T140 brake problem

pipercolt78z

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I have a 1977 Bonneville 750. I replaced both brake master cylinders with new ones. I have installed the front one in accordance with the shop manual but still can't get any brake pressure. While squeezing the brake lever I can see fluid being forced out of the bleed hole. If I open the bleed screw some fluid will gravity feed through the bleed screw. What am I missing?

Thanks
Bob
 

Rocky

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Grandpaul or Rudie should be along later and may be able to help.
 

grandpaul

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It's often tricky getting the last tiny bubbles out of the system.

Leave the master cylinder only half full, and take care to cover everything around with plastic to prevent brake fluid getting on paint, chrome, etc.

I typically remove the caliper from the rear, orient it such that the bleed fitting is the highest point, and let the bubbles "float" to the top while bleeding. This takes a helper or a lot of patience.

The front can be trickier. I do a full system bleed as usual, then repeatedly pulse the lever the slightest bit, just at the beginning of the piston's travel, then GENTLY pull it all the way in and let it snap back; almost every time, a large bubble results. This is where some brake fluid can squirt out. Another helpful tip in this process is tapping the brake lines with the handle of a screwdriver, do break the bubbles free to rise with gravity (tap from the bottom up while pulsing the lever).

TAKE CARE to keep adding brake fluid if/when it gets anywhere near the openings at the bottom of the reservoir, or near to uncovering the nut that holds the reservoir in place.

Lastly, some people report good success pulling the lever all the way in, then tie it to the grip with a nylon zip tie or heavy rubber bands; leave overnight, and bubbles will rise on their own.
 

pipercolt78z

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It's often tricky getting the last tiny bubbles out of the system.

Leave the master cylinder only half full, and take care to cover everything around with plastic to prevent brake fluid getting on paint, chrome, etc.

I typically remove the caliper from the rear, orient it such that the bleed fitting is the highest point, and let the bubbles "float" to the top while bleeding. This takes a helper or a lot of patience.

The front can be trickier. I do a full system bleed as usual, then repeatedly pulse the lever the slightest bit, just at the beginning of the piston's travel, then GENTLY pull it all the way in and let it snap back; almost every time, a large bubble results. This is where some brake fluid can squirt out. Another helpful tip in this process is tapping the brake lines with the handle of a screwdriver, do break the bubbles free to rise with gravity (tap from the bottom up while pulsing the lever).

TAKE CARE to keep adding brake fluid if/when it gets anywhere near the openings at the bottom of the reservoir, or near to uncovering the nut that holds the reservoir in place.

Lastly, some people report good success pulling the lever all the way in, then tie it to the grip with a nylon zip tie or heavy rubber bands; leave overnight, and bubbles will rise on their own.
Hi Grandpaul
Thank you for the fast reply. Would you mind calling me? I have a few questions and to much is lost in typing. I live in Western NY so I am on Eastern time. I am up till midnight each night so don't worry about calling late. I am anxious to get the bike on the road. My number is 765-346-2622. I do not answer area codes that I don't recognize. If you don't mind, what is your area code? Thanks in advance.

Bob
 

Rudie

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1977 Bonneville 750. I replaced both brake master cylinders with new ones. I have installed the front one in accordance with the shop manual
While squeezing the brake lever I can see fluid being forced out of the bleed hole.
"bleed hole"? From what you posted on TriumphRat, I'm guessing you mean the vent from master cylinder to reservoir? That and you can't get any brake pressure are likely because you haven't adjusted the master cylinder correctly in the mounting.

Plus the "shop manual" procedure was superseded decades ago (likely after someone realised advising the remedial class to blow bubbles into a poisonous liquid would probably decimate the class ...), the latest procedures are here. The adjustment procedure for both cylinders is:-

. turn the cylinder clockwise into the mounting casting until all the play between cylinder and operating rod is just taken up;

. turn the cylinder one more turn clockwise;

. turn the cylinder clockwise as much of another turn as is necessary to line up the flat in the cylinder thread with the locking grub-screw, even if that's nearly another complete turn;

... i.e. you never turn it anti-clockwise.

Although it it isn't in the Lockheed instructions, if you have good close-up vision (with glasses if necessary), you can check the seal position is correct in the master cylinder with a very bright and focussed light (e.g. LED penlight) - shine the light into the master cylinder vent closest to the hose end and pull the lever (front) or push the rod (rear) slowly - shortly after the piston starts moving, you should see the seal pass under the vent hole?

With the master cylinder adjusted correctly, I use a similar procedure to @grandpaul but with more patience - fill the reservoir about half-full, turn the forks fully to the left so the master cylinder's the highest part of the system (turn the mounting/switch cluster around the handlebar if necessary), "pulse the lever" a couple of times to start the bubbles appearing in the reservoir, then just leave it, usually overnight. A little more fluid usually needed before I go to bed, nice firm lever in the morning. (y)

Never understood the point of "pulling the lever all the way in, then tie it to the grip with a nylon zip tie or heavy rubber bands"; by definition, the hose and caliper(s) are then cut off from the reservoir, can't see how air'd get out or fluid'd get in?
 

grandpaul

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Never understood the point of "pulling the lever all the way in, then tie it to the grip with a nylon zip tie or heavy rubber bands"; by definition, the hose and caliper(s) are then cut off from the reservoir, can't see how air'd get out or fluid'd get in?
As I said "some people report good success"; I've never needed to do that...
 

triumph david

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I have used the tie wrap trick a few times and it worked a time or two but seems only to work when it is hot weather, probably has nothing to do with anything.
 

CarlS

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I have also tried a few times. And it worked. Now that you mentioned it, every time I tried it, it was warm weather.
 
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