lordoeuf
NAXJA Forum User
- Location
- Vancouver Island
I have a 1999 XJ with 33" tyres. Steel braded lines all around. Disc brake conversion in the back, I think from Teraflex, circa 2004 (was told that it is the same as the Ford Explorer rear discs). Removed the o-ring from the proportioning valve to increase rear braking ratio and this worked great. I'm using drilled and slotted rotors on the front, and I forget what style is on the back. I think I'm using Green and Yellow Stuff for pads. It has been many years since I've had to work on the car, aside from fluid service.
As of about a month ago, I've started to have an odd braking issue. Perhaps someone here has run into this before. If I am slowing down to an approaching red light, I hit the brake pedal, sometimes harder at first but then I want to ease up a little on the pedal to coast a little faster, before braking harder again. When I go to press the pedal down the second time (while it is still being pressed after having eased up), I have to push the pedal down a bit further for the same stopping force than had I not eased up on the pedal to begin with. Its as if the pressure which had built up in the brake lines during my first pedal press isn't being held during the ease up period. Its as if whatever holds pressure in the line, e.g. a check valve, is opening when I ease up on the pedal. Is there something which acts like a check valve in the brake lines? Is it in the master cylinder or is it the check valuve on the vacuum-operated brake booster?
If I sit with the car on at a red light and do a series: press down, let up half way, press down, let up half way, press down, let up half way, etc, I can get the brake pedal down pretty darn far. On the other hand, if I just release the pedal all the way up again at any point, then press down, the car brakes just as it should with the expected amount of pedal travel and force. The car, in fact, stops really well. And if you drive such that you never ease up half way on the brake pedal when coasting to a stop, then you might not notice that there is anything wrong. My wife doesn't notice anything and she drives the car regularly. I, on the other hand, have been driving the car since 1999 and noticed something immediately.
Do you experts have any idea what is going on? The symptoms are very repeatable. The issue seems to be a little worse on hot days with the A/C running. Perhaps today or tomorrow I'll follow one of these youtube videos on how to test your brake booster/check valve system with car on/off tests.
If I pump the brakes with the car off, the pedal stays hard. I bled the brakes last week, but it didn't help. The calipers aren't very old - perhaps 3 years old. The car only gets about 5,000 - 7,000 KM per year put on it. The brake fluid level isn't decreasing, that is, the mark stays at full.
Some ideas for failure I have are:
Brake booster check valve & gromet
Brake booster unit
Brake master cylinder
Moisture in brake line when hot
Air entering brake lines during during pedal ease up, but which gets dispersed into the resevoir at full release
Leaking tiny amounts of fluid, but not detectable
Master cylinder nuts loose
Is there a resevoir cap vent hose? Could it be clogged?
Soft or swollen caliper seals
As of about a month ago, I've started to have an odd braking issue. Perhaps someone here has run into this before. If I am slowing down to an approaching red light, I hit the brake pedal, sometimes harder at first but then I want to ease up a little on the pedal to coast a little faster, before braking harder again. When I go to press the pedal down the second time (while it is still being pressed after having eased up), I have to push the pedal down a bit further for the same stopping force than had I not eased up on the pedal to begin with. Its as if the pressure which had built up in the brake lines during my first pedal press isn't being held during the ease up period. Its as if whatever holds pressure in the line, e.g. a check valve, is opening when I ease up on the pedal. Is there something which acts like a check valve in the brake lines? Is it in the master cylinder or is it the check valuve on the vacuum-operated brake booster?
If I sit with the car on at a red light and do a series: press down, let up half way, press down, let up half way, press down, let up half way, etc, I can get the brake pedal down pretty darn far. On the other hand, if I just release the pedal all the way up again at any point, then press down, the car brakes just as it should with the expected amount of pedal travel and force. The car, in fact, stops really well. And if you drive such that you never ease up half way on the brake pedal when coasting to a stop, then you might not notice that there is anything wrong. My wife doesn't notice anything and she drives the car regularly. I, on the other hand, have been driving the car since 1999 and noticed something immediately.
Do you experts have any idea what is going on? The symptoms are very repeatable. The issue seems to be a little worse on hot days with the A/C running. Perhaps today or tomorrow I'll follow one of these youtube videos on how to test your brake booster/check valve system with car on/off tests.
If I pump the brakes with the car off, the pedal stays hard. I bled the brakes last week, but it didn't help. The calipers aren't very old - perhaps 3 years old. The car only gets about 5,000 - 7,000 KM per year put on it. The brake fluid level isn't decreasing, that is, the mark stays at full.
Some ideas for failure I have are:
Brake booster check valve & gromet
Brake booster unit
Brake master cylinder
Moisture in brake line when hot
Air entering brake lines during during pedal ease up, but which gets dispersed into the resevoir at full release
Leaking tiny amounts of fluid, but not detectable
Master cylinder nuts loose
Is there a resevoir cap vent hose? Could it be clogged?
Soft or swollen caliper seals
