Soft brake pedal...

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

1BADAWD

1BADAWD

10 Year 15 Year
Joined
Sep 12, 2009
Threads
13
Messages
76
Location
Racine, WI
So like the title says my truck has a soft brake pedal. Goes most the way with barely any braking, then brakes well jus before the floor. Bled the front brakes, no change. Can hear air leak from around mc/brake booster area. Me and my buddy think it may be the booster but i read in a few other similar posts the mc came up as a possibility. Im going to double check the rubber lines for leaks. Ideas? Thoughts?
 
We need more info..recent changes, lack of repairs, model, year, etc before we can give you an answer. Tried the FAQ's yet, and, oh by the way..

Welcome to Mud! :flipoff2: means friendly smiley banter. (Since i didn't say it in your other thread.)
:mad: :bang: means you're doing something wrong.

*Reason I say this is b/c I already know what you posted in the other thread, but for everyone's sake, always give the info.

Check everything on your system.

Fluid level and condition, booster diaphragm, lines, piston seals, etc. It may be just your master's inner seals are bad and with the truck turned off, when you pump the pedal it'll slowly drop to the floor. Listen for hissing, that'll tell you it's the booster.

:D
 
Last edited:
have you done any work on the brakes lately? are the calipers on the wrong side with the bleed screws down?

I had a situation once where a wheel bearing was bad, causing the rotor to turn sideways, and opening the calipers too much for the pedal to clamp in one stoke.

I would guess it's probably not the booster. most likely the master cylinder.

Don't forget to check and see if the rear wheel cylinders are leaking.
 
Yea 86 truck, just bought so idk recent repairs and i havent done anything to the brakes. Fluid level is good and fluid looks ok too. Like i said you can hear a air leak hissin by the mc/booster area. With the truck off the pedal is a bit harder and i dont believe goes to the floor if you push it.
 
1BADAWD said:
Yea 86 truck, just bought so idk recent repairs and i havent done anything to the brakes. Fluid level is good and fluid looks ok too. Like i said you can hear a air leak hissin by the mc/booster area. With the truck off the pedal is a bit harder and i dont believe goes to the floor if you push it.
Click to expand...

If you can hear air escaping when you press on the brakes and it isn't outside of the booster, I'd say the booster is done.....
 
NorCalBorn said:
It may be just your master's inner seals are bad and with the truck turned off, when you pump the pedal it'll slowly drop to the floor. Listen for hissing, that'll tell you it's the booster.

:D
Click to expand...

2ndGenToyotaFan said:
Check how it feels with the engine off. If it's the same, then I'd lean more towards the master cylider. If it firms up then booster. :cheers:
Click to expand...

Just in case we need to say it another way again?? :lol: If you hear hissing and you're not on a plane, it isn't Snakes on a Plane!
 
We can see a bubble in the little plastic tube off the resevoir to the front of the mc move as you push the pedal. W bled the mc a few times, still there.

I looked in the manual and did the brake booster air tightness checks they suggested and it seemed to check out fine with all the tests.

Should i start cheap and simple with a mc rebuild and go from there?
 
That's what I would do. Is the master cylinder new? Might need to bench bleed it, or crack the lines are the master and bleed it there.

LMAO at the snakes on the plane...............
 
install the master off of a 90's 3.0 liter pick up truck. they have a bigger bore and dual tanks no more suicide cylinder. i have a 1985 4runner and my brakes will put you through the winshield
 
Soft brakes can be from lots of problems, rear drums not properly adjusted, loose wheel bearings, contaminated fluid, air in the system, fluid leaks, etc.

A bigger bore master with the same wheel cylinders will make a less powerful system. Hydraulic leverage works like any other leverage, with the same peddle pressure, a smaller master will produce more psi, but will take more lever (peddle) stroke. A larger master will produce less psi, but will take less lever (peddle) movement. A larger master may produce a better peddle feel, shorter stroke, firmer, but will take more peddle pressure to deliver the same psi to the cylinders, so ultimately is a less powerful system.
 
Tools R Us said:
Soft brakes can be from lots of problems, rear drums not properly adjusted, loose wheel bearings, contaminated fluid, air in the system, fluid leaks, etc.

A bigger bore master with the same wheel cylinders will make a less powerful system. Hydraulic leverage works like any other leverage, with the same peddle pressure, a smaller master will produce more psi, but will take more lever (peddle) stroke. A larger master will produce less psi, but will take less lever (peddle) movement. A larger master may produce a better peddle feel, shorter stroke, firmer, but will take more peddle pressure to deliver the same psi to the cylinders, so ultimately is a less powerful system.
Click to expand...

Thats great to know, thanks. Do you have some suggestions then?

zombie said:
Has your truck been lifted? has the ride height adjuster at the back been adjusted? I would adjust the rear brakes before replacing anything.
Click to expand...

Truck has a 2inch bodylift on it. Stock suspension.
 
1BADAWD said:
Thats great to know, thanks. Do you have some suggestions then? ...
Click to expand...

On a "new" rig with no history, you need to do a full inspection. I start with the rear, pull the drums, check the axle seals and cylinders for leaks, do the adjusters turn, shoes have pad, hardware/springs intact? Repair any issues, put the drums on and adjust correctly.

Jack up the front, check wheel bearing play, should be none. Remove the wheels, any leaks from the calipers, are the pads good, the pins in place, rotors look smooth? Repair any issues.

At the master cylinder, look at where it mounts to the booster, any leakage?

The fluid is hygroscopic, absorbs moisture from the air, it can look good and be bad. It should be changed annually, most don't and is probably the number 1 cause of cylinder failure and gradual brake efficiency loss.

To flush I remove the strainer(s) from the reservoir(s), using a turkey baster or other sucking device, remove the fluid from the reservoir(s), refill with fresh fluid. Go to the first bleeder, open it slightly, place you finger over the opening to work as a one way valve and have your helper gently pump the peddle a dozen or so times until you see fresh fluid. The close the bleeder and bleed normally a couple of times until your sure all air is out. Refill the reservoir and repeat on the other bleeders.

A couple of points about bleeding: It not a race, use normal driving pressure on the peddle, operate it relatively slowly and briefly stop with the peddle fully at the top on each stroke. If the peddle is aggressively slammed the fluid moves at high speed in the lines, causing any air bubbles to be broken up into foam which is much more difficult to remove. Only open the bleeders enough to get a dribble or small arc of fluid and close before the fluid stops flowing. If the bleeder is opened too much and left until flow stops, there is a good chance of sucking air back in, not what you want.
 
You must log in or register to reply here.

Share this page

Back
Top Bottom