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Master Cylinder Bleeding? - No Brakes!
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mushisushi
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PostPosted: Sun Jun 26, 2016 3:29 pm    Post subject: Master Cylinder Bleeding? - No Brakes! Reply with quote

A few weeks ago I finished putting in a new master cylinder and wheel cylinders on all 4 corners, but my pedal goes to the floor and I saw that wheel cylinder is actuating a little, but not a lot - braking effort is minimal.

I have tried bleeding it from the wheels twice, and no air is coming out. None of the wheel cylinders or the master cylinder is leaking, and the reservoir is full.

This makes me wonder if the replacement master cylinder is junk (I did get it from SoCal Autoparts), or maybe I didn't bench bleed it correctly or enough.


When I did the bench bleed, I submerged the cylinder in a container of brake fluid and actuated the piston, with lots of bubbles coming out. Put it in the car and seemed good to go.


Before I spring for a new 'new' master cylinder, is there anything I can try? I did read that it was possible to break the seal of the master cylinder if you push the piston in too far, maybe that's the problem?
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VDubTech
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PostPosted: Sun Jun 26, 2016 3:35 pm    Post subject: Re: Master Cylinder Bleeding? - No Brakes! Reply with quote

You do NOT need to bench bleed a master cylinder in a Beetle. Did you make sure all of your brakes are properly adjusted before you bled them?
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mushisushi
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PostPosted: Sun Jun 26, 2016 3:37 pm    Post subject: Re: Master Cylinder Bleeding? - No Brakes! Reply with quote

I'm fairly certain that I did - I remember the frustrating experience of turning the star adjusters through the back of the bug.
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PostPosted: Sun Jun 26, 2016 3:40 pm    Post subject: Re: Master Cylinder Bleeding? - No Brakes! Reply with quote

mushisushi wrote:
A few weeks ago I finished putting in a new master cylinder and wheel cylinders on all 4 corners, but my pedal goes to the floor and I saw that wheel cylinder is actuating a little, but not a lot - braking effort is minimal.

I have tried bleeding it from the wheels twice, and no air is coming out. None of the wheel cylinders or the master cylinder is leaking, and the reservoir is full.

This makes me wonder if the replacement master cylinder is junk (I did get it from SoCal Autoparts), or maybe I didn't bench bleed it correctly or enough.


When I did the bench bleed, I submerged the cylinder in a container of brake fluid and actuated the piston, with lots of bubbles coming out. Put it in the car and seemed good to go.


Before I spring for a new 'new' master cylinder, is there anything I can try? I did read that it was possible to break the seal of the master cylinder if you push the piston in too far, maybe that's the problem?


hard to say what is wrong, it is important to have clearcne between the push rod tip and master piston.

frankly I have never bench bleed a Bug aster, just put in and fill it up. you say braking effort is minimal, that is good meaning it takes minium effort to stop the car, since you are having trouble I assume you mean braking is minimal, right?

make sure the shoes are correctly adjusted,

also use care in dunking a cylinder in fluid to bench bleed, often the outside of the cylinder is less than clean and may have non brake fluid compatible presrvatives on it. dont want that stuff to get in.

I also like to coat the stroked areas of the piston that are on the outside with brake compatible grease, VW called it genuine VW brake paste back in the day. helps prevent corrosion, and makes things slide better. brake fluid is not good to use there, as it will cause rust.

anyway, check the shoe adjustement and pushrod clearance, if ok, you may have to pull the master apart to see what is wrong

also make sure the four wheel hoses are not obstructed, they can internally swell, but usually the result is a dragging brake, not failure to brake.

good luck
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mushisushi
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PostPosted: Sun Jun 26, 2016 3:43 pm    Post subject: Re: Master Cylinder Bleeding? - No Brakes! Reply with quote

That's a fair idea - I will look at the pushrod clearance.

One thing I did yesterday was look at the braking action with the drum and wheel removed from the left rear. The left shoe was a tight fit against the drum, and was already dragging when I put the drum back on. The right shoe has a small gap.

I pressed the pedal with the drum off to see how far the pistons on the wheel cylinder moved. Barely anything!
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PostPosted: Sun Jun 26, 2016 4:45 pm    Post subject: Re: Master Cylinder Bleeding? - No Brakes! Reply with quote

X2 on pushrod clearance

Also, when bleeding brakes I have found this procedure to work best:
1. Put the car up on four jack stands
2. Adjust all the shoes out to the drum
3. Press the pedal a few times
4. Adjust the shoes again
5. Repeat until the wheels don't rotate at all. This allows you to push fluid only instead of wheel cylinders AND ensures the correct amount of fluid in the system.
6. Start at left front put a hose on the wheel cylinder.
7. Submerge the other end of hose in a jar partially filled with brake fluid
8. Open the bleeder and have an assistant pump the brakes repeatedly
9. Pump til only fluid comes out
10. Close the bleeder, refill brake reservoir and check it frequently.
11. Repeat at right front, left rear and finally right rear.
12. Adjust brakes looser by 2 clicks
13. Test brakes
14. If good remove car from Jack stands. Test drive carefully.
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PostPosted: Sun Jun 26, 2016 5:12 pm    Post subject: Re: Master Cylinder Bleeding? - No Brakes! Reply with quote

Eager to resolve this - I just went out and adjusted all 4 wheels via the adjusters.

Rear wheels were dragging very quickly when adjusting, then I backed them off 1-2 clicks to rotate free and the parking brake is tight between 3-5 clicks.

Front wheels had plenty of adjustment to do, got them both dragging and backed off 1-2 clicks.

I didn't get a chance to RE-bleed them - I wasn't sure it would make a huge difference.

I spun the wheels by hand and had my lovely assistant stop them with the pedal. The wheels did visibly slow but not the braking action you would expect.


There is 5-7 mm free play in the pedal as you would expect. Is this the pushrod clearance you are referring to?


A final thought - the pedal isn't totally free to move, it does show some resistance. But I have bled these brakes before and know the difference between air in the lines and what I'm feeling right now. There is a little pressure but it still moves to the floor - no "sponginess" as it were.


If I've tried everything you guys think I should have done, I will pull out the master cylinder and take a look at it.
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PostPosted: Sun Jun 26, 2016 5:40 pm    Post subject: Re: Master Cylinder Bleeding? - No Brakes! Reply with quote

I have done brakes on many types of vehicles before and NEVER ran into what we found last week .
After replacing brakes on my 63 at home I couldn't get them to bleed properly .
Totally frustrated I took it to my friends shop .
I had purchased what I considered to be the best parts from a reputable distributor WOLFSBURG WEST ....
The problem was the NEW RUBBER LINES on the front were EXPANDING when the brakes were applied .
Replacing the two " NEW " front lines fixed the problem .
Go under your car and watch the rubber lines when you apply the brakes .
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PostPosted: Sun Jun 26, 2016 5:49 pm    Post subject: Re: Master Cylinder Bleeding? - No Brakes! Reply with quote

mushisushi wrote:
Eager to resolve this - I just went out and adjusted all 4 wheels via the adjusters.

Rear wheels were dragging very quickly when adjusting, then I backed them off 1-2 clicks to rotate free and the parking brake is tight between 3-5 clicks.

Front wheels had plenty of adjustment to do, got them both dragging and backed off 1-2 clicks.

I didn't get a chance to RE-bleed them - I wasn't sure it would make a huge difference.

I spun the wheels by hand and had my lovely assistant stop them with the pedal. The wheels did visibly slow but not the braking action you would expect.


There is 5-7 mm free play in the pedal as you would expect. Is this the pushrod clearance you are referring to?


A final thought - the pedal isn't totally free to move, it does show some resistance. But I have bled these brakes before and know the difference between air in the lines and what I'm feeling right now. There is a little pressure but it still moves to the floor - no "sponginess" as it were.


If I've tried everything you guys think I should have done, I will pull out the master cylinder and take a look at it.


per my official VW 1200cc service book, you want 1 mm free play pushrod tip to the master piston. I dont know haw that translated to free play at the pedel, if you mean at the pade where you step on the pedel, your diminsion may be abit too little, as I am pretty sure the lever arm ratio of pedel pad to pushrod is uch more than 7 to 1. so 1 mm at the tip of the pushrod, of course that will be considerably more at the pedal pad, but use the 1 mm dimision at the pushrod. if in doubt, loosen the push rod nuts and back it off for more freeplay and see if your braking problem goes away or not, but in the end set it to 1mm. you might have it too tight now if your measuring 5 to 7 mm at the pedel pad, and it is a bit too much free play if the 5 to 7 mm is at tbe pushrod tip.



good luck, hope it is the push rod clearance, that would be a simple fix Very Happy Very Happy Very Happy Very Happy .
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PostPosted: Sun Jun 26, 2016 11:21 pm    Post subject: Re: Master Cylinder Bleeding? - No Brakes! Reply with quote

When changing master cylinder sometime a few days of slow driving is necessary to let the cylinder "burp" bubbles into the fluid tank.
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PostPosted: Mon Jun 27, 2016 7:20 am    Post subject: Re: Master Cylinder Bleeding? - No Brakes! Reply with quote

Single or dual circuit MC????? Confused
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PostPosted: Mon Jun 27, 2016 8:08 am    Post subject: Re: Master Cylinder Bleeding? - No Brakes! Reply with quote

it issingle circuit, on a 66.

It isn't driveable right now since the engine is in a different place than the bug! It has been sitting for far too long and I'm just getting it ready to sell. Brakes are a must have ! Haha
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PostPosted: Mon Jun 27, 2016 8:47 am    Post subject: Re: Master Cylinder Bleeding? - No Brakes! Reply with quote

Did you adjust the brakes until the wheels would no longer turn? Notice I did not say until they drag? I said until they no longer turn. Then pump the brake, and again, adjust them until they no longer turn, not drag slightly. You may have to walk around the car checking for wheels spinning several times (more than twice). Just keep adjusting/pumping until they stop turning.

Only then will you be able to effectively bleed and after that loosen all the adjusters an equal amount, one or two clicks. This procedure seats the shoes in the drum and centers them, otherwise you will not get a good adjustment. Leave the wheels locked in place until after you bleed.

The pedal rod adjustment is critical as well. It is not seen at the top of the pedal. It is felt and seen on the rod itself. Open the door, get down on your knees, put your right index finger on the Rod and your left hand on the pedal. Move the pedal fore and aft and you will see that there is ever so much slop where the pin that holds the Rod to the pedal. You need to know that so you can factor it out. Then you will feel, hear and see the Rod move in and out of the master cylinder. And when the Rod touches the piston inside, it will make a very faint "tap" that you will feel, see and hear. 1mm, that's all. No more, no less. Too much play and your pedal moves forever, not enough and it pushes the piston past the reservoir feed tube and goes to the floor!

I see you say you bled. I see you say you adjusted. I used to do it the way you described. I was wrong. And sometimes I had problems like you are describing, when the problem was actually me.

If it fails after checking all this above, your master cylinder is bad out of the box. Or your hoses are bad, as Grandpa Pete said.
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Last edited by flyboy161 on Tue Jun 28, 2016 7:01 pm; edited 1 time in total
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PostPosted: Mon Jun 27, 2016 9:42 am    Post subject: Re: Master Cylinder Bleeding? - No Brakes! Reply with quote

You need to rebleed the brakes AFTER you've properly adjusted them. Once they're adjusted they will bleed out and the brakes will be fine. Until they're properly adjusted THEN bled, you're wasting your time with anything else.
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borninabus wrote:
a measurement of your rod would be extremely useful.

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my dad wasnt a belittling cock when he tought me how to wrench on cars.

EverettB wrote:
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PostPosted: Tue Jun 28, 2016 3:41 pm    Post subject: Re: Master Cylinder Bleeding? - No Brakes! Reply with quote

Flyboy's post was right on the money. Thanks - brakes are functioning as intended!

Guess the 'adjust to drag' method doesn't really center the shoes. When I adjusted it like that, it just drags on one end of the shoe and not the whole thing since it isn't centered.

Thanks a bunch!
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PostPosted: Tue Jun 28, 2016 3:55 pm    Post subject: Re: Master Cylinder Bleeding? - No Brakes! Reply with quote

Common to adjust, then pump brakes a few times to re-center, re-adjust.

And you'll need to re-adjust like once a week for a few weeks as the shoe lining wears to the arc of the drums.
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PostPosted: Tue Jun 28, 2016 5:44 pm    Post subject: Re: Master Cylinder Bleeding? - No Brakes! Reply with quote

Glad to help! Brakes are funny things. I learned that trick here on the Samba!
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PostPosted: Thu Oct 27, 2016 5:57 am    Post subject: Re: Master Cylinder Bleeding? - No Brakes! Reply with quote

flyboy161 wrote:
Did you adjust the brakes until the wheels would no longer turn? Notice I did not say until they drag? I said until they no longer turn. Then...


Until '64 model this is not possible.

Drum openings to adjust star registers are accessible from the external part of the drum so the drum itself shall be rotated to gain access to each one of the two registers of each wheel.
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PostPosted: Thu Oct 27, 2016 6:49 am    Post subject: Re: Master Cylinder Bleeding? - No Brakes! Reply with quote

VDubTech wrote:
You do NOT need to bench bleed a master cylinder in a Beetle.


Yep and it's not mentioned in the manuals but because of Internet theory and misinformation it's somehow thought to be necessary now. We did brake jobs at two different shops for nearly 40 years without ever bleeding the MC. But who are we to rain on their parade? Good luck.
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PostPosted: Thu Oct 27, 2016 7:56 am    Post subject: Re: Master Cylinder Bleeding? - No Brakes! Reply with quote

herbie1200 wrote:

Until '64 model this is not possible.

Drum openings to adjust star registers are accessible from the external part of the drum so the drum itself shall be rotated to gain access to each one of the two registers of each wheel.


Are you sure of 1964? Here in N. America did not get the holes thru the backing plate till 1968.

For the earlier drums with adjusting holes.
Adjust first star till it is hard to turn the drum to the next star. Adjust the second star to fully lock the drum.

In all the years of wrenching on these VWs, have only needed once to bench bleed a MC.
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