Soft brake pedal...

1BADAWD · 10-03-09, 11:46 PM

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?

NorCalBorn · 10-04-09, 12:56 AM

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!

means friendly smiley banter. (Since i didn't say it in your other thread.)

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.

alteredraptor · 10-04-09, 01:36 AM

hes got an 86 pickup... 22-re... and the fluid is full, and the truck was recently purchased

black95 · 10-04-09, 08:04 AM

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.

1BADAWD · 10-04-09, 11:17 AM

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.

raydouble · 10-04-09, 11:29 AM

Quote:

Originally Posted by 1BADAWD

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.

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.....

2ndGenToyotaFan · 10-04-09, 10:07 PM

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.

NorCalBorn · 10-04-09, 10:09 PM

Quote:

Originally Posted by NorCalBorn

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.

Quote:

Originally Posted by 2ndGenToyotaFan

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.

Just in case we need to say it another way again??

If you hear hissing and you're not on a plane, it isn't Snakes on a Plane!

1BADAWD · 10-05-09, 12:03 AM

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?

black95 · 10-05-09, 12:17 AM

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...............

alteredraptor · 10-05-09, 02:07 AM

the hissing was with the truck off, without pressing brakes...

1BADAWD · 10-06-09, 01:16 AM

Quote:

Originally Posted by black95

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.

Yea we cracked the 2 lines off the mc and bled them. No change.

Quote:

Originally Posted by alteredraptor

the hissing was with the truck off, without pressing brakes...

Yup.

thetrekkerguy · 10-06-09, 03:34 PM

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

1BADAWD · 10-06-09, 11:33 PM

Ill look into that. Is it a direct swap in?

2ndGenToyotaFan · 10-06-09, 11:41 PM

Yes it's a direct swap. But you'll need to find a master that comes with the tank, as your old one probably won't fit it.

1BADAWD · 10-07-09, 11:42 AM

Ok, i found some on napa. Apparently with a tank is cheaper than without..... (odd).

Whats this "suicide cylinder" that was mentioned?

Tools R Us · 10-07-09, 12:37 PM

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.

zombie · 10-07-09, 03:35 PM

Has your truck been lifted? has the ride height adjuster at the back been adjusted? I would adjust the rear brakes before replacing anything.

1BADAWD · 10-07-09, 11:26 PM

Quote:

Originally Posted by Tools R Us

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.

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

Quote:

Originally Posted by zombie

Has your truck been lifted? has the ride height adjuster at the back been adjusted? I would adjust the rear brakes before replacing anything.

Truck has a 2inch bodylift on it. Stock suspension.

Tools R Us · 10-08-09, 11:40 AM

Quote:

Originally Posted by 1BADAWD

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

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.

toy4xfun · 10-08-09, 05:38 PM

hey if you here hissing or air leaking you need to see if it happens all the time, when the pedal is depressed or does it do it just as the pedal is depressed (stops when pedal stops moving). a master cylinder can leak internally and cause the problem you are talking about. it will stay full what happens is fluid leaks through the internal seal that is supposed to direct fluid out to separate lines.

1BADAWD · 10-09-09, 01:51 AM

The hiss of air is AFTER the truck has been ran and pedal pushed. Shut off truck, without trouching pedal you can hear the air.

toy4xfun · 10-09-09, 05:16 AM

i would say you have a leak in your booster. but i would still change the master cylinder. the last master cylinder that went out on my truck did not leak it went internally. started out the pedal was soft and it did not take long it started sinking to the floor with very little breaking.

1BADAWD · 10-09-09, 01:14 PM

Yea pedal goes close to floor before braking. Still brakes pretty good.... when it finally starts, haha.

raydouble · 10-09-09, 01:43 PM

I think you need both master and booster......
Got to pinpoint the leak (hissing) you are hearing though.

Maybe the master is leaking into the booster?

toy4xfun · 10-09-09, 04:01 PM

ray double could be right . but when i had one leaking from the back you could see the fluid running down the booster.

1BADAWD · 10-10-09, 12:29 PM

I cant see any fluid leaking or running out anywhere i dont believe.

1BADAWD · 10-10-09, 07:06 PM

Ok so we popped the rear wheels off today, bled both rear brakes and went to adjust them. Right side adjusts fine and it set pretty good now. The left side however... turns like it adjusting but when apply the brakes there is no change.

zombie · 10-10-09, 09:01 PM

You said it has a 2" body lift. You need to adjust the rear brake height adjuster (sorry I don't know the technical name for the part) to compensate for the lift. It has a bar that connects to the body and pivots according to ride height. Theory is that as your back end sits lower with more weight you need more rear brakes or if it sits higher the back end is lighter needing less brakes. It directly affects the pedal feel and right now your brakes are not working in the rear because of this. I adjusted mine by adding a 2" bracket to it where it attaches to the axel after doing a 2" body lift and it made the soft pedal firm again.

alteredraptor · 10-10-09, 10:34 PM

its actually just the driver side rear brake thats not braking... the passenger side does stop and quite nicely now since i had to adjust it, but good to know, me and him will have to try that