daopi Posted January 18, 2010 Share Posted January 18, 2010 Hi guys! I have a Pathfinder 97. My brakes have an awkward behavior. When I brake normal to hard I have good braking. But if the car moves slow and and I press light the brake, the pedal goes almost all the way down, and barely brakes. In these cases became a reflex for me to make a "double brake" or "double pedal" to get good braking. I suspected the pads are gone and I changed them. Now I have brand new pads and is doing the same... Anyone ideas? Thanks! Link to comment Share on other sites More sharing options...
beastpath Posted January 18, 2010 Share Posted January 18, 2010 have you bled the brakes? Link to comment Share on other sites More sharing options...
nismothunder Posted January 19, 2010 Share Posted January 19, 2010 Leaking master cylinder?On old cars that have vacuum operated brakes(I dont know if the pathy has this or not) and if you had a vacuum leak or a cam that didnt build anuff vacuum at low rpms it would cause this same issue... Link to comment Share on other sites More sharing options...
Precise1 Posted January 19, 2010 Share Posted January 19, 2010 I'm guessing something with the master cylinder or vacuum booster but I haven't heard of this problem before. B Link to comment Share on other sites More sharing options...
daopi Posted January 19, 2010 Author Share Posted January 19, 2010 have you bled the brakes? No, I didn't bleed them, don't know how to... but I will learn. Link to comment Share on other sites More sharing options...
nismothunder Posted January 19, 2010 Share Posted January 19, 2010 No, I didn't bleed them, don't know how to... but I will learn. I dought you would need to bleed them if you just replaced the pads,I think its the vacuum booster since you said it works good when you brake hard... Link to comment Share on other sites More sharing options...
daopi Posted January 19, 2010 Author Share Posted January 19, 2010 I think its the vacuum booster since you said it works good when you brake hard... What is interesting is that the troubles are only at low speeds, like moving in a parking lot. Plus is not doing always, just sometimes, random. Even more awkward is I brake now and the brakes will not work and if I press the brake after few seconds will work fine... But always at low speed. The vacuum thing I guess is related to the speed of the car or rpm? How can I check the vacuum pipes, booster? thks Link to comment Share on other sites More sharing options...
Precise1 Posted January 19, 2010 Share Posted January 19, 2010 Go here and download the appropriate one and then rear up on the brake section. http://www.nicoclub.com/FSM/pathfinder/ That is what I would have to do to give you a good answer. I have owned a previous model for years but am new to the 96-2004 models. I seem to remember someone mentioning a check valve... B Link to comment Share on other sites More sharing options...
daopi Posted January 19, 2010 Author Share Posted January 19, 2010 I just checked the brake booster following the proc described in owner manual and FSM. The brake booster is fine! Also I had a short look at the vacuum hoses and apparently they are fine. I will check the vacuum valve. Also I will have to bleed the brakes, who knows... Do you guys think is possible to be the master cylinder? thks Link to comment Share on other sites More sharing options...
MY1PATH Posted January 19, 2010 Share Posted January 19, 2010 ok, ocasionally if I jossle the wheels back and forth several times while not moving I get this. I also got this 3x climbing a V shaped camber slope w/ mr. jim.(other trail times too) I also get this when I slowly creep 1 front wheel on to high objects and slip off. I have no leaks, fresh bleed, vacum booster is fine, etc all brake components are good. My theroy; wheel bearings. if they are wearing out can they allow enough play that the disc presses the pad(& piston) in. thus requireing more fluid to return the pistion to an operating postion. that might explain why it will sometimes go to the floor onece and then be fine on pump #2. @ higer speeds the it requires less work to turn the wheels so rotors wouldn't be flexed against the piston. am I crazy or is this possible? Link to comment Share on other sites More sharing options...
Precise1 Posted January 19, 2010 Share Posted January 19, 2010 You are crazy. If the wheel bearings have enough play to do that, the truck would literally handle like the wheels were falling off. Also, regardless of play, even if it did affect the pedal stroke, it couldn't possibly be that much and the brakes would travel farther but then still have correct stopping power at the end of stroke. I think I understand what you are saying, I just don't think it could happen like that. I still don't know what the issue is though... Do you guys think is possible to be the master cylinder? Yes, it could be, but that's not a normal failure mode in my experience. I'd say check that valve, bleed the brakes and see how things are then. B Link to comment Share on other sites More sharing options...
Alkorahil Posted January 19, 2010 Share Posted January 19, 2010 (edited) Given the low engine speed mentioned, You should replace your vacuum check valve. I strongly believe everyone should do this at 100K. It is not an expensive part adn often overlooked. (I replaced mine back in May last year because we had a non-returnable one here, and noticed a much more responsive brake pedal and some 10-20% more braking power, esp at under 30mph speeds) You should also have the brake fluid drained and refilled. This would include bleeding the brakes. Brake fluid absorbs water molecules from the air, lowering your braking power raising the boiling boint. The chemistry/math is something like a 5% H20 containation raised the bioling point of brake fuild 130 degrees. Everytime you open your brake resevoiur it exposes the brake fluid to the air, that is why a tight fitting cap is so important. It also absorbs and retains dirt and dust. Most manufactures recommend every 100K, but it varies by opinion as to when it should be done. Vaccuum brake boosters dont really go out much. Master brake cylinders do but this doenst sound like a master cylinder problem at all, if it was the symptoms would be opposite almost. Edited January 19, 2010 by Alkorahil Link to comment Share on other sites More sharing options...
Channel595 Posted January 20, 2010 Share Posted January 20, 2010 sounds like master cylinder, when you press the brake in slow it wont seal internally allowing fluid to bypass. Link to comment Share on other sites More sharing options...
Precise1 Posted January 20, 2010 Share Posted January 20, 2010 That is along the lines of what I considered... I seem to remember something like that, but it is unusual. B Link to comment Share on other sites More sharing options...
daopi Posted January 21, 2010 Author Share Posted January 21, 2010 I changed the master cylinder almost 3 years ago. Few months before the complete failure behaved somewhat the same. Unfortunately the mechanic decided to go with the cheapest master cylinder on the market, a no-name (Ultra 8 Performance...?). Anyway, even after was changed I wasn't very happy with how strong were the brakes, and now I have again almost the same symptoms. What if I have 2 problems in the same time, eg. master cylinder and vacuum check valve? Anyway, as soon I'll have time (week-end), I'll go to buy a check valve and bleed the brakes. Are the normal first steps. thks! Link to comment Share on other sites More sharing options...
OldSlowReliable Posted January 30, 2010 Share Posted January 30, 2010 Im going to agree w/ master cylinder, just looked @ mine and it looks like its been leaking (explains why im halway between max/full after 3 months of filling it) Link to comment Share on other sites More sharing options...
dhardison Posted January 30, 2010 Share Posted January 30, 2010 I may be wrong but I always thought that a quick way to check your brake booster and check valve for leaks is there should be enough vacuum stored for one power assisted pedal push after you shut off the engine and wait a minute or so. If you get a hard pedal the first time you push the pedal after you shut the engine down then you have a leak somewhere. Link to comment Share on other sites More sharing options...
MY1PATH Posted January 31, 2010 Share Posted January 31, 2010 Given the low engine speed mentioned, You should replace your vacuum check valve. where is this valve located? Link to comment Share on other sites More sharing options...
daopi Posted February 11, 2010 Author Share Posted February 11, 2010 Finally I have the answer: Master cylinder. I just changed it, new fluid and I'm back in business. Now I have strong brakes. THANK YOU ALL FOR HELP! Daniel Link to comment Share on other sites More sharing options...
Precise1 Posted February 11, 2010 Share Posted February 11, 2010 B Link to comment Share on other sites More sharing options...
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