Suggestions on replacement caliper

[OrangeCrusher]

Plugged some guesstimates into this calculator

[Bruce2]

looks like you have the radii of the tires wrong. You've entered the diameter.

[OrangeCrusher]

nice catch thanks

[P_Vilefort]

Does Wilwood have calipers for a solid disc? (I found out that Wilwood has a caliper for a solid disc). You don't need much braking force for the rear especially if you have full sized solid or ventilated front discs. If you are using calipers that are similar to the originals that came on some Beetles or Super Beetles know that the caliper had a 40mm piston that really was 1mm smaller. The Karmann Ghia had a 42mm caliper. The rear should be smaller than the front if you don't want to diddle around with valves that restrict flow to the rear caliper. For the front you can get calipers from VW Brazil and they mimic the original ATE caliper. I understand that you can also purchase the original caliper from ATE for about $150 (that was the price before the pandemic). If you are trying to adapt to a Super Beetle you will have to make an adapter because the distance between the bolt holes is longer on the Ghia and 411/412 then on the Beetle or Super Beetle (52mm bolt spacing). The cross-sectional area of the original ATE front calipers was 1.85 sq-in times 2 = 3.70 sq-in X 198 lbf/sq-in = 733 lbf. plus the other front caliper 1,466 lbf. That is 73% of the entire weight of the Super Beetle. A normal person could stop the car without needing a booster.

Just to see what I could find I searched for Wilwood calipers for VW Super Beetle using this search string "wilwood brakes for rear VW Super Beetle solid discs 4 lug". This is the URL https://www.ebay.com/itm/114812820208. Look at the listings below this one item. It appears you would have to get an additional mechanical brake that Wilwood sells. You could have saved yourself a load of money by keeping the stock rear brakes.

If you want to know how to calculate the force on the pads it is quite simple. Assume you are in a panic stop and you are applying 50 pounds of force to the brake pedal in the car. Now you need to determine the length of the pedal arm; that is from the middle of the pedal to the point where the piston rod to the master cylinder is connected to the pedal arm. Modern cars have a pedal arm that is quite short compared to the Beetle. If I remember correctly, the pedal arm on the Beetle or Type 1 is about 7 inches> Next you calculate the cross sectional area of the master cylinder bore. On the Type 1 the bore is 0.75 inches or 19.05mm. The cross sectional area is calculated by the area of the bore which is a circle (Pi X D² /4.) that is in inches² times an assumed 1 inch of stroke. So the final volume is 1.767 cubic inches. To get the force on the fluid in the master cylinder take 50 lb X 7 inches = 350 lbf-in. Divide 350 lbf-in by 1.767 cubic in = 198 lbf/sq in. That is the force on the fluid in the caliper. To find the force on the pads or disc, determine the cross-sectional area of the caliper piston. If there are two pistons multiply the area by 2. Since you have two calipers in the front. Then multiply by the lbf/sq in. and that result is the force being applied to the pads and the caliper. In most cases, the force is equal to or greater than the weight of the vehicle. If that is the case, you will not need a vacuum booster; more correctly an atmospheric pressure booster.

The front VW kits on ebay look like they are using the VW caliper from Brazil. It is almost the same casting as the ATE.

Many years ago I put Avanti disc brakes on the front of my 1951 Studebaker. The master cylinder was the same cross-sectional area as the VW but the Bendix caliper pistons were 2.25 inches in diameter. When I calculated the available force on the front calipers it produced more force on the disc than the 1951 Studebaker weighed. Stopping the car felt like it had a brake booster.

[P_Vilefort]

This calculation has some problems. The hydraulic pressure is the same anywhere in the system as long as there is no air in the brake pipes, wheel cylinders or calipers. There is a solid fluid column from the master cylinder to the brake calipers or wheel cylinders. The force is the same unless the system has a proportioning valve. If the rear wheel cylinders are sized properly, the rear wheels with never lock up under normal stopping, not counting ice or bald tires..

[Piledriver]

Pads matter.
I ended up using (iirc) stoptech "sport" pads out back on my square to resolve not having quite enough stop out back, this replacing the std issue pagid pads for 944s. Use them on my cabby up front on the 16v brakes, it can do stoppies now. Big improvement, zero fade.
(Mk1 rabbits have the opposite problem a rear engined buggy has... rear tires just keep back end from dragging)

Residual pressure valves do work, but you might want better than EMPI. (although the empis working for me so far)

You can also check some of fjcampers racing threads, he has his preferences and knows places happy to put whatever friction material you want on whatever pattern pad backers you like. (or clutch for that matter)

[Bruce2]

.... the originals that came on some Beetles or Super Beetles know that the caliper had a 40mm piston that really was 1mm smaller. The Karmann Ghia had a 42mm caliper.

We've been through this before. Stop posting wrong info.
A Beetle, Super Beetle, and Karmann Ghia all had the exact same calipers and rotors. The pistons in the calipers were 40mm. A 42mm caliper was NEVER used on any Karmann Ghia.

. If you are trying to adapt to a Super Beetle you will have to make an adapter because the distance between the bolt holes is longer on the Ghia and 411/412 then on the Beetle or Super Beetle (52mm bolt spacing)..

The larger caliper with a 42mm piston was used on the Type 4s, and Porsche 914s. Along with the larger caliper, they also had a slightly larger rotor. A Karmann Ghia NEVER used the 42mm calipers!!!

Type 3s came with both sizes of calipers. 66 to 71 used the 40mm Type 1 caliper, while 72 and 73 Type 3s used the larger 411/914 caliper.

[Piledriver]

The T4 rotor/caliper setup also had a different (larger) rotor offset thus not bolt-on for T1s.

Cannot recall if late T3 used 914 rotors as well, but the offset is compatible with Wilwood superlites with steel std hats and 1.25" rotors.
(using the original rotors turned down as hubs)
Coleman also sells cast aluminum 8x7 hats that can have the rotor mount area trimmed a bit for various offsets.

Late T3 rotor bolt radius is ~same even, but spacing is off. I used one existing caliper mount hole and "moved" the upper hole with a bit of TIG magic on the spindle. (Have a junk superlight for an alignment/weld jig)

(I have a 73 square, 4x1.25" Wilwood superlights up front and 944T rear arms... but with front 944 T/928 FRONT (4x32 iirc) calipers on 965 32mm rear rotors out back)
The PF 14 pads out front work a bit too well, enough that I needed more rear piston area than the 28mm 944 rears AND very good pads to get good balance wet or dry.



Wilwood sells 300mm 8x7" rotors in just about any width, but you likely want solids unless you plan on tracking the vehicle.
(NOT AX, you dont need huge vented rotors in a parking lot no matter how fast you are)

[Piledriver]

Unless you are building a sand rail you will almost certainly find you need front brakes due to weight transfer.
Complete the calculation. Its going to give you gibberish balance#s with only rear brakes.

The calculator expects front and rear brake systems. (2) separate hydraulic systems.
If front and rear pressures differ greatly and you dont have 2 masters, you need to tweak the caliper bore sizes so they more or less match with the desired braking%... better pads and larger dia rotor centerlines make a huge difference.
(has been a few years since I used it)

I suspect you are going to find on a rear engined car the front and rear brakes are going to be close to 50/50 under max braking, unless vehicle is lifted.
The lower it is, the transfer to front is less.

If you are running super skinny tires up front and its a drag strip only car disregard everything I have said aside from buy good brake pads.