Out of the freeway today I noticed that braking was not as responsive as before. The pedal is hard, there is a very low hiss sound and when I put the the foot on the brake pedal, THE ENGINE RPM GOES UP.

May it be a vacuum issue with the master vac from one of the hoses or a failure of the vac itself and how to check?

My feeling is the vac......it is the original from 72 and the hoses are the same original from 37 years ago.

Out of the freeway today I noticed that braking was not as responsive as before. The pedal is hard, there is a very low hiss sound and when I put the the foot on the brake pedal, THE ENGINE RPM GOES UP.

May it be a vacuum issue with the master vac from one of the hoses or a failure of the vac itself and how to check?

My feeling is the vac......it is the original from 72 and the hoses are the same original from 37 years ago.

.....under further observation when I came home...the engine doesn't idle as smooth as before.....looks more as a vacuum problem.....is there a way to check and clean the valve?

Richard-

The hose from the check valve to the intake is easy to find........the check valve is easy to find...........the master vac to the intake is tough.........the Nissan part number for this is:

47471-E4603

I just replaced my entire master vac system this week with both hoses - clamps - master vac - check valve. There are still metal check valves out there, don't settle for a plastic one if you can help it. I think it cost me about $40.00.

The clamp part number is:

01555-00211-KT they were 1.93 each - the kit code consists of 2 clamps per package

The master vac was a reman one from Napa and it was $135.00 plus core of$35. plus freight - MSA wanted $300 core charge - that's just stupid - The guys at NAPA said I could give them my old one and they would send it off and have it rebuilt and then return the same on to me........that could be an option for you if you want yours back.

The hose off ebay was $40 some dollars and the hose from the other side took a little bit of grease to get it..........it was expensive!!

Edited September 19, 200915 yr by Travel'n Man
edit

After 37 years, I removed the valve and made the decision as a test, to clean the valve with W40 on both sides and blow compressed air out several times to make sure it handles its purpose as a "vacuum". Put back and the problem is solved.

I will order a OEM or a repro new metal one to take care of this issue.

At least, the source of the problem has been found.

Hey...in 37 years on this car......this part has never been a problem. We can conclude that some components were garbage on these early Zs but some were trouble free...at least for us,,,, as privileged owners of preserved originals from those early years.

I received the new OEM check valve today. The engine doen't anymore rev-up when the brake pedal applied.....it was defenitely a vacuum lost from the check valve.

For you guys who hear a "hiss" sound from your master vac, don't go straight to the conclusion the master vac is faulty.

I ordered the part from Courtesy and my cost was $36.00, shipping included.

Better than guessing about buying a new booster for a lot more money and more work to be done to not solve the problem.

I have all the Nissan books and many others and it was the right way to go for troubleshooting and diagnostic.

I received the new OEM check valve today. The engine doen't anymore rev-up when the brake pedal applied.....it was defenitely a vacuum lost from the check valve.

For you guys who hear a "hiss" sound from your master vac, don't go straight to the conclusion the master vac is faulty.

I ordered the part from Courtesy and my cost was $36.00, shipping included.

You can conclude, it was better than guessing about buying a new booster for a lot more money and more work to be done and not solve the problem.

I have all the Nissan books and many others and it was the right way to go for troubleshooting and diagnostic.

Edited September 30, 200915 yr by richard1