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Help please My front brake goes soft....

Discussion in 'Technical and Troubleshooting Torque' started by r.ellis, May 22, 2008.

  1. Hi guys, new to all this

    Im riding a 1992 CB 250.. the front brake goes soft randomly but with a few pumps is hard again. I have bleed the brakes and done every thing we can think of..

    the folowing has been sujested,
    -- dodgie seals in the master cilender?
    -- Soft spot in the pipe that expands?
    -- or a leaky calaper?

    Please note im not loseing any brake fluid..

    Please help, cos i need the bike to get around.

    Thanks in advance.

    PS, excuse the poor spelling.
  2. Check your brake pads.

    If they are really worn the first application of the brakes will all be taken up pushing them out to contact the disc.

    Also check disc runout (warped disc) and make sure that the caliper is secure.

    Cheers AdzA
  3. +1 to checking the pads.

    If you're not losing fluid, the seals are probably OK.

    Even if it's not the immediate problem, if the flexible hoses are original I'd look at changing them as 16 years is getting on a bit for an item that should be regarded as a semi-consumable.
  4. cheers guys the pads were new 6 months ago, and were checked about 3 months ago.

    if i do go for a new hose do i go for rubber or braided line?

    thanks once again.

  5. Braided lines will be a bit more expensive, and are likely to make your brakes a bit more 'abrupt': you will need to brake with more control to avoid locking up, because there's not that 'give' from the slight expansion of the rubber lines. If you're fairly experienced and looking for more precise braking go the braided, but if you're a reasonably new rider (or on a budget) the rubber lines are perfectly good and arguably better.
  6. I don't like to contradict you Bravus, but, in my own experience, braided lines have cost me between 1/3 and 1/2 the price of OEM rubber. That's with plain Jane cadmium plated ends. Flash, anodised fittings will cost more.

    Also, on older, low tech braking systems (such as that enjoyed by the CB250), there has been no detectable difference between an OEM equipped bike (with good hoses) and the braided jobbies. I suspect that much of the difference reported comes from the improvement in feel resulting from the renewal of old, soft, bulgy lines with pretty much anything.

    I'd go braided.

    Like I said, just my own experience. Contents may settle in transit :) .
  7. Oh, I'd definitely go with your realworld experience over my collated reading on this point! :D
  8. *snigger*
  9. If it's going suddenly and coming back after a few pumps, I'd be guessing some sort of pad knock.

    Make sure all the front end is all tight and the disc isn't too loose in it's carrier. Check for disc warp too.
  10. I bet you a cup o coffee its your master IMO, had this scenraio before. You have air in your system is other possibility. If it aint then it has to be caliper rebuild time for you. Piece o piss job if you mechanically inclined.
  11. Yo Guys, thanks for all the constructive help and to those that "sniggered" well i ask for help because i want to learn and not f up my bike....

    The out comes...

    A- Replaced the brake line - (Braided one)
    B- The front wheel bearings are in for replacement 1 - 2 mm movement side to side at the outside of the wheel
    C- if that don't fix it it will be a new Master as the caliper was a reconditioned one 6-7 Months ago.

    Once again thank you all for your help.

    Ps the braided line gives lots more feel and heaps more stopping power.

  12. Good decision on the braided line.

    Before you spend money on a new master cylinder though, find out if there are any special tricks to bleeding the brakes on your bike. Most service centres use vacuum bleed pumps, and this can result in some air left in the line. Other brakes always leave a little unless your do it just right, like the rear brake on my Ducati. That's usually because the brakes are bled from the bottom, rather than the top, which is where the air wants to go.

    Anyway, even though you have bled it at least twice recently, it might be worth checking if the CB250 requires a special technique.
  13. Pump teh lever, apply and hold good, hard pressure against teh lever. Hold it for a couple of minutes.
    If teh lever starts creeping down towards teh bars, or starts losing pressure because teh lever is bottomed out against teh bar, you have either a master or slave cylinder leak.
    By teh random sounds of it though, my money is on old fluid/air turning to vaopur in teh lines under heat. Please do teh simple test above though.

    Regards, Andrew.
  14. I think you answered your question by telling us the wheel bearings are shagged allowing the discs to knock the pads back. Fix them first before trying anything else would be my suggestion :)
  15. Zackly