Hey, let's play name that master cylinder...

[ubercrap]

OK, I've got two brake master cylinders here. Now, the one on the right was in an ATE box that appears to have part # 411 611 015F on it. Is this indeed a Type 4 power brake master cylinder? The one on the left has FAG S5201 cast into the body of it. On the FAG box, somebody has crossed out III and written IV. I'm thinking (real genius at work here!) that it's actually a Type III master cylinder? If you guys can shed any light on this subject, I'd appreciate it!

[raygreenwood]

Yep...you got it right, the one on the left is a type 3. The one on the right appears to be very similar to a type 4 power unit. The problem with having a power brake cylinder....is that you have to have the power brake unit and all of the linkage for it. There are probably several that could be used....but the power brake units "power" factor are different from unit to unit. Ray

[vwbill]

Hey, that is weird since I had the one on the left in my 74 412 2d sedan.
Which has 73 seatbelts. Is that applicable??? Bill

[DeathBus]

Even weirder, have the one on the right in the wagon I am parting out.

[ubercrap]

OK, well, the Type III one is going up for sale, anybody need one?

[raygreenwood]

Where the heck are you guys bolting these cylinders in? Notice the ears?...the type 4 cylinders bolt through the side. Now granted...I have installed one in the trunk....but I also had to fab a pushrod and rocker assembly to make it work like power brake configuration. I used a 21mm bus master cyl. Ray

[Guest]

Hey I just looked at the pic of my master and it has a side mount ears one near the pludger boot and the next three inches away. No front flange mount near the boot. Sorry I was way off. Bill

[MGVWfan]

First question...has locating the master cylinder in the trunk fixed the rust ring problem?

Second question...can you post a picture of the installation? I just got out from under the dash on my '73 412 Wagon, and I think I see where the pusrod goes through (the slanted sort of stamping near the center of the pedal bracket on the firewall?), but I'm having a hard time visualizing the rest of the fab job. I'm going to have to do SOMETHING with the brake MC before the 412 gets on the road again, either rebuild the (real live ATE) replacement put in 10 years ago, or fab a bellcrank/bracket/pushrod to mount a more readily available sub in either the original location, or under the front hood. I see how a bracket to mount a T2 or WCVW MC could be fabbed, but the bracketry and bellcranks for the underhood mount are a bit harder to visualize (I'm an electrical sort of guy, humour me )

Third question...I've got the original MC on the bench (the PO put it in the box for the ATE replacement they put in 10 years ago), and I can't get the pistons out. I've pulled the snap ring, washer, and stop screw, tried pushing down on the front piston, no joy. I've tried air pressure too, no joy. It's like something's hanging up inside, but I can't figure out what it is. Any ideas from the school of hard knocks?

Thanks folks...and welcome back from the Philippines, Ray!

[raygreenwood]

I will have pictures soon. Got a digital camera last week. But the car is 200 miles away in my storage unit . Look in the Haynes manual. There is an exploded view of what comprises the power brake unit linkage. I robbed an upright part from either a vanagon or an audi....been a while so I can't remember. Did some cutting to shape and tack welded on to the pedal cluster.
As long as its straight, position is not that important as you can adjust with the rod length and ratio slot.
Its basically pretty simple. You push the pedal....the rod is now flipped to face forward. The pedal pulls the rod. The rod pulls one end of a piece of bar stock...like a rocker arm. The other end of that rocker...llike a see-saw pushes forward....to the master cylinder. I put a bronze bushing in the center and ground each end flat and drilled a hole and bushed them. I had a slot drilled where the center bushing is so I can adjust the pedal crank ratio. You just need an "A" of sorts to mount the cross axle for the rocker in. Use an adjustable brake pushrod up top. I think I used two hooked together by a hex bar stock piece.

What started this...is a couple things. (1) I had always admired the pictures of power brake units in the book. Not because I particularly wanted them....but because I wanted to have a normal mounting master cylinder. Cheaper...easier to get. But...I did not want to destroy the originality of the car or make a crappy installation. (2) The ineterim stage of this....is a nice stiff bracket I jigged up and welded to the pedal cluster that allows perfect factory underdash bolt up of a late superbeetle master cylinder or a rabbit (late) cylinder. This bolted up just fine. Looked like factory! I was so proud ! .......'cept.....it didn't work.
Now mind you....I had stupendous brakes before I started this. The pedal moves about 1". At 1.5 inch...she's shuttin down!
Oh...basic brake specs. Rebuilt front 412 calipers with mintex metal pads...cross drilled and chamfered German rotors....custom anti-rattle shims, German rear drums (for the moment), mintex semi-metallic shoes...and teflon braided lines.......anyway.......The problem is....type 4 master cylinders are rather large.
The volume of your primary and secondary master cylinder circuits must be large enough to move the fluid volume to take up the space the piston vacates in the calipers and wheel cylinders. The type 3 cylinder would have been perfect as the brake volumes of late type 3 are identical. But....the type 3 master cylinder would not have fit the welded bracket properly...and still have room for the lines and switches. Without thinking, I used a super beetle cylinder. Figured it had disc brakes..rear drums...no prob! But...the front calpers on the super are about 1/3 less volume and the master cylinder is barely adequate for those. It would take 1/2 pump to get any pressure...then one more stroke and they would be rock solid. I eventually swapped the back and front pressure lines and it worked much better...but the rear braking was lame.

So.....I have worked this out. I may even be able to use the bracket under the dash for the long bus cylinder. Havn't checked that yet. I have built the "A" frame and linkage. I have hole sawed the knockout yet.....and welded in the strengthening ring with bolt holes (a modified exhaust flange from type 1 is almost perfect for this). I could finish the install in about 2 hours at this point....or maybe bolt it up under the dash.

The nice thing about the bus master (21mm)....is that the volume of both circuits is larger than what the type 4 needs. It should take maybe 3/4" stroke to get serious braking.
At the worst, I may be able to make a drawing with measurements this week for the parts. Ray

[MGVWfan]

Boy howdy, thanks for that great explanation. I think I have the mechanical part visualized now. I agree, the power brake assembly's useful mostly for allowing an easily replaced MC with a factory-appearing installation. I'm thinking that's how I'll go, since the above-the-pedal mount is such a pain to get to and R&R without spilling fluid everywhere.

BTW, I flushed the brakes tonight, on to replacing the front calipers and pads next. Progress, to be celebrated with a Saint Arnold!