Why is my front brake dragging?

Hello to those who know me (I spy Andy Hewitt at least),

I've got a D reg Honda VFR750FG (the first model year). It's very nice
- approaching 100,000 miles and still running well, Hagon monoshock,
taper roller head bearings, stainless steel braided brake lines, etc.

But I have a problem. I've replaced the original front discs with
pattern discs - solid, rather than semi-floating as Honda intended.
I've had the front brake working fine with the new discs, but now it's
dragging. It started dragging quite badly, probably due to winger crud
and me not spraying the pistons regularly (rubber lube - I've found that
WD40 beloved of many for this job destroys my dust seals rather
quickly). So:

I've had both calipers apart, cleaned them very thoroughly along with
the pistons, replaced the seals, and put the whole lot back together
with new pads with grease (high temperature waterproof grease or copper
slip, depending on where) in the right places and DOT 4 fluid from
Halfords (DOT 4 is what the master cylinder filler cap says to use) in
the hydraulics. The brake pins are fairly new and checked to be still
straight, as are the pad pins. The various rubber boots are sound. The
caliper mounting brackets got cleaned too - including cleaning out the
holes the brake pins go into.

I've not given the master cylinder any dismantling this time around - it
got stripped, cleaned, and the piston and seals replaced not all that
long ago, and what on Earth could have gone wrong with it? (I know, I
know - *something*'s wrong). I've got two bits of stainless braided
brake line running directly from the master cylinder banjo bolt - one to
each of the front calipers with no splitter (a previous owner did that).
I've fitted a bleed nipple equipped banjo bolt to the front brake master
cylinder and I use it after bleeding the calipers to squirt out any last
bit of air that's trapped at the top of the hose runs.

But the front brake still drags a touch - both calipers contribute a
little. I can't see anything obviously wrong. The caliper mounting
brackets seem to be undamaged, unbent, and (this was tricky to check -
feeler gauges and a bugger to get 'em in it was, I can tell you) and
also in the right place relative to the discs in the left to right
sense.

When I let go of the brake lever, I have a definite feeling that the
brake's not letting go all the way - which is quite right, 'cos it's
not. Despite a great deal of bleeding and the fact that the front brake
is working very effectively, I have a feeling that there's still a bit
of air in the system.

Anyone got any ideas? Can a bit of air left in your front brake
hydraulics cause this sort of thing? If so, how the blankety-blank do I
get it out 'cos bleeding the brake over the course of three days hasn't
sorted it. If not - well, could someone run down the things that can
cause a hydraulic disc brake to drag so I can check 'em all?

Cheers
Rowland.

 

Righto. I didn't see how it could be - but, well, one looks for straws
to clutch, y'know?

I know the very bit I need to grab - and now I know what it's for

Excellent! I've got something definite to look for tomorrow - ta.
Check for a spurt, and even if it looks okay to me, I'll check the lever
movement and if that looks okay - well, it's time for a master cylinder
strip and clean, I reckon.

Cheers,
Rowland.

 

(good - as I said elsewhere, I didn't see how it could be)

Okay... My front brake is, alas, still dragging.

Since I last posted, I've had the master cylinder off the bike, *very*
thoroughly cleaned, and put back on the bike with a master cylinder
rebuild kit to replace piston, spring, and all the seals.

The relief port is clear - before I put the master cylinder back on the
bike, I looked through it and saw a clear hole (tricky to get light up
the master cylinder bore to check this), then I sprayed brake cleaner
through the port and it shot through into the master cylinder bore
apparently unimpeded - I didn't try a probe on the grounds that I'm
working with an aluminium alloy casting and I don't want to damage the
inside of any holes. I kept things clean after I'd cleaned them.

I can't say I can see much of a spurt of fluid coming out of the hole
you mention when I operate the lever, but there seems to be something
and I certainly got lots of bubbles coming out of both the holes when
the air was pumping out.

The brake lever seems to be the shape Honda intended, and looking at the
operation of the brake lever against the master cylinder piston, I'd say
that's all exactly as it should be - the bits that need greasing have
had it, and there's no sign of the lever applying force against the
master cylinder piston when you let it go. The front brake lever action
feels different from what it did before I replaced the master cylinder
bits - different, and now it feels as if it's working correctly (I'd
cleaned and lubed the lever side of things before doing the calipers, so
the difference in feel has nothing to do with that).

But the front brake is still dragging.

I'm baffled by this one. I've cleaned the calipers and the master
cylinder pretty damned thoroughly, replaced all the seals, replaced the
master cylinder piston and spring, checked I've got a clear relief port
and correctly fitted brake lever, and I've still got a dragging front
brake.

Does anyone have any ideas? (He whimpered, pathetically.) The brake
lines are routed such that they're not responsible for forcing the
calipers somewhere they don't want to be.

Could it be something slightly wrong with the mounting of the calipers?

Rowland.
(really clueless on this one)

 

VFR750FG - 1986 model. A pair of Nissin two piston sliding calipers
each attached to an alloy bracket that bolts onto a fork leg.

The left hand caliper has a mounting bracket that pivots at the top so
that under braking, the bottom mount of the bracket presses up against
*that* nobble set into the fork leg - which is the anti-dive actuator
valve. I doubt any of that is relevant, but you never know. There's a
needle roller bearing in the top pivot point which has been rusted solid
the whole time I've had in the bike. It wasn't until I paid some
attention to Mr Haynes that I saw there was supposed to be a bearing in
there, and it took quite a bit of cleaning to make the fact obvious.
But that knackered bearing didn't make the the brakes bind then, and I
doubt it's doing it now. Why haven't I replaced it? It'll be a hell of
a job to remove the old bearing cage, and I'll have to take the fork leg
to someone with a hydraulic press to replace the equally knackered bush
the roller cage runs in.

Righto. I'm Mr Silly, I am. I've been using Silkolene RG2 racing
grease 'cos it's waterproof and v. high temp.

But Mr Haynes (now I've read *all* the brake section) says to use poly
butyl cuprysl grease or high temperature silicone grease designed for
brake applications.

So that's something to try.

Er, no?

In my case, the seals do appear to be symmetrical. Mr Haynes doesn't
say anything about fitting them one way or the other and there's nothing
mentioning anything at all on the seal packets aside from `Honda' (as in
Honda parts, not pattern - I've had an unhappy time with pattern seals
in the past) and a part code and all that. But it's a thought, isn't
it?

Hmm. Well. I suppose it's down to Halfords for some grease buying,then
off with the calipers and have a fiddle.

I wouldn't mind if I could find something that was obviously wrong, and
then fix it. But - well, maybe it is the grease. On the other hand,
I've had the calipers not sticking before and I've long used the same
grease on 'em.

Cheers,
Rowland.

 

partially seized / sticky calliper pistons springs to mind , might need a
strip down and rebuild or just freeing up cleaning etc

its amazing how much crud gets around the callipers , if the bikes not been
used for a while look for oxidation on the callipers and pistons / slides
etc
usually white in colour

 

I've seen calipers (and clutch baskets) that are sticky. Nothing to do with
hydraulics
but because the alloy case is worn away where the front edge of the brake pad's
steel backing plate rubs on it. My car's brakes have a stainless steel strip
to prevent this happening.

 

Thanks for the thought, but, erm...

The calipers have both been stripped and cleaned in the kitchen sink
with careful attention paid to the dust seal grooves with our patented
`cut up brillo pad and matchstick' method. (I did sort of mention this
in my first post in the thread). Then they get dried on a radiator.
The master cylinder got a similarly thorough cleaning - n matchstick,
but I did clean up the brake fluid reservoir sight glass with wet-n-dry
and some T-Cut. It still looks cracked (no actual leaks, but...) and
yellowed, but you can see through now.

Dunno about `amazing' - I mean, roads are pretty grubby places.

What amazes me is that Honda didn't fit brakes with rubber boots over
the pistons, as Suzuki does with a lot of its brakes. That `just stops
the crud getting to where it can do harm' and all that.

What I find reduces the rate at which the crud and corrosion gets to be
a problemm is to spray rubber lube on the caliper pistons as often as I
can be bothered (I'd like to do it every week, but guess what? After
lubing the pistons, I use brake cleaner and clean cloth to get the
excess rubber lube off the disc and pads). It doesn't destroy the seals
like WD-40, and it does help keep things freed up.

Cheers,
Rowland.
(used to cleaning crud off)

 

Hmm. Righto. I'll look at things in that light too. What it seems,
basically, is that `everything needs to be spot on including a bunch of
fiddly stuff you wouldn't necessarily have thought of'.

Argharghargh.

Cheers!



Rowland.

 

That's the badger.

Something similar, I'd guess - my 86 VFR's got pretty much the same
arrangement as my very poorly and sadly neglected non-running '84
VF500F2 (now *there's* a hooligan's motorcycle if ever there was one)
and - IIRC - the mid-80s CBX1000 owned by the bloke at the tyre shop I
use.

(btw, VFs and VFRs are very different - a lot of the VFs had problems of
some sort, while the VFRs were designed to deal with 'em. VF500F2s, for
example (`Interceptor' in the US), had weak bottom ends and inadequate
top end lube. VF400s were basically fine, except that they were hard to
maintain correctly and mostly owned by young hooligans who rode 'em into
the ground and didn't do the maintenace. I knew one such in the mid
1980s. I forget the list of VF750 woes, but the VFR750 was the
high-reliability design to overcome the reputation for awful reliability
that the VFs had given Honda)

(which is P+R Tyres, 4 Jamaica Street, Liverpool L1, 0151 707 1616 - I
find them a very nice place to do business with if only because if they
get something wrong (and who doesn't, from time to time?), they're dead
good at sorting it out with no hassle. Used to be PR Tyres, but there's
been a change 'cos the old owner was a bit too flaky - looked to me as
if he was more interested in his rock band. And no, aside from buying
tyres, I'm not connected to 'em at all - I just like the service and
attitude I get.)

What you'd expect, I expect ;-)

Righto - that's a start. Now to find something similar here...

Righto. What sort of asymmetry have your seals got? I've just looked
at a new front brake hydraulic seal (I keep a set `in stock', just in
case). I put it on a flat surface and checked it with a steel ruler -
it looks to me as if all sides are square and I can't see any sign of
asymmetry at all. Am I being stupid?

(Honda part no. for the seal: 45209-166-006 if anyone cares.)

If you can tell me what to look for and which way round are they
supposed to go with the brakes you're used to, I could see if I could
spot the same asymmetry and fit my seals the same way. After all, if
I've got no guidance at all here and I've been fitting 'em any old way,
it's hardly going to make things worse if I pick one way or another, is
it? And if I make a log of what I'm doing and it doesn't work - well,
I'll just try 'em the other way round next time. Two attempts max, and
it'll be right, right?

<grin> Yes... I shan't disagree with you on that point.

(But it's a lot more use than the Clymer manual I had to get for my
VF500. I'm told that modern Clymer manuals are pretty damned good and
far superior to Haynes manuals - which are famously iffy and generally
not very useful - but the Clymer VF500 manual is rotten.)

Yes, I suppose it would. Urgh. But if there's no other way to find out
which way round to fit the seals...

(I've used a genuine Kawasaki manual - there was this KH250 to look
after, and it was a Kawasaki manual or nothing. And could we understand
what it was saying? Well, eventually, probably, using all our
ingenuity, we worked out what we needed to. Probably. Mad, mad, *MAD*
bike when my mate got it for £30 with no airbox and jetted up to suit
the increased airflow. A power band as wide as a human hair but when it
hit it - well, you went deaf for starters. If that's what the 250's
like (when in mad mode - it calmed down a lot when he fitted an airbox),
how could anyone ride the bigger triples?)

Okay.

One problem: the shops I could get to today (Sunday) didn't have any
grease that matched the spec of what I need. Copper slip is all they
had on offer - both Halfords and Motorworld. Well, I've got a tin of
copper slip (hmm - two. One nearly empty, and an unused replacement).
It seems my cupboards contain pretty much the entire range of greases
one can buy at Halfords (and then some).

They hadn't heard of anything other grease for brakes.

(what a surprise: clueless shop staff in Halfords. I was once presented
with a pack of fibre washers by a Halfords shop assistant when I asked
if they had any copper sealing washers suitable for a hydraulic brake
system - yes, I did specify exactly that, being used to Halfords bods
being clueless)

Does anyone have a suggestion as to where I might find some suitable
grease for brakes?

Sil-Glyde doesn't seem to be a brand that's available in the UK.

I gather I need: poly butyl cuprysl (PBC) grease or high temperature
silicone grease designed for brake applications.

Somewhere that I can pick it up quickly would be good, 'cos I've either
got to get my MOT done by Tuesday or SORN this beastie... (I've had more
than one problem with it - and then I crashed and... Argh. Really - I
mean, *BOTH* bloody brake lights switches have broken recently, and the
rear one was a hydraulic switch I fitted about two years ago. Why me,
oh Lord, why me?)

Given that I can't find the right grease at the moment, I'm considering
trying the brakes with spray-on silicone rubber lubricant on the brake
pins/rubber bushes - not for more than a test ride or two in the dry,
just to see if that frees it up.

I've done some Web searching, and not been able to come up with much.

<http://www.forthgear.co.uk/htm/accessories1.htm>

Mentions some Würth silicone grease. Would that be the thing?

I've searched the Web. Even Castrol doesn't seem to make either of the
greases specified - Castrol Red Rubber Grease is one of their classic
products
<http://www.castrol.com/castrol/sectiongenericarticle.do?categoryId=9002
192&contentId=7002857>.

It's vegetable based - not silicone or PBC - but apparently suitable for
brakes:

<http://129.35.64.91/bpglis/lubtds.nsf/technicaldata/DA9E707906915D4C802
56C4E005B813F?OpenDocument>

Anyone got any idea where I could track down what I need?

I did find: <http://www.triumphspitfire.com/wirewheel.html>
which is a US car magazine that apparently sells PBC grease via its
spares organization. Not terribly useful for me.

Yep to all points - thanks. I replaced the seals but not the bushes -
they were all fairly new and look undamaged even internally, but I think
I might be replacing them in any case. The slider pins were all
replaced fairly recently - they're clean and uncorroded and checked for
straightness as best I can without taking them off again (I *know* I've
not done anything idiotic like ride off with my disc lock on since
fitting 'em not long ago - I'm pretty damned certain that they can't
have got bent).

I think the drag probably is caused by something to do with the calipers
not moving freely, so it's `replace all the bits you replace after
cleaning and checking everything' time, isn't it?

I've got stainless braided brake lines - I think the inner is PTFE
(fitted by a previous owner - they're actually a little bit too long,
but I'm pretty sure I've routed them to avoid this being a problem). I
doubt this'll be the problem, but thanks for mentioning it. It's
something to bear in mind that I wouldn't have considered.

FWIW, the standard front brake line arrangement is `Single brake line
from master cylinder to splitter mounted on the lower triple clamp, and
two lines from there, one to each caliper'. I've got two lines running
direct from the master cylinder, one to each caliper, and two spare
threaded bolt holes on the lower triple clamp where a splitter used to
be mounted.

I think you're barking up the right tree there.

It's just a tiny bit of residual drag - but it's definitely there, and
it's enough to affect the handling and acceleration.

(I doubt anyone would notice the acceleration effects unless they knew
the feel of what the bike was supposed to do when you cracked open the
throttle. I'm not worried about not having full thrust except that it
means something's not right and needs fixing before I come a cropper due
to poor maintenance).

Righto - easy and effective. Ta.

Cheers again,
Rowland.
(thinking `Sheesh! At least my old CZ had drum brakes that just worked
if you kept 'em adjusted[1] and cleaned.')

[1] I had a 1976 Model 476 Mark V deluxe (honest - and now *you* try
telling the copper who'll pulled you over that's the model of the bike
you ride when he's looking at a shabby Iron Curtain 125cc learner bike).
One of the `deluxe' features was a twin leading shoe front brake. It
was in fact damned good - saved my bacon many times.

The other `deluxe' features? Indicators, alloy rims, and an oil pump.
The paintwork was stonking quality. CZs had a lot of nice touches - as
well as that unmistakable Iron Curtain mankiness. But more style than
those bloody MZs, and better brakes, *AND* less starting trouble (hehehe
- sorry, I can't help it. Your particular MZ might have been fine in
that department - not all have been.)

 

sorry never picked up your original post

 

[snip]

No worries - but, erm, isn't it available for reading at the start of
this thread in your newsreader?

Admittedly, the first two posts in this thread have expired from my
local news spool (I was using a 7 day expiry on this newsgroup - I've
just upped it to 14 days). But it's still on the news servers, isn't
it? And the last time I heard about Outlook Express's handling of
Usenet news, it didn't do auto expiry at all (okay, that was about, oh
god, a decade ago, I think[1]).

Rowland.
(curious, not at all critical or anything)

[1]

It's all Macs here with a definite lack of any MS software. That's not
out of careful avoidance but because I'd have to buy the stuff, which is
rather expensive and not particularly useful for me, so I know nothing
of OE from personal experience. The newsreader I use looks a bit like
this:

<http://www.fen-net.de/mac/macsoup.html>

(I say a bit like that because that's the `classic' MacOS version, and
the UI has gone all fancy-dancy MacOS X Aqua swish shiny stuff now.
Stuff that the prophet Steve Jobs - high priest of the cult of Mac -
thinks we ought to want to lick. Argharghargh. Someone ought to
explain to these loons that it's just a bloody computer! It's just a
tool! Anyway, the page I pointed at shows off the main reason I use
this particular newsreader - the graphical thread display and explains
quite a lot about it, but in German).

 

No blueyonders news servers can be a bit flaky sometimes

 

Ah - all is clear.

Cheers
Rowland.

 

Gotcha - thanks. I'm pretty sure there's no such asymmetry on the seals
I've got. I've looked and looked again with brighter lights and a steel
ruler as a makeshift square and I can't see it. I'll have another look
later, just to triple check. Right now I'm waiting for the Araldite to
set - one of those blasted plastic piston caps dropped off. A 100W
lightbulb in an Anglepoise under cover is providing heat...

Before I'd got that far, I'd fiddled with the other caliper and
concluded that the dragging probably is down to something up with the
movement of the caliper pins in their slidey holes - one runs entirely
in rubber, the other runs into a bore in the caliper mounting bracket
with a rubber boot seal to the caliper (and the indicators are back on.
The word `perpetrated' is appropriate to describe what I had to do in
that case).

Cheers,
Rowland.