Trouble bleeding madass 140 master cylinder setup

Status
Not open for further replies.
J

joshtjeerdsma

Joined
Oct 11, 2015
Messages
95
Country flag
I am having trouble bleeding my front brake. I have the 1/2” master cylinder sold by madass 140, like this http://www.tritonmotorcycleparts.com/297620485/product/515646/norton-brakes?catid=146825. I have rebuilt my caliper with stainless pistons and used a new stainless line. I have traditional bled, vacuum bled a ridiculous amount of times, gravity bled, reverse bled,and ziptied the lever down with the master at the highest level a couple of times. The ziptie trick seems to work for a bit, but goes back to bad shortly after. I dont have any visible leaks, and I teflon taped the bleeder valve threads(only the threads) for the last round of bleeding. The lever still comes too close to the handlebar. The new restore is ready for a road test and the weather is warming, so I am anxious to figure this out. I have never had this much trouble bleeding brakes. Anyone else have this problem? Thanks.
 
I also had this issue...could not push any fluid through the system by pumping the lever....went all way to the bar grip with no resistence and any small amount of fluid flow complete reversed when lever returned to rest position.
The issue for me was the lever was not the correct length at the contact point with the new MC piston...so the piston primary cup was already positioned past the middle hole in the reservoir. If you carefully check where the primary cup is situated with respect to smallest hole in the reservoir (near middle of the reservoir), you need the cup to be just a little before this hole, not after it with no pressure on the lever.

You might be able to grind/file some aluminum off the lever contact "tongue"....but be careful not to do too much like I did. I had yo get a replacement lever. Seems only about 1/16" max is necessary to remove on some levers.
 
Trouble bleeding madass 140 master cylinder setup
 
The picture above is one that L.A.B. sent me.
Here's another one that helped me understand the importance of correct rest position of the primary cup.
 
Hi. I saw your post before and have been doing a bit of research and yes I think the lever may be the
problem not allowing the piston to come back far enough. This is my fault. its possible a couple of levers were
installed on the wrong mastercylinders on assembly. There would of only been a small number this has happened to
and looks like you may have one. A way to test this is temporarily replace the lever pivot bolt with something much
smaller in diameter , maybe a 1/8" or 3/16" pin, screw or even a drill bit and then bleed the system.
If this fixes it then you know what to do, a small amount removed from the lever contact area.
Don
 
I will give that a try after work tonight. I should mention that when I did bleed the brakes, clear bubble free fluid came out of the bleeder. Would that still happen if the lever is wrong? Thanks for all the good info.
 
I just had a look at a couple of fully functioning (rebuilt and easily bled) standard Norton disc brake systems.
All of the brake levers have a bit of clearance between the lever end and the fully extended piston.
It's easy to push in the piston with a finger and watch it return to full extension.
Is this the case with these hard to bleed brakes?
 
joshtjeerdsma said:
I will give that a try after work tonight. I should mention that when I did bleed the brakes, clear bubble free fluid came out of the bleeder. Would that still happen if the lever is wrong? Thanks for all the good info.
Click to expand...
Even without a lever installed fluid can flow down the hose to the caliper and bleeder just via gravity since the primary seal is sitting before/upstream of the small hole in reservoir....nothing to stop fluid moving down the path...but will be very slow.
With a lever that keeps the seal past/downstream the small hole, no new fluid can enter the hose/caliper since reservoir is sealed off. When lever is pulled in, only the fluid already in the downstream path is moved further down and this gets sucked back up the hose when lever is released. No fluid can progress through the system and no pressure can build up to operate the caliper pistons sufficiently.
 
Bob Z. said:
I just had a look at a couple of fully functioning (rebuilt and easily bled) standard Norton disc brake systems.
All of the brake levers have a bit of clearance between the lever end and the fully extended piston.
It's easy to push in the piston with a finger and watch it return to full extension.
Is this the case with these hard to bleed brakes?
Click to expand...

If by "fully extended piston", you mean that it's not under any spring pressure, then the answer for the madass kit is "no".
In the madass kit, the piston is moved about 1/4" or 6-7mm, compressing the spring against the bottom of the sleeve, before the lever can be fitted.
The spring free length is about 1.5", full compression is 0.5", so you have about 1" of travel avail.
With the lever installed, this drops to about 0.75" of travel. If my other calcs are correct, it will use about 0.34" of this, less than half, to bring the caliper pistons against the rotor.
 
And, with all respect to Don (madass 140) who knows a lot more than I do about this, I suggest that if you need to make more room, you file back the pivot stop area of the lever, seen in this picture with a round "pad", rather than filing the heel which contacts the piston end. The heel is carefully shaped and has to roll across the end of the piston without falling off.
 

Attachments

  • Trouble bleeding madass 140 master cylinder setup
    brake lever2.webp
    28.9 KB · Views: 300
One test to know if the primary seal is being held to far into the bore, if you try to force fluid up from the bleed screw using a syringe, you just pressurize everything and will blow the hose off the bleed screw...no fluid flow up into reservoir. Remove the lever, letting piston spring push seal well upstream of the small hole, then try pushing fluid in from syringe again and it will flow easily.

I suspect this same issue has lead to the front brake seize ups in hot conditions....when fluid gets too hot, can't expand back into reservoir and can only push against caliper pistons, locking front wheel.
Under cooler conditions, fully bled system feels good...solid lever etc...nothing seems wrong until you try to change fluid one day or get a lock up.
 
If your brake hose goes up above the level of the master cylinder before it goes down to the brake, then every time the bike sits for a while air will enter the brake hose through the master cylinder. One friend of mine had a bike where the only way he could bleed it properly was to turn his bike upside down. He found this out accidentally when one day his bike tipped over and then the brake was way better than he had ever been able to get it before.
 
I put a 3/16 allen key in place of the pivot pin so the lever put no pressure on the piston. I bled it both standard and vacuum to no avail. The fluid came out of the bleeder air free. I did notice when I had the lever off that the piston was leaking around where it comes out through the rubber boot. I didn’t notice this until I had the lever off. Could this be my issue? I haven’t allowed the resevoir to go empty.
 
Maybe you have an inverted or damaged piston seal? There should ne no fluid on inside of rubber boot...it is just a dust cover. The secondary seal keeps all fluid on inside of the sleeve.
 
I'm currently testing my whole stock.
remove reservoir cap and blow by mouth in to the fitting end, air will (slowly) come from the small hole.
while blowing I just depress the lever a little and no more air is expelled.
If you cant blow any air then the the piston is to far depressed already, meaning a little removed from the
lever contact area.
 
Josh, I'll ship you another mastercylinder, you shouldnt be having this much drama.
Don
 
In your original post, you say the lever is coming too close to the handlebar. IF this is your only problem, and the bleeding routine is otherwise normal , then I'd guess your piston is too far back, not too far in.

The cap shims supplied with the kit are designed to address exactly this issue.
Put one on the end of the piston and see if it improves, maybe? If so, select the shim which will position the primary seal/cup just behind the bypass port.
If/when you find the right shim, glue it onto the end of the piston so it can't jump off.
 
Josh, I sent you the original mastercylinder (the one in question) more than 2 years ago. What work have you done
on your brakes before this problem surfaced. Its been ok up to now? Don
 
Status
Not open for further replies.

Similar threads

65tiger
Brake bleeder flowing when.
Replies
12
Views
450
65tiger
65tiger
W
72 Disc Brake issue
Replies
15
Views
605
wbehning1
W
The yaki
Norton or triumph back master cylinder fitted ??
2
Replies
20
Views
582
L.A.B.
L.A.B.
N
Braided brake hose for '75 MKIII
Replies
7
Views
278
Desmopower
Desmopower
Jonez69
1973 850 Commando front brake M/C question
2 3
Replies
41
Views
964
lazyeye6
lazyeye6
Back
Top