Re: Getting ready for a Treadle Vac Replacement

Posted by HH56 On 2015/1/25 16:24:55

You really can't go by the stroke distance of a BTV because the operation is so different. Conventional masters will generally not have as long a stroke because the larger pistons push more fluid in a shorter distance. IIRC, the BTV is around 3 1/2" +/- max but PackardV8s method of checking is the way to be sure.

Your booster limits will determine part of the new max stroke available. You will have to decide on which booster you are going to use and see if it will work with the master you choose. The adjustment at the wheels will determine part of how much stroke you actually need or use. If the shoes are properly adjusted the master will move a small distance before brakes apply and conversely, wear or a bad adjustment where the wheel cylinders have to move the shoes quite a bit will require a large movement of the master. That last part is one thing to be concerned about with a small diameter master. Figuring worst case, can the small master move enough fluid before bottoming that the brakes can fully apply.

You also need to factor in mechanical design compatibility between master cylinder and booster. The bolt pattern, centering pilot arrangement, and spacing and size of the bolts connecting the two are important. The relaxed point of the booster has to be far enough back that the piston rod adjustment can ensure the master piston is in it's full relaxed position yet the actuating rod to master has to be the proper length so the booster doesn't have to travel far before the master piston starts to move.

It might be worth calling ABS or Master Power Brakes and speaking to one of the technical people to see if the Wilwoods will work with the 7" universal booster -- or the booster you are thinking of getting -- before spending any money. If not, maybe they have another option.