OK, so I have a 1934 Ford that is using 1948 drums, backing plates and master cylinder. I made a mounting bracket (will try to add a pic) and have an arm that pivots to change the pull of the brake rod- to a push to work the master cylinder It is equally long above and below the pivot point. My pedal ratio is 6:1, using the stock ’34 brake pedal and clutch assembly. I had always used DOT3 fluid but every few years, the wheel cylinders would start leaking and I got tired of replacing them, so when they started leaking this last time, I evacuated the system and switched to DOT5 fluid. I know exactly how to adjust the ’48 brake shoes and even as tight as I can comfortably set them, I cannot get a firm pedal. I can pump them until the cows come home and it still doesn’t give me the good solid pedal that I want/need and of course, it won’t stop the car worth a bag of beans. Question, did I mess up switching to DOT5? If so, how the heck do I keep from having to replace leaky wheel cylinders every few years?
If you bleed your brakes once a year to get fresh fluid to the wheel cylinders I don't think they would leak every 3 years. The old fluid in the wheel cylinders absorbs moisture and corrodes the bore of the cylinders and causes them to leak. By bleeding them you wash out the moisture filled fluid which causes the corrosion.
Sounds like there is air in the system. May need to pressure or vacuum bleed to get it out completely. The pushrod bolt should be done up in double shear, to be safe.
If you’re confident your adjustment is correct l would go with air still in system or maybe compromised flex brake line l am guessing you have somewhere in your system So the bores of your wheel cylinders looked good when you replaced the seals. There has been previous discussions about low quality seals /wheel cylinders
Try to locate a plug that will fit the M/C. Failing that, get a short section of tubing and pinch it off. Block the M/C outlet. Try the pedal again. If it's hard, reconnect outlet and move the plug to the tee and plug off the rears. Then try blocking the fronts. Yes, it's messy and it will make you roll around on the floor. It will also pinpoint the problem.
First thing that comes to mind when looking at the picture is, is the push rod long enough? Is it one that came with the master cylinder or one that you fabbed up? Is there any adjustment to the length? If you don't get a firmer peddle when pumping them maybe the stroke is not long enough?
I use DOT5 fluid in my 2 hot rods and my FED. One hot rod originally had DOT3 when I built it but made the switch when I blew it apart for paint. I read up on DOT a lot before I used it. One of the mentions was that DOT5 doesn't play well with other types of fluid. Did you flush out your brake system completely? One other thing I read is that DOT5 will hold micro bubbles in suspension for a long time, so it's important to not shake the bottle or splash it around that might introduce air bubbles. When I filled my empty brake systems I just filled the master cylinder, which was higher than any of the calipers or wheel cylinders, opened the bleeders and let it fill by gravity. I had to keep checking the master cylinder fluid level regularly so it didn't go dry during the process. Since that method filled the system very slowly and gently it didn't have as much chance of introducing air with the fluid pumping back and forth during the fill and bleeding process. DOT5 was sometime bad-mouthed in what I read because of a soft brake pedal feel, but I'm quite pleased with the pedal feel in my cars. One of them has had DOT5 for about 6 or more years, the other a bit over a year, and the dragster about a year. I'm sold on DOT5, all of my paint is still where I put it. It does seem to like being treated properly. Best wishes....I hope this might help in some way. Lynn
I've had DOT5 in my Olds for over 20 years. Always worked fine. Last summer I replaced brake hoses and refilled again w DOT5. I've had no problems.
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