Paging the brake issue isti

The VFR, bless it, still has problems with the back brake, despite me
refurbishing the caliper.

Before I spend any more money, am I right in thinking the following symptoms
point to a knackered seal in the master cylinder:

* Not much going on, on the initial prod of the pedal.
* Hit it again, and you get some braking, and slightly more if you prod it
again.

Leave it a bit longer then hit it again, and there's not much going on
again.

I've bled all five bleeding points (linked brakes innit, PITA) again, and no
air came out, just pure clean fluid.

TIA

--
JackH

98 Honda VFR800FiW
05 Sachs Madass
03 VW Passat TDI Sport
89 Vauxhall Nova 1.3 Pearl

 

The rear brake on my 748 is notoriously bad to bleed, but the
easiest way of bleeding it properly is to take it off and hold
it *above* the master cylinder so that there is no air trapped
in the line or the caliper. Take it off, string it up for a bit
then go back and bleed it thoroughly while it's off. Once done,
reassemble.

 

Ok... well I've stripped the master cylinder off the bike now, so the system
is nice and full of air anyway.

Methinks I'll be calling that nice Mr Silver in the morning and ordering a
master cylinder service kit.

On the plus side, I had it all fired up today, and can confirm that a bung
free Staintune end can is a beautiful thing. ;-)

--
JackH

98 Honda VFR800FiW
05 Sachs Madass
03 VW Passat TDI Sport
89 Vauxhall Nova 1.3 Pearl

 

No, you've just got air in the system somewhere. Bleed it properly.

 

Arse.

Ok... I suspect, given the complexity of the system, this will take 'some
time'.

<looks on ebay>

Anyone used either of these with any degree of success?

http://tinyurl.com/62lpve (1)
http://tinyurl.com/6x4qp6

(1) Yes, I know it needs a supply of compressed air - got access to that.


--
JackH

98 Honda VFR800FiW
05 Sachs Madass
03 VW Passat TDI Sport
89 Vauxhall Nova 1.3 Pearl

 

....is the wrong answer.

I used the back brake all the time on the last one.

That aside, it's not good enough for an MOT as is.

--
JackH

98 Honda VFR800FiW
05 Sachs Madass
03 VW Passat TDI Sport
89 Vauxhall Nova 1.3 Pearl

 

I've got one of those - completely empties a small motorcycle system in
seconds. Mine doesn't seal too well as the bike nipples are pretty small
compared to other vehicles so drags air around the seal.

I've used a Mityvac (that looks very similar) and it worked very well.

My new method of choice is simply a big syringe which is controllable and
effective.

 

New seals might help, but like champ says it still sounds like there's
air in the system. Depending on the age of the brake fluid a complete
change of fluid might also help. If air is in the system there's a
possibility that other contaminents are also in there.

Dunno the particular system, but on one of my trials bikes I had
similar symptoms when all was working fine with the brake pedal and
caliper, but the disc itselfwasn't sitting correctly in the caliper.
Someone, the previous owner possibly, had used a wrong sized wheel
spacer. It was only ~2mm too thin, but it meant the disc warped as the
brake was applied, so the pads were only applying pressure
'differently' ... might be worth a re-check. Not identical symptoms as
air in the system, but it felt the same through the pedal ... no brake
effect unless you pumped it.

 

It's not a knackered seal: that would mean a fluid leak. There's air
in the system still. Pump the pedal half a dzen times, hard, before
opening the bleed nipple. That really builds up pressure and expels
air that sometimes gets trapped higher up the line.

 

Ok, well I've gone for one of those - I kind of owe my mate a few favours
for letting me do all the work up at his workshop, and he can take custody
of it once I've finished with it.

Plentiful free supply of those down any one of a number of dark alleys in
Brighton, I should think. ;-)

--
JackH

98 Honda VFR800FiW
05 Sachs Madass
03 VW Passat TDI Sport
89 Vauxhall Nova 1.3 Pearl

 

'
That's probably because there IS air in the system but you've not managed to
get it out. An old indian trick is to get the caliper higher than the
reservoir and THEN do the bleeding. Obviously you have to have something
between the pads to take the place of the disc and fingers aren't
recommended.

I drop an allen key between the pads/pistons, coz there's always on which is
exactly the right size.



--
Beav

VN 750
Zed 1000
OMF# 19

 

So it would seem.

Anyway, as per my other post, hitting it with a decent bleeding tool as soon
as it arrives.

--
JackH

98 Honda VFR800FiW
05 Sachs Madass
03 VW Passat TDI Sport
89 Vauxhall Nova 1.3 Pearl

 

And if violence doesn't work, use more violence (I'm not whooshed either)

--
Beav

VN 750
Zed 1000
OMF# 19

 

Two wrongs don't make a right. There has been no definitive
proclamation as to the relative moral value of three or more, however.

 

Well... the Mityvac isn't the solution to all bleeding problems. It
doesn't seem to work well at all on the K100 sidecar; even with a
previous set of brake lines/calipers.

Odd that 'cos it worked well on the K75.

 

I've tried a variety of bleeders over the years and so far I've not found
one that's perfect for all jobs. Getting the caliper above the reservoir
works VERY well and using a **** off big syringe to shove the fluid UP the
system if the caliper removing is too much hassle also works well. Very,
VERY well.

Have you got a high point in the caliper where air can sit and not be
disturbed?


--
Beav

VN 750
Zed 1000
OMF# 19

 

My experience is similar and have recently going down the syringe route.
Very successful with bike systems - so far.

 

No. It's strange 'cos the K100 and K75 are virtually identical and I
didn't have problems with the K75 (or any of the previous K100s I've
owned (four of them I think).

 

Well other than a brake line that's porous, I can't think of anything that
would stop the system from bleeding.
A brake system needs..
A master cyl that pumps but doesn't suck
Brake lines/banjo's that don't leak
Calipers that don't leak
Pistons that move
Seals that seal
Nipples that close properly.

If you've got all that, get a syringe (big one from t' chemist) and a length
of tubing, attach the tubing to the caliper nipple, open the nipple and
squeeze the syringe. The slower the better because it avoids frothing the
fluid. Pump the fluid UP the system and the job "should" be sorted.


--
Beav

VN 750
Zed 1000
OMF# 19

 

You kinda forgot to say what the syringe should be full of, air or brake
fluid?