Soft/fading brake pedal (1 Viewer)

[72Roper]

Trying to confirm my suspicions and thought I’d check with the pros on the forum incase there’s something I haven’t thought of.

I have a 73 FJ40 with OEM power brakes.

Under formal driving conditions the brake pedal is very soft “squishy” on the first press and then you can pump it a few times to get full brake pedal feel back. If you press and hold the pedal after you get full brake pedal feel back it will slowly fade back to soft pedal feel.

No signs of fluid leaks from the wheel cylinders, master cylinder or line connections.

I ran through 2 jugs of brake fluid to bleed the lines. Seems to bleed fine although the back brakes didn’t yield as much fluid as the front did when bleeding.

I suspect a bad master cylinder but I’m fairly new to Land Cruisers so before I just start throwing parts at it, wanted to see if there were other suggestions on trouble shooting.

Thank you

 

[70fj40]

Master and slave cylinders are a good place to start. I would also consider replacing any soft lines you might have.

 

[70fj40]

well disregard my response, my reading comprehension is bad this morning. Your brakes need help not the clutch

 

[pb4ugo]

It sounds like you still have air in the system. Folks have had trouble getting drum brakes bled. There's a lot of info here using the search function here or on the internet and clicking on sources from this site. 1st clamp the rear soft line and check the pedal, then do the frt to isolate the issue. I think most folks adjust the brakes to the max, to remove any play in the shoes and the wheels don't spin, then bleed. Once successful in bleeding, then properly adjust the brakes.

 

[Sky King]

I agree, air in the lines, classic symptom.

 

[45Dougal]

Sounds like trapped air. Are your front cylinders installed the right way up? If not then they'll never bleed.

Turn off the engine and see how they feel - the servo can confuse the symptoms.

 

[Sky King]

I should have mentioned that failing components within the system can cause the problem.

 

[72Roper]

Do those Brake line “T unions” that are mounted on the axle housing ever go bad? I wouldn’t think there are any components in them to fail but again I’m not as familiar with the Landcruiser parts as I am with other vehicles.

 

[pb4ugo]

Do those Brake line “T unions” that are mounted on the axle housing ever go bad? I wouldn’t think there are any components in them to fail but again I’m not as familiar with the Landcruiser parts as I am with other vehicles.

No, they're just T's

 

[pb4ugo]

What's the history of your brakes. Did you just service or replace components?

 

[72Roper]

What's the history of your brakes. Did you just service or replace components?

Weren’t getting any fluid to the rear brakes at the fitting where it goes into the rear drum assembly. Ironically the brakes were firm and stopped well at that time but I was obviously only engaging the front brakes.

I changed out the rear flex line with a new brake line. Ran an entire bottle of brake fluid through it bleeding the system. Front bled great. Rear was ok. No air bubbles but not as much fluid as I would have thought. Pedal has felt soft since then. No fluid loss at ANY connections. While the rear system is obviously suspect I figured that the master cylinder may also be suspect since I bled the rear a ton, was getting no air when bleeding and no fluid coming from any fittings

 

[peesalot]

Do the test posted above, clamp rear soft line to axle and test pedal, if still soft, leave rear clamped, clamp front sift line to axle, test pedal, if still soft its the MC. If you identify the axle with the issue( usually rear) and its drums it may just need adjusting. Adjust the rear shoes with the wheels bolted on, rear axle jacked up, tighten til you cant spin tire, release one click or notch at a time, do both sides before you test drag, release until you can spin but there is still drag, drive it, rear drums may get hot, if so release 1 more notch each side. I like to take the drums off and get adjusters working well with cleaned and grease them, makes adjusting a whole diff experience. Adjust them to where you can just barely slide drum on.

 

[pb4ugo]

If you suspect the master, you should be able to unbolt it leaving the lines connected. Pull it back slightly and see if fluid is seeping from the rear of it. Also see if fluid is being sent from one resoiviour to the other. If you carefully clamp with vise grips the rear soft line does the pedal height change? Fyi, I haven't run drum brakes for yrs. There are a boat load of threads on this site on this subject and gallons of fluid have past the bleeder screws. Hopefully some folks will chime in. I know most folks have adjusted the rear brakes to the max so that the pistons can't move and fluid and air can be forced out. Once bled adjust the brakes correctly.

 

[72Roper]

If you suspect the master, you should be able to unbolt it leaving the lines connected. Pull it back slightly and see if fluid is seeping from the rear of it. Also see if fluid is being sent from one resoiviour to the other. If you carefully clamp with vise grips the rear soft line does the pedal height change? Fyi, I haven't run drum brakes for yrs. There are a boat load of threads on this site on this subject and gallons of fluid have past the bleeder screws. Hopefully some folks will chime in. I know most folks have adjusted the rear brakes to the max so that the pistons can't move and fluid and air can be forced out. Once bled adjust the brakes correctly.

Interesting technique! I’ll give it a shot as well as checking the back side of the M/C.

Thanks!

 

[72Roper]

If you suspect the master, you should be able to unbolt it leaving the lines connected. Pull it back slightly and see if fluid is seeping from the rear of it. Also see if fluid is being sent from one resoiviour to the other. If you carefully clamp with vise grips the rear soft line does the pedal height change? Fyi, I haven't run drum brakes for yrs. There are a boat load of threads on this site on this subject and gallons of fluid have past the bleeder screws. Hopefully some folks will chime in. I know most folks have adjusted the rear brakes to the max so that the pistons can't move and fluid and air can be forced out. Once bled adjust the brakes correctly.

Do the test posted above, clamp rear soft line to axle and test pedal, if still soft, leave rear clamped, clamp front sift line to axle, test pedal, if still soft its the MC. If you identify the axle with the issue( usually rear) and its drums it may just need adjusting. Adjust the rear shoes with the wheels bolted on, rear axle jacked up, tighten til you cant spin tire, release one click or notch at a time, do both sides before you test drag, release until you can spin but there is still drag, drive it, rear drums may get hot, if so release 1 more notch each side. I like to take the drums off and get adjusters working well with cleaned and grease them, makes adjusting a whole diff experience. Adjust them to where you can just barely slide drum on.

So I ran the recommended brake line clamping test. The results were:

Rear soft hose clamped- Same spongey pedal feel. No improvement.

Front soft hose clamped - extremely hard pedal but almost ZERO actual braking. When I say hard pedal, I mean it you could barely detect ANY downward pedal travel.

 

[pb4ugo]

Sounds like you still have air in the frt brakes. You might try adjusting them to the max and bleed them.

 

[Pighead]

So I ran the recommended brake line clamping test. The results were:

Rear soft hose clamped- Same spongey pedal feel. No improvement.

Front soft hose clamped - extremely hard pedal but almost ZERO actual braking. When I say hard pedal, I mean it you could barely detect ANY downward pedal travel.

Ok, when you clamped the front soft line, did you leave the rear soft line clamped? If both soft lines are clamped you should have no pedal movement. That rules out the MC. Now unclamp the rear while the front remains clamped and test again.

 

[rainingagain]

When was the last time you adjusted your brake shoes? Was it squishy before you flushed the fluid?

If this is not a new issue since the flush, what you describe symptom wise sounds like a master cylinder that is failing internally. Sounds like fluid is leaking past the rear circuit's seal under pressure. Sometimes you can see this if you watch the rear circuit's resovior while pressing the brakes.

Also do what @Pighead suggested.