Vintage Mustang Forums banner

1 - 8 of 8 Posts

·
VMF Ambassador
Joined
·
6,665 Posts
Discussion Starter #1
Started pulling off my old rear drums today to make way for the new brakes. When I pulled off the old brake line, I was kind of surprised to see... well, not that much fluid coming out. I checked the MC reservoir and both front and rear bowls were reasonably full, so I stomped the brake pedal a few times to convince the brake fluid to get flowing. Never did get it to flow, it would just spurt out a bit at a time when I stomped the pedal. Maybe the rear end was higher up than some point in the rear brake line circuit, keeping it from flowing, but I figured that holding the pedal should put enough pressure on the circuit to push out the fluid. Who knows though.

What I did find was that when I had the rear brake line circuit open, I had absolutely no pedal to speak of. It just went straight to the floor and there were no front brakes at all (that I could discern, at least). Very concerning! And as I pumped the pedal to drain some of the rear brake fluid, I also found that the front brake circuit was draining a bit as well. So - I assume that the master cylinder is dead? Leaking past the seals in the bore?

At any rate, this is just a curiosity thing as I have a brand new Raybestos MC coming sometime this week. I'm swapping out the master cylinder and putting in braided stainless steel brake hoses on all 4 corners (since it's been a while since I replaced the rubber brake hoses), so hopefully this will take the sponginess out of my pedal.
 

·
Premium Member
Joined
·
12,043 Posts
I don't understand exactly what you were expecting to see with the lines disconnected. Were you expecting a constant stream of brake fluid running out due to gravity until the MC ran dry? I've heard of "gravity bleeding" the brakes but I don't know how long that takes to work.
When you step on the pedal for the first time after disconnecting a brake line you will get a spurt of fluid but when you release the pedal it sucks air back up the line. Repeated presses of the pedal will then spurt a little bit of fluid and air. The better way to check would be to submerge the disconnected line in a clear jar with a small amount of brake fluid in the bottom and then press the pedal. The jar will slowly fill as more fluid is pumped out while pressing the pedal than gets sucked back in when the pedal is released. If you have a blocked brake line it will be evident that fluid is not filling the jar quickly.
Some people make it sound like a dual bowl MC is your savior if one side fails. I have found that you will have practically no brakes at all if one side fails. It can be downright scary the first time you experience it. I have had leaking calipers or wheel cylinders in the past and didn't realize it until the MC went dry and very little happened when I stepped on the pedal.
 

·
Registered
Joined
·
4,594 Posts
You should see fluid dripping out of the lines till it runs out unless you have the rear up so high the line is even or higher than the master. Are you getting the fountain in the reservoir on the front circuit also? Perhaps it was the rears after all that were working and the fronts were not...:eek:

I would eyeball the line all the way to the master and make sure you didn't accidently crush it somewhere. Don't forget to replace the hose to the axle with braided while your at it. That hose could be swollen closed due to age. If in the end after everthing is replaced. the lines still don't weap before you hook them up, I would consider replacing them as they are full of...
 

·
Registered
Joined
·
7,109 Posts
I would suspect the rubber hose section too, especially, if you don't recall it being replaced. yeah, I all of my flexible lines with braided.
 

·
Registered
Joined
·
35,874 Posts
The bleeder on a brake cylinder or caliper is supposed to be a check valve, preventing fluid from being sucked back in. I suppose one could fail and jam, but rather surprisingly, I've never seen it actually happen. Using a simple jar and plastic hose, I have successfully bled countless brake systems.

The collapsed hose suggestion is easily checked. Loosen the steel line on the feed side of the hose. Press the pedal. If it leaks profusely, the hose is trashed.
 

·
Registered
Joined
·
494 Posts
I’ve had one circuit lose all the pressure before as well with a two bowl and there was very little braking on the other circuit but there was some. Some people think the two are isolated but they aren’t completely, they have a divider but the moment one side opens and air is induced it allows air into the MC. The advantage is that in a single bowl ALL the fluid and braking is gone but in a dual bowl there will be some braking which is better than none.
 

·
Registered
Joined
·
954 Posts
With a dual bowl master cylinder you should have had some braking felt for the front. That's the purpose of the dual cylinder. Gravity bleeding a wheel cylinder usually takes an hour or two as you only get a slow drain from the master cylinder. It sounds like you have air in the front brake lines which would account for your "loss" of brake fluid in that bowl.
 

·
Registered
64 1/2 D Code Coupe,
Joined
·
3,326 Posts
I had an axel support fail and the tail pipe fell and smashed the driver side brake line. I only have brakes on three wheels. I couldn't bleed the left rear wheel cylinder because the upstream line was smashed against the axel preventing brake fluid to get to the wheel cylinder
 
1 - 8 of 8 Posts
Top