Master Cylinder cap hole?
Thread Starter
|
Cargo Master
Joined: Aug 2008
Posts: 2,661
Likes: 23
Master Cylinder cap hole?
I'm hopefully bleeding my brakes later today, but I have a question on the cap for the M/C.
It has a hole in it, right in the middle on top. Looks like it should be there (center and clean) but it seems wrong to me given how much effort is put in to keeping air out of the lines. I once put more fluid in, the brakes engaged a whole lot better, but it also shot fluid (like a foot high) out of the hole.
So does this have a purpose or was it one of those things that needs to be welded shut?
I know the truck was converted to air-brakes at one point, then swapped back by the original owner (worked in a gold mine for 50 years), so maybe the hole was put in for some reason with all of that. However with using fluid it just seems very wrong. I can't seem to find any pictures of caps with a hole in them, or even just a stock looking M/C cap...
I plan on upgrading this later on, but I'd like to be able to drive it around in the mean time.
Am I right in thinking this needs to be welded closed?
Thanks
It has a hole in it, right in the middle on top. Looks like it should be there (center and clean) but it seems wrong to me given how much effort is put in to keeping air out of the lines. I once put more fluid in, the brakes engaged a whole lot better, but it also shot fluid (like a foot high) out of the hole.
So does this have a purpose or was it one of those things that needs to be welded shut?
I know the truck was converted to air-brakes at one point, then swapped back by the original owner (worked in a gold mine for 50 years), so maybe the hole was put in for some reason with all of that. However with using fluid it just seems very wrong. I can't seem to find any pictures of caps with a hole in them, or even just a stock looking M/C cap...
I plan on upgrading this later on, but I'd like to be able to drive it around in the mean time.
Am I right in thinking this needs to be welded closed?
Thanks
Cargo Master
Joined: Jun 2001
Posts: 2,571
Likes: 22
From: Oxford, Indiana
That's an air vent. It you plug it up, you'll pull a vacuum in the reservoir and it won't drain into the cylinder correctly. Later cylinders had a rubber bladder in the cap that separated the fluid from the air vent to prevent the fluid from absorbing moisture but still allow the level to fluctuate. On the older vehicles, you were just expected to bleed the brakes more often to purge the moisture-contaminated fluid.
Roast em' if you got 'em
Joined: Mar 2005
Posts: 21,997
Likes: 9,887
From: Rio Rancho, NM
Brakes? what do you want with brakes? In that beast you won't need to worry about it, everyone will get out of your way....LOL
Yup, its supposed to be there, but, there should also be some sort of baffle in the cap as well to keep the brarke fluid from spraying up out of the hole. Typically there is a small cardboard looking disc that fits inside the cap with holes around the outside edge
Bobby
Yup, its supposed to be there, but, there should also be some sort of baffle in the cap as well to keep the brarke fluid from spraying up out of the hole. Typically there is a small cardboard looking disc that fits inside the cap with holes around the outside edge
Bobby
Thread Starter
|
Cargo Master
Joined: Aug 2008
Posts: 2,661
Likes: 23
Ok, I went and checked it out, still has the piece inside. Seems a bit odd that it shot out that one time, as it doesn't any more. Maybe I had it too full, it seemed full when I removed it this time, but it didn't look like the cap would submerged in it. The rust looking stuff whipped off with my fingers, I'm guess it's either residue or just from whatever
Also, why do the brakes build more pressure when they're pumped?
Also, why do the brakes build more pressure when they're pumped?
Trending Topics
Roast em' if you got 'em
Joined: Mar 2005
Posts: 21,997
Likes: 9,887
From: Rio Rancho, NM
They don't make more pressure when pumped. A given hydraulic system will only make so much pressure given the lever arm of the pedal, the cylinder bore diameter of the master cylinder, and the cylinder bore diameter of the wheel cylinders.
However, if there is some air in the system then pumping the brakes will seem like it does more. This is do to the fact that the air in the system will compress, depending on the amount of air in the system it might take several pumps of the brake pedal to fully compress the air. Fluids don't compress, so when there is no air in the system the initial step on the brake pedal results in the corresponding movement of the wheel cylinders.
Alot of the vendors the deal in brake components; Master Power Brakes, ECI, Speedway, etc have decent tech articles on hydraulic brakes.
Bobby
However, if there is some air in the system then pumping the brakes will seem like it does more. This is do to the fact that the air in the system will compress, depending on the amount of air in the system it might take several pumps of the brake pedal to fully compress the air. Fluids don't compress, so when there is no air in the system the initial step on the brake pedal results in the corresponding movement of the wheel cylinders.
Alot of the vendors the deal in brake components; Master Power Brakes, ECI, Speedway, etc have decent tech articles on hydraulic brakes.
Bobby
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
Thread Starter
|
Cargo Master
Joined: Aug 2008
Posts: 2,661
Likes: 23
That makes sense. I'm part way into bleeding my brakes, I'm getting more air than fluid at the moment! So if I've done my job when I'm done with the last wheel I should notice no difference in the "pumping of the brakes makes it stiffer" thing correct?
The first brake was pretty straight forward, but on the second (DR rear) I just can't seem to stop getting massive air bubbles. I'm thinking it would have to either be in the drum or in the hose I've got connected, I'm going to go get a better one now...as I sorta went through like 20oz of fluid on that one and am all out, lol
The first brake was pretty straight forward, but on the second (DR rear) I just can't seem to stop getting massive air bubbles. I'm thinking it would have to either be in the drum or in the hose I've got connected, I'm going to go get a better one now...as I sorta went through like 20oz of fluid on that one and am all out, lol
Post Fiend
Joined: May 2008
Posts: 7,641
Likes: 21
From: Poway, Ca.
Or another way of putting it is if you pump the brakes and there is no air in the system, you are basically pumping fliud into the wheel cylinder and pushing it out. As you pump they haven't given the brakes enough time to recover yet(blow th efluid back into the MC) and then you pump more in - so the pedal has less room to move because you have forced more brake fluid into the void created when you release the pedal.
It's like you are adding an extra slice of fluid with a pump or two on top of what got pumped down on the first push - the pumping has simply stacked more fluid behind the MC seals filling the volume normally left by the pedal pulling back (and allowing the fliud to flow back into the master cylinder - relaxing the wheel cylinder pistens and releasing the brakes shoes). Eventually after two or three pumps it won't allow you to pump any more - there is no more pedal travel, making it feel like the brakes are stiffer - it's an illusion related to the pedal position and stacked fluid in the MC.
It's like you are adding an extra slice of fluid with a pump or two on top of what got pumped down on the first push - the pumping has simply stacked more fluid behind the MC seals filling the volume normally left by the pedal pulling back (and allowing the fliud to flow back into the master cylinder - relaxing the wheel cylinder pistens and releasing the brakes shoes). Eventually after two or three pumps it won't allow you to pump any more - there is no more pedal travel, making it feel like the brakes are stiffer - it's an illusion related to the pedal position and stacked fluid in the MC.
Thread
Thread Starter
Forum
Replies
Last Post
markeyd
1961 - 1966 F-100 & Larger F-Series Trucks
10
Oct 30, 2016 04:54 PM
Macrobb
Pre-Power Stroke Diesel (7.3L IDI & 6.9L)
8
Apr 2, 2014 09:07 PM
danheit
1973 - 1979 F-100 & Larger F-Series Trucks
21
Oct 13, 2013 08:58 PM
Stephen67
1948 - 1956 F1, F100 & Larger F-Series Trucks
20
Jun 23, 2010 04:55 PM
