Are you using stock rear wheel cylinders in the rear drum brakes? I am running type 3 rear drums and a from what I remember, a 19mm single circuit (aka bus) master cylinder. I would have to check my reciepts... but I don't think it is the 22mm standard "buggy" master cylinder. When I was trying to come up with which wheel cylinders to use I found that the '72 super beetle I cut the IRS out of had 24mm front wheel cylinder pistons which as far as I can tell are the largest type 1 wheel cylinders. I bought a pair of new wheel cyinders for that application from Car Quest and installed them... properly bled and adjusted I can lock up the rear tires no problem which are 31x12.50 on a 8" wide wheel iirc. I went with the type 3 drums because I already had them off a parts car that came w/ my buggy, so I basically have about $25 in my rear brakes.
I just found this site which is a good summary of wheel cylinders and drum brakes and such, it's all stuff I had figured out through research and some measuring, but in one handy location, already figured out for you. (would have been nice to come across it a year ago) - from
http://vw.zenseeker.net/Brakes.htmQuote:
Drum Wheel Cylinders
The larger your wheel cylinders, the greater the braking potential (assuming your master cylinder and tire traction is up to the challenge). A stock VW Beetle comes with about a 22mm wheel cylinder in the front and a 17mm one in the rear. This is sufficient for most "normal" street use. For offroad use, you may want to decrease the braking power of the front by installing a proportioning valve in the front to decrease brake pressure their, or by altering your brake hardware configuration.
A 68 or later rear 17mm wheel cylinders (11 361 1053B) can be installed in the a Type 1 Beetle kingpin or ball joint front end to decrease the front braking potential.
A stock 71-on Beetle and need a little less braking up front you can use the the rear T3 - 65-73 22mm wheel cylinders (311 611 067C) can be used in lieu of the standard 23.8mm cylinder (361 611 067A) normally used on the front of 1971-79 Super Beetles to decrease front braking Other wheel cylinders can be switched around to the front, but you will need to check the distance from the backing plate to the center of the shoe first.
The rear brakes require more than just installing a new wheel cylinder if you are using a swing Axle trans. (up to 67). First you must replace the swing axle backing plates with 68 or later IRS ones. The IRS backing plates allow you to install 57-on ( 131 611 057 ) 22mm wheel cylinders. (Note: You can NOT use the wider 1 5/8" 68-on brake shoes with the stock 5-lug brake drums).
On the rear of 68-on IRS Beetles, you can install the larger 22mm wheel wheel cylinder (131 611 057) or switch to a rear T3 Brakes setup. The 68-on IRS rear brakes also have a wider ~1 5/8" brake shoe than the 1 3/16" wide swing axle shoes.
The Type-3 rear brake (65 & earlier for 5-lug drums) linings are wider ( 1-3/4") than those on Type-1s, the drum diameter is larger and they already have 22mm wheel cylinders. You can also upgrade the wheel cylinders to use the 23.8mm (361 611 067A) front SB wheel cylinders with the T3 rear brakes. If you get the complete setup with backing plate; drums and all it's an easy bolt on installation. 5-lug axle splines are 1 7/8" & 4-lug axel splines are 2 1/2" long. You will have to remove about .550" off the outside snout of the drum to use these with a short swing axle transmission.
There are other set ups that can be made to work, to include some type-2 and "Thing" brake upgrades. These other options often require hard to find parts and the cost of these modifications may be higher than just converting your brake system to discs.
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