Brakes problem
1999 Nissan Truck V6 Front Wheel Drive Automatic 99850 miles
----------------------------------------------------------------
One week ago the left front brake locked up. I replaced the front calipers and brake pads and had the rotors cut.
The front left brake continued to lock up. After bleeding the brkae line the brake released but after one push on the brake pedal the brake locked and would not release.
Next, I replaced the left front rubber brake hose.
Still locking up.
Replaced the Master cylinder.
Still only the front left brake locks. up.
Van has abs. I removed the front abs sensors and boad tested. Still right front bake locks up.
Bled brakes over and over again. Bench bled master cylinder. Still no remedy.
Whats next to do?

4wheel ABS? Souns as though the ABS unit is holding pressure to that wheel. Is the ABS light in the dash on? Might not be a bad idea to have it scanned and see if the ABS controller has stored any trouble codes.

2CarPro Jack wrote:

4wheel ABS? Souns as though the ABS unit is holding pressure to that wheel. Is the ABS light in the dash on? .

Hi Jack,

I have the same problem with my 1999 Nissan Quest. I have replaced the pads, caliper, rubber hose, and in the process of replacing the master cylinder now.

If I release the hydraulic pressure by cracking the line, the caliper will free up the rotor. I did it at the caliper bleeder, then up the line to the ABS distributing block, then at the line between the master cylinder and the ABS block. At all those points, the locked wheel will free up. So, my conclusion is the master cylinder have a clog preventing the back flow, (right?).

This happens with and without the engine on. The ABS warning light never came on at any time. You would think the ABS would have a fail mode that would not put a hold on the brakes. When the ABS fails, I thouht it would be "removed" from the brake system.

Thank
Bill

It is supposed to.Does the master cylinder have a line for each front wheel on it? If only one, then the ABS may be the problem, that is where it distinguishes one side from the other

Jack,

Thanks for the quick reply.

The master cylinder have two lines coming out. They both goes to the ABS block. The ABS block have 4 lines coming out of it, one for each wheel.

I crack the line from the ABS block to the problem wheel, the release of hydraulic pressure releases the wheel. I repeat the test, lock the wheel again, and crack the line to one of the two lines at the master cylinder, I took a guess since I don't know which line, and that releases the wheel.

Does it look like the master cylinder is at fault? Engine on or off, the hydraulic fluid should be allow to flow back THROUGH the ABS block, which it did, and THROUGH the master cylinder, which it did not. Any holes in my analysis?

I am getting the part in two days and will be installing this weekend.

Thanks again.

It would seem to me that the master cant distinguish left or right, it is front and rear. The ABS however meters left and right. If it were the master I would think that it would hold both front wheels since it cant determine left from right, only front from back

2CarPro Jack wrote:

If it were the master I would think that it would hold both front wheels since it cant determine left from right, only front from back

Jack,

That is the one point that bothers me. I do not know how the two lines from the master cylinder is distributed in ways of one line for the two front wheel, and the other line for the rear wheels, ... or ... each circuit will take care of diagnal wheels. Either way, each circuit takes care of two wheels and I only have one wheel locked.

Well, since I came this far, countless hours spent, I am pretty tired. I have already commited $200 in a new MC from the dealer. I'll find out soon enough. After that, if it is not fix, I'll have it tow to a dealer.

Thanks again.
-bill

The master is a front/rear arrangement

I decided to go for the master cylinder for the following reasons ....

1/ ABS warning light never comes on.
2/ ABS should fail, if failed, in a "safe" mode, such that it would be removed from the normal brake system. It should never fail in a "locked wheel" mode. That would be big time liability.
3/ MC is easier to change. ABS requires the MC to be remove anyway.
4/ MC is a lot cheaper in parts cost (BTW, AutoZone gave me a wrong part, their database list a wrong part. One of the two hydraulic port use a different type flair on the steel line)
5/ The MC suppose to have free flow upstream and it was not doing that. THIS is the direct evidence pointing to the MC.
6/ "Evidence" pointing to the ABS modulator is not directly observable. Only in a questing of why only one wheel is locked.

The answer ...... after $200 for a new MC from Nissan .....

FIXED !!!!!

Mistakes along the way ...

1/ I jump the gun in replacing the caliper, that was not it. Should have done a better job in the problem analysis. You know how it is. No spare car, everything have to be zip up by sunday night! I figured, 3 hours job.....

2/ A friend had a lock up wheel and it turned out to be a rubber brake hose. By this time, I had already diagnosed this to be the MC. I figured a hose is easy to replace and only $20. Low price to pay. Little did I know that it'll cost me a whole day trying to get the flare nut loose and the mangled flair nut back on and maintained a good seal!