Disc brake conversion on rear

Feb 17, 2021 12:06 PM - 170 Views Create A New Thread

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Watauga, TN

should I or not?
I have a 34 glass car , frame was built by a local shop, very reputable shop, disc in front drum in rear stops ok but not great, I have owned and driven 20 yrs. called shop guy few weeks back to ask if he thought putting disc on rear would give me better brakes ? He said I was wasting my time and money converting to disc on rear that the drum rear were as good. My question is anyone else converted rear drums to disc and were you satisfied or not with the swap? thanks in advance, Bob


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  • tofol69
    Feb 21, 2021 at 1:39 PM

  • I had thoughts of doing the same thing to my Plymouth but was talked out of it and was told that a larger booster would be better, faster to replace and cheaper.

  • bobalou1934
    Feb 20, 2021 at 8:02 AM

  • Thank you Jaybird, all comments are good thoughts and give things to check out.

  • Jaybird
    Feb 19, 2021 at 8:09 PM

  • I battled the same issues on my Roadster. I had an adjustable proportioning valve in the system. Two changes made a big difference. I removed the adjustable valve and also replaced the Maverick master cylinder with a larger 1" dia piston cylinder from a Turbo Coupe T-bird if I'm not mistaken. Vette master from Summit works well. Ports on both side to accommodate tube runs.I just installed one of those on my 57 Ford Wagon

  • bobalou1934
    Feb 18, 2021 at 8:59 AM

  • thanks guys, there is some good thoughts here, delux39: great thoughts I contacted a guy couple years back on an an ad about hydro boost for street rods he helped me figure out my about the 5to1 ratio at that time I dropped from a 1inch master cylinder to a 7/8 inch and it helped a bunch but I had problems when I installed a double booster, it worked worse I went back to single one. I think maybe I should look into bigger disc on front possibly wilwood as tazhog54 suggested, to get bigger on back would I have to get from backing plate out? I think my rear id from a Mavrick not sure what year just know its an 8"

  • tazhog54
    Feb 17, 2021 at 8:14 PM

  • I have had both , But really like drums the best rear 11" dia and 2 " wide shoes, The bigger ones . and disc up front 4 piston wilwood ! Seems to be the best of all !

  • delux39
    Feb 17, 2021 at 7:20 PM

  • I go with the shop guy, waste of money for the returns you will get. The residual valves you have installed are correct. They prevent fluid from flowing beak into the M/C when it's lower than the wheel brakes. I have never been a fan of proportioning valves, fixed or adjustable. A fixed valve was designed for something completely different i.e. different M/C, different booster, different weight (and distribution) and different size tires. Other than that it's a perfect match. The adjustable valve just strangles fluid flow to the back. As I understand it most M/C already have a small hold off feature built into the plunger. The above is just my opinion. Now, onto better brakes. First is pedal ratio. Should be above 5:1. Any increase in ratio will give more leverage for better braking. Tuff to do with under floor M/C. Second is a duel diaphragm booster. Third is smaller bore in the M/C. Say yours is 1 1/8", just reduce it to 1" will make a difference. By the way the pin adjustment between the booster and the M/C is very critical, worth researching it. Last is upgrade the front disc/calipers. Wilwood has a nice upgrade but wheel clearance could be an issue. Hope this gives you a few thing to think about for better brakes.

  • 32 Dodge
    Feb 17, 2021 at 4:00 PM

  • The proportional valve is usually in the line to the rear brakes. They close the rear brakes off a little to make the front have more stopping power. Just like when we used to ride bicycles, put on the front brake hard enough, and you went over the handle bars. Remember? Any way, the red and blue hold a certain amount of pressure- I don't remember, but its somewhere around 3 pounds or so. (Different for drum and disc). Also since your master cylinder is below the brakes, pressure needs to help the brakes work without the fluid flowing back into the master cylinder.
    Have someone check this out for you.
    I bet this is where your stopping problem lies! I hope so, because this would be an easy and cheap fix!

  • bobalou1934
    Feb 17, 2021 at 3:12 PM

  • Thanks, all comments are worth considering. I dont think I have a proportioning valve It does have two valves in line close to master cylinder under floor a blue one and a red one!

  • 32 Dodge
    Feb 17, 2021 at 1:47 PM

  • Is it possible you have a proportional valve problem? Your car should stop fine with disc/drum. Mine does!
    I guess this doesn't answer the question you asked above..........sorry!

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