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Posted By Discussion Topic: Bleeding brakes -- page: 1 2     Dustbowl 02-17-2020 @ 12:13 PM reply profile send p.m. Member Posts: 74 Joined: Feb 2011 I had to replace my 39 Ford master cylinder because of crack and leak. I bench purged the new one before installing. Then I used a power bleeder to purge about a quart of new fluid thru each wheel. But the brake pedal is still soft after this. I have done this bleeding successfully before and went exactly by instructions this time keeping about 25-30 psi on the power bleeder. I noted this time that there was a seemingly low flow of fluid out of each bleeder (done one at a time). It took about ten minutes of flow to collect one quart of fluid in my receiving jar. I have three specific questions for you: 1. Is the flow rate I observed normal or low in your experience? 2 If low, what could cause this? 3. If low, could this slow rate fail to purge air out of high spots in the hydraulic system? thanks Phillip kubes40 02-18-2020 @ 4:57 AM reply profile send p.m. Senior Posts: 3368 Joined: Oct 2009 I too use a power bleeder on all of my projects. I start with 20#. The flow is smooth - difficult to describe in words. However, all of the air is forced through. I place a translucent line over the bleeder vale with the "open' end in a jar of fluid. That way, it is easy for me to see when the bubbles stop. If you still have a soft pedal after installing a new master, I'd suggest the master is defective. That is of course assuming your system was good prior to the (first) master becoming problematic. Mike "Kube" Kubarth 37RAGTOPMAN 02-18-2020 @ 6:10 AM reply profile send p.m. Senior Posts: 1940 Joined: Oct 2009 HI try just applying a little pressure on the brake pedal and hold it there, and see if it goes down if it does the master cylinder is defective, [brake fluid is passing the piston,bad seals ] also make sure you have some free play in the brake pedal rod, so piston returns,fully 1 inch of free play is normal also test your power bleeder, to see if brake fluid is not restricted, dirt etc, I do it the old fashion method by foot, with a clear hose and bottle, and with a helper, hope this helps 1937 RAGTOPMAN TomO 02-18-2020 @ 6:57 AM reply profile send p.m. Senior Posts: 7243 Joined: Oct 2009 Are you using DOT 5 fluid? A pressure bleeder is not recommended for DOT 5 fluid as it can introduce air into the fluid. If you are using DOT 3, 4 or one of the newer synthetic fluids, are you still getting air out of all of the wheel cylinders? if you are, the master cylinder is defective. You should be able to purge the air from the system using about 1 pint of fluid. If you are not getting air out of the system and still have a spongy pedal, the master cylinder or one of the wheel cylinders could be bad. Tom This message was edited by TomO on 2-18-20 @ 9:00 AM Dustbowl 02-18-2020 @ 8:55 AM reply profile send p.m. Member Posts: 74 Joined: Feb 2011 Thanks for useful replies but I'm still hopeful to hear from someone who has info on flow rate with power bleeder. TomO 02-19-2020 @ 9:53 AM reply profile send p.m. Senior Posts: 7243 Joined: Oct 2009 It is almost impossible to define the rate of flow when using a power bleeder. There are too many variables to give you a good answer. If you believe that the flow is less than when you have someone pump the pedal for you, then you could have a problem with the master cylinder. Tom Dustbowl 02-23-2020 @ 12:41 PM reply profile send p.m. Member Posts: 74 Joined: Feb 2011 My brake problem remains a mystery to me even after I am sure there is no air in brake system. My overall situation is as follows after installing new master cylinder: -brake shoes adjusted well -have bled brakes twice - about a pint each wheel both times - with power bleeder -there is no leak in system as 15 psi holds steady in the power bleeder -have adjusted the plunger from minimum to maximum with no significant change in results after all this, my brake pedal goes all the way to the floor using only hand pressure!!!!!! Separately, I adjusted all brake shoes tightly against the drums. In this case, the pedal goes about half way to the floor and stops hard. It does not seem "spongy" before stopping and no "fade" when holding pressure on the pedal. So my guess is that master cylinder is not pumping any/much fluid during part of its travel but I'm not confident in this conclusion. My next step is probably to replace the master cylinder again but first I would like to know is any of you come to a different conclusion when you consider the above information. Many thanks 37RAGTOPMAN 02-23-2020 @ 1:08 PM reply profile send p.m. Senior Posts: 1940 Joined: Oct 2009 HI how old are the 3 rubber hoses, they might be expanding giving you a soft pedal , it does not take much, have somebody pump the brakes and check the rubber lines,also try sliding the rubber boot on the master cylinder back 'do you see any brake fluid , if so replace the master, brake fluid is by passing the piston, like I tried to explain my last post. also I replaced the wheel cylinders on a 1938 Woodie I was doing a brake job for a customer, I had replaced all the wheel cylinders, bleed brakes , could not get a pedal went home,. next day removed the front wheels to find out the NEW REBUILT WHEEL CYLINDERS, were leaking, had filled up the grease retainer cups, WITH BRAKE FLUID, ARE YOU LOOSING BRAKE FLUID, called the supplier and return them, and bought 2 BRAND NEW wheel cylinder, PROBLEM SOLVED, hope this helps 1937RAGTOPMAN you have to be care full were you buy your parts, This message was edited by 37RAGTOPMAN on 2-23-20 @ 1:13 PM kubes40 02-23-2020 @ 2:01 PM reply profile send p.m. Senior Posts: 3368 Joined: Oct 2009 Dustbowl, It would be nice to know what you had BEFORE you replaced the master cylinder. It's possible you have a defective cylinder. It happens. I have experienced a number of dual reservoir cylinders wherein the fluid goes between the reservoirs but not too much out to the wheel cylinders. While the rubber hoses can cause this symptom, it's highly unlikely. I'd suggest (without knowing why you had replaced the cylinder) that you go to your local NAPA and buy a NEW master (about $52) and swap out the one you currently have. Mike "Kube" Kubarth Dustbowl 02-23-2020 @ 3:20 PM reply profile send p.m. Member Posts: 74 Joined: Feb 2011 I forgot to mention that the brakes were working perfectly before I had to replace leaking master cylinder. So I believe it not an issue of expanding rubber hose or similar faults which would have shown up before i replaced the master cylinder. Does this automatically mean my new master cylinder is bad or did I do something wrong when installing it?

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