Topic: Spongey front brake 500

[flatlander]

Slightly of topic. I keep postponing it, but I have to renew the brake fluid one of these days. Can I top up with 5.1?

yes. only dot 5 is silicone based. the rest (5.1, 4, 3 etc) are compatible with each other.

[gmoss]

I had the same thing happen, and it turned out to be the bleed nipple not quite tight enough. Turned it until it was ridiculously tight & the brake was fine.

oh god, please don't turn it ridiculously tight. have ruined a caliper this way, on another bike.

[Bodi]

"That's quite a statement, Bodi, and I'm afraid it's directed at the wrong person, seen not only my personal experience but also of others I know."

Not directed at anyone specific.
That caliper arm pivot needs attention - meaning disassembly, cleaning, new O-rings, and lubrication - eventually. It takes an hour or so. What reason is there to not do it on a bike with unknown maintenance history if you have the caliper off anyway for pads or whatever? And most owners after 40+ years are not the original owner so the maintenance history is often unknown. Once you know it was done, you can forget about it again for a few decades.
Wheel bearings: OEM are single shield. The outer side shields keep sand out but dust can (will) get in. The inner side is wide open, nothing to keep grease in except hope and luck. By now, original bearings on any 70s bike will be dry and dirty with rock hard remnants of the original grease. I've had bikes to fix with failed wheel bearings. The bearing heats up (which softens the grease for some lubrication but it eventually goes totally dry), the cage fails, and the balls fall out. Hopefully not a disaster but the wheel goes mighty wobbly. There's no way to inspect and lubing is far from easy, new bearings are dirt cheap... why take the risk? There isn't much "feel" until they are close to their end, once one is feeling grindy it's not long before it self destructs... while riding.
So in my opinion it is exactly idiotic to suggest that tasks not on the maintenance schedule never need to be performed.

[Deltarider]

Bodi, I-am-impressed. Actually, I already was, not only by your pinpoint accuracy of 99% in reply #11, but now you even show knowledge of the condition of our frontwheel bearings, thousands and thousands of miles from where you are. Yes, the bearings are one side shielded, and? Not much of a problem as long as it is the right side. But I'll be a sport: at around 90.000 km, my rear wheel bearing was shot, only... it was not by wear. It was immediately after I had been so foolish to use a pressurized steam washer at a gasstation. Not only my rear wheel bearing, but also the drive chain came out lubeless and the engine would not even start, due to a soaked ignition, knowing the 4 HT leads/plugcaps and possibly even the ignition plate. That's when I learned, one can do overmaintenance.  And this forum is - this is a personal view ofcourse - full of it. Luckily for me I can skip most of it; the most popular thread here is: 'What did you do to your bike today?' and it has 1224 posts sofar... That's telling, don't you think? Yes, this forum is about our bikes, but it is also about us.

[RAFster122s]

Forgive Delta's bickering, he is oft to do this and it is embarassing to watch.

[scottly]

Did you install the caliper piston backwards?

[bryanj]

As i remember it there is a schedule for re greasing wheel bearings in the dealer manual but as you have to hit the inner race to get the outer out of the hole MY opinion is that it will cause damage and be stupid to refit especially at the minor cost of new plus you can fit 2rs bearings which are sealed for life

[Spanner 1]

Ahem... getting back to the problem, I'm with Aussie Dave. If your confident the system is bled with no air remaining then the m/c piston is the wrong size. Easily verified with the cap off the m/c and observing the fluid as you pull the brake lever. If any fluid is visible spurting out of the fluid return hole ( the tiny one ) as you pull the lever, then wrong piston ( too short ). Happened to me on a 78K 750 rebuild kit.....good luck.

[Kevnz]

Update: With the minimum setup, I clamped the piston into the caliper so it couldn't move and tried various bleeding methods to no avail. So I plugged the outlet of the m\c and started pumping and the lever was still spongy, but, at least bubbles were coming out. After 1\2 an hour or so the lever eventually went rock hard, so m\c = OK. So I just reassembled the whole system back on the bike and started again, bleeding from the m\c. Bubbles were coming out, albeit very tiny, and only after pumping up a lot and then releasing. But the lever was very slowly firming up, and after about an hour of this I've ended up with a firm lever and working brake. So really, no idea what the cause was, but it's fixed. I will keep a very careful check on fluid levels and for leaks, but, for now, looking good. For a while I was seriously thinking about finding a new hobby To think we do this for pleasure.
Anyway, thanks for all the input Guys. Knew I could rely on you.
Kev

[Kelly E]

I use red brake grease on the bleeder valve threads. Sometimes air can get in that way during bleeding. It also helps prevent the bleeder valve from seizing in the caliper between services.

[RAFster122s]

Got a brand for that red brake grease Kelly?

[dave500]

i use teflon tape on bleeder threads.

[Deltarider]

Ate

[Kelly E]

Got a brand for that red brake grease Kelly?

No I don't have a brand. Every time we order master cylinder or caliper kits from brakecrafters.com they come with a small container of red grease for assembling that is more than you need. With all of the bikes we've done over the last couple of years we have 8 or 9 containers of it.