Do research into HOW MUCH stuff is vaccum controlled. Instead of electronics they used a vaccum pump. Oh yeah....and rememeber the motor itself does not produce a vaccum like a gas engine, it uses a SEPERATE vaccum pump which also has failed on the 81.
The drivetrains on those cars are easily probably the most reliable ever produced but nothing else is.
Pneumatics, or air pressure control, is a common item in all cars. However, nobody uses it as extensively as does Mercedes-Benz. Many have used it only for off-on control of timing and emissions devices.
M-B has extended off-on control to the following items: Door locks (brought out in the '60s), seat back locks (two-door models), A/C mode door controls, door closing assist (pulls doors to final lock on '92 and up *-Class car doors and trunk), seat lumbar support controls and other devices, such as the position indicators that rise from the trunks of *-Class cars. Variable control also has been used for such things as cruise control, variable EGR control and intake manifold pressure regulation in turbo diesels.
Probably the most interesting of these variable controls are the ones that M-B uses for shift control in M-B diesels. It'* interesting because the engines have no manifold vacuum, actually having positive pressure most of the time in turbo-diesels (they run with small boost at constant highway speed). These vacuum-controlled transmission systems appeared in the first 300SD in 1978. That system was pretty simple. All subsequent systems added more layers of control. Variations of this system are on all M-B diesel automatic transmissions until electronic control took over in 1996.
The basic idea was to create a system that presented vacuum to a transmission modulator. The trick was to simulate the vacuum-to-load relationship in a gas motor. With a gas motor, under heavy load the vacuum would be low as the throttle would be fully open. These diesels have no throttle so there never is any vacuum; the only differences in manifold pressure occur during boost.
What makes this system so special is the variety of ways the system can be adjusted. The basic book adjustment might work for an out-of-the-box, by-the-book transmission. As it happened, M-B made numerous after-production changes to these transmissions. The combinations of pieces and the variety of wear conditions cause these transmissions to exhibit numerous offensive shift conditions. Among these, the number one condition in diesels is a harsh 1-2 shift. The next most common is a 3-4 shift flare. Others include double shifts into either 3rd or 4th, harsh 4-3 downshifts, and various shift overlap and sequence irregularities.
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