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Extreme Veteran
Posts: 363
 
| Anyody else out there running front disc brakes with the original single pot m/cylinder?
My car has a very good pedal and braking ability BUT I did notice on one longer trip through steep roads, with my foot regularly on the brake peddle, at the end of it the brakes were starting to lock on. Now I know/presume what the issue is, the return/residule valve which would normally keep minimal line pressure on the drum brake w/cylinders, will not allow the fluid/ line pressure to return fast enough from the disc calipers to the m/cylinder most notably when I'm pumping those discs going down continuous steep winding hill country.
So has anyone got around this whilst still retaining the original master as I can't pull the entire valve out of this type of system right as I'd have no pressure on my rear w/cylinders? I suppose I could run a valve just in the rear line?
Please no "just put a dual circuit aftermarket m/cylinder on it". I realise that is one option but I'm curious if I can fix the original to work with discs, as I said before, otherwise the braking ability of this car is really nice.
Thanks
Owen |
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Expert
Posts: 3396
 
Location: Chestertown, NY ( near Lake George) | You really need the proper disc/drum master, with 2# residual for the discs, 10# valve in the master for drums is excessive. Also
Why would you insist on a single pot master, when all vehicles with disc /drum set ups are oe engineered with dual masters and proprtioning valve. Also for optimum operation you need to move fluid with the large bore calipers. |
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Extreme Veteran
Posts: 363
| I hear what you're saying, but I do recall a lot of guys were still running the single pot with front discs and was curious if they had same issue and a possible fix.......guess I'm being a little lazy and not wanting to change out m/cylinders when I have such nice brakes and pedal feel......probably put the dual on and get a slushy pedal... 
Thanks |
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Expert
Posts: 3396
Location: Chestertown, NY ( near Lake George) | You have to pick the appropriate bore size mc to get a normal pedal feel, this changes if you have a power booster. None of the conversions we have done in the shop had mushy pedals. The system requires properly balanced components. A smaller bore mc will have increased pedal travel. A larger bore mc has less pedal travel. This assumes everything else is done right. Lottsa good advice on this issue from conversion kit sources. The prop valve will balance brake application and timing.
Edited by Shep 2021-10-17 5:39 PM
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Extreme Veteran
Posts: 363
| I've done a few over the years mainly with the AAJ kit and I must admit they have worked out well, one or two have a slightly softer pedal but those cars are running silicon fluid.
This 300D just stops so,so well on that little single pot, I've only had the brakes tighten up once, but I'm sure it will happen again if I leave it.....time to get motivated and do the swap.
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Expert 5K+
Posts: 6500
 
Location: Newark, Texas (Fort Worth) | Using a single pot and you will probably die. NOT ENOUGH VOLUME. Kiss your wife before you go on your first trip. https://www.rockauto.com/en/moreinfo.php?pk=309082&cc=1082360&jsn=57... if your push rod is adjustable; you should be able to use it. other wise there is a mopar adjustable push rod you can find. Measure to make sure. https://www.doctordiff.com/62-70-adjustable-master-cylinder-push-rod...
http://www.forwardlook.net/forums/forums/thread-view.asp?tid=62876
Edited by mstrug 2021-10-18 5:25 PM
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Extreme Veteran
Posts: 363
| Actually, if you measure the volume of large original single pot versus the low early B body m/cylinder that we need to fit under out boosters on these cars there is very little difference in volume you just have safety of two seperate circuits. Been driving around for sometime and car performs very well so lets not get over dramatic here........
But appreciate the input, thanks. |
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Expert 5K+
Posts: 6500
Location: Newark, Texas (Fort Worth) | It would be insane not to put a 2 pot master when the brakes are switched to disc.
 (well ackually.jpg)
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 well ackually.jpg (52KB - 120 downloads)
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Expert 5K+
Posts: 5006
| if the original is working so well... stick with drums..
the big master cylinder were all using is made for the truck calipers were using so its all good.
my brake pedal feels as good as my new truck and I have all 4 disc. |
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Expert 5K+
Posts: 9666
Location: So. Cal | Actually,  I have been running the original master with disc brakes on my '56 Savoy for over 40K miles. No issues whatsoever. I have also used it on my '57 Windsor and '58 Firedome without issue. I've driven the '58 Firedome about 15K miles with the original master. In fact, these cars worked so well, that it led me to believe that the original masters don't actually have any residual valve in them. If they did, the discs would drag while turning, but I have tested it over & over and found that not to be the case. If you are suddenly having issues, you may just need to rebuild it, or it may be caused by something else in the system. The dual master is definitely more safe, but so are 3 point seatbelts & airbags. If you mitigate your risk by keeping the system in top shape (especially the rear drum wheel cylinders!), you should be OK. If you convert to discs on all 4 wheels, calipers tend to not fail as much as wheel cylinders so that may make it even more safe with a single pot master. And like I said, if it has a residual valve in it, it doesn't work very well at all; and I really doubt that it actually has one.
Edited by Powerflite 2021-10-19 4:45 PM
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front discs with original FWDLK m/cylinder
