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Old 03-29-2001, 05:25 PM
Bob U
Posts: n/a

We have a 87' 420SEL and the auto transmission has started to shift very rough when shifting from 1st to second and less rough shifting from 2nd to 3rd. It feels the way a manual transmission feels if you "drop" the clutch. The rough shifting is more pronounced when you accelerate slow and not as bad when you give it a little gas. The filter and fluid were changed about 25 k ago. Fluid level is fine, driveshaft, u joints, and rear end are fine. What could be the problem here? Is it a repair, and adjustment, or do I need a new tranny? If I need a new tranny would I be ok to get a rebuilt? And what are the potential costs of all this?
Thanks in advance for any help.

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Old 03-29-2001, 06:18 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Modulator pressure is adjustable. The 420 and 560s have the additional common fault of the vacuum line to the modulator falling off the vacuum port. The port is hard to see but the line can be seen with the air filter off looking down the backside of the intake manifold. The large vacuum line going to the brake booster starts in this area. There is a banjo fitting and the small port is in that area. Look for the white plastic line passing under the crossover exhaust pipe. That is the line to the modulator. Be sure it is plugged in.

BTW the complete symptom package is a rough idle (vacuum leak) with harsh shifting.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 03-30-2001, 12:19 PM
Bob U
Posts: n/a
Steve, you nailed it!!

It was just as you suspected. The vacuum line was disconnected. Thanks!!!!!!!!!!!!
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