Brakes still soft after rebuild

[Blapper]

No offence intended to embee's advice, just an alternative view:

I have found the best way to bleed brakes is to buy a whacking great syringe and reverse fill the system. If you have one of these twin 'racing' hose set ups, just fill one caliper until you see fluid entering the reservoir, then do the other filling the reservoir up the the max line. I've only ever had perfect results from that system, and a wind of ptfe tape around the threads of the nipples would be insurance against paint eating drips. Split set-ups like the standard SV systems are a little less simple to fill as they have a splitter, but just do the same, it works.

I do have a vaccum kit and don't like it as it is trying to such fluid out downwards while air bubbles are trying to go upwards plus it drags air past the nipple. There are some nipples available for around £27 for three that may stop that, I'll find out next time I rebuild my calipers. You may find ptfe tape helps there too. My brakes are ROCK hard.

[SV650rules]

Originally Posted by Blapper

No offence intended to embee's advice, just an alternative view:

I have found the best way to bleed brakes is to buy a whacking great syringe and reverse fill the system. If you have one of these twin 'racing' hose set ups, just fill one caliper until you see fluid entering the reservoir, then do the other filling the reservoir up the the max line. I've only ever had perfect results from that system, and a wind of ptfe tape around the threads of the nipples would be insurance against paint eating drips. Split set-ups like the standard SV systems are a little less simple to fill as they have a splitter, but just do the same, it works.

I do have a vaccum kit and don't like it as it is trying to such fluid out downwards while air bubbles are trying to go upwards plus it drags air past the nipple. There are some nipples available for around £27 for three that may stop that, I'll find out next time I rebuild my calipers. You may find ptfe tape helps there too. My brakes are ROCK hard.

When I did our cars with MityVac I had to get an 'O' ring kit and put a couple of fat 'O' rings over the nipple threads so that they filled the gap between caliper and nipple even when unscrewed a bit, this stops the sucking in of air by MityVac and also as a bonus stops any dirt and water getting onto the threads when in service. Haven't tried this on the SV yet as not due for fluid change yet.

When the master cylinder piston is in its fully retracted position the line from brakes will have free access to reservoir from a port in top of master cylinder (otherwise how does fluid get from reservoir into brake lines in the first place, and how does the fluid lost from a slave cylinder leak get replaced) and any air bubbles should find their way out of system back into reservoir (highest point of whole system), when the piston starts to move forward a small amount of fluid will be pushed back to reservoir via 'self-bleed' port (sometimes called equalisation port) but this port is closed by piston after a very small amount of movement so that all the fluid now has to go to slave cylinder(s). The Bleed nipple will be designed to be highest point on the slave cylinder and the reservoir will be highest point on the whole system (unless there is a 'loop' of brake hose above reservoir, this is where air can get trapped) so any air bubbles will automatically find their way to one or the other.

[shiftin_gear98]

2 cents,
I'm not an expert by any means when it come to fettling on bikes. I have however bled my brakes a few times, due to 11,000 miles a year commute in all **** bag weather.
I have a big bugger syringe, and bleed them like Blapper suggests (also how you bleed a mountain bike - from my Cycle Surgery days). Never had an issue.
I do also use a toe clip strap to hold the brake on over night, as per Ntecuk's advise.
My brakes have been spot on every time. (probably be a right ******* next time now I've said this)

[Bibio]

tying a brake lever back overnight does nothing to dispel the trapped air, what happens is that the larger bubbles get 'gassed' to tiny bubbles. yes those tiny bubbles do get sent up to the rez over time but they can also get trapped at the banjo union.

when bleeding brakes tap the brake lines with a spanner on the pull stroke, this dislodges the air bubbles that are stuck to the inside liners.

almost every single bleed nipple i have used weeps from the threads so i always wrap ptfe tape on the threads, you need to wind the tape the correct way though.

Syringe = easy. As above.

[Markylemin]

Hi, rather than start yet another brake thread I'll join in this one!

My K3 is driving me crazy with poor brakes, even my wife's CBF125 stops better!
I have exactly the same symptoms as the O/P - soft lever after new seals & pistons. I've PTFE'd the bleed nipple threads as one was a tiny bit weepy (now ok) and I have bled through about 1/2 litre of fluid to no avail.
As a last resort I reverse bled it all with a big syringe and clamped lever overnight but still soft.

Yesterday I tried clamping off each caliper hose one at a time to see if one caliper was the cause of the problem. Lever very firm in both cases.
I then tried clamping the main hose at the splitter end & once again firm lever. I then bled the master cylinder at the top hose union but only fluid & no air.
With no hose clamped the lever is soft again, hitting the bars in position 4 on the span adjuster.

The only remaining bits to renew are hoses & master cylinder seals.

Thanks for reading and apologies for the thread hijack.

[R1ffR4ff]

Originally Posted by Markylemin

Hi, rather than start yet another brake thread I'll join in this one!

My K3 is driving me crazy with poor brakes, even my wife's CBF125 stops better!
I have exactly the same symptoms as the O/P - soft lever after new seals & pistons. I've PTFE'd the bleed nipple threads as one was a tiny bit weepy (now ok) and I have bled through about 1/2 litre of fluid to no avail.
As a last resort I reverse bled it all with a big syringe and clamped lever overnight but still soft.

Yesterday I tried clamping each caliper hose in turn to see if one was the cause of the problem. Lever very firm in both cases.
I then tried clamping the main hose at the splitter end & once again firm lever. I then bled the master cylinder at the top hose union but only fluid & no air.
With no hose clamped the lever is soft again, hitting the bars in position 4 on the span adjuster.

The only remaining bits to renew are hoses & master cylinder seals.

Thanks for reading and apologies for the thread hijack.

I've been though this Umpteen times with my old CX500 rebuilds.Do yourself a big favour and get a new cheap M/C off Ebay.Will save a lot of time and further frustration.

[Bibio]

Originally Posted by Markylemin

soft lever after new seals & pistons.

did you clean the seal recesses out of all the oxidisation before fitting the seals?

did you use RRG to put the new seals in?

did you use the old pads and if so how old were they?

[Markylemin]

Hi Bibio
I cleaned the recesses thoroughly before fitting the new seals.
The inner ones were a lot cleaner than the outer dust seal recesses and neither particularly corroded.

The new seals did get RRG and everything went together with no sticking or forcing needed.

The pads are the old ones and are at least a year old as I've not changed them since I got the bike.
They are stock Suzuki / Tokico HH pads so nothing fancy.

R1ff R4ff, I'm keeping master replacement as a last resort.
Funds are limited this month due to road tax etc so trying most obvious until pay day.

[aesmith]

Originally Posted by Markylemin

Yesterday I tried clamping off each caliper hose one at a time to see if one caliper was the cause of the problem. Lever very firm in both cases.

Not sure I quite follow, are you saying that when you clamp either hose the lever is very firm? Rather than when you clamp both hoses. Either way the part you're pointing to as the culprit is the calipers, since the hydraulic system from lever all the way down to your clamp is firm without sponginess.

Have a look at the caliper when you squeeze the lever through that spongy travel, is anything moving down there?