Strange things. - PeachParts Mercedes-Benz Forum

The Gears · #1 08-22-2009, 10:47 PM

Lost the brakes to day, very skarry! No Vacuum for the brakes but the door locks worked for a few cycles. Also the oil pressure was almost at the pin on an idle with a warm engine.
Before you ask. 1984 300D turbo
I there a connection between loss of vacuum and high oil pressure?
Before I start to remove the vacuum pump is there any tests I can do to prove the pump or pump valve.
Any help very much appreciated.

pawoSD · #2 08-22-2009, 10:50 PM

Check the line itself before removing the pump. Run the engine and disconnect the booster hose at the pipe nearest the pump, if there is suction (test with a gauge if you have one) then its likely not the culprit....no vacuum, replace pump ASAP, as something has failed.

Not sure on the high oil pressure. Is the engine idling any higher than before?

The Gears · #3 08-23-2009, 12:28 AM

Idle speed the same. Could a loaded oil filter cause a high pressure?
Will disconnect the line from the pump and check there.
Thanks
Gears

pawoSD · #4 08-23-2009, 01:20 AM

Not sure on the filter....the system has an automatic bypass if the filter clogs....how long have you been running your current oil/filter? With a 617 engine you don't want to go much over 3,000 miles on normal/dino oil, and not much over 4,000-5,000 miles on synthetic....they make a lot of soot vs. the newer engines.

kerry · #5 08-23-2009, 01:32 AM

Could also be a bad booster. You still have brakes. You just have to stand on them with both feet and really push hard. Don't give up on them just because they're hard.

Wodnek · #6 08-23-2009, 08:31 AM

There is also a rubber seal between the master cylinder and brake booster that needs to be able to hald a vacuum. I spent the better part of a year trying to figure out the brake problem on my 78 300d before i discovered that to be the problem.

tangofox007 · #7 08-23-2009, 09:54 AM

Quote:

Originally Posted by The Gears

Could a loaded oil filter cause a high pressure?

No.

The Gears · #8 08-25-2009, 04:07 PM

Removed the line from the vacuum pump. Air flow in and out, not a vacuum. Removed the check valve that the line was fastened to. The guts of the check valve were laying in the horizontal part of the suction passage on the top of the vacuum pump. Also a lot of white corrosion power. I retracted the check valve parts, the valve plate, spring and a thin washer with a magnet, sucked up the powder with a vacuum cleaner. To reassembly the valve I turned a new valve assembly body from a high temp plastic rod. (that lathe sure comes in handy) Pressed the new assy into the brass fitting, screwed it back into the vacuum pump, fastened the main line back on. When the engine started the gauge jumped to 15 - 18 " and stayed there.
Thanks to the guy that suggested looking at the check valve before pulling the pump.
And for the rest of you. Thanks for your input and help
The Gears

Stevo · #9 08-25-2009, 07:58 PM

That sounds like the rule with those 'newer' pumps, "check the check before you pull the pump"

Good show.

Skippy · #10 08-27-2009, 11:37 PM

Quote:

Originally Posted by kerry

Could also be a bad booster. You still have brakes. You just have to stand on them with both feet and really push hard. Don't give up on them just because they're hard.

True. The pump on my '77 busted the diaphragm last week and I'm still driving it. I don't even have to use both feet. I just press hard with my right. Turning the engine off is accomplished by putting it in gear and stalling it.

Before you ask why I'm doing such a boneheaded thing when I have two other cars, there is a reason for that. The other cars are back home and I'm not, and I haven't had time to pull the part I need from the junkyard yet.

The Gears · #11 08-28-2009, 12:48 PM

Kerry. When you get to the junk yard look for a piston type pump from a 84 300D turbo. it will fit your 77. I did this swap on a 74 240
The gears

Stevo · #12 08-28-2009, 01:14 PM

I'm wondering, which pump would be better. I was thinking the older diaphragm type because its simpler and cheaper to rebuild. (by allot). I swapped a diaphragm type for the piston type in a "later" 240 I had once. Is the piston pump a better pump for some reason??

rrgrassi · #13 08-28-2009, 01:40 PM

I wonder if an old style would be better since the new style, when it fails, takes the engine out as well.

Stevo · #14 08-28-2009, 05:23 PM

Both styles can fail because of the steel balls which come adrift if the bearing fails, but I think the piston is an added potential failure point in the later style, thats what went in mine but i caught it in time. I;m thinking the older style would be a better choice.