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Vacuum Leak & Brakes

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Erin

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1980 240D
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Discussion starter · #1 ·
Can someone tell me if a vacuum leak can start to affect your braking system.

I know that I have a leak somewhere (my locking mech doesn't work and the car takes awhile to shut off) but after just getting back from a 2000 km trip, my brakes are now starting to act up.

I know that the vacuum line also runs to the brake booster but not sure if a leak would cause the brakes to go soft. I've had the brakes themselves checked out twice and have been told they are fine.

If the vacuum system could be the cause, I'd have to take the car to a shop 1.5 hrs away :( becuase there aren't any close by familiar with that type of system. But if the vacuum is unrelated and its something like the master cylinder then I can take it to my regular shop.

Thanks for your help

Erin
 
#2 ·
My 1980 300D was having similar problems and just about all problems vanished when the vacuum system was dealt with. Almost every system on your car - brakes, climate control, locks, fuel injection, automatic transmission - rely on the vacuum system. There is a spaghetti bowl of vacuum lines under the hood and dashboard with rubber connectors that in turn connect to plastic actuators and metal components, as well as to the brake booster. While the brake booster does not have a rubber connection to its vacuum hose, the vacuum hose that supplies the brake booster is connected to other lines by rubber connectors. The rubber connectors deteriorate and leak, reducing vacuum strength for braking assist and other functions. Only one connector need by leaking and everything is affected. Have the vacuum system checked - you probably have a leak. Start with the dynamic vacuum connection atop the cam cover that apportions vacuum to most systems and should be replaced first, as if it is not leaking it soon shall be.
 
Discussion starter · #3 ·
Its good to know that fixing tha vacuum system may solve the rest of the problems. I had begun on the small stuff, like replacing the rubber fittings but was hoping to put off fixing the major systems until spring. Its already full blown winter here, and replacing the vacuum lines in the driveway in the blowing snow wasn't my idea of fun. :) But now that its affecting my brakes, I've made the appt to take it into the garage.

Thanks for the help.

Erin
 
#4 ·
First are you sure it's the vacuum system? Check the brakes if they are in good condition. The spongy feeling could also be attributed to the cold weather. Did you have the brake fluid changed before fall/winter? If so then good. If not, it could have alot of moisture in it leading to the spongy feeling of the brake pedal itself.

Also, is the fluid level at the maximum? If so then good.

Move on to the vacuum system. When my car had a small leak (main vacuum line going to brake booster had to be replaced), I didn't notice any significant brake power loss. When I changed it my vacuum doors locked faster, and it felt like it ran better.

Anyhow, what I did was change all the vacuum fittings under the bonnet (the + and the Y shaped ones, plus the U and L shaped ones, then got 2 meters of vacuum hose just in case I run out).
 
Discussion starter · #5 ·
Karugs,

I'm not certain that the vacuum system is the source of THIS particular problem, but I do know that my vacuum system has many problems of its own. Like I said, my central locking doesn't work, nor has it since I got the car, and it always takes a good 2 minutes to shut off. 2 minutes on an exceptionally good day, usually more like 5 . :)

The reason I'm leaning towards the vacuum system as the cause of this problem, is that while on our long, long trip this weekend, we had a little hiccup. While my husband was on his leg of the driving, he noticed the brakes went SUPER spongey, almost no brakes at all. He gave them a good three or four pumps, and while he pumped the last time there was a horrible screaching, crackling noise from the heating system. (We had it cranked because it was -10'C).

Since Sunday, its been all down hill. The brakes are more spongy than they are hard, and now just today while driving into town, my brake wear indicator light comes on when I hit the brakes. I know that the brake pads are nowhere near needing replaced, I had them all checked out less than 3 wks ago in preparation for our long trip.
 
#6 ·
The lack of vacuum will make the brake pedal feel very hard and it will take a lot of effort to bring the car to a halt. The soft feeling could be either air or water in the system. With the soft feeling and the light coming on I would suspect brake fluid leak. Please check the fluid level and look at each wheel for any leaks. The other item that could cause a soft feeling is the hose that goes to the calipers. If they have developed bulges due to the rubber breaking down then that will give a soft feeling
 
#7 ·
MB-owner has a good point too.

Hard feeling = no vacuum assist
Soft feeling = check brake system (fluid, pads, lines, etc)

Since the brake light lit up I would check the brakes again, even if I know it's been checked already. It's a 2000km trip. Anything can happen.

I would also suspect a combination of vacuum problems and the brake system problem because as you mentioned the heater made some noise when it shouldn't. If the brakes became spongy there could be a bulge, leak, or moisture in the system. Bleed it and refill as necessary. Then when the cold weather disappears, check your brakes again. That's why they recommend changing brake fluids before the cold season sets in so that moisture can be avoided when flushing the fluids.

By the way, how was the trip?[;)]
 
Discussion starter · #8 ·
Okay, the loss of vacuum makes the brake feel hard...thats good to know, because I have the exact opposite happening. I have checked the levels and have looked for leaks and there are none that I see.

I am completely paranoid now with and have been checking it before I go anywhere, but the level is not going down, which is adding to the mystery. I have had to replace the master cylinder and brake lines on an old car I used to have and my symptoms were similar. :(

I am going to try to bleed the lines tomorrow before I go to work and see if that makes a difference. I read somewhere that I can loosen the screws on the master clyinder and have someone pump the brakes until fluid comes out line, then re-tighten. this will purge any air from the line. Does this sound right?
 
#9 ·
As I haven't done any bleeding yet, I cannot tell if that's right. Maybe somebody can help you better with this.

But just don't let it EVER get into contact with the body paint. That brake fluid will eat it alive.

You mentioned that symptoms are similar to your older car. Maybe recalling what you did and attempting to do just that will resolve your problem here. It seems that you have no vacuum assist problems, which is good. We can now isolate the problem to the brake system.

I'm not sure if it's supposed to go down. From what I understand of brake systems, when you apply pressure on the pedal and it feels spongy the brake pressure does not push the pistons as it would normally. The force could be lost somewhere between the pedal and the pistons, which could easily be the brake lines themselves. There would be no leak, otherwise if there was a leak then the pedal would go straight to the floor without any problems.
 
#10 ·
Erin - 11/30/2004 7:35 PM


I am going to try to bleed the lines tomorrow before I go to work and see if that makes a difference. I read somewhere that I can loosen the screws on the master clyinder and have someone pump the brakes until fluid comes out line, then re-tighten. this will purge any air from the line. Does this sound right?
Click to expand...
No! That does not sound right, that would bleed the master if you done it right and it will allow air to enter if you done it wrong. To properly bleed the system you must start at the right rear attach a hose over the bleed valve and open it while someone is pressing down on the pedal. Be sure to catch the fluid in a jar and make sure the hose is down in the fluid so there is less likely to have air going back in the system. When the pedal is at the end of travel, close the valve and then let the pedal return. Repeat several times then top off the reservoir and repeat on the left rear. Continue to the right front, then the left front. At some time you will feel the pedal get very hard if there is air in your system. Be sure to top off the reservoir with fresh fluid every time.
 
#11 ·
Your engine shutoff problem is most likely your vacuum shutoff valve. It's a common problem on 123's. I just had to replace mine. Do a search on this site, you'll find lots of info on the valve. Good luck.

Gary
 
Discussion starter · #14 ·
Okay, I'm done tinkering with the car myself. This is getting to be to large of a job in the driveway in the blowing snow :)

It goes into the shop tomorrow, and they're going to look for obvious brake problems (Again) and then tackle the vacuum system.

Thanks for all your help everyone.

By the way, the trip went great, although full blown winter has hit and we were traveling 10 hours north :) But the car handled Excellent in the snow and this brake problem was the only thing we encountered. Not bad for a 25 year old car :)

Thanks Again,
Erin
 
Discussion starter · #17 ·
Yikes, I love my benz to death....which is good for the car because I was momentarily re-thinking my decision to do away with my reliable car to purchase the retro benz :)

Well, I got my car back from the shop on Friday. It turned out that the car wasn't shutting off due to a hole in the diaphragm, and my brakes were spongy because I needed my master cylinder replaced. It was apparently only working off one valve.
Well those both got replaced, along with a brake line that snapped when they were bleeding the new master cylinder.

I was happy happy to have my car back, even after paying the $583.00 bill. At least my car now turned off, and my brakes were no longer spongy.

Unfortunately, when I got home, I had the complete opposite effect. My brakes were so hard that I could barely stop the car....yup, now I come to find out that my vacum pump is putting out less than half of what it is supposed to. So back to the shop it went. It's now awaiting a pump replacement, which I hope can happen quickly because in the meantime I'm forced to rent a car @ 70$ a day to get to work :(

Owning a cool car is fun :)
 
#18 ·
Nice story!

After reading that it was the master cylinder, I'm glad that your brakes held up during that trip though.

It pays to know how your car functions. At least you know what to expect and how to deal with it. [;)]

"Owning a cool car is fun" <--- I second that!
 
#20 ·
OneMnk,

Where in SoCal are you? Don't take it to the dealer, they will charge you an arm or a leg for that.

If you are in the Garden Grove area I could recommend a mechanic to you. Or you could go to Enriquez in LA. Somebody else knows more about him, he is a reputable guy who specializes (I think) in MB's.

If it's hard I would check the vacuum lines/system. Trace the leak if you can, or get a vacuum pump repair kit and DIY it. You mention the transmission is jerky. Sounds like a combination of vacuum problems.

Make a search for "vacuum modulator" for the jerky transmission and "vacuum leak" for the brake system if you do find any.
 
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