Topic: "Spongy" brakes

[Eucalypta]

Hi guys,

I have a 1994 YJ, 2.5 running with stock axle, diff, brake on 33"x12.5 tires.

I have this config. since over 2 years and just since about 5 or 6 months my brakes seem to get soft or "spongy".
Also, when my Jeep is at a very steep angle (nose down) and brakes applied, the brake pressure is gone after I released the brakes and want to brake again. Few times applying the brakes and the pressure is back again....

No leakes vissible anywhere...

Because I drive it alot through mud, the pads wear off quite fast and in the mean time I have exchanged the front brakes, complete with "claw", pads and cilinders and the brake shoes on drumbrakes on the back.
The brake fluid has also been refreshed.

Does any of you know what could be the problem or is it all in my mind?
Coud it be the brake booster or the vacuum hose?

Hope you can help me...

John

[neale_rs]

My '95 once had an internal leak in the master cylinder, could be that.

[sharpxmen]

that ^ or air in the system, check your brake fluid level also (re: on an incline) as it could get air in it if it's low

[aw12345]

Does the pedal sink when you apply and hold it? then get better when you pump it or, after a bit it sinks to the floor again slowly? if so go buy a master cylinder. Otherwise find the leak air gets in it because of a very low fluid level or a leak.
My money is on the master cylinder. Now if the pedal is soft but pumps up hard and there are no leaks and the pedal will stay firm after a few pumps and you bled the system and there is absolutely no air in it. Then start looking for swelling brake hoses or the calipers flexing. Another thing that can cause the last symptom I described is changing the rear brake shoes and not backing of the parking brake cable before you adjust the rear brakes.

[Eucalypta]

Thnx guys,

-Level in reservoir is ok
-not sure about the pedal sinking or not....will check tomorrow.
-with my "normal" car; when I apply brake and then start engine, the pedal sinks as the vaccuum is applied to the booster. Should this also be the case with the YJ?
-Cannot find any leaks; Art, what do you mean by calipers flexing?
-I did replace my rear brake shoes; Art, what you mean by backing of the parking brake....?
-@neale: how did you find that internal leak??? Is that normal wear&tear or production error?

[neale_rs]

In my case, I blame it on a bad rear axle installation that did not include replacing the rear brake cylinders.  The crud in them got back to the master cylinder somehow and messed it up.  The diagnosis is just based on the pedal behavior you described, mine was acting similarly.

There is another strange thing that was happening to my YJ.  Since you mention your problem happens when nose down, does this also include with the wheels turned sharply?  In my case the problem was that the bolt that holds the brake hose onto the caliper was hitting the shock absorber. This was holding the caliper piston compressed (empty of fluid) so that when the pedal was pressed about double the fluid had to be moved to get it to brake (with the bolt no longer hitting the shock), so the pedal would go all the way to the floor.  The problem never showed up again after adjusting the steering stops. Smaller diameter shocks would have solved the problem too, my Skyjacker front shocks are very big in diameter.

[sharpxmen]

-with my "normal" car; when I apply brake and then start engine, the pedal sinks as the vaccuum is applied to the booster. Should this also be the case with the YJ?

if your brake booster is good and the check valve is good then it should hold at the same level, sounds like your "normal" car loses vacuum from the brake booster overnight. You can replicate the same behavior on the YJ by pumping the brake before starting the engine, you'll notice the pedal getting harder, then keep it pressed and start the engine, it will sink in just like the other one - if it doesn't then your booster is gone or you have a problem with the vac line.

[aw12345]

Thnx guys,

-Level in reservoir is ok
-not sure about the pedal sinking or not....will check tomorrow.
-with my "normal" car; when I apply brake and then start engine, the pedal sinks as the vaccuum is applied to the booster. Should this also be the case with the YJ?
-Cannot find any leaks; Art, what do you mean by calipers flexing?
-I did replace my rear brake shoes; Art, what you mean by backing of the parking brake....?
-@neale: how did you find that internal leak??? Is that normal wear&tear or production error?

When you replace the rear brakes you have to loosen up the parking brake adjustment on the parkbrake cable or the shoes will not sit properly on the shoe anchor and will cause spongy brakes. Calipers can actually move and spread a bit.
Yes the pedal should sink down just a bit when you start the engine and the brake booster gets vacuum

[Eucalypta]

Thnx guys,

Last sunday we went wheeling with JeepClub Nederland and this time a budy of mine had the same problem with loosing brakeline pressure when on an extremely steep hill. I looked at the brakelines and saw what Neale was talking about: the bolt hits the shock absorber. Inspecting my own shocks: both of them are dented with a patern that looks like a brake caliper bolt.
I will have to see what to do about this.
Kudo's on finding this Gremlin!!

Furthermore; I never loosened the parkbrake cable when changing or cleaning the rear brakes. I will do this next weekend, when I will clean them.

@Sharpexmen: vacuum seems fine: tested it and it acts as it should.

[sharpxmen]

Thnx guys,

Last sunday we went wheeling with JeepClub Nederland and this time a budy of mine had the same problem with loosing brakeline pressure when on an extremely steep hill. I looked at the brakelines and saw what Neale was talking about: the bolt hits the shock absorber. Inspecting my own shocks: both of them are dented with a patern that looks like a brake caliper bolt.
I will have to see what to do about this.
Kudo's on finding this Gremlin!!

Furthermore; I never loosened the parkbrake cable when changing or cleaning the rear brakes. I will do this next weekend, when I will clean them.

@Sharpexmen: vacuum seems fine: tested it and it acts as it should.

now i remember this problem being described here before, there was another thread couple of years ago (or so) - can't remember who started the thread (maybe it was neale but not sure, it was the exact same thing he describes and the pedal was gone after a steep incline or some major flex on one side of the front axle - something like that).

glad you figured it out.

[neale_rs]

Glad to hear you found the problem.  It was my thread from before, sharpxmen helped figure it out.

[sharpxmen]

Glad to hear you found the problem.  It was my thread from before, sharpxmen helped figure it out.

well, my memory failed me - good call