So fill me in, bearing in mind I have been away from bikes for a long time........ I'm wondering if I have got a sh*tty brand of brake fluid....or the wrong grade??? It's Comma Dot4 Synthetic......purchased about two and half years ago, opened about 12 months ago and tightly resealed. I have fitted some used Goodridge stainless braided hoses (confimed with Goodridge they are theirs)......Old OEM hoses (the originals) removed....fluid needed a change as well; the Goodridge ones cleaned out with appropriate alcohol. Fitted them easily and master cylinder filled......hoses are virtually self bleeding as any air rises to the master cylinder as the lever is squeezed; however bled them from the bottom a bit too. In fact I have bled them several times just in case any air is trapped in there, because I expected the lever to be rock hard (how I like my brakes) but they seem to be 'two stage'..........I changed the master cylinder banjo bolt just incase the OEM one with lots of washers was impeding the fuid flow......also cracked the bolt and bled there as well. It's as though a minor pull on the lever is a bit soft, so a slightly harder pull and they work perfectly.......It's almost as though one disc is braking before the other. The original OEM hoses felt better. The brake lever has the correct freeplay at the pivot bolt and the lever moves about 20mm before pressure is felt.... a litte more and the lever goes hard, but even though I can't pull it back to the handlebar, it feels springy (not spongy). Pads have only done a few thousand miles so they shouldn't be an issue (shouldn't be anyway).....So is the fluid cr*p, wrong grade or are the piston seals pulling the pistons back too far?.....but why didn't it show with the OEM hoses? Any thoughts? AL
The rate at which DOT4 brake fluid absorbs moisture Al suggests you shouldnt keep it for longer than about 6 months once opened. I get through loads of it so for me its not a problem I've come against.........sounds like the master cylinder may be leaking back into the reservoir though.......as pressure in the narrower than std braided hoses will be higher and therefore worsening the ability of the master cylinder seals to withstand the pressure? Just a theory.....
Hi Dave......based on your thoughts, maybe new fluid is the answer.... .....I don't think it can be leaking back because I have tried hooking the lever back with the system under pressure overnight (several times) and the lever position and pressure hasn't changed in the morning, which I reckon it would if there was a leak past the seal. I wondered if it is the caliper piston seals slightly stuck on the pistons pulling the pistons back too far, hence the almost 'double pull' to move them back to the disc. Let's put it this way, it wouldn't fail MOT on brakes, because they work perfectly on a 'full' pull of the lever, but it a bit confusing when riding and I'm looking for the gentle application of the brakes. I suppose there could be a tiny air bubble in one of the banjos high up at the master cylinder, but given the number of times they have been bled, it would be a highly resistant little b*gger if there is. Thanks AL.
Al, what you MAY find is the problem is this...I dont know how you bleed your brakes, but this is how we do the BSB bikes....cos any OTHER way leaves old fluid immediately behind the caliper pistons and we get that "spongy" feel....... Remove the caliper from the fork leg. Remove the pads....one caliper at a time, push the pistons RIGHT back in...then, with the lever cable tied back to the bar, crack the bleed nipple on the caliper...that clears old fluid from behind the pistons.....and replaces it with new fluid.....Put that caliper back on the bike with pads in, and repeat on the other caliper...you may need to use some old pads to hold the pistons back in order to cable tie the lever back, but you get the gist....it works......and its amazing how that little bit of fluid affects brake performance......
I thought I read that then as Al may not know how to bleed brakes phew Was waiting for the swearing
Shaddap! Actually I didn't remove the calipers, but while the system was empty (and no hoses fitted) I pulled the pads back wiv my fingers......I had a bleed nipple in the hose banjo thread with a tube on it to drain it...... ....what I didn't do was keep the pads wedged back when I refilled the system, so the calipers probably weren't flushed......but then as the brakes had been working OK with the OEM hoses (changed them because they had been chafed) and the old fluid, I wasn't too concerned about residual fluid. A different brand of new fluid will be purchased and it will all be done again.......longest run first (left hose is approx 2" longer than the right, but so are the OEM hoses). Cheers, AL.
You wouldnt have noticed it with the original rubber hoses Al, as they expand with the pressure anyway.....similar feel to spongy grot fluid behind the caliper piston methinks.....I have AGIP DOT4 in stock if you want proper brake fluid.....
