Front brakes.

[Graeme77]

I had to take the lines of my front brake. After i re-fitted and bled it, it felt crap. Could get the lever all the way back to the bar. Dont know what they were like before though, never ridden it and didnt notice.

Found one of the hoses had a split outer so ive ordered new ones from hel.

Took the caliper apart and it was all a bit stuck, after cleaning it all up i found the piston is very poor. Very corroded right where the seal would be.

Are there any new replacements? Its an F1 and has a bigger piston, 42.8mm or there abouts.

I have another caliper but it has a smaller piston. Its not great either, but if this is also 750 i might be able to get a new piston. Is this my only option, or are the bigger ones available?

I might see if the engineers in work could turn me up a new one from stainless (i assume aluminium is no good?) as a last resort.

Also, thinking about the master cylinder. Is there any way to check this? I want to get all the parts ready so i can re-fit everything in one go at the weekend.
Could the master cylinder seals be why the lever felt soft and could come back to the bars?

Could i test it by putting a solid bolt in the outlet and see how it feels? I guess it sould be nice and solid, if not, theres a problem?

[Spitfire]

The front brake piston on the F1 is no longer available, I replaced mine with a stainless one from eBay US, however there are others about,
here's discussion on the subject from a while back
http://www.sohc.co.uk/index.php?topic=2792.0
Here's more
http://www.sohc.co.uk/index.php?topic=2308.0
More
http://forums.sohc4.net/index.php?topic=23037.msg244590#msg244590

Cheers

Den

[Grizzly]

This caliper was only fitted to the K7, K8, F1 and the automatic. The calipers fitted to the 550's and 400 four are the same style but are smaller. They were rubbish when new and 30yrs of use won't have helped. Good used calipers are like hens teeth. This might have something to do with the fact that they aren't sided and a lot of people have decided that a double disc conversion is a great idea

I believe you can still get the master cylinder repair kits. But be aware that the bores inside the cylinders wear, which means no amount of bleeding and/or repair kits will fix that.

Keep checking Silvers. a while back he had a few new calipers for the automatic in stock, people twigged (different part no same part) and they went quick.

Using a stainless piston is fine.

My brakes were a real bitch to sort out. Read 4 calipers and 3 mast cyls. You would have to be dead unlucky to have the same problems as me. keep at it, it will come good in the end

[david451]

I had to take the lines of my front brake. After i re-fitted and bled it, it felt crap. Could get the lever all the way back to the bar. Dont know what they were like before though, never ridden it and didnt notice.

Found one of the hoses had a split outer so ive ordered new ones from hel.

Took the caliper apart and it was all a bit stuck, after cleaning it all up i found the piston is very poor. Very corroded right where the seal would be.

Are there any new replacements? Its an F1 and has a bigger piston, 42.8mm or there abouts.

I have another caliper but it has a smaller piston. Its not great either, but if this is also 750 i might be able to get a new piston. Is this my only option, or are the bigger ones available?

I might see if the engineers in work could turn me up a new one from stainless (i assume aluminium is no good?) as a last resort.

Also, thinking about the master cylinder. Is there any way to check this? I want to get all the parts ready so i can re-fit everything in one go at the weekend.
Could the master cylinder seals be why the lever felt soft and could come back to the bars?

Could i test it by putting a solid bolt in the outlet and see how it feels? I guess it sould be nice and solid, if not, theres a problem?

If you clamp the flexi pipe then that eliminates the caliper and the lever should be solid.

There's two ways to bleed brakes the one where you open and close the bleeder as you pump, and that's shit. The best way to do it is to pump the lever 5-6 times, hold it back, release the bleeder and close it once the pressure has released, just a second. Keep doing that until you get a good brake, and no air.

[kaceyk2]

Sometimes I am astounded by learning something new.
Thought I would share this with you.
My rally car building and driver neighbour showed me a magic trick to bleed bike brakes.
Take the claiper off the fork leg, and put a piece of wood inbetween the pads.
Get it held up in the air HIGHER than the master cyclinder on the handlebars.
Then do the bleeding, the air bubbles will now rise to where you want them to rise too....... The bleed nipple!
This really works well.

Tip no. TWo:  Use silicone brake fluid, it will polish chrome and paint work instead of wrecking and stripping it, well worth the extra couple of quid. It's purple, and goes in er, (sweary word coming up avert your eyes)
harleys.
there said it, but I did use a lower case h.

Hope this helps.

[david451]

Sometimes I am astounded by learning something new.
Thought I would share this with you.
My rally car building and driver neighbour showed me a magic trick to bleed bike brakes.
Take the claiper off the fork leg, and put a piece of wood inbetween the pads.
Get it held up in the air HIGHER than the master cyclinder on the handlebars.
Then do the bleeding, the air bubbles will now rise to where you want them to rise too....... The bleed nipple!
This really works well.

Tip no. TWo:  Use silicone brake fluid, it will polish chrome and paint work instead of wrecking and stripping it, well worth the extra couple of quid. It's purple, and goes in er, (sweary word coming up avert your eyes)
harleys.
there said it, but I did use a lower case h.

Hope this helps.

When my bikes came one of them horrible things fell on the delivery man, blood all over the place so there was. The daft step thing folded up and it pinned him to the side of the van. All huff and puff so they are and want to fall over all the time.

Silicone fluid or dot 5 is not compatible with all applications because of its poor lubrication properties, it compresses more, wont absorb or displace water like dot 4 and needs changed more often. dot 4 absorbs water in the system that's why it changes colour to brown and if you change it every 2 years it's fine, and cheep anorl. The last thing is that you are not meant to use silicone if it had mineral in the system.

The racing lads use it but I don't like it, it has a habit of collecting air.

[Spitfire]

I fitted braided hoses and Speed Bleeders to my calipers, they work great.
http://speedbleeder.com/
Cheers

Den

[Graeme77]

The saga continues.

I temporarily bodged the caliper piston, ill get a new one, i just wanted to get some pressure in the system.

I fitted the new Hel lines but it was still the same. Pumping the lever gets a little pressure (but it still comes back to the bars).

I stripped the master cylinder (that circlip is a pain when its corroded in!) and cleaned it all out. Bore looks great but i havent measured it. Anyone know the wear limit? I can measure internal bores very accurately at work.

I put it back together once all the crap was out (lots of gell type stuff) and re-bled but its still the same. I figured it would be. The seals looked ok, but thats no guarantee!

So, if the master cylinder bore is ok ill order a re-build kit. Are the repro ones any good?

No fluid is leaking from the lever, but i guess the pressure could be escaping past the piston cup.

Bit annoyed as i failed my bike test yesterday, shouldnt have, but thats another story. Unfortunately it means spending another 240 quid so funds for repair items are thin on the ground now

[Spitfire]

I used the master cylinder rebuild kit from David Silvers and it worked great, there is a very tiny hole in the master cylinder connecting the cup with the bore, it is very easy to block, is it clear on yours ?

Cheers

Den

[Graeme77]

Yes, i checked that right at the begining.

There are re-build kits on ebay for 20 quid, worth it, or should i go for a genuine one?

Anything i can save a bit of money on is helpful, but its no good if the cheap parts are cr*p LOL.

[Graeme77]

Had another play today.
I blocked the master cylinder to see if its creating pressure. It seems to be, lever goes solid when its blocked off.
I took the caliper off and bled it with the nipple at the highest point. I bled it from every connection too.

Then i let the piston pump out, filling up the reservoir with fluid as needed, then clamped the piston back in the caliper to back bleed it to the master cylinder.

So, MC seems to be ok, im 99% positive there is no air in the system.
Caliper seems to work properly and doesnt leak.
No other leaks.

But i can still get the lever back to the bars
Not as easily as before, but still can.

Ive left the lever clamped to the bars, ill leave it overnight and see what its like tomorrow.

I bodged the piston by filling the pits with JB weld (i know, ill get another). The seal looked good.
If there was any problems with this though it would leak right? Still might when i eventualy get pressure. I want to make sure i can get pressure before i buy a piston.

Only other unknown is the fluid. I had it already. It had been opened before but only a little was used. Lid was replaced nice and tight, been on the shelf for a couple of years i'd guess.

This leaves me with two possibilities i can think of.
1, the fluid is cr*p.
2, the master cylinder seals arent good enough to pressurise the whole system.

Any other thoughts?

Not expecting any revelations here, just talking out loud as it were.

I know these are old bikes, with old brakes, but the lever should go solid right?

[Bryanj]

No the lever never went "solid" even when new, as long as the wheel is locked with the lever about 3/4 back thats about it, also old/new fluid can absorb moisture even in a what you thought was a sealed container

[Spitfire]

As Bryan has said, always use new fluid, bin the old stuff.

Cheers

Den

[Graeme77]

I had left the lever tied back to the bars last night and its a bit better today.

The main news though is i tried the brake levers on a suzuki van van and a honda vrf750 last night and there the same as my cb.

I assumed the lever should go solid, but it doesnt. Even on the vfr and new suzuki i can get the lever back to the bars.

Looks like my front brake is fine.

I need to bleed it agian anyway as the lines arent linked up as i want them, i was too busy trying to get it to work!
So ill get new fluid for the final set up.

Thanks.