While working on my brakes, I decided to check the vacum pump pressure.

At the brake booster (with all the other lines plugged up) I'm getting about 24 to 25 PSI at idle. But, in the Haines manual, it says that vacum should increase as the engine RPMs increase. My vacum remains static, however, not changing at all as the engine speeds increase.

I also have some vacum related problems I am trying to diagnose so I wonder if I need to start at the pump with a rebuild or replacement?

__________________
1987 300TD
1985 300TD (sold)
1980 300TD (sold)
1972 280SE 4.5 (sold)

I will assume that you mean 24 or 25 inches of Mercury, not PSI. The system draws vacuum, it does not make pressure.

With that assumption, your vacuum pump is fine, and your brake booster is okay. Whatever vacuum problems you have are due to a leak or two.

Since you did not elaborate on the vacuum problems that's about all I can offer. If you will describe the vacuum related problems I'm sure we can help you work through them.

Good luck,

Thanks for the response.

As for vacuum problems, the primary problem I am having is with the transmission and secondary problem is with the climate control.

Transmission has a harsh 1-2 shift and a pronounced flare from 2-3. I have looked up previous threads on transmission adjustments and I haven't gone through the diagnostic work. It could be a bad transmission however.

I just replaced the brake master cylinder because the old one was leaking into the brake booster. I also pumped about a pint of fluid out of the booster. It seems to hold vacuum still however. Changing the MC seemed to help with the shifting however... is this possible or is it just my imagination.

Now, the new master cylinder seems to be leaking again. I noticed a dribble of fluid working its way down between the MC and the Brake booster. Also, the fluid level is diminishing in the reservoir. I'll try another Master cylinder since I'm not sure what else it can be and this seems like a typical MC failure.

Climate control seems to operate very slowly. IE; a 5 second delay between the time you push a button and anything happens. Also, sometimes it always blows hot even when you turn the temp wheel all the way down. I thought that this could be vacuum leaks and or temp sensor hose that needs replacing.

Thanks for your thoughts as there are many question embedded in this rambling post.

__________________
1987 300TD
1985 300TD (sold)
1980 300TD (sold)
1972 280SE 4.5 (sold)

Do a search for transmission modulator or maybe transmission vacuum. There are several good threads with links to some invaluable articles regarding the transmission vacuum contraption. Use your vacuum gauge on the line to the transmission and check against the information in the articles. It very well could be your problem there.

I am unaware of leaking m/c reservoirs being a common MB problem. There are two rubber grommets in the m/c into which the reservoir mounts. Also don't overlook the possibility of a cracked reservoir. If the reservoir is cracked, replacing the m/c will not help, as the m/c does not come with a new reservoir.

The climate control could very well be a leaking diaphragm. Ensure that you have your 22 or 24 in Hg going through the firewall to your accessories. If you do not have it on one or more of the accessories, the leak is probably in the accessory, not in the vacuum supply.

Hope this helps,

Thanks...

Yes it does help.

__________________
1987 300TD
1985 300TD (sold)
1980 300TD (sold)
1972 280SE 4.5 (sold)