1971 Beetle master cylinder

[Oliver Closeoffe]

Hello. I am new here so please forgive any errors in etiquette. I recently installed a new master cylinder and wheel cylinders on my 1971 Beetle Formula Vee. The master cylinder I took off had what appeared to be residual pressure valves on it where the brake lines connect. The new master cylinder does not, and the ones off the old master cylinder wont fit on the new one. I bled the master before installing it, but I am having a hard time bleeding the system. Could this be because the system no longer has the residual pressure valves it had before?

[V8Nate]

Disk or drum? Do you have adjustment on your brake pedal rod?

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[Oliver Closeoffe]

Its drum brakes. The brake shoes are new on all 4. and adjusted. The wheel cyls are new, and the master cyl. is new. The brake pushrod is adjusted
to the correct length.

[V8Nate]

In the past I have seen residual valves used if the wheel cylinders are higher than the master/reservoir so that could be an issue. You could have a bad new master or it could be assembled incorrectly

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[Oliver Closeoffe]

Thanks for the reply..This is the second new master cylinder that's on it now. I was thinking the same thing about maybe the first one was bad. However after working on it all day yesterday I am starting to make some headway. At least I now have brakes. although spongy. I have heard of residual valves on master cyls that were mounted under the floor of a vehicle like the old pickups were. I'm sure the original master I took out was the one it came from the factory with. I don't understand why it had the valves if they weren't necessary, and why the new one didn't if they were.

[V8Nate]

I had to put residual valves on my bug but it is on air with a trans raise so the calipers are above the master and reservoir. Cb performance sells them, hopefully you just have some air trapped in the system

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[SCOTTRODS]

If the system has all been replaced except the flexible brake lines... I will suspect them as the problem with getting hem bled... the insides of the rubber hoses delaminate and get holes in them and when you press the brake pedal, forcing fluid between the walls of the inner tube and the outer walls, they tend to close off the hose and cause issues like the ones you are having. I recommend anytime you start working on an old one (especially since you think the original MC was the FACTORY original... then replacing those brake lines is the next piece and should be done while it's all apart. I do the hoses ANYTIME I work on older bugs I have purchased... even if the last owner tells me they were replaced last year or last month... It's impossible to look at the old hoses and tell whether they are good or not as they will almost always look OK with minimal surface cracks or none. Replace the Hoses on all 4 wheels and save yourself some heart aches.

[Ol'fogasaurus]

Scottrods beat me to the discussion on the flexible hoses; they can be a pain in the no-speak-about for several reasons. I don't recommend using the use of braided SS hoses but the stronger braided hoses seem to be OK. The stock style of hoses should be sufficient as long as you look and test them regularly; the test is mostly a squeeze to see if they have swollen or gotten stiff.

Pre-bleeding the MC is correct but there is a trick us old dudes were taught when dealing with drum/"can" brakes. Jack you toy up so all four wheels are off the ground then adjust the shoes, on all four corners, to a full lock position: this is to guarantee that each of the shoes are centered in the drum. One shoe not being centered in the drum is one of the more common reason for soft brakes, that and air in the lines. Using a buddy or a pressure bleeder bleed the system, one corner at a time (I have seen this miss-done a few times) while all four wheels are off the ground which should guarantee a good no problem/proper setup of the shoe's relationship to the drum. When the bleeding is done and you are satisfied with the feel of the brake pedal then readjust the brakes so when turning the wheel you hear the required drag of both shoes against the drum surface. Theoretically this method should give you a good feel for the brakes.

As far as the residual pressure valves I wonder.... Their use is to stop bleed back in the system to keep the line pressure which keeps the shoes from backing off and giving soft or uneven brake application. They were more discs than drum originally but do work well in both applications. I have seen some master cylinders that did have them directly attached and I have seen some setups where the valve was remote but on a dual MC as long as they are hooked up to the proper cylinders things should be OK.

Without more information or seeing them I'd start checking the threads (Metric vs. SAE), the style of the connection fitting on the line vs. the style in the MC you are using and the metrics of the spacing between the MC and the pressure unit.

Got a picture of both cylinders?

Lee

[Oliver Closeoffe]

Unfortunately the old master was thrown out. I did keep the residual valves that were on it. I made up a remote reservoir last night that
I can put my pressure bleeder on and I 'm going to try that today. The one thing that is in the back of my mind is, the wheel cylinders are mounted vertically on the front wheels. With the bleeder in roughly the center of the cylinder I don't see how all the air can get out the bleeder valve and not be trapped in the upper half of the cylinder. I'm hoping that with the pressure bleeder things will work out.

[Ol'fogasaurus]

Unfortunately the old master was thrown out. I did keep the residual valves that were on it. I made up a remote reservoir last night that
I can put my pressure bleeder on and I 'm going to try that today. The one thing that is in the back of my mind is, the wheel cylinders are mounted vertically on the front wheels. With the bleeder in roughly the center of the cylinder I don't see how all the air can get out the bleeder valve and not be trapped in the upper half of the cylinder. I'm hoping that with the pressure bleeder things will work out.

Are those stock VW units but just mounted 90 degrees? If the top part of the wheel cylinder has an air pocket that might be your answer. the pressure bleeder may or may not work with that.

Imagination is so important... or not!

Lee

[SCOTTRODS]

58-67 Beetles had the vertical mount wheel cylinders on the fronts... Your car may be running the older units for a specific reason... It's a Formula Vee So it should be a very custom build to begin with... but within a certain set of rules for the class of car. Could be what the Original builder had available or whatever... but after the 67 years they went with Horizontal mount wheel cylinders.

You could always pull the wheel cylinders off and capture them with clamps to bleed them, then re-install properly to insure the air is gone from them... you have a pressure bleeder so you should be able to accomplish that... Still gonna be a weird final assembly and adjust, but bleeding will be do-able at that rate... I'm guessing you already know to bleed brakes from starting at the farthest from the master cylinder, in order, to the shortest distance one...

[Ol'fogasaurus]

Since I don't run front brakes... The units I have I taken off but never paid much attention to them I guess. Sorry!

Lee

[Oliver Closeoffe]

Well I did the pressure bleed thing. It made virtually no difference at all. When I hit the pedal the first hit they feel spongy and go 2/3 of the way to the floor, if I give them a pump, they fell like brakes. I have done quite a bit of research, and am convinced that with the master cylinder I have I am going to have to run some type of residual valves. Most likely a single 10 lb on the rear line, and a 2 lb on each front line. And to think... This whole deal started out to be a simple "change the master cylinder".

[Ol'fogasaurus]

I'm still having problems posting here: 3rd try.

I did find a pix and Scottrods is correct, the front brakes have a vertical sitting slave cylinder.

The job of the residual brake valve is to keep an even line pressure to each slave cylinder (say 10#'s or 20#'s) not to limit brake line pressure (is there a chance they on backwards ?) until the brakes are actuated.

If the brakes are adjusted properly, the bleeding is proper I am confused.

I wish I could help more. I'll keep thinking about it and looking around.

Lee

[Ol'fogasaurus]

I did a look around doing an line search on this and while interesting it didn't solve the problem. Most of the valves I saw were remote and not part of the MC. I did see a type 3 unit with the valve built in but it has the mounting flange of the MC at an angle so that is a question: is your MC mount at an angle but the fill area is still sitting straight up?

VW residual valves are 2#s on discs and 10#s on drum brakes.

The TOS had an interesting but very short "Ta-do" as to the hows' and whys' the valves are needed.

I am still interested as to the need for a pump up to get good line pressure. Since you have a pressure bleeding system would it be possible to very carefully crack open each of the cylinder's bleed valves individually, in succession, to see if one or more of the pistons are the problem?
Lee