300E twin turbo: pressure on brake pedal
 

My W124 300E twin turbo needs appreciably more pressure on the brake pedal than either my W124 E320 Coupé or my W126 300 SE. The braking is fully effective, but definitely requires more effort. All cars are properly serviced. My mechanic can't pinpoint why there should be this difference, although wonders whether the turbo (Garrett) system may have some bearing on it. Any views?

Sure seems logical to me that it would be the problem. Of course a poor check valve at the booster could also be involved.

Many turbos use a separate vacuum pump to maintain enough vacuum for boost. The obvious test would be to monitor the vacuum between the check valve and the booster.