SOHC.co.uk Forums > CB500/550

550 front brake rebuild

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Mike_Berkshire:
On my long to do list is a rebuild of the grotty front brake system. I’m thinking that fitting a new master cylinder makes sense rather than a rebuild of the master cylinder. As for the rest of the system, is there a how to guide available anywhere I could follow? Also, are there any common mistakes I should be aware of? I have never done work on hydraulic brakes before. Thanks

McCabe-Thiele (Ted):
There is a downlodable workshop manual & parts book on this site for most variants of the sohc models.

Something you might want to consider is using Silicone based brake fluid especially useful for little used bikes.
Silicone based fluid is not hygroscopic like normal mineral or synthetic fluids so does not need routine fluid changes.
Unless you are racing the specification is imho good enough.
Goes without saying the whole brake system needs to be drained of old fluid if changing to Silicone based fluid.

On my 400 & 500 I used a SS piston and the DS Master cylinders they sell - no sloppy brake lever & it bled easily. I used a Syringe to push the new brake fluid up from the Caliper until it appeared in the m/cyl reservoir then topped it up from the master cylinder. I left the system to stand overnight, next day the lever was nice and solid. I probably used less than 75 ml for a final bleed through.

Some folk find you can bleed the brakes normally, some have trouble getting a good solid lever easily.

PS I would try to remove the caliper piston first by using the existing brake hydraulics to push the piston out as far as possible.

Johnwebley:
The system on the sohc is very simple,

David Silver does a complete replacement master cylinder for less than £40 I seem to remember,

The caliper will possibly need a new seal,also check, and if corroded replace the caliper piston,

Also check the hoses for cracks and splits,

That covers the hydraulic section,

The only other thing is make sure the alloy arm that the caliper mounts on ,the swivel is free for it to move,



Sent from my SM-A546E using Tapatalk

Mike_Berkshire:

--- Quote from: McCabe-Thiele (Ted) on April 14, 2024, 09:06:05 PM ---
PS I would try to remove the caliper piston first by using the existing brake hydraulics to push the piston out as far as possible.

--- End quote ---
Thanks Ted. I have seen some useful clips on Youtube that all show forcing out the piston using the existing system. Given that my system is so grotty (see picture) do you think that hooking up a new master cylinder after flushing out the old lines is worth trying? The current master cyclinder is completely seized and I am sure the brake lines are filled with muck as is the master cylinder reservior?

McCabe-Thiele (Ted):
I see what you mean about grotty - I would be minded to try as you said with the new m/cylinder in place.
If you do a search on here from the search box at the top there are other ways to force out the piston involving a grease gun.

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