Hi , this is a follow up to something that started a while ago and sparked my interest. It's been two weeks since this started and this is what I have been able to determine about the occasional leak problem with 1939-48 Ford replacement wheel cylinders. First of all this may happen to some people and not to others based upon the care and procedure that the cylinders are handled during installation. While these cylinders are not defective they are not made as original design and may produce leak issues if installed incorrectly. The offending cylinders are imported and have the input line port drilled at the incorrect angle as pointed out in previous posts and can be identified by a counterbore ridge where the inlet line screws into the cylinder. Unfortunately in all the wheel cylinders that I have examined this seems to have replicated itself in different versions from different people or everyone is buying from the same place and will not divulge the MFG name or source. The newest source I found has a similar incorrect port but that with some saving grace it is 1/16" further in the bore than the major offender and this slight distance seems to prevent accidental leaks. Should you be purchasing new wheel cylinders for replacement this is information before you install the cylinders and charge the system. First pop the dust cup and remove the piston and seal cup from the large bore side of the cylinder noting position of the seal and piston to insure correct re***embly. Second check the inlet port location of the cylinder, if it is up the bore and not in the center of the cylinder this is where care should be taken. Relube the bore with a slick of brake fluid, plug the inlet port and fill the wheel cylinder with a small amount of fluid to a point just below the inlet port and re***emble cylinder, spring,seal cup, piston and seal boot. Install wheel cylinder on backing plate and install brake lines. Fill master cylinder with fluid. Now to check for leaks take a small "C" clamp and carefully tighten the clamp up to just touch the wheel cylinder pistons and keep them from expanding. Do not contract the pistons in the bore, the clamp should just touch to prevent them from expanding. Do this on all non retained brakes. If you are changing out the rears you must do this on both sides not one side then the other. Now bleed the brake system as per procedure. If you have a leak it will show up at this time. If you have no leaks clean up any excess brake liquid and install the shoes carefully making sure that you pull the return spring from the small bore wheel cylinder side to the large bore side. This will prevent accidentally exposing the port opening and producing a new leak. If you attempt to install the brake shoes and spring before charging the brake system you run the risk of positioning the wheel cylinder seal cup to far down in the cylinder when you clip the shoe return spring and this will position the seal cup below the opening of the inlet and a leak may be produced. At the present time I have notified the importers I deal with on the situation that has developed and have left the modifications required to them and their Mfg. If you are using old ford style brakes please keep this in mind and an occasional BTT to remind other readers.
I am glad I stumbled upon this thread. I already had my wheel cyl. on the pick up, so instead of clamps,I was careful not to push in on the wheel cyl. and set the lining out as far as I could without touching the cyl. pins. Bleed the drivers side first and the pins popped out to the shoe, everything OK backed off the shoes. Same on right side, cyl. pins popped out, adjusted brakes and no leaks yet. Glad I found this thread in advance. Juice brakes`39-42 rear --`45-48 front.
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