I bought a new (to me) 81 300td. and i have a bad leak in the shut off system, which i had little power assist in the brakes, so i blocked it off temporarily. but my question is when i hook the vacuum line that gos to the transmission straight to the nob on the thick vacuum line (from the brake booster to vacuum pump) my car shifts like butter i don't feel the shifts at all. but when i hook it up according to the diagram with the three way rubber hooking up the vacuum control valve and surge damper to the automatic transmission line the car runs quieter but shifts harder, and i think it may be leaking since after a while i don't have power assist brakes. so i was wondering if the vacuum control valve and surge damper is really needed?

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1974 240d
1983 240d -sold
1989 420sel with om606
1994 s350 turbodiesel - sold

Yes, the Vacuum Valve (the one for the Transmission) and the normal setup is supposed to work.
Below is what is supposed to happen.
http://www.continentalimports.com/ser_ic20242.html

There is a restricted fitting in the Vacuum Circuit that goes to the Vacuum Valve on the Fuel Injection Pump and on to the Transmission. It reduces the Vacuum to 10-15.

I am guessing that if you are running the Vacuum From your main line without your the restricted fitting that your main line Vacuum must be poor; and that is why the Trans is running OK on it. But, but that is just a guess.

Since you have not mentioned any Vacuum Readings I am also guessing you have not put any sort of Gauge to take a Vacuum Reading.
It is always helpful to know from the beginning if the Vacuum Pump itself is putting out enough Vacuum.

Also, when I did some work on my Car and knocked off the Vacuum Line to the Transmission Modulator the Transmission shifted OK during up shifts but thunked during down shifts.

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84 300D, 82 Volvo 244Gl Diesel

i didn't buy a mityvac yet, but what your saying is that my vacuum pump might be producing not enough vacuum with the stock set up and that when i hook up the transmission vacuum line straight up to the main line its getting enough vacuum? because when i was diagnosing my weak brake problems i thought that the servo was bad, i didn't think the vacuum pump was bad since the records from the PO show the pump was rebuilt in 2005. i saw a test for the servo and pump in a different thread that i should try. and also i was wondering am i suppose to feel any shifts when the car is all straightened out?

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1974 240d
1983 240d -sold
1989 420sel with om606
1994 s350 turbodiesel - sold

It is more normal when the Vacuum Pump is going out for you to have hard braking due to the Power Brake Booster not getting enough Vacuum. However, what if you were barely making just enough Vacuum for the Brake Booster to work?

If the Previous Owner did the Rebuild they most likely did not change the Check Valve on the Vacuum Pump (Brass Colored part that screws directly into the Vacuum Pump and where the Main Line Connects to the Vacuum Pump) because it is about a $60 part all by itself I doubt if home rebuilders replace it.

Years ago I had a bad Vacuum issue and it turned out the Vacuum Check Valve was gunked up. Removing the Check Valve and spraying it out with WD-40 cleaned it out and resolved the problem.

Others have found the innards of the Vacuum Check Valve Broken.
Another issue is that if the Vacuum Shutoff Valve Diaphragm gets a hole in it Oil Vapor gets sucked towards the Vacuum Pump where besides the Check Valve there is I believe 4 other Disc Valves inside of the Pump that can get gummed up.

While a Mighty Vac type tool is a better investment in the long run a regular Vacuum Test Gauge (Automotive Fuel Pump and Vacuum test gauge combined) will cost less. One of your Neighbors might have one.

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84 300D, 82 Volvo 244Gl Diesel

It's a straight-forward, albeit time-consuming process to do it correctly.

Get the mity-vac, get your vacuum diagram, read the threads, ask questions but you've got to get your hands dirty as well.

You wont find folks here that'll spend much time doing it 'good-enough'.

This is German-technology.

1,2,3,4
2,2,3,4
3,2,3,4
4,2,3,4

There's method and purpose. You learn the technique and the technique will serve you.

Oh. BTW, there's a good chance that the butter smooth shifts you describe were due to you, in essence, 'riding the clutch' throughout the entire drive.

Welcome to MB diesels.

.

When there is not enough Vacuum or the Power Brake Booster/Servo goes bad the braking effort needed on the pedal becomes scary.
Another area that can leak Vacuum is there is an O-ring between the Master Cylinder and the Power Brake Booster.
Also if the Master Cylinder rear Seals leak Brake Fluid gets into the Power Brake Booster. I am not sure what symptoms it causes but Brake Fluid and Rubber are not a good mix.

If you look up the Cost of a rebuilt Power Brake Booster you will want to test your system better to pin point what the cause is because it is around $350 each for one.

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84 300D, 82 Volvo 244Gl Diesel

Polk around this site it has some Vacuum Diagrams.

http://peterschmidtransmission.com/

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84 300D, 82 Volvo 244Gl Diesel

I think they are up in the sticky on this Diesel Discussion as well.

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i had no power brakes but when i unhooked the shut off system the brakes worked. i got a good place to check the brakes a way from cars. i'm going to borrow a mityvac from autozone and test the pump tomorrow. i had an extra booster that i swapped out same thing. i'm really thinking its the pump. since when i had everything hooked up the brakes worked fine but after a few feet the power assist would go out. i gotta check the brass check valve. i think your right about just enough vacuum.

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1974 240d
1983 240d -sold
1989 420sel with om606
1994 s350 turbodiesel - sold

also sjh what do you mean by "riding the clutch"?

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1974 240d
1983 240d -sold
1989 420sel with om606
1994 s350 turbodiesel - sold

Howdy,

I've written some stuff but this link is much better -

MB Transmissions

The transmission has something called clutch packs. They're wear surfaces that smooth the shift. Since I've never held one in my hand I'm limited in the specifics.

The vacuum to the tranny moves a diaphragm which moves a plunger which tells the clutch pack to engage or disengage.

The vacuum control valve which is connected to the throttle position, working with the vacuum from the vacuum pump sends the appropriate vacuum to the vacuum modulator on the tranny.

That controls if the shift is hard or soft. Soft shift means clutch-like surfaces are wearing inside of the tranny. Hard shifts mean much less wear is occurring.

Now a properly maintained tranny can go 400K (maybe more) so there is no reason to be concerned about clutch-packs wearing out. But that means that the packs should be engaged for X number of milli-seconds per shift. If instead it is engaged 100X milli-seconds per shift you are wearing them out 100 times faster.

So part of the process is getting your vacuum signal to the transmission set correctly.

The other two parts are adjusting the correct hydraulic pressure in the tranny and setting the Bowden cable correctly.

I spent a number of months before I got mine right. There are many people here who know this much better than I.

But I'm pretty sure what I've said is a useful place to start.

Enjoy.

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so the vacuum thing on the IP sets the vacuum right to engage those clutch packs so that the tranny shifts smooth but not so smooth as to wear the transmission? I'm wondering how smooth the shift suppose to be? i never had a 617. and my 240 is stick. thanks for the replies

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1974 240d
1983 240d -sold
1989 420sel with om606
1994 s350 turbodiesel - sold

I drove my w123 for 18 years with fairly abrupt and hard shifts. I thought that's how it's suppose to be.

I got my w124 a year ago, read about the process here, set everything by FSM procedure and specs and experienced a completely different drive.

I started with getting the vacuum perfect everywhere.

Glad I could help.

It's a small repayment for that others have done for me here.

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so today i got a chance to look at the check valve on vacuum pump, every thing looked clean in it doesn't look to be the problem.

my dad was looking at the vacuum and he looked at the surge damper and he thinks its broken and swapped it out with a blue white black one we had as an extra i hooked everything up to spec and everything works well, i have smooth but not to soft shifts everything locks and shut off works and i have power brakes, so I'm wondering what does the surge damper exactly do is it suppose to go only one way? and is the blue white black one the same?

i also forgot to mention yesterday i unhooked the vacuum to the EGR and the spider on the valve cover, but i don't think that had any leaks. I'm planning to block it later.

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1974 240d
1983 240d -sold
1989 420sel with om606
1994 s350 turbodiesel - sold