KJ 2002 - Braking issues. Anyone seen or heard of this?

Scratch · **Posted:** Tue Jul 08, 2008 2:56 pm

So - last week I'm getting in my KJ to head to work (all city driving baby) and as I pull out of my driveway (where I park) - I hit the brakes to slow down off the drive, and the pedal is so soft - I'm at the floor while the truck is still slowing down.

I rolled back up the drive, and back a few times, soft pedal all the time.

Revved her up, pumped the pedal in park, and rolled down the drive again - little better now. As I headed toward the exit of my cul-de-sac - braking seemed fine again (nothing stellar - the pads are at 60%) but - safe.

Since then - every few starts I have little to no braking for a few minutes after a start, and then it returns, and is fine until I'm parked again.

Thoughts? Suggestions?

Xodius · **Posted:** Tue Jul 08, 2008 3:23 pm

Power issue me thinks. When I just did my OME OME OME lift

and re-hooked up the battery I had no brakes but after about 2-3 pumps they came back. Just an idea. Maybe your battery (sounds very odd even as I type it) is going out or your master cylinder perhaps?

jeepkj02 · **Posted:** Tue Jul 08, 2008 3:35 pm

Check fluid. Try bleeding the brakes.

Guest · **Posted:** Tue Jul 08, 2008 5:01 pm

Air doesn't get in the lines for no reason, so bleeding the brakes wouldn't do any good IMO. You'd need to figure out WHY there's air in the lines. Check your vacuum lines going to the booster too...even though if there was a cracked line going to the booster, the pedal would be stiff. Hmm.

Crawl underneath first thing and look for any obvious leaks...the hoses going to the calipers/wheel cylinders, hard lines coming from the master cylinder

Scratch · **Posted:** Tue Jul 08, 2008 6:45 pm

Ok - so I have looked at the following:

Booster vacuum lines:
Visually inspected. Still pliable and no visible cracks or leaks.
Engine off 30 minutes wait time, first pump of brakes was soft, and successive pumps stiffened up - so the vacuum isn't being lost.

Brake fluid: Checked level - still 1/2 inch below MAX, fluid is dark but appears 'clean'.

Hard lines from booster to manifold, no apparent leaks, no fluid visible. Hard lines to chassis - same. Have not inspected the lines the rear or calipers yet - thats next - but I have seen NO fluid dropping to brakes, wheels or chassis anywhere.

Pads / Rotors: I have not checked the pads, however 7000km ago at time of purchase they were at 60%. Rotors are not warped or discolored - but do appear to be glazed (They are like mirrors). Is it possible that the brakes are at full strength but the glazing is preventing a good grip? Nahh... don't buy it. If I'm at the floor - the drums (even at 30%) should be locked up - but they don't lock tight either...

So - I'm guessing:

1. Possible air in Brake manifold? Bleeding them should take care of that if so... but wouldn't the other wheels brake properly?
2. Leak inside master cyl / Booster where fluid is blowing past and getting recirculated? Is that even possible?
3. Vacuum leak? Though - if that were the case - I'd have trouble pushing the pedal to the floor right?

Does that make any sense?

RE: The 'power' question - In my case, I think I can rule that out. If I had the ABS option - then yes I think it was built with an electrically assisted booster, but in my '02 sport I don't have ABS - and therefore I believe it's a vacuum driven hydraulic system, purely mechanical.

Thanks for the ideas so far - I'd really like to nail this without paying a fortune. I love my Libby - but frankly it seems like 'something' waiting to happen...

tjkj2002 · **Posted:** Tue Jul 08, 2008 6:57 pm

Quote:

SPONGY PEDAL
A spongy pedal is most often caused by air in the
system. However, thin brake drums or substandard
brake lines and hoses can also cause a spongy pedal.
The proper course of action is to bleed the system,
and replace thin drums and substandard quality
brake hoses if suspected.

Quote:

PEDAL FALLS AWAY
A brake pedal that falls away under steady foot
pressure is generally the result of a system leak. The
leak point could be at a brake line, fitting, hose, or
caliper/wheel cylinder. If leakage is severe, fluid will
be evident at or around the leaking component.
Internal leakage (seal by-pass) in the master cylinder
caused by worn or damaged piston cups, may
also be the problem cause.
An internal leak in the ABS or RWAL system may
also be the problem with no physical evidence.

Quote:

LOW PEDAL
If a low pedal is experienced, pump the pedal several
times. If the pedal comes back up worn linings,
rotors, drums, or rear brakes out of adjustment are
the most likely causes. The proper course of action is
to inspect and replace all worn component and make
the proper adjustments

Quote:

DIAGNOSIS AND TESTING - MASTER
CYLINDER/POWER BOOSTER
(1) Start engine and check booster vacuum hose
connections. A hissing noise indicates vacuum leak.
Correct any vacuum leak before proceeding.
(2) Stop engine and shift transmission into Neutral.
(3) Pump brake pedal until all vacuum reserve in
booster is depleted.
(4) Press and hold brake pedal under light foot
pressure. The pedal should hold firm, if the pedal
falls away master cylinder is faulty (internal leakage).
(5) Start engine and note pedal action. It should
fall away slightly under light foot pressure then hold
firm. If no pedal action is discernible, power booster,
vacuum supply, or vacuum check valve is faulty. Proceed
to the POWER BOOSTER VACUUM TEST.
(6) If the POWER BOOSTER VACUUM TEST
passes, rebuild booster vacuum reserve as follows:
Release brake pedal. Increase engine speed to 1500
rpm, close the throttle and immediately turn off ignition
to stop engine.
(7) Wait a minimum of 90 seconds and try brake
action again. Booster should provide two or more vacuum
assisted pedal applications. If vacuum assist is
not provided, booster is faulty.

All above from the '02 FSM

I'd be checking the rubber brake lines and/or you got a booster or master cylinder internal leak.

Scratch · **Posted:** Wed Jul 09, 2008 12:31 am

Thanks for the FSM information!

So - from that... Low pedal - perhaps - though I've not driven another Liberty so I can't say if it's truly 'low'.

I have done the power booster test, and it seems acceptable. I'll try again with a slightly longer wait (2 min?) and see. Under 45 seconds - I get about 5 pumps till the pedal goes hard. (Get your mind out of the gutter you...)

I wonder if this is a case of wear, and the 'self adjusts' are 'unadjusting' while the car sits? But over 4 hours I wouldn't expect that. Very strange.

I'm thinking of replacing the rotors and pads, plus doing a full flush of the lines and then seeing if the problem returns. I hate intermittent problems as much as the mechanics that have to look at them.

KJ 2002 - Braking issues. Anyone seen or heard of this?

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