Brake Bleeding Problems!! Wisdome appreciated

[Bluegrass40]

In advance, I apologize for lack of pictures.. My gloves were covered in brake fluid and I didn't to be handling my phone.

I'm working on a rear disc conversion. As part of the conversion, I switched to an FZ80 master and booster.

Here is the master I have....

I stated by bench bleeding the master. No problems here.

- Then I started bleeding at the rear drivers side caliper. I backed off the bleeder screw, attached a hand vac pump and pumped it up. I kept vac on it but after a minute saw no fluid coming out. I checked the reservoir and found that there was no change in fluid level.
- I then backed off the rear line connection at the master and noticed that there was no fluid coming out of the port???? The reservoir was full. I figured that gravity would allow it to weep out.
- Out of curiosity, I put the vac pump hose right on the rear outlet of the master and pulled vac... a lot of vac..and no fluid came out???? I figured then that there may be something blocking the port.
- I pushed on the brakes to see if one of the seals was blocking the ports from a piston seal that was not fully retracted or something.. fluid squirted out. I was confused.
- Then I pulled the master off to verify that the piston was fully retracted. It was.
- Next I pulled snap ring off the master to inspect further. Things started to make sense, but I wanted to get a second opinion. It looks like the way the rear piston and seals are oriented, rear outlet of the reservoir is not communication with the rear outlet port of the master when the piston is fully retracted. Once you start to stroke the piston, they are now in communication. This would explain why I could not bleed the rear with a hand vac pump and why no fluid would weep out of the outlet of the master when then the fitting was removed.

Can any one validate that this is all working properly? It looks like I will just need to recruit my wife to work the peddle while I bleed the rear brakes.

Any and all comments are appreciated!

 

[shawnfj40]

Yes it is a good idea to have someone help you bleed the brakes. Many Masters work that (progressive) way.

 

[snaggletto]

I have a mity vac tool and it did not work effectively for brake bleeding. Maybe you have a different tool, but I found that having someone press on the brake pedal was 100x more efficient.

 

[diogenese]

That's not right. The reservoir should be open to the master cylinder bore only with the piston fully retracted so fluid can return from the brakes back to the reservoir. Any amount of travel on the master piston should close off the port to the reservoir and force fluid to the wheels.
It is possible that the servo pushrod is not adjusted properly and not allowing the piston to come back fully.

 

[Bluegrass40]

That's not right. The reservoir should be open to the master cylinder bore only with the piston fully retracted so fluid can return from the brakes back to the reservoir. Any amount of travel on the master piston should close off the port to the reservoir and force fluid to the wheels.
It is possible that the servo pushrod is not adjusted properly and not allowing the piston to come back fully.

I didn't think it was right either. I pulled the master from the booster and verified that the piston was fully retracted.

 

[diogenese]

Are there any check valves inside the middle of the master piston? It may have a residual check valve that has stuck shut with lack of use.

 

[Bluegrass40]

I did some investigation today. It looks like the seal on the rear piston is parked right in line with the small compensation port (I think that's what it's called).

I put a small wire through the hole and it was definitely running into the rubber seal. I don't think that this is how it is supposed to be. I believe that the seal should sit between the large port and small port. Any comments or thoughts?

I connected a rubber hose to a section of line, put some fluid in the reservoir and tried to vac it into the tube.

Very little if any fluid moved. The I blew in the hose and was able to get bubbles to show up fairly easily. I think that when blowing, it flexes the seal down. When sucking, it it pulls the seal against the hole. The seals don't seem swollen and the piston is definitely all the way retracted (at least there is no gap between the piston and the retaining clip)

Def confused.

 

[Fast Eddy]

Why not punt the pump and have someone pump the pedal for you? I use a bleeder helper tube with a check valve at the caliper so I can pump it by myself. It was cheap and works great.

If you f' with it long enough you'll f' up that seal.

On most rigs, the line from the frame is closer to the right side, so you would want to start on the left side. Same for the front, so LR, RR, LF, RF.

 

[ferg]

Is there a piston stop screw? If so could it be that the piston is/was not in the correct position prior to stop screw being installed? This was discussed before somewhere else and found to be the cure for that problem.

 

[Bluegrass40]

Good thought. It is installed correctly. I also removed it so that it did not restrict the position at all and there was no change.

 

[Bluegrass40]

Why not punt the pump and have someone pump the pedal for you? I use a bleeder helper tube with a check valve at the caliper so I can pump it by myself. It was cheap and works great.

If you f' with it long enough you'll f' up that seal.

On most rigs, the line from the frame is closer to the right side, so you would want to start on the left side. Same for the front, so LR, RR, LF, RF.

Thx for comments!

I'm conceded that the fact that the seal is over the compensation port will make the master not operate correctly so I want to be sure it is operating correctly before moving forward.

I did start on the left rear ( drivers side). I agree with your order for bleeding!

 

[Fast Eddy]

I'm conceded that the fact that the seal is over the compensation port will make the master not operate correctly so I want to be sure it is operating correctly before moving forward.

You should bleed it and make that determination once the lines are properly filled with fluid. My guess is that the front-piston seal will move out of the way just-in-time. You're overthinking it.

 

[Bluegrass40]

You should bleed it and make that determination once the lines are properly filled with fluid. My guess is that the front-piston seal will move out of the way just-in-time. You're overthinking it.

@Fast Eddy

That's a good call. I'll report back in the next few days.

 

[Pin_Head]

When the MC pistons are fully retracted, they should be open to the reservoir so that fluid will flow by gravity when you open the bleeder. If not, then something is wrong with the MC.

When I worked in a high volume shop that did an average of 10 brake jobs a day we always had 2 mechanics bleed the brakes because it always worked the first time quickly and we had two independent people who could testify that the brake pedal was fine when the job was done.

 

[sggoat]

X-2. Hydraulic systems are just that-hydraulic. They have in-compressible fluid in them. If you get fluid flow BACK into the MC, then there is a compressible fluid in the system(read air). Two folks working is always good.