I drove my '05 LE from NYC to St. Louis this past week.

I do all of my own repairs (replaced front struts, rear shocks and coilsprings), replaced all fluids before the trip, and brake pads/discs looked fine.

Halfway along the trip, I accelerated (WOT) to overtake a slow 18-wheeler. as I was passing the cab, there was a cop on the side of the road. I immediately let off on the gas and stomped the brake to find that the pedal was incredibly impossible to press down. I panicked (thought I lost brakes).

After 1/2 to 1 second, I ragained the brake pedal.

While driving through the mountainous roads of PA, I would accelerate uphill, and then when a car jumps into my lane, I would try to slow down, and find that the pedal is again hard to press down (for a second).

While I was in St. Louis, I had no choice but to bring it to local shop, and they said that the master cylinder failed test (I think they were BS'ing me). I had to pay $475 to get it replaced, and on the trip back, noticed the same thing.

I then tested it to find the exact symptoms:

The pedal goes completely stiff when the engine is straining. If I am cruising at 60mph, and then press the accelerator 1/2 way down and after car starts to take off, then at the same time try to press down on the brake (while foot is still on gas), I get the hard brake pedal forever, until I let go of the gas, or if the car goes to steady cruising.

I have also tried 3rd gear to rev the engine high, and as long as I am not touching the gas, high-rpm alone does't make the brakes act up.

So it seems that my pathfinder gets hard brake pedal while engine is straining under load... The pedal feels just like when you turn of the engine and then pump the pedal with engine off until all vaccuum is gone.

The only place I found that has exact same problem is a ford super-duty diesel forum but them I think diesels do not have same brake system that we do...

I have searched the internet for two hours and couldn't find anything except the ford pick up forum and a VW bug forum where a cracked vacuum line from engine to air filter box OR vacuum line to brake booster was the culprit.

Does anyone have any clues on what could be causing my problem?

To complicate things even further, I paid for a pdf FSM for my pathfinder years ago. I put the pdf files on my home NAS RAID server, and the file server DIED. If anyone has pages of the FSM that tells you the steps to accessing the vac lines on my '05 I would also be greatful

-Sage

Welcome to NICO.

Download a copy of the FSM. To save a copy of the FSM, right click -> Save As on every PDF, save them into a single folder, then use fwd.pdf to navigate.

Sounds like your brake booster check valve took a dump. If you give me your VIN I can provide you with an exact OEM part number.

What towncivilian said. Check valve. Before buying a new one, I'd pull it out and have a look. You should be able to blow through it one way but not the other.

Chuck

I know this is a late response, but I wanted to thank Towncivilian and Chuck for the advise.

It WAS the check valve. Plus the vacuum hose was hard and looked like it needed replacing.

Unfortunately, I was on a roadtrip, and the meineke shop in missouri said it was the booster. Got ripped off for the booster then on the drive home, it was the same.

I read your posts, and then checked the valve. It was blocked in both directions. Got a new one from courtesyparts.com and all was good.

Unfortunately, the tranny died on my R51, but I just picked up a new R52 (SL premium package) last night.

I can't stop buying nissans because of the online community support like nicoclub.

Thanks again,

-Sage