Long brake travel, but holds pressure

RatLabGuy

RatLabGuy

You look like a monkey and smell like one too
Joined
May 18, 2005
Location
Churchville, MD
Can't figure this out. When I first press the brakes, the total pedal travel is a little more than I'd like. The truck stops OK, coudl even lock them, just not until the last bit of travel distance.
But, if I pump a few times, it builds more pressure and the total travel decreases. If I do this and hold it (e.g., stoplight), it holds this pressure fine, but then the 1st time I let off, it goes back to the longer travel.
This seems to me liek some kind of residual pressure issue? i've bled all corners and LSPV well, and replaced the rear soft line. Haven't done front lines yet but I'd think if one of those was bad/old, it'd pull a bit? (which is dosn't). No signs of leaks that I can find, and the bottle is staying level. MC is relataively new.
 
Yep, it has to do with the compressability of air versus brake fluid. Bleed your brakes really well, and it will go away.

A Mityvac or similar brake bleeding tool works really good. I was working on a jeep a few weeks ago that had so much air in the lines the rear shoes wouldn't even move when the fronts were at full pedal pressure. Therefore, no fluid was coming out the rear bleeders. Stuck the mityvac on it and pulled till fluid came out, then they worked great.
 
jeepinmatt said:
A Mityvac or similar brake bleeding tool works really good. I was working on a jeep a few weeks ago that had so much air in the lines the rear shoes wouldn't even move when the fronts were at full pedal pressure. Therefore, no fluid was coming out the rear bleeders. Stuck the mityvac on it and pulled till fluid came out, then they worked great.
Click to expand...

That's the thing, I'm using a Mityvac-type tool (the Autozone $30 one) to bleed them.
I don't get it, I've bled everything, run about 1/3 bottle of fluid through. All ends look find when bleeding, there are some teeny tiny bubbles when "sucking" but I know that's probbaly from it leaking inward just a little around the threads of thefittings. I've been doing in this way for years and it's always worked.
Any idea how I might pinpoint where the air is?
 
Sometimes at work if normal bleeding or vacuuming the bleeders doesnt work I've had good luck forcing fluid from the bleeders back to the master. If you have help they can watch the reservoir and tell you when the air bubbles stop. That also eliminates sucking air around the bleeder threads cause some fluid will seep out under pressure.

You can fill your mityvac reservoir with clean fluid and hook the pressure side of the hand pump to the top where you would hook the vacuum line normally.
 
so I've re-bled all 5 corners, using the MityVac clone, same deal. Been through almost a whole can of fluid now. Haven't tried back-foring it like mentioned yet, i guess you have to lower the fluid in the MC first to keep it from overflowing?
One thing bugs me, just on the right rear - no matter how much vacuum I pull up on the MityVac (clone), that one is very slow to bleed. It bulds vacuum fine, just the fluid only comes out at a trickle compared to the others, even w/ the valve very open. i assume this is just a little crap blocking it? in order to get the vac to work, I had to add a little yellow teflon to the bleeder valve threads, I've been asuming this is probbaly just a little bit of the tape blocking the hole.
is there anything else that coudl cause this?
It stops ok, just that it stops much better after a few pedal pumps.
 
Well I pulled that screw off, cleaned it well and replaced the teflon, it still bleeds real slow :-(
 
whens the last time you actually adjusted the brake shoes ( manually ) ?

This could have a great effect on the pedal feel and operation.
 
Blkvoodoo said:
whens the last time you actually adjusted the brake shoes ( manually ) ?

This could have a great effect on the pedal feel and operation.
Click to expand...

This is a good point... it's been awhile... but wouldn't that just make it chronically bad? E.g. pumping a few times shouldn't improve drum performance? Or am I wrong about that.
 
the springs bring the shoes back to the pin, and collapse the wheel cyl. first push sends the cyls almost all the way out, second push gets it set good, third makes it all work well. Adjust the shoes, the bottoms are pushed out so the shoes rock into the drum, there ain't much room to move if things are adjusted right.

I had same issue with mine a few times, hell, even my '97 does it.

YOu need to remember, you aren't moving much fluid when you push the pedal, 10ml at best per push ( a guess, but figure how much you are loosing each push when you are bleeding ) it's really not much.
 
Hmm... just played with teh parking brake, realized that pulling it all teh way out, it still dosn't lockup the wheels... so you may be onto osmething. It's an A/T so I rarely use it 9yes, I know I should...0
That adjusting wheel is such a PITA to get to through that tiny hole, it's location is really hard to get to.... right above the leaf springs so I can't get my head in to see it. Grrr. Isn't there some way you can tighten them by just repeatedly using teh e-brake?
 
the rear drums are supposed to auto-adjust, but it only takes a couple trips through the Carolina mud to freeze the threaded adjuster up....If they worked good at one point in time (and you haven't changed anything in the braking system), you should prolly pop the drums off and have a look at the adjuster and do a manual adjust.

FYI, usually the auto-adjuster works as a result of stopping while in reverse. Usually the procedure goes something like this:
firm stop in reverse (5-10 mpg), firm stop in fwd (5-10 mpg)
repeat 3-4 times

Hope that helps
 
Use the mighty vac at the master cylinder. Just like the same way you would bleed a clutch master cylinder. If you can bring the vac to 15 psi without bringing any more bubbles, it is definitely bled good. I had the same problem until I got the MV
 
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