Sudden Brake Failure 85 300sd - PeachParts Mercedes-Benz Forum

coachgeo · #1 09-23-2008, 09:50 AM

Yes, Ive done some searches

My daily driver VW golf diesel, has been down for close to 8 weeks now. Short, or something not powering computer. It' killing me. 44+MPG no more

Anyway..... been driving my 85 300sd backup car. Fuel milage is KILLLING ME since I live half hour from work. That and I've gone thru three tires, tranny cooler line, and now.....

I lost my brakes.

Well I got no power brakes would be better way to say it. Have brakes just my legs are not that strong.

No shut down either. No shut down has been appearing irregularly for a few weeks now.

reading of searches seems to tell me to suspect the vacuum pump?? Windows seem to work though.??

Any thing else I should suspect first?

Stuck in a parking lot at work, sleeping in my office... AGAIN. Hungry dog at home!

tangofox007 · #2 09-23-2008, 10:04 AM

Quote:

Originally Posted by coachgeo

reading of searches seems to tell me to suspect the vacuum pump?? Windows seem to work though.??

The windows are electric and unrelated to the vacuum system.

You definitely have a vacuum problem. There are plenty of possible causes. Given the sudden onset, I would place the vacuum pump inlet check valve at the top of the list of suspects. It's inside the fitting (nipple) where the hard line attaches to the pump. The valve has a habit of breaking internally, then the broken parts obstruct air flow.

kerry · #3 09-23-2008, 10:04 AM

Yep, either a bad vacuum pump, line or brake booster. Windows and doors are not vacuum on an 126SD. Check the main vacuum line first for cracks and breaks. After that put a Mity Vac on it to check pump output.

coachgeo · #4 09-23-2008, 10:14 AM

Quote:

Originally Posted by kerry

... Windows and doors are not vacuum on an 126SD.

That's what I suspected. Thanks

Quote:

Check the main vacuum line first for cracks and breaks. After that put a Mity Vac on it to check pump output.

Main vacuume line? Are you speaking of the one from the vacume pump itself to it's first junction?

How much vacuume should the pump hold in the mity vac test? Where do you recommend hooking it up to the pump? Link would be fine.... dont need to go expaling all over again. I'll do search too.

SD Blue · #5 09-23-2008, 10:17 AM

It sure sounds like a vacuum pump to me. However, another possibility is a disconnected or cracked vacuum line. It would have to be part of the major line that goes from the pump to the brake booster if this was the case. Since the booster requires a fairly significant vacuum, you could probably do the "thumb over the end of the line" check and see of it gives a pretty strong pull. If there seems to be little vacuum, remove the main check valve on the top of the vacuum pump and see if you can blow through it in one direction only. (Ensure it is clean first.)

If all of this appears to be fine, the vacuum pump is a fairly easy and straight forward rebuild. About the only slightly difficult part is removing all of those socket head screws holding it on to the engine. (Make sure you order the "late series" rebuild kit in order to get the proper internal spacers.)

compu_85 · #6 09-23-2008, 10:19 AM

What year is your golf diesel? If it's a 1999 or newer does the glow plug light come on and go out when you turn the key? If not check your fuses, and check the relay marked 109.

If it's older then that, like one from the 80s, there is one wire going to the injection pump. Check that it has power when the key is turned on.

-Jason

tangofox007 · #7 09-23-2008, 10:23 AM

Quote:

Originally Posted by coachgeo

How much vacuume should the pump hold in the mity vac test?

You want to determine how much vacuum the pump is creating, not "holding." Hook up the tester at the pump if you can. You would like to see around 20" Hg.

redassag00 · #8 09-23-2008, 10:35 AM

My SDL did this a year ago. IT was the large vac line that goes to the booster via the bulkhead by the fuse box. I think it was 20 bucks.

coachgeo · #9 09-23-2008, 10:49 AM

I find no breaks/cracks in the main line.

How do you remove it for closer inspection. The vacuum pump ends make since it unscrews (metal line portion)

What about the other end?

Is the white distribution plastic thing the check valve that has been mentioned as a possible culprit? This white one is located up by the master cylinder and; after the distribution of many little vaccum send offs, it has a short big line that goes to the Master cylinder

thanks for all the help thus far.

any parts I need.... and a mighty vac are either a 3 hour walk to my house and 3 hour back or a 20 min walk to nappa and 20min back. I have some metric sockets here that's it.

coachgeo · #10 09-23-2008, 10:57 AM

Quote:

Originally Posted by compu_85

... check your fuses, and check the relay marked 109....

Thanks passed this info on. it's an 03 golf.

Don't know about GP light, would check it myself but car is at someone elses house far from here.

The security system is on.. Car starts but the security shuts it down. Lindy (guy working on it) has vag com and all the other software that your not suppose to have such as key recoder etc.... but still got us all baffled.

HERE IS THE THREAD on the VW no go help call out.

coachgeo · #11 09-23-2008, 11:02 AM

Quote:

Originally Posted by SD Blue

... Since the booster requires a fairly significant vacuum, you could probably do the "thumb over the end of the line" check and see of it gives a pretty strong pull.

Will do.

Quote:

If there seems to be little vacuum, remove the main check valve on the top of the vacuum pump ...

hmmmmm.... on top of my pump is a hard metal line. Everything else looks to be part of the pump. Am I seeing something wrong here?

tangofox007 · #12 09-23-2008, 11:16 AM

Quote:

Originally Posted by coachgeo

Will do. hmmmmm.... on top of my pump is a hard metal line. Everything else looks to be part of the pump. Am I seeing something wrong here?

Yes. See post #2.

http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2G51AXQU82GZ0O6I88&yearid=1982%40%401982&makeid=MB%40%40MB%40%40X&modelid=300%2DDT%2D001%40%40300D++Turbo&catid=D%40%40Diesel+Injection&mode=PA&subcatid=D3012@@Vacuum+Pump+Check+Valve&source=www.peachparts.com&clientid=catalog.mercedesshop

Observe the valve in the lower right portion of the photo. Note the round plate with the small hole in the center. Frequently, that plate (which is under spring pressure) breaks off, then it and the remainder of the valve internal components fall into the vacuum pump and obstruct air flow.

If I were troubleshooting a sudden vacuum system failure, that valve would be at the top of my list of things to check.

coachgeo · #13 09-23-2008, 11:26 AM

Quote:

Originally Posted by coachgeo

Quote:

Originally Posted by SD Blue

... Since the booster requires a fairly significant vacuum, you could probably do the "thumb over the end of the line" check and see of it gives a pretty strong pull.

Will do.

I have vacuum at end of hard metal line. don't know what " a pretty strong pull." is though. It sucks in and pulls on my fingerpad. Does not sting, does not want to eat my finger, can easliy pull finger away.

When I turn off the key..... and the car does not turn off. If I floor the go pedal it will shut down. I assumed it was running out of fuel and shut down cause of that. Maybe its building vacuum from higher RPM thus activating the vacuum opperated shut down?

maybe related maybe not? At start up when cold the rpm's are slow to return to idle.

coachgeo · #14 09-23-2008, 11:31 AM

Quote:

Originally Posted by tangofox007

Yes. See post #2.....

well slap me up aside the head with a 2x4

Answer's right there under my nose.

Will pull it and do the blow test.

coachgeo · #15 09-23-2008, 11:51 AM

main check valve's plate w/hole is intact and it passes blow test.

It appears it was installed with some plumbers putty type stuff.

I have none here but do have teflon plumber tape. Should I reinstalll with this?