my wife's complained that the brakes in her '79 300D started acting up last night. I drove it around for about 30min and it seemed fine....but then I drove it about an hour later and the brakes were rock hard. Really difficult to bring the car to a stop.

After reading some other posts, I see that this is probably either a vacuum leak or the brake booster. Since I'm not having any other vacuum assumptions (engine run-on, locks not working, etc) shall I assume it is the brake booster? If not, what sort of diagnostic should I be doing?

And I wonder where I can get a brake booster on a Saturday?? -Harv

actually, it might not be the brake booster because in looking at it, it looks like it was replaced by the previous owner, less than one year ago. -Harv

Do you have a piston-type vacuum pump?

it could be the checkvalve in the vacuum line, it could be a damaged vacuum line feeding the booster. it could be collapsing flex lines on the calipers.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

May not be relevant, but here you go:

Worn front brake pads=high pedal effort

__________________
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

Hmmm, I'll inspect the check valves and the lines. Don't think I can do too much beyond visual inspection tho.

The brake pads should be at about 50% tho and the calipers were also new in the last 2-3 years (previous owner always used new parts, never put a used part in the car....not sure if I can keep up to his standard.).

-Harv

I would suspect vacuum failure first.

Related data.

Brake:
Brake:

Couldn't figure this one out and finally dropped it at the mechanic today. Everything looks fine to me...all the lines visually inspect, the calipers look good, pads about 50%, rotors are fine, no fluid is leaking. So I guessing a vacuum leak or the booster....both seem strange to me because the booster was new about 9 months ago, and I have no other vacuum related issues.

Guess I'll find out in the AM from the mechanic.

I did check out the price of brake boosters:
NAPA: $120
PeachParts: $427

why such a huge price difference??

NAPA is probably a rebuild, or a made in China part. PeachParts typically carries what the dealership would use.

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RRGrassi


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

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

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Have you or anyone else actually put a vacuum gauge on the system ?
Those are old vacuum lines and old check valves...
Hard to tell just looking....if they are working correctly...
Look at VStech's post...

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

Haven't put a vacuum tester on it as I don't have one, which I why I characterized it as a visual check. The lines are not actually old just because it is a '79. The previous owner had installed only new parts, and in the case of the brakes it included the calipers, master cylinder, booster, and all lines. Same goes for the vacuum system. It is pretty amazing, you look at it and it looks like it just rolled of off the line 6 months ago.

Anyway, it is in the shop and we should hear within the hour. Thx -Harv

Don't forget to tell us what is wrong after you find out.

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84 300D, 82 Volvo 244Gl Diesel

yup, it was the vacuum pump. And I just learned the hard way that those are expensive parts ($550) plus 2.5 hrs labor. I'm probably fooling myself that this is something I can do right? I think I'll go ahead and have the shop do it, especially since I'm an hour into them and I've got another car at home on the fritz.

-harv

Wow, what does 2.5 hours of labor run? That seems like a lot. If it were me, I would give it a go. Is it your daily driver?

It's my wife's daily driver. And she really flippin out without it. At this point I'll have the shop fix her's and I'll fix mine which also has a vacuum related problem I just need to get a pressure guage and learn how to diagnose these vacuum problems.