brake problem

[SavannahZ]

Hello all,

This is my first post. I have been reading articles on here for awhile now and think this is a wonderful site.

I just bought my first Z a couple of weeks ago. It is a 1971 240 with an L6 engine. I was coming home tonight and lost most of my brakes. When I press on the pedal, even slightly, I hear a hiss. Also, the rpm shoots up about 500. I did a search and a couple others in the last four years have had the same problem. In their posts there are no solutions.

Thanks for all replies!!!

SavannahZ

[ksls94]

my 71 has a bad brake booster and it does the same thing

[SavannahZ]

the brake booster is the black cylinder that says "master vac"?

[SavannahZ]

ok, I figured it out. Does anyone know the best place to buy this part online?

[beandip]

You are just going to need to shop around . Be prepaired for sticker shock , because these thing are spendy. Go to Motosports at zcarparts.com . Try Victoria British at VictoriaBritish.com , CourtesyParts.com ( Courtesy Nissan ) . Be sure to tell them it is a '71. To intense Restoration may help also. I dont have the address for him. You can watch ebay I have seen them there from time to time. At least this is a start. Maby some kind sole here has an extra one. Gary By the way welcome to the club.

[Bambikiller240]

Before buying parts, you might want to check to be sure the problem isn't a vacuum hose that leads from the intake manifold to the Master Vac.

If you end up needing the Master Vac, MSA will sell you one on an exchange basis, so make sure that if you have the new part installed by a shop, that they give you all of the old parts so you can return them to MSA for the core charge credit.

[SavannahZ]

Thanks, I ran out of light tonight. I checked the main large hose and didn't see anything. I'll just need to investigate in the morning.

Thanks for the advice

[ksls94]

just remove the hose and with the engine running put your finger over the hose and see if it pull vac. if it does then you know thats ok but if it makes noise when you press the brake pedal you already know it is the booster. you can drive it with out vac boost but the pedal is harder to press but safe to drive i drive mine all the time that way

[SavannahZ]

I am going to try some more things in the morning. I didn't have much time today.

Thanks a lot for the advice. The brakes, although I'm pressing them pretty hard, don't really have that much strength to them at all. Maybe, I just need to press harder. There definitely is a vacuum.

I need to look up what is involved with this procedure. I have never dealt with brakes before. Do I just unbolt the master cylinder and the booster from the firewall, then, just replace with the new unit?

Take care-

[hls30.com]

Johnathan,

The master vac is also availablefrom www.Rockauto.com, Advance Autoparts, Napa, Autozne, NOPI, and Kutcheys all are on an exchange basis.

I don't think anyone stocks it, so order it several days before you need it to be sure it is here and correct before your work day. If you need a hand, sing out-I don't know how I missed this thread until now.

Right now touching a Z that actually runs on the street would be good motivation for me to get my '72 OTRA (On The Road Again)

I pm'd you my number. If the Z is headed off the street, sing out, we'll keep yours on while mine is on holiday.

I am replacing my master vac as well, and while our master vacs (brake power booster) are not the same, the unbolting and re-bolting should be pretty close.

I have factory manuals-and all of the other books-if that would help.

Will

[Alan Pugh]

This is something to try that I got shown years ago by an old guy that worked on brakes most of his life.

To check the operation of your master vac, first with the engine off depress and let up the brake pedal a number of times, until you can no longer hear any hissing of air and the pedal gets hard.

Leave your foot on the brake pedal with moderate pressure and start the engine, if the master vac is sealed and working properly your brake pedal should move down as the vacuum is created inside the unit. This movement should start as soon as the engine is started.

No movement or very slow movement means there is a leak in the system.

Also check the one way valve (check valve) for proper operation.

Hope this is of some help.

Alan. P.

[sblake01]

Also check the one way valve (check valve) for proper operation.

Alan. P.

I was going to mention the check valve as I once had a problem with mine. My car is a 78 and I'm not sure how similar it is to a 72 but when mine went out I didn't hear any hissing. It just wouldn't allow the booster to hold vacuum. Replaced it and the problem went away.