New 411 owner

[raygreenwood]

[scirocco81]

The 411 continues to give me no love........

So the master cylinder arrived earlier than I expected. It is definitely old stock (box is marked Made in W. Germany), in a Bendix box but inside was a Fag master cylinder.


I bench bled it, had great flow so I rolled the dice and installed it. And this is why I am not a gambling man I guess. I bled 2 quarts of fluid though the system, and have very little brake pedal. Disgusted, I let it sit on the lift overnight and tried again today, 1.5 quarts this time, no change in pedal. The pedal stops about an inch off the floor. All the brakes grab, I adjusted the rears twice, I get no change in pedal with the parking brake on.

So just to recap......

Calipers are rebuilt
Wheel cylinders are new Centric units
All 4 brake hoses have been replaced
Brake hoses from reservoir to the master cylinder are new

All I can think is that the master cylinder is leaking internally, just not as badly as the original that was on the car. All 4 brakes work, there is just excessive pedal travel.

I was pretty disgusted with the whole thing so I put the wheels back on the car and drove it out of the shop.

I put the original master cylinder (an Ate) in the vice and took it apart, here is what I found. Now, I am not sure what a bad master cylinder seal looks like but nothing is torn or damaged.

Bore looks clean, I am not sure where the failure in this lies or if the master cylinder are really the issue at this point. The only thing I see is that the seals on the inner piston do not oppose each other as pictured in the Type 3 rebuild kit.

My plan of attack now is to rebuild the new stock unit. Looking at rockauto at the Type 3 master cylinder kit, I will have to remove the seals from the pistons and swap them onto mine if they come assembled as pictured

Ray, is this the kit I should be purchasing? I read your rebuild thread and you mentioned some differences in Ate and FAG seals if I read it correctly.

https://www.rockauto.com/en/catalog/volkswagen,197...r+kit,1840

[raygreenwood]

Yes....that should do fine.

The failure of old....NOS.... master cylinders....is that the seals get hard with age....while they are confined to the shape of the bore....and therefore will jot dlex and infpate to seal the bore.

Also....from the looks of the corrosion of those pistons....its probable that when you remove the inner seal on each piston closest to the spring.....you will find corrosion of the brass flap valves causing leakage at the compensation ports.

That seal faving the wrong way......I have seen it that way and seen functional cylinders....but....it should be facing the outer piston in most MC.....its purpose is to help seal against the primary piston pushing fluid into the inner circuit.

Technicall the pistons never wear out....but they can corrode to a point where the brass flap valves do not seal.

Also....and I cant remember.....is yours a wagon or a four door? If you have a four door or twk door coupe you also will need to deal with the functionality of the rear brake pressure regulator.

If you need one of those......strip and inspect it. If its not rusted....you can get the rebuikd kit from PMB.....or havd yours rebuilt, zinc plated, adjusted and painted for about $185. A bargain.
Ray

[scirocco81]

Thanks Ray, I will order a rebuild kit.

The plan is to remove the NOS master on the car and reseal that one, I would hope the brass flapper valves wouldn't be corroded in that one but I will post some pics when I get it out...... probably after Thanksgiving.


I have a 4 door sedan, and the rear valve is concerning but shouldn't stop the brakes from functioning or cause the low pedal as I understand it.
I will most likely replace it with a Willwood or Tilton prop valve in the future. I quick look on PMBs site I did not see a rebuild kit for the valve.

[raygreenwood]

[scirocco81]

Well yesterdays snow meant for a slow day today so messed with the 411 a bit.

With the original master cylinder I had no pedal, with the new one the pedal would stop an inch off the floor.
I tried pinching off the hoses to see what would happen. With ALL 4 hoses pinched off I had a pretty normal brake pedal, if I removed the clamps off the front or the rear I had no pedal again. Front clamped, rear open, no pedal. Rear clamped, open front, no pedal, all 4 clamped normal pedal.

This is leading me to believe the maser cylinder is leaking internally. So I did an autopsy on both master cylinders.

First up is the one that was in the car originally.....

Close up of the flap valves, corrosion seems negligible to me.

This is the "new" NOS master cylinder

See that little flake of black, whatever it is. It was between the seal and the flap valve on the inner piston. I do not think it was in that position in the cylinder, me pulling the piston up put it there, but it had to have been floating around in there.
Note that the piston seals are opposed on that piston unlike the original. You can see the little sliver of whatever in this pic better.

Close up of the flap valves in the "new" cylinder.

The seals on the new unit are so not seem to be what I would consider hard, but I am not sure what the difference between soft and too hard to seal is.
My concern now is that the seals in the kit will be hardened by age as well, I wont know how long they have been boxed up for and I am sick and tired of brake fluid at this point.
Seal kit will be here tomorrow, I will have time to reseal and install the master cylinder Monday I believe. I will update with results and hoping that update is that the brakes work!

[raygreenwood]

Ok....Im not on my computer so I cannot snip your pictures and draw arrows.

But.....here are some concepts to understand about master cylinders.:

1. The level of corrosion on the pistons and the brass flap valves in the original MC.....are significant. Understand......when brass (and most metals) corrode....the surface gets rough....as metal gets removed as corrosion. . If I can I will measure the difference at some point between new, clean flap valves and "green" and tarnished flap valves.
But.....I can tell you that to the eye.....and even your fingernail....it looks smooth.....but the difference is about 8-10 microns or more. Doesn't sound like much?.....then just remember that .001" is only 25.4 microns and .0001= 2.54 microns.

Add to this.....corrosion on the magnesium piston face. Yes....those are magnesium. Its also about 8 microns. That right there is easily close to .001" and sometimes more...so they can leak.

But.....I consider flap valves that are not flat out green....just tarnished penny colored....maybe a 5-10% issue.

The big issue is that the seals have a combination of wear...and most importantly they are hard from age....and the biggest issue is that they have been sitting in the bore...squeezed inward by the bore walls.....WHILE they hardened up. Not getting any excercise.

This means that when you step on the brake.....they either cannot flex outward because they are just too damn hard....or in just as many cases...they flex outward.....to seal...but the second you reduce foot pressure they collapse. More on this in a minute.

2. Your NOS master cylinder is actually a good thing. The bore walls should be unrusted and the pistons uncorroded.

But....notice carefully.....on the flap valves from the NOS cylinder....that you can see the outline circles of the compensation port holes of the pistons. This is "tarnish" from age. It means that they have been sitting in that bore in the collective moisture trapped in the assembly lube for eons.

They are fine....not "corroded" yet....but what it means it that the seals are in the same condition as the ones from your old cylinder. Stiff....and due to being in the bore....constrained.....they are now shaped like the bore and have memory that flexes them back inward and breaks seal as pedal pressure lets off.

3. New kits that are a few years old.
In general...these are not,a problem....even if they harden up a little....because they have not been compressed/constrained by the bore. As long as they are flexible enough to get onto your pistons they are usually fine.

The nice thing about an NOS MC....is that it has not been rebuilt yet. On factory fresh cylinders....the tolerance between bore and piston heads....is at very best .002". But most are between .0025" to .0035". A few are even right at .004". The maximum allowable bore to piston head tolerance is .005"....and even that is at the wear limit. A .005"-.006" tolerance bore WILL work....but will not last very many miles. Maybe 30-50k before normal seal wear start causing bypass and leakage.

4. The biggest and most common symptom of old seals that have sat too long without occasional driving/excercise.....is the complaint that you can pump the pedal up....hard as a rock. Brakes stop great. If you keep about normal pressure on the pedal.....you can keep this rock hard pedal all day.

But....if you decrease your foot pressure slightly....mind you....not removing your foot from the pedal and not letting it up.....it collapses all the way to the floor or to the level of the inner circuit.

This is the "memory" of the stiff cup seals pulling them away from the bore walls.

And...... this may be in my master cylinder rebuild thread.....take your NOS pistons and chuck them into a drill lightly. Take 2000 grit or finer paper....and radius the sharp edges of the piston where you are going to stretch on a new seal.....AND....DO NOT.....heat the seals in hot water. This weakens old seals that are going to be stretched because it causes them to flow.

Lastly.....411 and 412 are hard to bleed. The sequence is NOT like a type 3.

Start right rear. Then left rear, then right front, then left front.

You MUST seal the threads of the bleeder valve with some teflon tape...or better yet...buy speed bleeder valves. You ONLY crack the bleeder open....about,1/4 to 1/5th turn.

Why is this?

You seal the threads because they leak air in hoth directions.

And you want a very small bleeder valve opening ....Because all during the bleeding.....you want to have even the weakest pedal stroke create PRESSURE. You want a very small orifice.

In fact...the best way to do this is to pump the pedal up hard with the bleeder closed. Hold the pedal to the floor with a padded rod against the front of the seat....and then go crack the bleeder valve. DO NOT let the pedal up until the valve is closed.

This is necessary in the 411/412...because the brake line system is circuitous and it has high spots where bubbles can stay and fluid bypasses them. When an air bubbleis squeezed by pressure...yes in contracts....but it also stays ROUND instead of flattening agaibst the tube wall like a water drop...so its easier for the fluid flow to move.

When just starting out and the system has a ton of air in it....the MC pistons will shuttel that air back and forth and draw no fluid in from the reservoir because the viscosity of the fluid is higher than the suction pressure.

To get around this and get it started.....sit on the ground next to the car with the door open. Push the pedal t9 the floor with your hand 3-4 times. Hold it down with the rod. Go crack a bleeder open. Any bleeder....left front is fine. Close the bleeder. Then.....let the pedal up very SLOWLY.....about 10 seconds it should take. This allows the piston.... even with a lot of air..to draw fluid in without breaking the film stength of the fluid by moving too rapidly.

This works EVERY TIME.....to get fluid flow started. Ray

[scirocco81]

Thanks for the tips they will be used!

I tried the conventional pump the pedal open the bleeder method at first Lastly I used my Mightyvac fluid evacuator and did another 1.5 liters of fluid with no change. This method has never failed me in the past but on the 411 it did, which makes me think there was no air in the system. I flushed 3.5 liters of fluid total.


I have speed bleeders for the front ready to put on, rears couldnt get here before the holiday so I will apply Teflon tape and give it another go.

[raygreenwood]

The mighty vac.....will not work well on type 4...and most especially if any bleeder ls have leaking threads....and double especially if you have any bypassing from circuit to circuit inside the cylinder.
Same problem.....it just moves air around.
Others may disagree....but its been my experience.

What does work EXCELLENTLY is the method I outlined.
Next in line is a pressure bleeding system......BUT with a pressure bleeder.....you need to make sure your fluid lines between reservoir and tank....are very new, tight fitting and flexible. Keep pressure at 20 psi or less.

Yes its uncommon but I have seen hoses blow off.

The mext best in line.....are those crappy "one man" bleeders with the 4 oz bottle.....and a piece of clear vinyl hose.....and most importantly.....a ball and spring check valve on the end.

Not all of those are equal. I looked around....and think I bought the "Lisle" brand.....and I still had to disassemble the check valve, clean it up and put in a stronger spring. As noted...you want to build at least a little pressure before the check valve pops open.

And.....with higher pressure....you will need to clamp the line to the check valve with a small spring clamp....and zip tie the tube to the bleeder valve....and as usual....the bleeder valve threads MUST be leak free.

The one man bleeder has saved my tail before out on the road. At one point in time I had a soft line start to leak on a long road trip. Replacing both of the front lines was a snap. It was storming outside....and with the master cylinder already bled snd pumping well.....the 9ne man bleeder in my tool box made it quick and dirt simple.

Ok.....about your old MC....and for that matter....your new one.

Your old MC appears to be an ATE and the new one is an FAG. To clean away the corrosion on the pistons....DO NOT use a scotch brite. Use a soft tooth brush and at minimum use cleaning vinegar which is 6% acetic acid. This will take a few minutes and slowly dissolve the corrosion.
Most of that corrosion is oxidized "white rust" from the magnesium which has formed a compound with stuff in the brake fluid.
DO NOT leave them to soak and walk away. Magnesium is electrolytically active....and will start to corrode farther at some point.

Or......you can use a toothbrush....and hot water and a,product called "bar keepers friend".....which you can find at any grocery store on the cleaning,aisle.

https://www.target.com/p/bar-keepers-friend-multip...lsrc=aw.ds

Do not be fooled. This is a serious cleaning powder. Wear gloves. It uses calcium carbonate....which is a micro abrasive on the same level as tooth paste.....but the real cleaning power is the small amount of oxalic acid in it. It will dissolve all of the corrosion.

Wash everything well in hot water and soap.....then dry them well.....and treat the cylinder and pistons with automatic transmission fluid......WHICH MUST BE FULLY CLEANED AWAY OF ALL TRACES BEFORE PUTTINY NEW SEALS IN....BECAUSE ATF EATS BRAKE SEALS.

The object of putting ATF on the cylinder and pistons and flap valves....is that you can then store the cylinder and pistons in a nearly,airtigjt bag....for eons.....without corrosion.

Do not rebuild your old cylinder for a spare UNTIL you are ready to install and use it. Rebuilding them now and letting tnem sit on the shelf for years with new seals in them.....creates the same seal problem you have now.

And....the pistons....until they are installed and submerged in brake fluid....MUST....be stored in an airtight, moisture free, anti-corrosion environment......especially after the cleaning I outlined above.....because....if the pistons are magnesium and most are up until the late 70s snd then they went to aluminum.....then they were coated with a pinkish brown "Alodine" coating.....which greatly slows...but does not prevent.....the slow sacrifical corrosion of magnesium. And.....it is primarily this coating....oxidized....that is forming the crappy looking corrosion on your ATE pistons.

This is also a good time to carefully measure both MC bores and pistoj heads....to see what you have.
Since the ATE cylinder had one piston seal facing the wrong direction.....its highly possible that the cylinder has been rebuilt at least once. If this is correct...and its been honed....it may now be nearly oversized. It would be good to find this out now....instead of some desperate day five years in the future when you need a MC just to drive.

Ray

[scirocco81]

Master cylinder resealed, reassembled, and reinstalled, speed bleeders on the front calipers, teflon tape on the rear bleeders, bled as you described Ray, still no pedal.

Rear speed bleeders will be next week. I may try to fashion a pressure bleeder next week as well.

As for now, I am taking a break from the 411 brakes.

[raygreenwood]

[scirocco81]

I bought the kit for a Type 3 I linked to off Rockauto and swapped the seals off that kit onto the pistons in the NOS 411 master cylinder. I did them one at a time and put them in the same spots they were on the pistons in the kit.

I cleaned up the flap valves very gently with 2000 grit sandpaper.

I have loads of fluid flow, flow to or from the master cylinder isnt the issue I feel. Bleeding the brakes, I get loads of fluid out of the bleeders.

I have adjusted the rear brakes twice and had a coworker with 35+ years aircooled experience recheck them, they are good. With the parking brake applied there is zero effect on pedal effort or travel.

I have plenty of freeplay, I can install the master cylinder with no effort having to push it to get the bolt holes to line up, I checked it again today, no issues with freeplay.

I am really at a loss with this at the moment. I will get back to it late next week maybe.

[raygreenwood]

I know you hate to pull it out again....but pull the guts out and take some close clean pictures of all of the piston heads and seals. I want to see the faces where the flap valves seal on the pistons.

Also....do the ID bores of the seals fit tight on the pistons....or are they easy to spin around?

And....as I noted.....check the grommets and elbows. That problem will produce this effect.

Also....make sure that you are only using the top bleeder screw on the front calipers.....and even with the speed bleeders...again...only crack them open a fifth of a turn. You need to be able to build pressure on each stroke.

The interesting thing is that you note you are getting plenty of fluid through the system. If you bleeders are barely cracked....you should not be. If the bleeders are only cracked a smidge....you should not be getting much out

Also...putting the parking brake on should give you a considerable difference in the rear.

Lastly.....with the pistons out....get a telescopic gauge and a micrometer and measure the bore. Then the piston heads. Post that.

Also...where did you buy this NOS MC? I have a reason for asking that.

There was someone a year ago that had a LARGE amount of NOS 411/412 MC's....very old. The one in my build for Titan3C.....was one of those. Great shape....just dead seals.

I am wondering if someone has rehoned the one you have. Ray

[scirocco81]

If you are wondering if the small holes in the pistons were open behind the flap valves, they were.
I did not try to spin the seals when once they were on the pistons.

Flow from the reservoir is not as issue. If I crack the speed bleeders on the front calipers open less than 1/4 turn they will shoot fluid 6-8 feet. I've been though over a gallon of brake fluid, trust me, its getting where it needs to go.

I know applying the parking brake SHOULD have an effect on the rear, but it does not. Today I adjusted the rear brakes all the way out and tried bleeding the rear, no change.

Old master cylinder, new master cylinder, new master cylinder with new seals, it has made no difference, maybe the problem isnt the master cylinder. Today I made a fitting and cap for the pressure bleeder we have to give that a go after the rear speed bleeders arrive.

The NOS master cylinder was on ebay, from a surplus seller with other 30,000 feedback ratings.

[raygreenwood]

Was the seller in the midwest?

Also....its time to check the rear regulator. Ray

[scirocco81]

MC was shipped from Texas, came in the original well worn Bendix labeled box.

[raygreenwood]

[scirocco81]

Pretty sure what we have here is a case of Bendix buying a new maser cylinder from FAG and putting it in their box. Not an uncommon practice even today.

Its not a reman, its a new unit. Even the box is labeled "Made in W. Germany"

When bleeding the brakes I am not doing it alone. I have a coworker in the car running the pedal.

Not against the idea of taking the MC back apart, but I'd like to find loose seals this time rather than ones already installed on pistons that I have to remove and reinstall.

Taking the regulator out of the system may be on the table as well just to see if I can get pedal.

I have an 84 Rabbit GTI project to finish up and the 411 has been taking up too much time. I accomplished the temporary goals of getting it running/braking well enough to move it around the lot. I may back burner the 411 and get back to the GTI, or at the very least concentrate on other small things the 411 needs and let the brake issue sit on the back burner.

[raygreenwood]

[scirocco81]

Bendinx had to be doing SOMETHING in West Germany or a box with their logo and "Made in West Germany" on it wouldnt exist.


Enough with the 411 brakes for awhile, we've got turkey to eat and family to spend time with! Happy Thanksgiving Ray and everyone else lurking on this thread!