I am readying a 2010 IM for a road trip. While examining the Vintage Air AC (which is not working, unfortunately), I noticed that the brake master cylinder was angled. It looked like the top nut was loose. Apparently, having the bottom nut tighter was a way to angle it to fit since there doesn't seem to be room before it would hit the rack. I am told it is a Super Beetle 19mm master. I wonder if anyone might know of a slightly smaller replacement.
Replies sorted oldest to newest
does it have front and rear drums or disc brakes ?
Front and rear disc brakes
@imperial wonder why you ask. Does it make a difference? Any suggestions for alternatives that might fit without needing to be angled?
"Wonder why you ask. Does (the master cylinder piston size) make a difference?"
Yes, it makes a difference.
Disk calipers require less fluid to make them work than drum brakes (which have to move farther, requiring more brake fluid). The typical later VW master cylinder (after 1971) has two different pistons (front and rear) of two different sizes, the larger servicing the rear (drum) brakes in order to keep all four wheels balanced in their braking effort. If what you had in there was braking your car well, I would be inclined to replace it with the same master cylinder because you know it worked right even if it was cock-eyed in mounting it. Any VW master cylinder you buy will expect to be mounted to a surface that is straight and perpendicular to the pan floor. Period.
Now, on that thing of the master cylinder at an angle: Having looked closely at your photo, all I can offer is this:
The master cylinder mounts to what is commonly known as the "Napolean Hat" (NH), so-called because that is what it looks like as it straddles the central tunnel of the VW pan. In engineering terms, it is a "lower, two-wall, 1" bulkhead, meaning that it is at floor level, and is made from two sheet metal pieces, sandwiched roughly an inch apart.
In order to mount the master cylinder (henceforth called the "MC") and keep it from compressing the NP, there are a couple of roughly 1" spacers inside of the NP so that when the MC is mounted to the NP and the bolts are tightened, everything stays in alignment and isn't pulled one way or the other. In other words, the MC stays straight.
In YOUR case, it looks like the internal NH may be missing one spacer, allowing one MC bolt to pull it towards the pan and thoroughly distorting what the Sainted German Designers intended. If that's not the case (i.e. both spacers are in there) then something else if going on that I'm not privy to and you need to find someone local, like a recommended Hot Rod mechanic, who can see what's going on and correct it, if need be. The end result may be that nothing need be done and just live with an interference (it had been working OK, right?) These are, after all, custom-built cars, but it would seem to me that the Henry Reisner builders of years gone by would have had a more nuanced solution than what I see in your lone photo, if need be. If it was working just fine as far as braking action be concerned, then I would just leave it.
Hope this helps. gn
It's not a VW pan. He's got a 2010 IM. I'd like to see more pictures. I've got a tube-framed IM with a beam and a Golf rack and a normally mounted disc brake master cylinder. I'd like to see what it has the potential to hit if mounted straight.
Thanks for the responses. I am currently away from car. As Stan says it is an IM with no pan. Henry says it is angled because there is little or no clearance between the top of the master and the rack boot. He says the master is Super Beetle 19mm master. I was mainly asking if there might be a compatible master that is a bit smaller and thus doesn’t require an angle to fit. Having it angled seems wrong to me.
Why wrong? It might even help to bleed it being angled and if the brakes can completely bleed out the air then I can’t see the issue except if you look under the hood so to speak.
Bespoked automobiles are nuanced and you get to appreciate them more as you see more of them . Having said all that maybe it’s the madness getting to you … it’s a disease one gets on this list 
A washer to angle the master cylinder is not a problem. The master cylinder pushrod has a ball end that engages the piston inside. This enables everything to function without binding, as the pushrod will move slightly in the vertical plane as the pedal moves through its arc.
My solution to this is to do nothing as long as your brakes work well. Flush and bleed annually and don't worry about the slight misalignment and attempting to "fix" it.
Now with regards to disc, drum or front disc/rear drum master cylinders:
I believe the early hydraulic brakes(remember, the original super-old Beetles had cable brakes) used a single piston 17mm master, which may have increased to 19mm. Later, they switched to dual piston 19mm, and finally 20-point-something millimeters. As car weight and brake drum diameter/width increased, master cylinder sizing changed. The dual-circuit master cylinder was for safety/redundancy(great idea!). Plus the VW factory finally switched to front discs.
I've never seen a master cylinder with two different bore sizes. I have seen different length chambers for the two separate but consecutive piston areas.
Master cylinder sizing depends on 3 things: pedal ratio, wheel cylinder or caliper piston size, and swept area of shoe/pad contact. There is also the factor of actuation distance and pad/shoe wear to consider for volume of fluid displaced.
To arrive at a hard and fast number or direction to go for sizing needs a qualified hand. All factors should be considered to get the proper size and feel.
Who knows who may have replaced what, on a 2010 car.
If that is the original mounting, and it has worked all these years, then what's the issue?
If the master cylinder bore is cast iron, then I agree that a slight misalignment shouldn't be a problem. However, if it is aluminum, then that could cause asymmetrical wear in the bore, which will eventually leak. I had an aluminum master cylinder for a hydraulic clutch conversion I put in the Speedster that failed for that reason.
I believe that most - if not all - brake MCs are cast iron, so you should be ok.
@Lane Anderson posted:If the master cylinder bore is cast iron, then I agree that a slight misalignment shouldn't be a problem. However, if it is aluminum, then that could cause asymmetrical wear in the bore, which will eventually leak. I had an aluminum master cylinder for a hydraulic clutch conversion I put in the Speedster that failed for that reason.
I believe that most - if not all - brake MCs are cast iron, so you should be ok.
I would think that the angle has to be steep for it to do so, and in the case of the IM brake MC Piston I would doubt that those issues in the build would not have been worked out by the IM Team of course like Bob said presupposing it was not modified which I doubt they would have modified it. KISS principle still goes as all Type I were.
It's nice to just wash over what I wrote, isn't it? They are ALL misaligned at some point in their travel, Lane.
My old Neal clutch slave lasted 22 years and was aluminum. Even though it has wear from asymetric pull.
After-market master cylinders used in all manner of racecars, be it Girling, Wilwood, Tilton, or others are all aluminum. Most every one used is a single circuit. My car has three, two Tiltons for the front and back brakes with a balance bar between them and a single Wilwood for the clutch.
OE dual-circuit car stuff tends to be cast iron.
From the looks the MC is cast iron. It just seemed a bit Jerry-rigged to me and generally out of character for the IM. I have been impressed by most of the IM design with the exception of wiring. Thought there might well be a suitable MC replacement that fit in the space without needing to be angled but suspect as everyone else that it is fine the way it is. More of an aesthetic issue than practical. I appreciate the responses.
It looks like there are VW Bug master cylinders with different body shapes. Here, for example, is an EMPI large bore 20.6 mm one where the body seems slimmer. JBugs says it's designed for a super beetle with 4 wheel disc brakes.
As I mentioned, I’m sure if you keep doing a deep dive spend enough time you can find something to substitute just for that quarter inch or that 2% angle that the MC is off
