Disk Brake Pressure

nickguzzi · Jun 25, 2014

Dosen't look right or very confidence inspiring.
My Guzzi, like most others, has linked brakes. The relatively small master cylinder just didn't displace enough volume to move the air through the system. By conventional methods, it was impossible to bleed it satisfactorily from "dry".
Most bikes also have have a fairly rollercoaster path for the brake line to follow. Have you tried unbolting the caliper and hooking it up higher than the mastercylinder overnight? Some times the air is trapped as very fine bubbles and leaving it on high allows Archimedes to do the work for you.
What worked reliably and consistently for me was a Gunsons Easy Bleed. Only about £15 many years ago. The device uses a lowish air pressure from a tyre to force the fluid through without the "backstroke" of releasing the lever which could be drawing in air.
It sounds as if you have totally overhauled the brake system. Mistakes have been known ...
If your system uses banjo bolts, have you checked them? The washers are use once really - people do anneal them but that doesn't get rid of the chewed up surfaces.

CHARGER · Jun 25, 2014

Well I haven't had much road time with it yet, just round the block a few times and the front didn't feel close to
locking up and didnt have any slight brake pressure until where I pulled it back to in the pic.

Is it true that the pressure can get better with road time?

I'll re bleed the rear with the line down as I think it definitely has issues, ill get it registered and
take her for a few good easy rides and see what comes of it.

Thanks Lads

CHARGER · Jun 25, 2014

Nortiboy said:
CHARGER said:

Upper loop scenario sounds very plausible in my case thanks for that tip! Makes sense I will definately look at that.

Click to expand...

I have the sleeved master and if I could get the lever to the position you show, the front wheel would be locked up solid. When originally fitted I had air "in the loop" and a spongy brake. After all else failed, (including vacuum bleeding) I cracked the brake hose very slightly at the master cylinder while holding down the lever and air came out. Fixed.

Interesting will try this also

concours · Jun 25, 2014

CHARGER said:
Well I haven't had much road time with it yet, just round the block a few times and the front didn't feel close to
locking up and didnt have any slight brake pressure until where I pulled it back to in the pic.

Is it true that the pressure can get better with road time?

I'll re bleed the rear with the line down as I think it definitely has issues, ill get it registered and
take her for a few good easy rides and see what comes of it.

Thanks Lads

Your front brake is not right. A good hard lever at less than 50% travel is tp be expected. Keep retracing until until you find it.

kerinorton · Jun 25, 2014

phil yates said:
L.A.B. said:

phil yates said:

Modern brakes don't run out of lever pull at 50%. They come back to where yours is.

Click to expand...

Indeed so, but of course it ain't a modern brake, but a modified old brake, and with the sleeved (presumably his is 13mm?) master cylinder and a braided line I wouldn't expect the lever to pull back quite as far as that, not with one finger.

Click to expand...

Maybe not with one finger Les, but again mine is similar easily with two. I am thinking yours probably has that hard dead feeling when you pull the lever in and it suddenly stops. Mine actually feels like a modern brake. So if mine needs bleeding (which it doesn't) I'd advise everybody to get some air into the brake line, it makes the brake feel good.

NO BLOODY WAY MAN. AIR EXPANDS WITH HEAT , THEN NO BRAKES AT ALL. USE YOUR HEAD.

kerinorton · Jun 25, 2014

nickguzzi said:
Dosen't look right or very confidence inspiring.
My Guzzi, like most others, has linked brakes. The relatively small master cylinder just didn't displace enough volume to move the air through the system. By conventional methods, it was impossible to bleed it satisfactorily from "dry".
Most bikes also have have a fairly rollercoaster path for the brake line to follow. Have you tried unbolting the caliper and hooking it up higher than the mastercylinder overnight? Some times the air is trapped as very fine bubbles and leaving it on high allows Archimedes to do the work for you.

iT WOULD BE BETTER TO DO IT THE OTHER WAY ROUND, THEN THE AIR WOULD ESCAPE BACK INTO THE RESERVOUR, ESPECEAILLY IF YOU PUSH THE PISTONS BACK ALL THE WAY INTO THE CALIPER.

phil yates · Jun 25, 2014

it makes the brake feel good.

NO BLOODY WAY MAN. AIR EXPANDS WITH HEAT , THEN NO BRAKES AT ALL. USE YOUR HEAD.

Are you telling me you took this seriously?????

Phil

lwmcd1 · Jun 25, 2014

The absolute best way I have found to bleed brakes is at the nipple on the caliper it'self. I use a syringe with the proper size short hose that fits over the nipple, remove the fluid from the master cylinder then slowly inject the fluid being careful not to over flow the MC. This pushes all the air ahead of the fluid as it fills from the nipple up.

Time Warp · Jun 25, 2014

The front lever on my (stock piston) Mk2a M/C goes nowhere near that.
The lever from the resting position moves only a small amount (seal past the reservoir bleed hole) and stops hard for the perfect wooden brake.
Maybe a Mittyvac or similar might help or syringe from the caliper up.

Edit - Missed the last post.

CHARGER said:
Front lever pressure

CHARGER · Jun 25, 2014

Think what I am going to do is drain all fluid, buy a Garden Pressure sprayer from Bunnings, rig up some fittings
to it, put brake fluid in it and pump it straight from the caliper nipple up nice and slowly with straight lines.

lwmcd1 · Jun 25, 2014

CHARGER said:
Think what I am going to do is drain all fluid, buy a Garden Pressure sprayer from Bunnings, rig up some fittings
to it, put brake fluid in it and pump it straight from the caliper nipple up nice and slowly with straight lines.

LOL I wouldn't go that far. A simple syringe will do the job. A pressure sprayer and you will have a shower of brake fluid everywhere.

ML · Jun 25, 2014

Charger,
I agree with the others (except one) that the travel is excessive. A good point was made to tie the lever back to the bar overnight, it does work.
Another thing that may be of help - the Mk2 lever and Mk3 lever have different pivot symmetry. The Mk3 brought the lever closer to the bar, but does not fit well at all on the Mk2 cylinder mount.

batrider · Jun 25, 2014

Finally a real answer...

phil yates · Jun 25, 2014

ML said:
Charger,
I agree with the others (except one) that the travel is excessive. A good point was made to tie the lever back to the bar overnight, it does work.
Another thing that may be of help - the Mk2 lever and Mk3 lever have different pivot symmetry. The Mk3 brought the lever closer to the bar, but does not fit well at all on the Mk2 cylinder mount.

Being the "except one" I consider myself very lucky. Baxters in the USA obviously have done a great job in transforming a wooden feeling brake into a progressive feeling one. I thought the MkIII might have had something changed in the brake but no, my second MkIII has the standard horrid wooden feel. But not for long it won't.

If I could try Charger's brake, I'd have a better idea whether he has a problem or not. There is little point in trying to describe my brake's feel any further if you are used to nothing but a wooden feel. You can have it on your own.

Interesting point you make about the MkIII pivot symmetry. That in itself changes the 50% position relative the handlebar. But if it stops dead at this point, it's wooden (my opinion).

If Charger does indeed have an air problem, all the advice offered sounds better than I could offer.

All I started out saying was mine is about the same. A progressive feeling brake and better stopping power than normal.

Phil

contours · Jun 25, 2014

I am the furthest you can get from having expertise on this problem since I only learned the procedure for the first time ever a few months ago (and why did it have to be the brake on my Norton). I bled the air out multiple times, But wasn't able to improve the feel in the front brake lever until I traced a very small leak in the line junction where it fastened to the bottom of the triple tree. I was making such a mess that I ignored the slight wetness in that area for days. Finally, after I tightened the nut really well I got good pressure for the first time. Just a thought.

CHARGER · Jun 26, 2014

Ok so I got my pressure sprayer, drained the front system, pushed pistons in as far as I could, pulled caliper off to get braided line dead straight and reverse filled from the nipple.

Made sure I primed the line from the pressure sprayer with no air bubbles then put it straight on the opened nipple and pushed fluid up noting no air bubbles at all between sprayer and nipple. Noticed the master slowly fill with tiny air bubbles going to the top. Tested brake and no pressure at all? Should I have had pressure then?

I then proceeded to bleed system traditionally pumping the lever and cracking the needle, I did this for probably two master cyl resovoir fills until I found pressure and as no more air coming out, after that process I'm back at square one with the same pressure and can pull lever to the bar if I try hard.

I made sure all connections are tight, I thought a reverse fill would have done the trick, I left the lever out while doing this is that correct?

Time Warp · Jun 26, 2014

A pressure sprayer

One good source for large syringes is veterinarians who tend to horses. (fwiw)

JimC · Jun 26, 2014

Pressure bleeding brake systems works well. I use a master cylinder cap with a nipple and a small pressure sprayer, sometimes called a weed sprayer, on any brake system I work on. Never had a spongey brake yet. I'm pretty sure the reverse pressure bleeding, pressurizing from the caliper nipple, will work on non-ABS brakes, too. I'm not too sure how well reverse bleeding works on a brake system with ABS. The thing I like about bleeding from the master cylinder rather than the caliper is that you are expelling old fluid rather than forcing it back up the system.

lwmcd1 · Jun 26, 2014

JimC said:
Pressure bleeding brake systems works well. I use a master cylinder cap with a nipple and a small pressure sprayer, sometimes called a weed sprayer, on any brake system I work on. Never had a spongey brake yet. I'm pretty sure the reverse pressure bleeding, pressurizing from the caliper nipple, will work on non-ABS brakes, too. I'm not too sure how well reverse bleeding works on a brake system with ABS. The thing I like about bleeding from the master cylinder rather than the caliper is that you are expelling old fluid rather than forcing it back up the system.

Definitely more than one way to skin this cat."expelling old fluid rather than forcing it back up the system." True that,but I drain the old first. ABS is not an issue with my Norton, too primitive

motorson · Jun 26, 2014

I don't have a pressure bleeder right now but I plan to build one like one I had built before. Take a canning jar and put two holes in the lid. Solder a copper tube into one hole that goes all the way to the bottom of the jar and one in the other hole that you can put a rubber hose onto. Fill the jar with brake fluid and hook a line from the long copper tube to your brake bleeder screw. Gently blow into the other tube and fluid will be forced up through the caliper into the master cylinder.

Disk Brake Pressure

nickguzzi

CHARGER

CHARGER

concours

kerinorton

kerinorton

phil yates

lwmcd1

Time Warp

.......back to the 70's.

CHARGER

lwmcd1

ML

batrider

phil yates

contours

CHARGER

Time Warp

.......back to the 70's.

JimC

lwmcd1

motorson

Similar threads