Thoughts on stock master cylinder.

[Multi69s]

As I get ready to rebuild my 2110, I plan on upgrading the brakes on my 69 bug. This is my game plan, mostly because I have the ALL of the parts laying around.

I plan on using the front discs from a Gia, and the rear brakes from a Type 3 Squareback. When we used the Type 3 drums on our Bajas, with a stock master cylinder, the brake pedal would be closer to the floor before full engagement. This was due to the larger wheel cylinders on the Type 3 brakes.

So my question is, how are the Gia discs (and Type 3 drums) going to affect the pedal action with the stock MC? Will it be useable, or will I need to switch to something else?
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[nextgen]

I have Ghia front brakes with drums for for a few years, stock MC.
Then put on 914 rear discs and still have that set up with stock MC, no problem.

Was going to go with a larger MC when I was putting on new brake lines and actually had a larger MC, but got confusing info on this NG.

Which I believe you are going to hear shortly.
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[oprn]

A larger master cylinder diameter will reduce peddle travel but it will also increase the effort it takes to stop the car. Simple hydraulic theory.
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[raygreenwood]

What are you calling a stock master cylinder?

So since you are not using the stock brakes on the car you have.....you might have to intdrpret a bit.

The type 3 rear brakes are the identical set of parts that went onto a type 4 car. Same 22.2mm wheel cylinder diameter and part #.

The type 3 front brakes are also almost identical to type 4 car (late type 3 are 100% identicql to type 4....and have 2mm larger piston diameter than type 1 front calipers with the same travel throw and windage.

My point.....is that both the type 3 and 4 cars with the same overall brake system with just a 2mm larger diameter front caliper pistin......both get the job done perfectly......with a 19.05mm master cylinder piston diameter.....and both circuits in the master cylinder are 15mm in stroke length.

In fact.....I commonly buy type 3 kits to steal the seals to rebuild type 4 master cylinders. The only reason I cannot use complete type 3 piston and seal assemblies in a type 4 MC....is because the two cars use a different MC casting.....and the piston shapes will not meet up with the fluid supply ports.....but otherwise the functional output of each is identical.

Personally.....I would simply go with a type 3 master cylinder which should be pretty close in the MC casting size and shape. In fact a lot of vendors and books list the same replacement MC for type 1 and three. I have always thought that to be less than accurate....depending on the model and year.

The type 1 master cylinder listing in the "without guesswork" book.....shows:

From chassis # 111 2 000 001.....shows a 19.05mm MC...with a 17.5mm fromt circuit stroke and an 11.5mm rear stroke. Just keep that in mind for a refernce. That should be a beetle with front and rear drums....right?.....and that is with 23.81mm front wheel cylinders and 17.46mm rear wheel cylinders.

BUT.....
The book also shows that from chassis 117 000 001.....and INCLUDING model #14 from chassis # 144 2 000 001....which is the ghia.......it also had the 19.05mm diaketer MC (which has the calipers you are using).....but with a 15.5 front circuit stroke.....and a rear MC circuit stroke of 12.5mm......using drums in the rear with the same type 1....17.46mm piston diameter.
It next shows that ghia chassis from 147 000 001......reduced both front and rear circuit to 14mm.

So.....my takeaway is that using the ghia front calipers....you should be able to feed them just fine with an MC diameter of 19.05 and a front circuit stroke of minimum 14mm and maximum of 15.5mm. I would bet that the extra 0.5mm stroke was just brake bias tuning.

And.....being that every car that came with stock type 3/4 rear drum brakes with the 22.2mm whel cylinders worked perfectly with a 19.05mm diameter MC with a 15mm stroke.....you will be fine with that.

I would get a type 3 MC.

One of the things I see that a lot of people....and a handful of aftermarket parts mfgs..... do not quite get....is that of the most important brake tuning items betaeen VW cars that pretty much use the same master cylinder casting with the same bore and fluid inlet/outlet port drilling locations .....is that the piston sets for one model of car to another... . had longer or shorter tail pins on them to alter stroke length.

They also had stronger or weaker springs in them to affect when or how fast the rear brakes came on versus the front.

So on your set up.....you could easily use a type 3 MC to run it with no issues for how much hydraulic pressure it produces to give you normal stroke . It will be plenty .....but.....to get them exactly correct amount for the weight, length and balance point of the car.....you may have to do some tuning.

Since this is about hydraulic pressure......the correct way to do this....if you need to limit the amount to the rear (which would be the equivalent of a shorter MC stroke on the rear circuit).....is to use an aftermarket hydraulic adjuster.....pretty cheap.

If you need to increase the hydraulic pressure on the rear (the equivalent of a longer stroke).....the most correct way is to increase the travel of that piston by grinding a small amount off of the tail pin or stop of that piston in the MC. Yes....it increases pedal stroke by that amount.
Thats also a lot of work. It meanings bleeding, driving, testing, stopping and pulling the MC apart....grinding, cleaning, reaseemhling, bleeding, driving and testing.

Across several of the same type of MC.....you find this same piston stroke adjusting feature for the front circuit is accomplished by swapping the steel thimble shaped seat that is holding the outer piston spring onto the piston.....with one that is shorter or longer

If what you need is to have the rear brakes come on sooner or later.....that is done by changing the spring on the piston in the MC.

What this does.....is that as you push the pedal...the first/outer piston starts moving and operating its brakes first (usually the front brakes). If the inner spring for the rear circuit is really stiff......the front circuit piston may move several millimeters......before its spring compresses enough to move the inner (rear circuit) piston enough to start operating the rear circuit.
Likewise....if you want some small amount of rear brake to come on early......the inner spring on the rear circuit will be soft.....and that piston may start moving at almost the same time as the front/outer piston starts moving but will not move at the same speed or rate until quite a bit of pedal travel.

So....start with a stock type 3 MC.

Sorry for the length. Ray

[stanthedog]

I had that same setup in my 69 bug. it would almost put you thru the windshield if you landed on the brakes. if i remember right, on the front circuit of the mc, you have to remove the check valve or the disks will drag.

[Bruce Amacker]

I put T3 rear drums on my '69 Ghia and it would put you through the windshield on a stop, quite noticeable improvement. In theory you should remove the check valves from the front feeder lines if it has them, as drums brakes "need" a check valve in the line but discs don't. In theory you need a Ghia MC but vendors show that Ghia and Beetle use the same MC, I've watched this for many years and it seems like many have eliminated the check valves. The AC bus disc kit comes with an MC where they have modified the check valves to make them inactive. In reality I'd bolt it together and go with your stock MC, just make sure the front wheels spin freely after a test drive.

I noticed no difference in pedal height after the install. Beware if the rears lock it will spin the car around. If this becomes a problem go with a smaller wheel cylinder bore- several VW cyls interchange except for the bore size.

Good Luck!
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[raygreenwood]

[neil68]

I run 4-wheel discs on my street-strip 68 Beetle with 2332cc using a 19mm OEM German dual-circuit MC. I needed to remove the stock residual pressure valves. This MC has worked for years and pedal pressure is normal.
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[Multi69s]

[EVfun]

[oprn]

This is all really good information. Thanks guys!
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age)

[Multi69s]