8 cylinder front engine iconic vehicle
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By G8RB8
#44483
It seems we're weak on auto transmission troubleshooting and repair. If you have info, links, how-tos, or anything to contribute to the knowledge pool post it up. Let's see where we really are.
http://www.ganzeboom.net/images1/gan...3,%20722.4.pdf
http://www.w124performance.com/docs/...722_repair.pdf
http://www.w124performance.com/docs/...2_Mitchell.pdf
http://avtopedia.ru/akpp/722-3%20722-4.pdf
http://members.rennlist.com/pirtle/s4atrans.htm
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http://www.ligeti.com/928/
Last edited by G8RB8 on Thu Dec 24, 2020 9:53 am, edited 1 time in total.
User avatar
By G8RB8
#44486
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AUTO TRANS DIAGNOSIS - 722 SERIES
Article Text (p. 7)
1996 Mercedes-Benz C220
Copyright © 1998 Mitchell Repair Information Company, LLC
Wednesday, January 26, 2000 12:03PM

TROUBLE SHOOTING

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
replace transmission.
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 necessary).
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.
NO KICKDOWN
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 PAWL 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 (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 & 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.
User avatar
By G8RB8
#44488
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Default Auto Transmission Troubleshooting (from trans manual)
AUTO TRANS DIAGNOSIS - 722 SERIES
Article Text (p. 7)
1996 Mercedes-Benz C220
Copyright © 1998 Mitchell Repair Information Company, LLC
Wednesday, January 26, 2000 12:03PM

TROUBLE SHOOTING

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
replace transmission.
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 necessary).
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.
NO KICKDOWN
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 PAWL 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 (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 & 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.
Last edited by UncleMaz; 12-01-2012 at 03:10 PM. Reason: Added Title
User avatar
By G8RB8
#44490
About That Infamous B2 Piston
Why it breaks

The broken B2 piston problem is a well understood and easy to fix transmission problem with certain Mercedes 722.xxx automatic transmissions found in 126, 123 and 107 body cars. Although the car is drivable with a busted B2, it's a bit tricky. There is a school of thought that says any pre 1994 MB with one of these should be replaced as preventative maintenance.


Busted B2 Piston
Broken B2 Piston


In this picture you can see two parts to the B2 piston. The problem is it is supposed to be one piece, not two!

There were a couple of design flaws with this part, common to most 80s and early 90's Mercedes cars.

The piston actuates the B2 band, that is it helps shift gears. It's about 3" in diameter and this piston has about a 3" stroke. There is a deal around the outside of the piston, much like a piston ring. This piston rides in a metal sleeve.

The seal was originally round, and the sleeve was metal. I saw was, because that design had problems that usually show up bewteen 100 and 200 thousand miles.

What happens is the piston is activated and pushed inward in its bore. But, the round seal sometimes gets stuck (for whatever reason) and hydrauic pressure builds up to tremendous force so eventually it does move but by now there's so much pressre that when it does move it does so with increadable fource and eventually it snaps' the 3" collar and the flat disc separate by breaking at the base. That's what happeneed to that poor piston above. it happens to most of them eventually.

Mercedes had several upgrades to these parts over the years and now we have new improves beefier B2 pistons that have a square seal instead of a round one, and a plastic sleve instead of a metal one. That seems to have fixed the problem. These new B2 pistons do not seem to fail.

The symptoms of a B2 piston failure are unmistakable:

Fails without any warning whatsoever
Slips out of gear in 1st with any load
Massive flaring going into second
3rd and 4th work normally
Reverse works normally

They fail anywhere between 100K and (in my case) 400K miles; chances are very high your first major problem with this transmission will be this one.

But, things could be worse, the car is drivable when this failure occurs, although it takes some patience. It's worse when cold, and is made worse by how much load you put on it. The object of driving a car with a bad B2 piston is to never give it much load in 1st and 2nd gears.

Think of parking on a hill facing down. You want to get the car into 3rd as soon as you can and 3rd and 4th are unaffected by even catastrophicB2 failure. You might even consider pulling the transmission vacuum line so it shifts way much too early into 3rd. I did. Seems to make driving in a car with this problem a little easier.

On level ground what you'll find is it will go into gear once you put it in drive but will pop out almost immediately after you give it even the smallest amount of throttle. But, then it'll go back into great and now you might actually be able to get going withvery light throttle. Or it may pop out again and you're ok now till it shifts into second and you get to hear it pop out again, then it'll go back in and you'll be ok now. It'll probably shift into 3rd and 4th quite normally, so floor it and don't stop. If you stop you have to go through this ordeal of starting the car moving again. Starting the car going uphill is a near impossability, but it can be done. It's unlikely the car behind you will have the same kind of patience you have though. Wave and smile.

Once the B2 piston has failed it's unknown how long you can actually drive it for before it pack in completely. I drove mine aroiund for 3 months till it warmed up enough outside to be able to fix it. It is not the end of the world.

The good news is the repair can be made while the transmission is in the car in the case of a 126 it's pretty easy - in other chassis the trans needs to be dropped just a little although people have reported success, with some effort, of doing it to 123 and 107 chassis with the tranny in place. It's not a terribly expensive repair either, the part is about $100 and it'll take you a couple of hours. While there's a few steps to this it's really only a little worse than changing a spark plug and you don't need of be a master mechanic to do this.

Here's how

Credit to: Richard Sexton
User avatar
By G8RB8
#44494
Shifter Cable Replacement
>Can someone tell me (in general) what parts to remove to replace the shifter
>cable?
>
>928S Euro Auto 1981


1) Remove ground cable.

2) Remove shift handle and rubber boot.

3) Remove cover frame.

Put lever in "2" and push rear locking bar forward against stop with a scribe.
Put lever in "R", disconnect gate and push as far forward as possible.
Push front locking bar forward against stop with a scribe.
Put lever in "P" and carefully pop out left rear corner of the cover frame.
Put lever in "N" and remove cover and frame to the rear.

To Install:
Put lever in "3".
Push gate in frame forward all the way.
Insert cover and frame, and move lever to "P".
Lift left rear corner slightly and insert right and front of cover and frame, then push down on left rear.
Put lever between "R" and "P", disconnect gate on selector lever and push forward.
Push front locking bar toward rear until it locks.
Put lever in "3" and push rear locking bar back until it locks.
Reinstall gate, rubber boot and shift handle.

4) Pull bulb carrier from clips.

5) Mark selector base, then remove mounting screws.

6) Loosen intermediate muffler shield and push aside.

7) Disconnect selector cable from transmission lever and detach cable sleeve on brackets.

8) Take off ball head, hex nut and mounting parts.

9) Attach a strong wire to cable at transmission, and then pull selector base and attached cable forward and out.

10) Remove cable from base.

11) Reinstallation is in reverse order.


Wally Plumley
928 Specialists
User avatar
By G8RB8
#44495
Transmission, Automatic
Replacing Burned-out "Drive" Indicator Light
>yesterday the light for 'Drive' [shift sequence] in the instrument cluster went dead.
>all the other pattern lights work except for 'Drive.' am i going to have to pull
>the cluster and replace a dead bulb? are there contacts under the manual
>shifter that turn these lights on? hopefully -- i don't know why porsche
>would do this -- it is something pathetically easy like replacing a burnt fuse.

Q1. Yes
Q2. No
Q3. No.

Drive bulb burns out, because it is ON all the time. Direct replacement bulbs are unavailable. They are 12V, however. Maybe you can look for one at a large electronic parts supplier. If the bulb is replaced with a different one with slightly different wattage, it may be dimmer (or brighter), than what you are used to. Instrument cluster must be removed from pod, then tachometer must be removed from cluster. Tachometer must be taken apart - only difficult part is pulling the pointer off without breaking it (good luck). To remove the pointer, you need the equivalent of a gear puller to grab the round part of the pointer and pull evenly, otherwise the shaft may be damaged. Once it's off, the circuit board can be unscrewed from the face assembly, the bulb removed, and a new one soldered in place.

Send it to Hollywood Speedometer (?), advertisers in Excellence. They can replace bulb for you. Or buy a used tach that has all the lights operational (contact 928 International). If you have the bulb replaced, better have all of them replaced at the same time, because PARK will be the next to go, maybe REVERSE. Replacing them all will assure that they all illuminate with the same level of brightness (and you don't want to have to pull the tach out again, if you can avoid it).

*Steve; 87S4/auto/GPW
928 Tips Home Greg's Home
User avatar
By G8RB8
#44496
Found two other ways to adjust the 4-gear AT-box shifting points.

Govenor plastic adjustment screws:
https://rennlist.com/forums/928-foru...ed-only-2.html

on mine, it turned out to just be the govenor adjustment - 2 white plastic screws that we turned out 2 turns each. takes about 20 min to pull it out, 2 min to turn the screws, 20 min back. easy to do.

turning the screws 2 turns out on my old gal put the 1-2 shift consistantly at 6100, others are just above 6200/redline finally. the old gal rips now!! it's about 3mph faster (64mph) on my 600' driveway (and back to 0) yeehaa! can't wait to put it back on the track to see what that means in the 1/4mi

all shifts were higher, but 1-2 was noticably higher/now at redline from 4500-5400 before. other shifts at about 6200/a tad over redline but not enough to worry about on this motor, imo and it just seems faster overall as a result, but the track timers will tell the story better than my assometer

two screws are on the govenor body. it pulls out the side of the trans, and you can't miss'em - one on each side/white plastic.

I also did the trans bypass switch, but it only seems to affect shifting under part throttle (ie nicely drops down a gear when activated w/out any additional throttle input), and forces the trans into 1st while moving at low speeds w/no throttle input (impossible to do before).

I've also found some articles that indicated a low rpm shift (assuming everything is adjusted properly) could be from a dirty valve body circut or bad/spring or worn 1st gear clutch packs.


In fornt of the valvebody:http://avtopedia.ru/akpp/722-3%20722-4.pdf

Page 16. The arrow indicates the position of allen screw for full throttle control pressure. Turning clockwise results in earlier full load or kick-down upshifts. Turning counterclockwise results in later upsihfts.


I have seen both screws, but haven't touched them yet. Has anyone else used those before?



Some other related links and information:
More about WOT shifting issues and tuning: http://www.w124performance.com/docs/...pshift_RPM.pdf
More about modulator replacement and vacuum adjusting: http://www.benzworld.org/forums/w201...l-replace.html


Good S4 AT rebuild thread by atb:https://rennlist.com/forums/928-foru...ld-thread.html

About tranny pressures:
Hydraulic pressure controls Shifting.

-Hydraulic pressure is set by the primary pump and governor. This is NOT adjustable.

-Some pressure can be adjusted externally to control timing and quality.

-4 types of pressure work in concert:

a. Working Pressure: From the front driven primary pump, and its the basis of all pressures. Cannot be adjusted, but can be measured by a port.

b. Governor Pressure: Builds pressure with centrifugal force in a gradual proportion as the speed of the tranny increases. It works directly against control pressure to regulate the shift depending on vehicle speed. Cannot be adjusted, but can be measured by a port with the car driven a certain speeds.

c. Modulating Pressure: controls the working pressure, from partial to full throttle. Modulator can be adjusted to harden or soften the spring inside it. One way is constant, by turning the key inside it and the other way is constantly changing because is vacuum. This vacuum is also controlled by the VCV which leaks vacuum in proportion of the throttle position. Modulating pressure controls the shifts by varying the applied pressure to the bands on the clutches. Modulating pressure acts as a control for the working pressure in proportion to the torque of the engine. Can be adjusted by turning the key in the modulator and checking the pressure in the port close to it.

d. Control pressure: This is relative to the pedal position. Obtained from the modulator by means of the control pressure valve, which is influenced by the linkage or cable from the tranny to the accelerator linkage.
User avatar
By G8RB8
#44498
So yesterday I watch the Jay Leno video about the new Jag F type and they talk about their new 8 speed auto tran that has really quick shifts, 0-60 4.2 sec, and I wonder about it. What really is an auto tran, what goes on? It seems it's all bout the Torque Converter. So what happens inside the torque coverter. Lots of Voodoo! I watched youtube video's, still its tough to grasp. Some coincidence that this thread pops up.

see the tc here - http://www.floridatorqueconverters.c...ons-722-3.html

and here - http://www.gopnh.com/Transmissions.c...ssion=%20722.3

and I was wondering Has anyone here ever opened up one of our torque converters?

All TC's have an impeller, turbine, and stator, with some having a friction plate clutch thing that works as an overdrive. I don't think we have that. (I cant find a parts diagram that opens up our TC) The TC is a torque multiplier at take-off. The reason my particular 928 Euro is so fast is because of the optional A.28.06 tranny and in particular the TC. The Voodoo is strong in mine. So if your 928 auto is not quick, many things to look at, engine, linkages, but especially what tranny and what TC in that tranny and how is it functioning.


User avatar
By G8RB8
#44499
Additional reference docs- albeit from the MB community, but 722 related:
http://www.w124performance.com/docs/mb/transmission/

Big repository of Merc threads:
http://www.benzworld.org/forums/w123...ent-722-a.html

User avatar
By G8RB8
#44500
CAUTION: Mercedes Post,

But I expect it is applicable. Includes pics to aid I.D.

http://www.peachparts.com/shopforum/...odulators.html
A link for a PDF of the .3 and .4

http://www.makcotransmissionparts.co...-pdf/722-3.pdf
User avatar
By G8RB8
#44501
Referral sheet for MB approved transmission oils: http://bevo.mercedes-benz.com/d/d/en/Spec_231_1.pdf

All approved oils which should be used: sheets 236.1, 236.6, 236.7, 236.9, 236.10,236.81 (see here and select from dropdown box http://bevo.mercedes-benz.com/bevolisten/236.1_en.html)
Oils which can be used: sheets 236.8 (artic climate only), 236.12
http://www.yellowbullet.com/forum/forumdisplay.php?f=30
https://www.928gt.com/t-928trans.aspx
User avatar
By worf
#44507
Good thread. Most dense concentration of 722 info I can recall.

The MB community, by definition, must know more about the 722s than we do; no need to apologize for MB links.
User avatar
By G8RB8
#44510
I copied the good posts from the original RL thread. Some comments are not mine.
Worf, I'm pretty sure you posted in there.
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By Charlie
#44746
Dean Fuller's 2 part video on single handed torque tube removal is fantastic. That needs to be preserved for posterity. Dean is not posting as much on RL anymore and he sold Marvin, the green car. But that guy knows how to use a wrench, or just about any other car tool. His paint thread is amazing.

I remember when my TT broke and Dave, master of understatement, said "You don't want that to be your first 928 DIY."

Another “One & Done?” Hope not ☹[…]

Well Joel, you would also have a pretty strong sup[…]

Formula 1 2020 And Beyond

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