This is about a 5 gear automatic 722, but many things are similar to our 4 gear transmission in a 928.
AUTO TRANS DIAGNOSIS - 722 SERIES
Article Text (p. 7)
1996 Mercedes-Benz C220
1998 Mitchell Repair Information Company, LLC
Wednesday, January 26, 2000 12:03PM
Transmission slips in all gears
Incorrect modulating pressure. Modulating pressure control valve or pressure relief valve is dirty or sticking. Vacuum line to transmission vacuum capsule clogged or leaking. Working pressure control valve dirty or sticking. Low working pressure. Defective primary pump.
Transmission Slips When Starting Off In 1st Or 2nd (Reverse Is Okay)
Band B-2 shift valve sticking. Band B-2 piston worn or damaged. Band B-2 adjusted incorrectly or worn or damaged. Adjust brake band B-2 by installing a longer thrust pin (if necessary). If transmission operates properly with selector lever in "2", but not in "3" or "D" position, one-way clutch may be slipping.
Transmission Slips In 2nd Gear Or Shifts From 1st To 3rd Gear
Check control valve B-1 for ease of operation. Replace valve body (if necessary). Remove and install brake band piston B-1, check sealing ring and replace (if necessary). Replace brake band B-1 and thrust body for B-1. Command valve binding.
Transmission Slips During 2-3 Upshift Or Slips Initially, Then Grabs Hold
Check modulating pressure and adjust (if necessary). Check for temperature throttle installation (if equipped). Valve body worn or damaged. Replace valve body (if necessary). Replace inner plates of clutch K-1 or recondition clutch (if necessary). Check front cover Teflon ring.
Transmission slips during 3-4 upshift
Check and adjust modulating pressure. Governor damaged or working pressure incorrect. Valve body worn or damaged. Replace valve body (if necessary). Check Teflon rings supporting clutch K-2. Replace inner plates of clutch K-2 or recondition clutch (if necessary).
Intermittent no 5th gear
Check loose connections at throttle valve switch. Check for poor or loose wiring connections between TCM and transmission. See WIRING DIAGRAMS. Ensure proper TCM is installed.
No 5th gear or transmission shifts to 5th under load
Check and repair vacuum line between intake manifold and ignition control unit.
No positive engagement in reverse
Check plates and sealing rings on brake B-3 piston. Replace if necessary.
Harsh engagement when shifting gears
Incorrect working pressure. Check and adjust modulating pressure. Check
vacuum line and connections for leaks. On vehicles equipped with diesel engines,
check vacuum control valve. Coolant entering transmission oil cooler and
contaminating transmission fluid. Replace radiator. If necessary, replace all
friction linings and/or
Harsh engagement when selecting "D" or "R"
Idle speed too high. Check pressure receiving (pick-up) piston in valve body
for ease of operation and correct installation. Replace valve body (if
NOTE: Pressure pick-up requires a running period of approximately 2 seconds. Harsh engagement may occur during repeated shifts between "N" and "D". If harshness takes place within 2 seconds, condition is considered normal.
Harshness on 4-3 downshift
Sealing ring on release end of band B-2 worn or damaged. Band B-2 piston worn or damaged. Band B-2 thrust body damaged.
Chatter during upshift
Valve body malfunction. Check and repair or replace valve body.
Will not upshift
Incorrect governor pressure. Defective governor assembly. Check for stuck kickdown solenoid or for constant voltage to solenoid caused by a defective fuel pump relay or sticking kickdown switch. Valve body dirty or valves sticking. Repair or replace valve body.
Upshifts at higher speeds than specified
Check pressure control cable engagement, condition and adjustment. Check for stuck kickdown solenoid or for constant voltage to solenoid caused by a defective fuel pump relay or sticking kickdown switch. Check governor pressure. If regulator pressure is too low, replace centrifugal governor. Ensure control pressure regulating valve is operable.
Upshifts at lower speeds than specified
Check pressure control cable engagement, condition and adjustment. Check full throttle stop by accelerating engine and ensuring throttle valve rests against full throttle stop. Readjust throttle stop (if necessary). Check governor pressure. If governor pressure is too high, replace centrifugal governor. Repair or replace valve body.
Check throttle control and pressure control cable engagement, condition and adjustment. Connect kickdown solenoid to battery and check for proper operation. Replace solenoid (if necessary). Check kickdown valve in valve body. Replace valve body (if necessary).
No 4-3 or 3-2 downshift
Control pressure cable out of adjustment. Leaking vacuum hoses and/or connections. Ensure brake shaft piston is operable. Replace valve body (if necessary).
Uncontrolled downshifts outside range of kickdown switch
Remove kickdown solenoid. Check "O" ring on kickdown solenoid for damage.
Check kickdown switch for sticking in pushed-in position. Replace switch (if
necessary). Check for kickdown solenoid stuck in
opened position. Replace kickdown solenoid (if necessary).
Poor acceleration from stopped position
Check stall speed. If stall speed is 400-700 RPM less than specified value, one-way clutch in torque converter is slipping. Replace torque converter (if necessary).
Parking brake will not engage
Check rear engine mount. Replace engine mount (if necessary). Check adjustment of selector rod. Adjust selector rod (if necessary).
Selector lever does not engage in "R" or "P"
With engine running, clean centrifugal governor and ensure correct operation. With engine not running, check operation of detent piston in lower cover.
Engine will not start in "P" or "N" position
Adjust shift rod and starter lock-out switch. Replace starter lock-out switch (if necessary).
Smoke in exhaust (and transmission fluid loss)
Diaphragm in vacuum control unit defective. Transmission oil is being drawn from engine through vacuum line. Replace vacuum control unit (if necessary).
Fluid loss between torque converter and primary pump
Seal torque converter oil drain plug. If leak continues, replace radial sealing ring and "O" ring on primary pump. Check primary pump "O" ring groove for porosity. Replace primary pump (if necessary).
Howling noise when changing gears (under full load)
Replace transmission oil filter.
Howling noise which increases as engine rpm increases
Check primary pump and replace if necessary.
1st gear & reverse too loud
Replace front planetary gear set. Reverse and 1st gear are louder than forward (driving) gears due to gear reduction. If noise seems too loud, or if in doubt, a similar vehicle should be used for comparison.
3rd gear too loud
Replace rear planetary gear set.
Rattling noise at 1500 rpm in all positions except "R"
Brake B-3 plates are vibrating in transmission housing. Replace brake B-3 plates, install damper spring and set release clearance to minimum value.
Light grinding noise in "P" & "N" positions
This condition is normal if a "rolling" noise of front planetary gear set is heard. If noise seems too loud, or if in doubt, a similar vehicle should be used for comparison.
"Rolling" noises when driving in reverse
Disc brake B-3 release clearance too great. Adjust release clearance to
.06-.08" (1.5-2.0 mm) or replace disc brake plates. Outside plate carrier of
clutch K-1 contacts piston. Primary Pump Bushing Loosens After A Short Operating
Period - Dowel pins for centering transmission to engine are not in place.
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