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  #1  
Old 08-04-2019, 03:32 PM
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Vacume pump pressure

Looked in the FSMs and searched here. While there is some discussion of vacume pumps failing and brake boosters, I havent seen anything about official specs for the vacume pump. Haynes just says to run the throttle and see if it increases, but no numbers.



At idle, how many in hg should the pump be producing? Where is this data located?

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Old 08-04-2019, 04:19 PM
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Vacuum pump for what? Space shuttle, 1902 Velocipede, '06 Stanley Steamer?
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Old 08-04-2019, 04:57 PM
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78-83, 240d and 300d


Uh, I was told that all years are interchangeable.
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Old 08-04-2019, 05:12 PM
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A good vacuum pump will produce 16-21 inches of vacuum.
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  #5  
Old 08-04-2019, 05:15 PM
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In the Factory Service Manual at the top of the column you will see it say it is supposed to be measured in bar. But for my year and model that if you go down the numbers can't represent bar.

At idle with no abnormal leaks you should get at lest 22 mmHg. The seat of the pants telling point is if you do not have power brakes or after a pump on the brakes you don't have power brakes.

When the Check Valve that is built into the fitting that screws into the vacuum pump is not working your vacuum drops but you still have vacuum in the teens of mmHg.
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Last edited by Diesel911; 08-04-2019 at 07:43 PM.
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Old 08-04-2019, 08:07 PM
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Quote:
Originally Posted by Diesel911 View Post
In the Factory Service Manual at the top of the column you will see it say it is supposed to be measured in bar. But for my year and model that if you go down the numbers can't represent bar.

At idle with no abnormal leaks you should get at lest 22 mmHg. The seat of the pants telling point is if you do not have power brakes or after a pump on the brakes you don't have power brakes.

When the Check Valve that is built into the fitting that screws into the vacuum pump is not working your vacuum drops but you still have vacuum in the teens of mmHg.

Where in the FSM? I looked in two engine manuals and didnt find anything on the vacuum system. Volume/title/chapter/page?


Also checked startek.

Dont quite understand the check valve issue. This car has serious trans shifting problem, wont get 4th until its spun up to what must be redline. Cant remember the brakes, they worked fine but usually if you hold light pressure with a vacuum problem they will slowly release. Dont remember if that was an issue. Almost all of the vacuum lines have been cut.
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Old 08-04-2019, 09:31 PM
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Quote:
Originally Posted by mark82 View Post
Where in the FSM? I looked in two engine manuals and didnt find anything on the vacuum system. Volume/title/chapter/page?


Also checked startek.

Dont quite understand the check valve issue. This car has serious trans shifting problem, wont get 4th until its spun up to what must be redline. Cant remember the brakes, they worked fine but usually if you hold light pressure with a vacuum problem they will slowly release. Dont remember if that was an issue. Almost all of the vacuum lines have been cut.
Mercedes unique way is to put the vacuum pump stuff in the bakes, pneumatic system. Section 43. (On a W123 that means it is in one of the 2 Chassis Manuals. It is in volume 1)

I am attaching the a PDF from the FSM but I think someone translated the test figures wrong or you have to posses the actual gauge setup used in the Manual.
Attached Files
File Type: pdf 43-660 Checkng Vacuum Pumps all types.pdf (154.8 KB, 44 views)
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Old 08-04-2019, 09:45 PM
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Quote:
Originally Posted by mark82 View Post
Where in the FSM? I looked in two engine manuals and didnt find anything on the vacuum system. Volume/title/chapter/page?


Also checked startek.

Dont quite understand the check valve issue. This car has serious trans shifting problem, wont get 4th until its spun up to what must be redline. Cant remember the brakes, they worked fine but usually if you hold light pressure with a vacuum problem they will slowly release. Dont remember if that was an issue. Almost all of the vacuum lines have been cut.
I rebuilt the Transmission on my Chevy van and am entirely surprised it worked. But, besides filter changes I have only changed the B2 Piston on my 84 300D.
However, this info is from an ATSG transmission manual. This is the closet one that fit your description. (Note the ASTG Manual while widely available is not noted having great info in it.)

Complaint: Transmission slips during 3-4 shift. 1 Check Modulating Pressure and Adjust if Required, 2 Exchange Shift Valve Housings (note that the shift valve housing is the block that contains all of the shift valves), 3 Renew Inner Plates of Clutch K2, Recondition the Clutch According to Condition.

Note that people have had various springs inside of the shift valve break. There used to be kits for that or you used to be able to get individual springs from Mercedes.
Also note that there is different variations of spring packs from model year to model year.
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Old 08-04-2019, 09:55 PM
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From a Mitchelle trans mission manual for Mercedes trans. Keep in mind the same transmission is on gassers. So don't be thrown off when you see something like fuel pump relay which is on gassers. I have not read of any sort of relay on the diesels.

"WILL NOT UPSHIFT
Incorrect governor pressure. Defective governor assembly.
Check for stuck kickdown solenoid or for constant voltage to solenoid
caused by a defective fuel pump relay or sticking kickdown switch.
Valve body dirty or valves sticking. Repair or replace valve body.
UPSHIFTS AT HIGHER SPEEDS THAN SPECIFIED
Check pressure control cable engagement, condition and
adjustment. Check for stuck kickdown solenoid or for constant voltage
to solenoid caused by a defective fuel pump relay or sticking kickdown
switch. Check governor pressure. If regulator pressure is too low,
replace centrifugal governor. Ensure control pressure regulating valve is operable."
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Old 08-06-2019, 01:29 AM
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As I recall from working on the vacuum system on my 2 300D's, 14" Hg will work OK as far as stopping the engine and the door locks functioning, but 20" Hg is better and probably needed for the transmission to shift as designed. I suspect Diesel911 meant 22" Hg. BTW, 29.9" Hg is a pure vacuum. These values (and the measuring gage) are relative to local atmospheric pressure, but you still need the same values since all controls which use the vacuum operate on the difference from atmospheric pressure.

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