Should transmission vacuum modulator hold a vacuum? - PeachParts Mercedes-Benz Forum

surfblau · #1 07-01-2002, 05:02 PM

I am trying to get to the bottom of my intermittently hard shifting SDL.

I pulled a 20psi vacuum on the line running to the transmission modulator from the 'blue plastic vacuum amplifier'. Within 30 seconds, all the vacuum was gone.

I will replace the rubber connector between the vacuum line and the modulator this evening (when I get out of my work clothes), but the connection doesn't look bad.

Should the vacuum modulator hold vacuum?

I can't find any note about it in the shop manual....

thanks

jcyuhn · #2 07-01-2002, 06:04 PM

Yes, it should. Thirty seconds isn't the worst leak, but I bet it impacts your shift quality.

The culprit is almost always the black rubber cap which covers the modulator, down on the transmission. It has to seal that sucker up airtight. After many years, they tend to harden, crack, etc. I've repaired them using permatex type sealants, but a new one doesn't cost much at your local dealer.

surfblau · #3 07-01-2002, 06:46 PM

The only reason I ask is that the price difference is +/- $40 compared to $0.25.

thanks

jcyuhn · #4 07-01-2002, 08:49 PM

You just need the cap - the 25 cent part!