nipple. It wasn’t until a started looking at images of 550s that I realised the Caliper was on the wrong way round.. I’m going to swap the forks back round and position the caliper in the correct location before bleeding it.. Also, when I apply the brake, it sounds like the pads or something are rattling around


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[Bankerdanny]

Now that you have 5 posts you can start adding pictures. When looking for tech advise advice pictures will make it much easier for us to try and help you.

[Anthub]

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[Stev-o]

Some guys relocate the caliper to the rear of the fork legs as a "performance mod".

[Anthub]

Ahhhh... how strange


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[DaveBarbier]

Some guys relocate the caliper to the rear of the fork legs as a performance mod.

I'd put "performance mod" in quotes.

[Stev-o]

Some guys relocate the caliper to the rear of the fork legs as a "performance mod".

I'd put "performance mod" in quotes.

Done!

[DaveBarbier]

Some guys relocate the caliper to the rear of the fork legs as a "performance mod".

I'd put "performance mod" in quotes.

Done!

Haha

[Anthub]

So.... I’ve taken the caliper off today and the piston is working fine with no leaks and is nice and clean... I did however notice that both pads seem to rattle about a bit and there is nothing securing them... is that the norm?


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[Anthub]

First thing I’ve noticed is the absence of a pin that goes between the 2 halves of the caliper... can’t work out what this actually does but it doesn’t seem to have anything to do with the pads rattling around


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[Anthub]

Actually, it’s a split pin that goes through the fixed pad


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[DaveBarbier]

Yeah, all the cotterpin does is keep the pad from falling out. Pad needs to be able to rock back and forth to keep square on the disc. Other pad with the piston behind it shouldn't rock too much or else it could get cocked, but shouldn't be tight or else it won't retract properly. Nothing keeps that pad in but the disc itself.


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[Anthub]

Thanks for that Dave.... The pads do seem overly ‘rattly’ mind but I’ve got nothing to judge that against ... I just noticed it when I was riding the bike and applied the front brake


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[Anthub]

Although I’ve bled the brake, I’m still getting bubbles in the master cylinder when I apply the brake lever.. Will that be a failed valve in the master cylinder?


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[scottly]

Air bubbles in the MC indicate there is air trapped in the top of the brake line/banjo bolt. Try wiggling the lever in and out a short distance, until no bubbles appear. When all the air is out, there will be a pulse of pure fluid, which can squirt up out of the open reservoir if the lever is pulled too quickly, making a bit of a mess.

[Anthub]

Thanks for that Scottly.... I did that last night but thought I’d give it another go this morning... Started losing the will to live after bubbles still 20 mins later. Did it nice and slowly with the cap off so as not to cover myself but when I put the cap on and did it more rigorously, I opened it to what I can only describe as fizzy pop!!


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[Stev-o]

Thanks for that Scottly.... I did that last night but thought I’d give it another go this morning... Started losing the will to live after bubbles still 20 mins later. Did it nice and slowly with the cap off so as not to cover myself but when I put the cap on and did it more rigorously, I opened it to what I can only describe as fizzy pop!!

Did you bleed the system too?