Transmission Vacuum Part - PeachParts Mercedes-Benz Forum

rmmagow · #1 06-25-2011, 04:31 PM

85 300D
there's a blue canister on the drivers side fender under the hood. Two black rubber connectors coming from the top. One is stamped TRN. One of the black rubber elbows connects to a small green plastic piece, Pierburg 7.20841.00 and 5065 (looks like heat branded in number).
The part does not act as if it were a one way valve. It does hold vacuum if one holds a finger over one end and sucks on the other.
What is this thing? is it supposed to be a one way valve or is this some kind of orifice control? The other end connects to a long black vac line leading to the back of the engine and I am betting to the transmission.

Thanks.

punkinfair · #2 06-25-2011, 04:51 PM

it's the vacuum amplifier, aka the BFS (blue flying saucer). it's function is well explained in this article, near the bottom.

http://www.continentalimports.com/ser_ic20242.html

Quote:

The most important modification came with the 1985 model and is continued on all subsequent ones. It involved the addition of a vacuum amplifier to the system (see Fig. 7). The amplifier takes a large vacuum supply, the proportioning vacuum signal and a boost signal and creates the final signal to the transmission. This device did two things. First, it incorporated the input of boost to further tailor the load control of the modulator vacuum signal. The vacuum at the modulator now starts high - 12-17 in. - and is reduced to about five inches through straight throttle movement. As boost builds, the vacuum is further reduced to zero only at full boost.

sixto · #3 06-25-2011, 04:54 PM

Is it a green cylinder about an inch long and an inch around? If so it's a damper. If it's more like a coupling barely larger than the rubber hose it's either a filter or an orifice.

Sixto
87 300D

rmmagow · #4 06-25-2011, 08:11 PM

interestng article. My car does shift hard at low speed, small pedal movment operation like in bumper-to-bumper traffic. I'm going to play around a little to see what can be accomplished without screwing up an otherwise good shifting W123.