PeachParts Mercedes-Benz Forum - View Single Post

Jeremy5848 · #4 02-12-2012, 11:59 AM

that "vacuum" and "gauge" are two of the most frequently misspelled words in this forum?

But anyway . . .

Almost all vacuum gauges sold into the automotive market in the US of A are 0-30" Hg. The typical MB diesel vacuum pump operates at 20 to 25 inches of mercury so you'll be fine with a 30" gauge. Vacuum gauges aren't much fun to monitor as they never change (unless there's a problem) so you forget to look at them.

Another option is to get an gauge cluster from an MB gasser. Swap the left-hand 1/3 (with 4 gauges) for your diesel's left-hand 1/3 (with 3 gauges). The fuel, oil pressure, and temperature gauges, in my experience, use the same meter movements in diesels as they do in gassers. I saw no difference when I installed the gasser gauges in my diesel (does not apply to tach and speedo -- they are definitely different).

The fourth gauge is called "Economy" but is simply a vacuum gauge connected to the intake manifold of the gasoline engine. You can connect it to one of lines from your vacuum pump and monitor the pump that way. The cluster in the following picture is actually from a 1984 300SE -- I wanted a panel without the "Unleaded fuel only" markings, see discussion, below.

The "Economy" gauge is not calibrated but you don't really need to know the exact reading, just use the gauge to monitor for unusual changes. If the needle suddenly shifts to a new place, you will know that you have a leak or a problem with the pump.

In my car, I have connected the "Economy" gauge to the line that goes to the transmission. If the tranny suddenly develops hard shifts, I should be able to see a change in the vacuum gauge, providing it is a vacuum problem.

This is the finished cluster before I installed it in my '87 300D Turbo. Note that you should get a panel from an early 124 or 126 gasser or the gasoline pump symbol will have an "Unleaded fuel only" note that you will have to paint out. The earlier cars didn't have that note.

Note: The red and amber LEDs are warnings for low oil pressure and high coolant temperature that I added. They blink when the oil pressure drops below 15 psi or the coolant temperature rises above 100°C.

Jeremy