Bad Brake Booster?

[TobyB]

Quote

 i did notice the idle would change when i pumped the brakes.

 

That's normal boosty behaviour.  

The thing is a controlled air leak, so

 every time you use the brakes,

it leaks a bit of air into the intake manifold.

 

t

 

[ray_]

20 hours ago, TobyB said:

 

That's normal boosty behaviour.  

The thing is a controlled air leak, so

 every time you use the brakes,

it leaks a bit of air into the intake manifold.

 

t

 

 

 

toby's right.

 

[rhariz21]

On 12/2/2016 at 5:35 PM, ray_ said:

 

If you have a Z in your board name, you're jinxed!

 

 

On 12/2/2016 at 5:51 PM, zinz said:

HA !!!!!!  I'm double-jinxed !

 

I think i am safe!! Drove the car around and its stops great! got pretty lucky  

[xr4tic]

It's always nice when it's an easy fix.

[drola]

reviving this thread.

my 73 does the opposite when i step on the brakes. it actually drops idle and stumbles instead of raising the idle. the pedal doesn't really feel any different other than it takes a lot more force to get the car to stop. any suggestions?

[Simeon]

Definitely your booster. Follow the diagnostic steps of blocking the vacuum hose between the intake manifold and the booster and see what difference it makes. If the vacuum leak is massive enough it won’t just lift idle speed a bit. 

[ray_]

Also I wonder if brake fluid is being drawn into the motor...

[Simeon]

2 minutes ago, ray_ said:

Also I wonder if brake fluid is being drawn into the motor...

 

Pretty sure you would get a big cloud of smoke but anything’s possible. 

[TobyB]

Quote

my 73 does the opposite when i step on the brakes. it actually drops idle and stumbles instead of raising the idle

 

your idle mixture is on the lean side, then, rather than a bit rich...

 

t

 

[Einspritz]

I found this business to rebuild my boosters, but have not used them yet, but I will.

 

http://www.pwrbrake.com/

they will either rebuild yours or you can exchange.

For caliper rebuilding:

http://www.pmbperformance.com/catalog.html

 

Use the proper spiral wound hose that won't collapse under vacuum.

 

With something as serious as brake systems, don't cheap out.

[Brandon]

A hard brake pedal could also be bad rubber brake lines.  The inside of the rubber lines gets narrow with age and when that happens the brake fluid won’t travel through them as easily which results in a stiff pedal. I had it happen on a ‘72 automatic that I had, changed the lines and the pedal was normal again.

[drola]

Thanks to all who replied. It will be a couple of days before I can devote the time to diagnose but will report back when I do. I've been working on old Porsches for many years so I'm pretty mechanically inclined. But this 2002 never really needed anything after all the years I've had it. just turn the key and go. Although I did do a 5 speed swap but that's about it. Amazing little car.

 

5 hours ago, Simeon said:

Definitely your booster. Follow the diagnostic steps of blocking the vacuum hose between the intake manifold and the booster and see what difference it makes. If the vacuum leak is massive enough it won’t just lift idle speed a bit. 

I will check this

 

4 hours ago, ray_ said:

Also I wonder if brake fluid is being drawn into the motor...

Will check this also. Low brake fluid in the reservoir should be easy enough to check. But I don't think so

 

3 hours ago, TobyB said:

 

your idle mixture is on the lean side, then, rather than a bit rich...

 

t

 

I'll check this also but I was actually thinking the opposite. I sometimes get a whiff of the exhaust at idle if I'm standing outside the car and it smells rich to me. Car has a 32/36 weber. I rejetted it and now it runs much better but I can double check

 

1 hour ago, Brandon said:

A hard brake pedal could also be bad rubber brake lines.  The inside of the rubber lines gets narrow with age and when that happens the brake fluid won’t travel through them as easily which results in a stiff pedal. I had it happen on a ‘72 automatic that I had, changed the lines and the pedal was normal again.

A hard brake pedal is not what I'm dealing with. my experience with bad rubber brake lines is sticky calipers as well as hard pedal which is not the case. pedal feels normal. just have to press harder on it to get the car to stop

Edited August 15, 2018 by drola

[drola]

So i finally got to tinkering with it. I pulled the vacuum line off the manifold and left it connected to the booster. I sucked and sucked and it would not hold vacuum telling me the diaphragm is shot. 

Does anyone sell a kit to rebuild them? Is sending it off to be rebuilt my only other option? Other than sourcing a used replacement? Which is no guarantee that the used replacement is any good anyway