1 Attachment(s)
Re: Dong Fang DF 250 RTB Bobber Information
Attachment 19298
Could there be a problem with the master cylinder check valve which I assume the DF has? Maybe a bit of something that does not allow the valve to seal?
I would bleed/flush the fluid first to see if that would cure the problem. If that didn't work then disassemble the master cylinder to look at the check valve.
Re: Dong Fang DF 250 RTB Bobber Information
The check valve holds about 2psi in the system to keep the pistons from returning when the lever is released but it's not enough pressure to cause brake drag. Over on chinariders, there was a member that had a similar problem. He removed the master cylinder and did an old fashion bench bleed. During the bleed, some hardened chunky brake fluid debris came out of the hole that allows fluid to travel down through to the piston. You should be able to disassemble and clean the master cylinder without dmaging any seals. I have done it on my Jap bikes with no problems.
Re: Dong Fang DF 250 RTB Bobber Information
ya ill clean it out before killing myself looking for a rebuild kit...
EDIT:
cleaned it out. nothing to be found.
no definitive measurements but the piston/seals seemed to fit a bit loose in the bore for a high pressure sealing brake system.
well i guess the definitive measurement would be almost not enough pressure to push fluid out the bleeder so... need new seals.
but it seems the rebuild kits are a bit confusing as each seems to be built a bit differently.
Does anyone have a part number on a kit?
Thing is entire new master cylinder parts i'm finding just as low priced...
And there are no nicks or tears in the seals, im not so confident new seals would improve things, these brakes have always been weak, perhaps my bore was a bit wide...
i did find what seems an exact new part though...
http://www.ebay.com/itm/181969475724
i may well go this route short of a definitive rebuild kit part number, and hopefully reuse my modified adjustable levers without having to do all that work again.
Re: Dong Fang DF 250 RTB Bobber Information
Quote:
Originally Posted by
barnone
Attachment 19298
Could there be a problem with the master cylinder check valve which I assume the DF has? Maybe a bit of something that does not allow the valve to seal?
I would bleed/flush the fluid first to see if that would cure the problem. If that didn't work then disassemble the master cylinder to look at the check valve.
Snap, taking a close look at this diagram, when i took the cylinder off and up to the bench, i remember seeing the primary cup, secondary cup, but no check valve?!
also rebuild kits don't seem to come with one so i didnt notice anything missing...
I cant imagine they even worked as poorly as they did before without a check valve...
thanks for the pic, I'll investigate, but like i mention none of the similar rebuild kits even list a check valve, are you guys sure there is even one?
Re: Dong Fang DF 250 RTB Bobber Information
Quote:
Originally Posted by
ben2go
The check valve holds about 2psi in the system to keep the pistons from returning when the lever is released but it's not enough pressure to cause brake drag. Over on chinariders, there was a member that had a similar problem. He removed the master cylinder and did an old fashion bench bleed. During the bleed, some hardened chunky brake fluid debris came out of the hole that allows fluid to travel down through to the piston. You should be able to disassemble and clean the master cylinder without dmaging any seals. I have done it on my Jap bikes with no problems.
This video matches and displays what parts are found in the DF master cylinder pretty well...
there is no check valve, im not sure what you're talking about...
Re: Dong Fang DF 250 RTB Bobber Information
Some don't have check valves. Usually, the master cylinder being above the caliper will do the trick. Also, the reservoir getting low can cause a bit of suction pulling the caliper in. The rubber seal doesn't let air into the system because brake fluid is hygroscopic and absorbs water from the air. As the fluid level drops, if the bellows in the seal doesn't drop as well, there will be a vacuum created in the master cylinder, which will pull the caliper piston back. This is why the master cylinder cap seal is made the way it is.
Re: Dong Fang DF 250 RTB Bobber Information
Quote:
Originally Posted by
ben2go
Some don't have check valves. Usually, the master cylinder being above the caliper will do the trick. Also, the reservoir getting low can cause a bit of suction pulling the caliper in. The rubber seal doesn't let air into the system because brake fluid is hygroscopic and absorbs water from the air. As the fluid level drops, if the bellows in the seal doesn't drop as well, there will be a vacuum created in the master cylinder, which will pull the caliper piston back. This is why the master cylinder cap seal is made the way it is.
some dont have it eh... plenty of info on the web about other bikes wouldnt you say.... you had me running around for an hour looking where i could have dropped the seal :rolleyes1:
Re: Dong Fang DF 250 RTB Bobber Information
Quote:
Originally Posted by
axa
some dont have it eh... plenty of info on the web about other bikes wouldnt you say.... you had me running around for an hour looking where i could have dropped the seal :rolleyes1:
Sorry bout that. I should have known the china bikes wouldn't have them as a cost cutting measure.
Re: Dong Fang DF 250 RTB Bobber Information
Quote:
Originally Posted by
axa
some dont have it eh... plenty of info on the web about other bikes wouldnt you say.... you had me running around for an hour looking where i could have dropped the seal :rolleyes1:
axa, we were trying to help you.
Re: Dong Fang DF 250 RTB Bobber Information
Quote:
Originally Posted by
ben2go
Sorry bout that. I should have known the china bikes wouldn't have them as a cost cutting measure.
That is the thanks you get for trying to help axa!