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Harsh 1-2 shifts, late upshifts that wind the engine out, or soft, slipping shifts are common R107 complaints. Most of the time the cause is an adjustment or a vacuum problem, not a failing transmission.
Hard or late shift causes
- Vacuum modulator: controls shift firmness based on engine vacuum. A leak or failed diaphragm makes shifts harsh.
- Bowden (throttle) cable: controls shift points based on throttle position. Out of adjustment, it makes shifts late or early.
- Fluid level and condition: low or burnt fluid causes slipping and erratic shifts.
- Engine idle and vacuum leaks: a vacuum leak lowers the signal to the modulator.
- Worn internal parts: clutches and bands, but only after the external items are checked.
Vacuum modulator test
- Find the modulator on the side of the transmission, with a small vacuum line.
- Pull the line off with the engine idling: there should be strong vacuum.
- Check the line for cracks along its route.
- Pump a hand vacuum pump onto the modulator: it should hold vacuum. If it will not, the diaphragm has failed; if transmission fluid comes out of the line, replace it immediately.
Bowden cable adjustment
The Bowden cable runs from the throttle linkage to the transmission. At idle, there should be a small, specified gap at the cable’s end fitting. At full throttle, the cable should pull fully to the kickdown stop. A stretched or misadjusted cable makes shifts late (too tight) or early and soft (too loose). Adjust at the threaded fitting near the throttle linkage, following the manual.
Kickdown solenoid
Floor the pedal: a switch on the linkage energizes a kickdown solenoid on the transmission, which forces a downshift. If kickdown does not work, check the switch, the wire and the solenoid. Pelican Parts and the factory manual both cover the test.
Fluid level check
Check with the engine warm, idling, in Park on level ground, as described in transmission fluid. Burnt smell or dark fluid suggests internal wear.
When it is internal
If vacuum, cable, kickdown and fluid are right and the transmission still slips, flares or will not upshift, it is time for a transmission specialist. See automatic transmission problems.
Quick answers
- Can a vacuum leak make shifts harsh? Yes. Less vacuum at the modulator means firmer shifts.
- Is a firm 1-2 shift normal? These transmissions shift with some firmness, but a jolt that throws you forward is not normal.
