Bubbles or F**ked Master Cylinder?

[buster]

Got back to UK last night, a pair of discs I'd won off ebay were ready and waiting, so this morning I fitted them. Well actually first in the info is last time I was back I stripped and cleaned the 6 pot callipers, didn't pop any pistons out but did force them out a little to give a thorough clean, put all back together and left alone (this was December).

So I fit the discs (very rusty but looked sound) to my track front wheel, fit front wheel, pump brake lever to get get pads seated, went off down the road slowly to try and bed them in and slim the layer of rust and every time I braked I'd have to pump the lever several times to get pressure, when pressure there brakes fine.

Went off up the bypass and same thing, brake discs are ok, not warped and with pressure stops fine. I'm going to bleed the brakes anyway as I've also got a HRC kit for the back brake so might as well do both front and back.

Just wondering if by forcing (gently pushing back) pistons back in I've shagged the front master cylinder?

[Ascalon]

Short answer is, no. You are highly unlikely to have upset the master cylinder by pushing the pistons back.

What could be the problem is that the discs are not sitting exactly right on the wheel, in relation to where the old ones sat.

Try this, get down infront of the bike, with it stood upgright and pump pump the lever till you feel good pressure. Then release the lever altogether. Then, very gently press the lever a small amount till you see the pistons move out to the disc again. Does one side contact first? does it deflect either disc at all? If so, you may need to shim the disc.

What happens is that the side that contacts first will retract a little, but the side that has further to travel retracts the normal amount, but ends being further from the disc. The next squeeze of the lever has this distance to make up as well as normal distance so the lever feels longer, but will be OK, once full pressure is on.

Is this on a Kawasaki by any chance?

A

[Mr.Pigdog]

Its quite common for corrosion to build up in the caliper seal seats(behind the seals),this usually makes the dust seals act like springs by gripping onto the piston surface and retracting it rather than letting the piston slide past the seal-only answer is to pop them seals out and clean the corrosion away-i use car alloy wheel cleaner,brake cleaner and a 90degree pick.Also try removing the caliper complete with pads in and pumping the pistons and pads out so you have to wedge the calipers back onto the discs(working the pads out and over the disc)

[buster]

Cheers guys.

Yep its a kawasaki, I've got some 4 pots on order for it/bidding against so I'm not wanting to spend too much! Stripped the callipers off one side this morning and checked, one side of the pistons are reluctant to move, so stripped the halves and yep, loads of corrosion around the dust seals, so cleaning them up at the moment not going to renew the seals as I've got the 4 pots coming.

Seeing as its only short term, is it worth running without the dust seals?

[Mr.Pigdog]

Yes mate-people do remove the dust seals for racing to reduce stiction,short term it will be ok-i pity the poor mechanic for the next guy though.The dust seals tend to stretch when they been binding for a while and you have to kinda cram them back in-they end up gripping the piston then so you're probably better off leaving them out for the short term.

[buster]

I've put them all back together, including the dust seals, yep still binding, so waiting for the 4 pots. The corrosion was awful, all crystallised.

[gurninman]

The Tok 6 pots are pretty shite if you get a bad set - I remove the dust seals as a rule, and it seems to work ok.

Thankfully my 6 pots are pretty decent, just clean them up every week or so and they're fine.Nissin 4 pots are *very* good on the ZX6/9s with 6 pots

[Ascalon]

OK, before you go putting anything back toegther, get yourself some Castrol red rubber grease. It is compatible with the rubber seals and is your best friend when rebuilding brakes.

Use it liberally on all exposed surfaces on the caliper seal seats and dust seal seats. Instead of smearing the pistons with fluid when reassembling, use the lightes smear of red rubber grease instead. It will ensure that the pistons move smoothly in in the seals withour rocking the seals in the seats, particualrly if they are now a bit more generous that they were previously due to removed corroded material.

I learned this the hard way on two ZZ-R400s and one ZZ-R600 and aZX-636R with the six pots. Thankfully I had it figured out before I did the ZXR750!

A

[buster]

Only problem with the dust seals is half of them are knackered and deformed that no amount of red rubber grease will save them. Last time I stripped them fully I did this and a year later, same problem but worse.

[buster]

This is getting beyond a joke!

Third time I've now stripped them down, this time I've removed the dust seals, pistons not binding. Still go for the brake and end up with no pressure and have to pump the lever, brakes bled until no bubbles from either side, lever still comes all the way back to the bar, so I've put a cable tie on to allow any trapped air to rise to the top.

Fortunately I've won some 4 pots off ebay and order a complete seal kit and master cylinder kit, I had a similar problem with my 1000RX a few years ago and that turned out to be the internal rubber seal on the MC.

Just occurred to me, will I need different lines for the 4 pot callipers?

[lorenzo]

The lines'll be OK, they're in a slightly different position, but only by a couple of mm. If you're swapping from nissins to tokicos or vice versa then you'll have different threads on the banjo bolts.

The other thing of course, is that if you're going from a 6 pot system then yu'll probably want another master cylinder on there, something that's designed to work on a 4 pots system, otherwise you'll find that your brakes are very on/off. I did the same swap on my 7r, and had this issue, it felt OK on the road but as soon as I started doing any heavy braking, or trailing the brakes going into a bend on the track, then I found it really tricky to be able to gentley release the fronts off, they were either on or off. I stuck a master cylinder off a late zx6r on there and it felt way better.

Last months mag (or was it the month before) had the exact same thing with the brakes on the gsxr1000 project, where they were trying the different master cylinders. It's not just about power, but about feel too, the ability to control the power.

[thorlz]

i'm more than likely talking shite but any..

Had a simllar problem a few years ago after fitting second hand discs together with my existing pads

I figured that the discs / pads were not worn square to each other and as such, not all of the pad was making contact with the disc, this also caused the pads/disc to flex giving piss poor performace.

I found that with new set of pads they soon worn to the correct contour of the disc

as i said at the start though i may be talking bollocks

[Mr.Pigdog]

You could try reverse bleeding them--get a syringefull of brake fluid and make sure your reservoir is low on fluid then squirt the fluid through the bleed nipple.Also find it can help to have the calipers and pads free from the disc-pump the pads out then wedge them back onto the disc so they're being forced apart.also undo fork pinch bolts on axle and make sure the front wheel is running central.

[buster]

Cheers for all the tips guys Especially Loz, mm that's going to cost me more money, another master cylinder, wonder if I can convince Mrs B I need a new one made by Brembo or the like.

I'm really pissed off at the moment as all my bits I've ordered from Wemoto have arrived, the ebay TL1000S callipers I've won, good condition, 2 business days delivery haven't, now in day three in the Buster waiting for new callipers house and no reply to my emails

The guy has 400+ positive feedback, I just reckon its buggeration factor, I'd like them by the weekend so I can rebuild and hopefully have a decent ride across the tops to Huddersfield next week.

[lorenzo]

See how you get on with the master cylinder, you may like it, you might not? So long as you don't go and buy a bling one there's no real reason why another would be any more expensive than the one you've got at the moment, which you can sell to fund the new one, IYSWIM.

[buster]

Right the saga is now ended, the story goes something like this....

Received the callipers finally on Wednesday, only a week after the 1-2 business days delivery, opens the box, LHS calliper is the first one I go to fit , top mounting bolt OK, bottom mounting bolt spins and spins, remove calliper and closer inspection reveals its been drilled out and re-tapped. Contacted seller, he said they were ok when sent, is it a scam. On closer inspection on the listing photo you can just make out its oversize, point this out and sent the LHS one back to him, RHS is perfect, so rebuild with the wemoto kit I bought.

I then scoured a few on-line sites and used an ask the breakers form for a LHS calliper first one got back to me in 15 minutes, Abbey (?) in Nottinghamshire, £45 for a matching model year calliper, bonus, only problem is I'd found a refurbished pair from a guy in Stamford under the name of bits4beans, top guy received them the next morning and they were perfect, lovely job done on them. I still bought the other calliper from the breaker, I figured that I want a 6R trackbike so I'll have a pair ready, refurbished and waiting, when I buy one. Also ordered some standard EBC pads for the 4 pots and fitted them at the same time. Will later get some EBC HH pads for the track front wheel.

Whilst fitting the refurbished callipers I noticed the LHS disc was not running true, mmm swaps wheels over and hey presto, no more problems, all the palaver was due to a saucer shaped disc, saucer shaped but didn't cause brake judder. After reading Heds' post regarding Brakes4U I rang them Thursday morning and managed to secure the last pair for my model and they arrived Thursday morning, fitted them but didn't have time to swap the wheels as Friday was my last full day in UK and my only chance in the break to get out on my bike.

So Thursday night I finished off bleeding (must get a hydraulic bleeder) the brakes, fitted the HRC rear kit, found the Goodridge banjo pressure bolt pitch was not right for my rear master cylinder so left it without rear brake switch actuation, hardly use rear anyway and on the odd occasion I do I always apply the front, its a 10 minute swap at MOT time for the standard pegs anyway.

Found HRC kit ok to fit, only fiddly bit was due to the cold, the pipe was rather stiff and nearing brittle, old trick of hot water and submersing pipe made it easy to fit onto the master cylinder.

So a couple of pics, I reckon the HRC kit could do with being a bit shorter still, so will tackle that next time I'm back.

Surely there should be 6 pots on a Kawasaki?

Valtermoto rearsets (see Tootall if you like them) and HRC (HRC on a Kawasaki )

[lorenzo]

How does the front feel now you've got the new pads, calipers and discs on?

[buster]

Only had one decent ride with the new setup, pads are standard EBC and not HH like I had on the 6 pots, also it was damn cold but initial thoughts are that I don't think initial bite is as good, standard pads don't hiss as nice as HH one's, I didn't find the brakes grabby and due to conditions some trail braking was needed and response seemed fine.

I'm looking forward to being back in April to give it a real good workout, however, I think its more likely to be a road trip this time rather than a trackday. I certainly don't think they're any worse than 6 pots, I've just got to ascertain if they are better and if so how much better.