Troubleshooting Automatic Transmission - Porsche 928 Workshop Manual

928 Automatic Transmission/Gears, Valve Body
38
l
TROUBLESHOOTING AUTOMATIC TRANSMISSION
Note: If transmission oil is black and smells burnt or there is an unusual large
amount of metal particles in oil pan, either repair or replace transmission.
Condition:
Transmission slips in all selector lever positions.
Cause/Correction:
1. Check modulating pressure, adjusting if necessary.
If not adjustable, check movement of modulating
pressure control valve.
2. Check whether vacuum line from intake branch to
vacuum box is plugged. If yes, replace.
3. Check operating pressure. If too low or not available:
a) Disassemble and clean shift valve housing and
service valve. Replace shift valve housing if
necessary.
b) Remove and inspect primary pump, replacing if
necessary.
Condition:
2nd gear slips or transmission shifts from 1st to 3rd gear.
Cause/Correction:
1. Check movement of control valve B 1, replacing shift
valve housing if necessary.
2. Remove and install brake band B 1 piston and check
seal, replacing if necessary.
3. Replace brake band B 1 and pressure element for B I.
Printed inGermany VIII, 1984 Troubleshooting 38. 111