Hello,

I had another post going on about my car not stopping when applying the brakes.

Found there was a master cylinder leak that was leaking into my brake booster.

Replaced MC and removed all the fluid that leaked into it - no help, brakes still not working correctly (also car would not shut off, and other vacuum related issues).

Replaced booster as well, and now the brakes work great, unless repeated use of "slamming the brakes" mutliple times in a matter of seconds. So now safe for the road, because that never happens, but know its not 100% of what it could be.

There is still an issue where my car takes a few seconds (5-10 seconds) before the car shuts off.

When I turn off the car and put my ear near the brake booster/MC, I hear a slight noise, like vacuum is being released. I took off the MC and made sure the gasket is up tight against the MC and the booster, then re tightened.

So at this point I know I either have a vacuum leak somewhere or the vacuum pump is weak.

My questions are:

1. Since the booster deals with so much more vacuum than the line for engine shut off, why can I now have "working" brakes but the car still takes a long time to shut down?

2. Is it normal to hear some vacuum activity at the booster after shut off? If not, what possibilities could there be, since the MC and booster are new and the seal has been checked?

3. Could it be that there is a leak in the shut off line segment of hose, causing it to especially be affected?

4. Could this all be an issue with the vacuum pump?

Thanks!

Make sure the booster vacuum line doesn't have a leak in it:
http://catalog.peachparts.com/ShopByVehicle.epc?q=1981-Mb-300sd-Brake&yearid=1981%40%401981&makeid=MB%40%40MB%40%40X&modelid=300%2DSD%2D002%40%40300SD&catid=N%40%40Brake&subcatid=N4020@@Booster+Vacuum+Hose&mode=PA

Do you have any other vac issues other than the shutoff? Like door lock problems?

__________________
Chad
2013 Jeep Unlimited Rubicon
OBK#44
"Pleasure in the job puts perfection in the work." - Aristotle (384-322 B.C.)

SOLD
1985 300TD - Red Dragon
1986 300SDL - Coda
1991 - 300TE
1995 - E320
1985 300CD - Gladys
2006 Nissan Pathfinder LE
1998 Acura 3.0 CL

If I'm not mistaken, there should be an o-ring on the shaft, sealing the booster. Did you replace it when you replaced the booster? If not, It'd be the first thing I'd suspect.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Check too, the shut-off valve itself...I had one that had a slight leak in the diaphram and I swore it was a leak somewhere else.

Check too the condition of the vacuum lines around the area of your cylinder...a cracked vacuum line, swollen boot, or worn out boot would slow the stop.

Also, if your brakes dont work 100% but "enough for the road" you might wanna MityVac your vacuum pump at the source and then check the vacuum pressures at other places...a lazy vacuum pump could take away from your brake performance drastically, causing insufficient vacuum in other places!

Thanks for the replies so far.

Yes I did replace the o-ring at the MC/Booster connection.

Any other suggestions or feedback as to why there would be that "hissing" sound at the brake booster after the MC/booster was replaced?

Is that normal?

That hissing is a vacuum leak.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D

you may also want to try disconnecting the brake booster vacum line and putting your thumb over the hole, see if the car shuts off any better. That is one way to eliminate the vacum booster as a source of problems. Depending on the mileage, have you checked the vacum pump? If you have a vacum guage you should read approx 18" of vacum when the car is running.