loosing brake pedal
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Junior User
Joined: Dec 2003
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From: Maryland
loosing brake pedal
I know that this may not be the correct place to post this but I have always gotten great help in here 
, besides, I guess I am in a little bit of denial that my truck is in the "Antique and Classic" catagory. I depend on it everytime I drive it the same as I did 10 years ago.
The problem is that when I am stopped at a long light the brake pedal very slowly goes down. The first couple of times it happened I thought it was my imagination it was so slight. But it definately drops. Am I right in assuming it is a vacuum problem? Should I suspect the brake booster? Unfortunately, the booster and the air pump were both replaced about 20,000 miles ago. I don't seem to loose brakes.
What do you think?
Thanks, Bill
, besides, I guess I am in a little bit of denial that my truck is in the "Antique and Classic" catagory. I depend on it everytime I drive it the same as I did 10 years ago.The problem is that when I am stopped at a long light the brake pedal very slowly goes down. The first couple of times it happened I thought it was my imagination it was so slight. But it definately drops. Am I right in assuming it is a vacuum problem? Should I suspect the brake booster? Unfortunately, the booster and the air pump were both replaced about 20,000 miles ago. I don't seem to loose brakes.
What do you think?
Thanks, Bill
Laughing Gas
Joined: Dec 2006
Posts: 1,008
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Same problem.
I just did the rear brakes after finding that one of my cylinders was gushing fluid and the other one didn't move at all...
Replaced both cylinders, bled the brake system...
I'll bleed the fronts, even though I didn't touch em and see what happens, but I'm also looking for suggestions.
I just did the rear brakes after finding that one of my cylinders was gushing fluid and the other one didn't move at all...
Replaced both cylinders, bled the brake system...
I'll bleed the fronts, even though I didn't touch em and see what happens, but I'm also looking for suggestions.
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Joined: Aug 2007
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I'm just getting into the truck world, but I have worked on lots of motorcycle brakes and some cars and for this symptom I would suspect leaky master cylinder / booster seal. There are only so many ways hydraulic brakes work??
The booster is what I would suspect. Because that is where pressure is built and maintained. That pressure has to go *somewhere* either leak outside anywhere in the entire brake system or back past the seal into the reservoir.
Air in the system in my experience means the brakes start soft and have to be pumped up to pressurise the air. That pressure is lost quickly once you're off the brakes.
NB, buyer beware, YMMV, I know little specifically about truck brakes. Mainly motorcycles and cars. Just trying to put some useful info out in this very helpful forum.
The booster is what I would suspect. Because that is where pressure is built and maintained. That pressure has to go *somewhere* either leak outside anywhere in the entire brake system or back past the seal into the reservoir.
Air in the system in my experience means the brakes start soft and have to be pumped up to pressurise the air. That pressure is lost quickly once you're off the brakes.
NB, buyer beware, YMMV, I know little specifically about truck brakes. Mainly motorcycles and cars. Just trying to put some useful info out in this very helpful forum.
New User
Joined: Jul 2007
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I had the same problem with my 85 F-350 6.9 the pedal would slowly sink, it was that way for about a month before it just dropped to the floor in traffic no warning. No fluid leaks, master cylinder stayed topped off. Replaced master cylinder and solved the whole problem.
Post Fiend
Joined: Nov 2003
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From: Nutter Fort, WV
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Elder User
Joined: Aug 2007
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the master cylinder is bypassing internally thats why the pedal sinks and there is no loss of fluid ,you should replace it immediately
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Junior User
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Just out of curiosity, are there rebuild kits for these master cylinders or is replacement the only or for some reason best option? I'm a fix it kind of guy where possible and inquiring minds like to know... my new-to-me truck ('89 e350 7.3) does have some fade as well, but it's not too bad yet. brakes work fine under normal operation but but do fade to the floor in about 60 seconds of steady heavy pressure.
Any tips from those who have gone before me? Have done motorcycle m/c rebuilds several times but this is obviously a different beast.
Hope your brakes are sorted easy Bill!
Any tips from those who have gone before me? Have done motorcycle m/c rebuilds several times but this is obviously a different beast.
Hope your brakes are sorted easy Bill!
Last edited by lmnr0026; Aug 29, 2007 at 01:17 AM.
Thread Starter
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Junior User
Joined: Dec 2003
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From: Maryland
Thanks for all the responces, I would have gotten back sooner but the computer at home took a lightning hit (surge protector too).
I guess I will look into replacing the MC. I will honestly say that of all the work I have done on this truck and other vehicals, this will be the first one I have done. Anyone have any helpful tips? Whats should I expact to pay for a MC from say NAPA?
Thanks again to all! Bill
I guess I will look into replacing the MC. I will honestly say that of all the work I have done on this truck and other vehicals, this will be the first one I have done. Anyone have any helpful tips? Whats should I expact to pay for a MC from say NAPA?
Thanks again to all! Bill
Laughing Gas
Joined: Dec 2006
Posts: 1,008
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Originally Posted by BlueHeavyD
Thanks for all the responces, I would have gotten back sooner but the computer at home took a lightning hit (surge protector too).
I guess I will look into replacing the MC. I will honestly say that of all the work I have done on this truck and other vehicals, this will be the first one I have done. Anyone have any helpful tips? Whats should I expact to pay for a MC from say NAPA?
Thanks again to all! Bill
I guess I will look into replacing the MC. I will honestly say that of all the work I have done on this truck and other vehicals, this will be the first one I have done. Anyone have any helpful tips? Whats should I expact to pay for a MC from say NAPA?
Thanks again to all! Bill
Some boosters have an adjustable actuator rod that'll actually push on the Master cylinder's piston... Put a dab of grease on the tip of that rod... Not a lot, just enough so that you can see the outline of your fingerprint.
Then slowly install the master cylinder. If you don't feel the rod hit the piston, check the grease dab... If you still see the fingerprint, the rod needs to come out. If the rod hits the piston, the rod needs to go in... Quickest method I've found for adjusting that rod, because you can't really get a feeler gauge in there.
Once you've adjusted the rod, bench bleed the cylinder. Just fill up the resivour and pump the piston with a screwdriver till fluid comes out the ports.
Once that's done, drop it in, connect up your steel lines, bleed the entire brake system, and you're done.
Elder User
Joined: Oct 2006
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Another suggestion is to bleed the master cylindar into an external container rather than into itself. That way, any residue/shavings will not be recycled and do damage. They don't make things like the used to...
i ain't rite
Joined: Mar 2005
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From: Marlboro Mental Hospital.
Originally Posted by Pele
What was the larger cylinder from?
it originally had the 1 1/8 piston master cylinder. i upgraded to the F450 master,that unit has a 1 5/8 piston.
a word of advice though. you need to modify the mount to make the master fit in the 350/350.