Brake Bleeding ??

[Tim Kay]

Getting to final stage of front suspension upgrades and can't seem to get the front brakes to bleed.

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The m\c reservoir appears to have two compartments each feeding one booster which are dedicated to either the front or the rear brakes. The forward compartment, which directs fluid to the front booster, is empty and I can’t figure how to get it filled with fluid.<o></o>
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Pumping the pedal, holding it down while opening a bleed screw – air comes out but no fluid or fluid level change in the reservoir. Any help?<o></o>
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[Jim Cowden]

Take the brake pipe out of the master at the front port.
Use the same bleeding method as you have been using.
finger off hole when pedal depressed.
Finger over hole when pedal released.
Bleed master first.
Hook up pipe
bleed brakes.

It is the air in the lines moving back and forth because the lines are long and lack of gravity(mastercyl height to cal height)Meaning they are at similar heights.

I use a tool called a mityvac,you can generate vacuum by squeezing the handles.
I have a container with 2 outlets on it,1 to the mityvac 1 to the bleeder nipple.
This is the best thing,I cant get a clutch at all on my 40 or a decent brake pedal without this tool.
It is better on master cylinders as well.

Jim

 

[Tim Kay]

Thanks Jim. Into the garage I go to give it a try.

 

[Tim Kay]

Before I disassemble the whole thing to figure it out maybe someone can instruct me on the mechanics of the master cylinder in terms of the reservoir(s).
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I have never fully inspected a single master cylinder that feeds two separate lines. What I can’t comprehend is the two reservoir compartments mounted on top of the m\c that seem to be isolated from one another. Does one feed the other? If so, how?

Jim, per your suggestion I went to the auto parts and bought a mityvac. I'm sure it will come in handy in the future as well :thumbsup:

 

[Jim Cowden]

Yes the reservoir is one container,it has a dam wall between the front and rear reservoir outlets.
The reason is a safety issue.
If you run out of brake fluid on the rear brakes you still have fronts as the fluid is isolated via the dam wall.
Better to have 1/2 than none.

It is 2 masters in one cylinder.(dual master).
As it is depressed the primary piston travels down the bore applying pressure to the front brakes, at a given point the primary piston then starts to push the secondary piston and apply the rears.

Did you try the mityvac by sucking the fluid through.
Or are you suspecting the master has failed.

You have trouble sometimes with the air.
Another technique but you need 2 people.
Bleed the master on the bench.
Or on the car( with brake pipes disconnected).
If you have trouble at this point then it likly the master.
Hook up pipes after bleeding.
Open 1 nipple at caliper.
Person in car must hit brake pedal as hard as they can and I mean hard.
Close nipple.
lift pedal
open nipple and repeat operation.
Do each nipple
repeat if you have to.

This forces the air out.
They call it Zepher bleeding.
Jac and Russ will know what that is.

Jim

 

[Jac Mac]

Early MkII IIRC?

Oops, sorry Tim, didnt read the whole post.
Both those fluid compartments should be able to be filled from the same Cap on the M/Cyl prior to even thinking about bleeding etc. The 'Dam' between front/rear must be blocked or faulty to prevent you topping off the fluid. IIRC those type master cyls in the original application would be mounted with the firewall/pedal end lower so that the cap itself is horizontal, but this should not interfere with fluid replenishment to both compartments.

 

[Jim Cowden]

Opps myself I missed that bit on the res not filling.
Only got the bit on getting air out of the lines.

Jim

 

[Tim Kay]

This is a big help Jim and Jac Mac. It’s beginning make sense.

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No, the master was working correctly prior to new brake upgrade.

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Did you try the mityvac by sucking the fluid through.

Yes but of course just air because the front reservoir is empty.

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One concept eluding my simple mind right now is how does the forward (I assume the primary, front brake) reservoir fill with fluid? As in the pic above it was empty.

The 'Dam' between front/rear must be blocked or faulty to prevent you topping off the fluid.

Jac Mac, this might be the culprit. I have put my finger inside the reservoir to feel for any blockage. I can not find anyplace that remotely feels like a passage way to the front reservoir.

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I removed the front brake pipe away from the m\c (leaving the rear brake pipe connected) and managed to ‘back door’ some fluid into the front reservoir. I feed a clear line from a full container of fluid and connected it at the m\c in place of the brake pipe then pumped the brake pedal quite a few times (oh yea, I am doing this solo, it’s 1 am right now!!). Slowly but surely fluid was sucked into the front reservoir. I stopped when the fluid reached about half full and essentially quit taking more. Unless I can figure how the fluid is replenished in the reservoir then bleeding the lines will be futile.

 

[Cliff Beer]

Tim, sometimes the "top" of the dam can be pretty high, meaning that you have to fill the darn thing almost right up to the level of the screw cap to get any brake fluid to flow over the dam and into the other resevoir. If, for some reason, you can't get the forward reservoir to fill at all, even with filling almost right up to the level of the screw cap then you could take the reservoir off the cylinder and drill a hole (perhaps 1/4") in the dam about 7/8th of the way up it (make sure you clean out all the plastic filings). Then re-install and fill and you should have fluid in the forward resevoir.

I recommend using either a pressure bleeder or a vacuum bleeder - either of these are better than the pump the pedal routine.

 

[Tim Kay]

After a couple hours of sleep and further examination of the reservoir I find there are several tiny holes at the very rim where the screw cap goes on. As you suggest Cliff, I put fluid to the level of the rim and put the cap on, vacuumed from a bleed screw and voila, some fluid sucked right into the forward reservoir. But under continuous vacuum only the initial amount came forward and stopped.
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Now that I see that the fluid has to enter the front reservoir via the holes in the rim at the screw cap, is it ‘vacuum’ that keeps drawing the fluid through?<o></o>
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Still not sure how it is the fluid replenishes as I bleed the front lines. I am assuming it must need adequate vacuum, the cap screw tight, and somehow the fluid is pulled up through from the rear reservoir…….defying gravity?<o></o>

 

[Jim Cowden]

It is probably not spilling over because the master is not at the angle it was origanaly intended to sit at on the fire wall.
Have you considered drilling another hole lower down but still at the top.

I would like to apologise again for miss reading your origanal post.

Jim

 

[Howard Jones]

OK. Here's the deal. Take a pare of long nose pliers and a 1/8" diameter steel rivet. A nice nail will work. Hold the rivet by the long nose pliers and heat the rivet up with a candle or gas stove or what ever. Get it good and hot.

Now pierce the dam between the front and back at the bottom so that it forms a passage through it between the front and rear reservoir. One is enough and be careful not to do anything else with the hot rivet.

Done. I did mine that way 10 years ago. Has worked fine ever since. This is a common fix on GTD's like yours. Don't worry about the safety thing. This is a race car and needs to be maintained like one. Check things like the master cylinder often. (A lot more than you road car).

 

[Howard Jones]

OK. Here's the deal. Take a pare of long nose pliers and a 1/8" diameter steel rivet. A nice nail will work. Hold the rivet by the long nose pliers and heat the rivet up with a candle or gas stove or what ever. Get it good and hot.

Now pierce the dam between the front and back at the bottom so that it forms a passage through it between the front and rear reservoir. One is enough and be careful not to do anything else with the hot rivet.

Done. I did mine that way 10 years ago. Has worked fine ever since.

 

[Tim Kay]

Howard, great suggestion. I was getting frustrated here. Hot pierce here we go!

 

[Tim Kay]

Thanks for the above input guys.

Another example of how this site’s value far exceeds any amount one may pay.

With JacMac’s astute recognition that the reservoirs won’t work as intended due the mounting position, it then became apparent to consider alternatives. With Jim educating me and suggesting a Mityvac I now have one which I know will be handy again in the future. Jim and Howard ‘nailed’ it. I got a small nail red hot and simply melted a hole in the plastic wall between the two reservoirs.

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Job done, system is bled and reservoirs are both seeking the same level.

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Since I’ve owned the car, seven years, I have never had to add brake fluid. Won’t need to again until I decide to update the rears and\or put a pedal box with balance bar (next on my wish list !!) Oh yeah, and new updated master cylinders!!

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BTW, when using a vacuum bleeder (Mityvac) should the brake pedal be fully depressed, released or does it even matter where the brake pedal is?

 

[Bob Putnam]

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BTW, when using a vacuum bleeder (Mityvac) should the brake pedal be fully depressed, released or does it even matter where the brake pedal is?

It totally matters. There is a port that allows fluid into the master cylinder that is only open when the pedal is released to the rest position.

 

[Randy V]

Using Mityvac you may need to build up an inordinate amount of vacuum when you're using residual pressure valves (many of our cars do)..

There's a couple of websites here that explain the operation of a MC - both look fine to me;

TECHCO AUTO INDUSTRY IMP.&EXP.CO.,LTD.

Automotive Brakes: How Does a Tandem Master Cylinder Work?, by Curtis Jacobson

So yes - FULLY RELEASED must be the position of the master cylinder when using either a pressure bleeder or a vacuum bleeder like the Mityvac.