SOHC.co.uk Forums > CB750
CB750F1 Rear Disc Brake
Johnwebley:
Ideally both pistons should push back into the caliper.
Make sure they can slide.
But it seems like an issue with the returning fluid into the master cylinder.
Sent from my SM-A750FN using Tapatalk
hairygit:
Many years ago I had a similar problem with an F1 rear caliper. In the end after discussing with a local Honda dealer, he suggested re assembling the master cylinder but WITHOUT the restrictor valve (the little black domed bit of metal sitting at the top of the spring in your photo. I did just that, problem solved. A word of warning though, the restrictor is there to reduce the amount of pressure reaching the pistons, as the rear brake without the restrictor is incredibly powerful, and if you're not careful you can lock the rear very easily under braking. That said, I learnt very quickly to use it very gently, as 80% of your braking should be on the front anyway. Try it, if it works, it's your choice to either search out another restrictor valve or run without it.
Sent from my POT-LX1 using Tapatalk
Doswen:
Both pistons slide freely with the bleed nipple open. I agree it all points to the pressure not being released in the master cylinder, however I can’t find the fault.
Sent from my iPhone using Tapatalk
Doswen:
Aaarrrhhh, that’s what the dome cup is. I have swapped that too and it made no difference.
It sounds like a good idea to remove it and see if it cures the problem. Many thanks.
Sent from my iPhone using Tapatalk
Doswen:
--- Quote from: hairygit on October 09, 2020, 07:09:31 PM ---Many years ago I had a similar problem with an F1 rear caliper. In the end after discussing with a local Honda dealer, he suggested re assembling the master cylinder but WITHOUT the restrictor valve (the little black domed bit of metal sitting at the top of the spring in your photo. I did just that, problem solved. A word of warning though, the restrictor is there to reduce the amount of pressure reaching the pistons, as the rear brake without the restrictor is incredibly powerful, and if you're not careful you can lock the rear very easily under braking. That said, I learnt very quickly to use it very gently, as 80% of your braking should be on the front anyway. Try it, if it works, it's your choice to either search out another restrictor valve or run without it.
Well Hairy Git, it looks like you cracked it. I’ve removed the restrictor valve and it seems to have cured the problem. Thank you so much.
I’ve run the bike up on the centre stand with heavy braking under load and there are none of the old binding symptoms. Waiting for the roads to dry out and then I can give it a road test but all the signs are looking good.
As per my original message I can’t really see how the restrictor valve worked when it blocked the oil way. The brake doesn’t seem any sharper than with it in but I will be able to judge it more on the road.
Thanks again 👍😀
Sent from my POT-LX1 using Tapatalk
--- End quote ---
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version