Spongy Brake Pedal - Please help

[olysan]

I could really use some help troubleshooting and fixing a spongy brake pedal in my 2000 TJ.
Here's what I've done:

• Bled the master cylinder. I did this in the vehicle using lines from the MC outputs feeding back into the MC. I jacked up the rear of the jeep so that the MC was sitting level. I struggled with this to start because one of the line fittings I was using was introducing air in the system. As soon as I fixed that it bled easily and I saw 0% air in the tubes as I depressed the brake pedal.
• Bled the rest of the system starting with the rear passenger wheel. My wife worked the brake pedal while I worked the bleed screws under the jeep. Fluid ran clear and air free at each wheel. I'm assuming bleeding the Master Cylinder would have introduced some air into the lines since they were disconnected. How long would it take for that air to get back to the right rear wheel? We ran through 7 cycles but I did not see significant air in the tubing.

Background - I just finished a full frame swap. The jeep has all new brakes, calipers, master cylinder, and hard lines. I have checked all connections and I don't see a leak. I did not relace the soft lines that go to the front calipers and I'm wondering if they could cause this. I had the same issue with the brakes before the new parts and th soft lines are the only thing I didn't replace. Thanks for any help.

Mike

 

[TJ Jim]

I’m no expert on brake bleeding but, I’ve always had great luck with one man brake bleeding. Never seen it suggested on here so might get flamed, but like I say it has always worked great for me.
Attach a tube to the bleeder screw. Nice and tight so no air is introduced. Open the bleeder to max flow.
Fill a bottle like a 12 oz water bottle so the small hose is in the bottom and covered with fluid.
Fill the reservoir and pump the pedal keeping the master full !!
Of course starting with the back passenger wheel working your way from farthest wheel up to the front drivers wheel.
The one man bleed has always worked for me.

 

[olysan]

I’m no expert on brake bleeding but, I’ve always had great luck with one man brake bleeding. Never seen it suggested on here so might get flamed, but like I say it has always worked great for me.
Attach a tube to the bleeder screw. Nice and tight so no air is introduced. Open the bleeder to max flow.
Fill a bottle like a 12 oz water bottle so the small hose is in the bottom and covered with fluid.
Fill the reservoir and pump the pedal keeping the master full !!
Of course starting with the back passenger wheel working your way from farthest wheel up to the front drivers wheel.
The one man bleed has always worked for me.

How do you know when it’s bled?

 

[TJ Jim]

If you didn’t have new brake fluid in it already it’s easy. Old fluid turns into clear fluid and you know by that you’ve cleared the line. Since you’ve already cleared the old fluid out it’s take a guess time. The other way is watch for air bubbles and make sure there are none. That turns into a two man effort.

 

[TJ Jim]

Oh yeah. This method will move the shuttle and light your brake light. Mr Blaine sells a pin to prevent this from happening but I’ve been able to clear the light just by pressing the brake pedal numerous times. Haven’t tried this on this Jeep.

 

[TJ Jim]

Not trying to be ugly but, don’t reuse the waste bottle with the hose in it. Just buy the large bottle of new brake fluid and use a lot of it.

 

[TJ Jim]

Do you have anti-lock brakes?

 

[olysan]

I just bled the system again and I am pretty sure there’s no air in the system. I also pulled the rear wheels and verified that the drum brakes are adjusted so that there’s just a bit of drag on the drums. I’m at a loss. Could it be the booster?

 

[olysan]

Do you have anti-lock brakes?

No

 

[TheBoogieman]

Stop guessing and ask the expert. There's only one on here. I'm not poking the bear on a Sunday.

 

[mrblaine]

I just bled the system again and I am pretty sure there’s no air in the system. I also pulled the rear wheels and verified that the drum brakes are adjusted so that there’s just a bit of drag on the drums. I’m at a loss. Could it be the booster?

A few things for you. The reason we call it "bench bleeding" the master is because it really needs to be done in a vise. The circulating hose method tells you nothing. You need to do the plugged port method and all your corner bleeding needs to be done with the ignition on so you can watch for the brake light to come on if the shuttle valve gets shifted.

But, before we get there, when is the pedal spongy and what are you comparing that to? You said the problem is pre-existing, what and when was it doing the spongy pedal thing?

FYI- no, not the booster, a bad booster produces the opposite of spongy, the pedal will be high and hard since there is no vacuum assist.

 

[TJ Jim]

My guess at this point is the master cylinder. Since @TheBoogieman is being a sissy

 

[mrblaine]

I’m no expert on brake bleeding but, I’ve always had great luck with one man brake bleeding. Never seen it suggested on here so might get flamed, but like I say it has always worked great for me.
Attach a tube to the bleeder screw. Nice and tight so no air is introduced. Open the bleeder to max flow.
Fill a bottle like a 12 oz water bottle so the small hose is in the bottom and covered with fluid.
Fill the reservoir and pump the pedal keeping the master full !!
Of course starting with the back passenger wheel working your way from farthest wheel up to the front drivers wheel.
The one man bleed has always worked for me.

You and Mac should try that on a TJ and get back to us. Why fluid in the bottle covering the end of the hose??

 

[TJ Jim]

You and Mac should try that on a TJ and get back to us. Why fluid in the bottle covering the end of the hose??

So it doesn’t suck air back up into the cylinder

 

[TJ Jim]

You and Mac should try that on a TJ and get back to us. Why fluid in the bottle covering the end of the hose??

Actually now that I’ve thought about it, when I first bought this Jeep I did bleed the old fluid out using the one man method. It’s been stopping fine for three years now. And it did light the brake light which went away after pumping the brake pedal numerous times. I bought your shuttle stop pin for the future brake bleed.

 

[mrblaine]

So it doesn’t suck air back up into the cylinder

That's not really how it works. If you walk out to your rig right now and open a bleeder, what will happen?

 

[mrblaine]

Actually now that I’ve thought about it, when I first bought this Jeep I did bleed the old fluid out using the one man method. It’s been stopping fine for three years now. And it did light the brake light which went away after pumping the brake pedal numerous times. I bought your shuttle stop pin for the future brake bleed.

That bleeding method is actually spelled out and described in a CJ-5 factory service manual. I've tried it and every other bleeding method you can think of on the TJ and the most consistent method that works every single time is the 2 person modified CJ. Open the bleed screw, pedal down hard and fast, hold at the bottom, close bleeder.

Like always, if you have something that works for you, great. I prefer stuff that works every single time for every single person that does it.

To be clear, the shuttle lock is merely to prevent annoyance. With the key on, you know when it shifts and what to do to shift it back.

 

[TJ Jim]

That's not really how it works. If you walk out to your rig right now and open a bleeder, what will happen?

Never tried it but I’d suspect temp changes it would suck air or leak fluid out. Gravity drain since the master is higher than the bleeder.

 

[mrblaine]

Gravity drain since the master is higher than the bleeder.

Always. And, if fluid is being forced out by hydrostatic pressure, air is not going in.

 

[TJ Jim]

Was always curious if the scrap bottle was necessary. Haven’t done it often enough to confirm it one way or the other.
Next bleed I’ll omit the scrap bottle.