**MOST Common 928 Issues AND Fixes**

[MPDano]

[dcrasta]

Issue : The headlight actuation rod pivot lever (wshew..sorry cant describe this) is retained by some small 'e' clips. If your car has had front end repair, or the headlight rod removed for any reason the retaining clips could be missing. If the clips are missing, the lever could become detached, and when you turn on the headlights instead of moving the light up could puncture the radiator.

Solution :
1-Inspect for lost clips as soon as you can
2-Replace any missing E-clips with factory replacements (or 5/16th replacements.)
3-Retrofit with self-locking clips [8mm]

8mm self-locking circlips from McMaster-Carr: McMaster-Carr

Part# 94824A400, mcmaster about $5 per pkg of ten. Fit fit good, and seem very secure.
They are just a black-oxide finish, so rust might be a problem in some areas. I would use white lithium or grease on them to retard rust.

[153bigblock]

Troubleshooting your Mercedes 722.xxx/G28 Auto box from the Mercedes Trans WSM (longish):

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
AUTO TRANS DIAGNOSIS - 722 SERIES
Article Text (p. 8)
1996 Mercedes-Benz C220
Copyright © 1998 Mitchell Repair Information Company, LLC
Wednesday, January 26, 2000 12:03PM
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
AUTO TRANS DIAGNOSIS - 722 SERIES
Article Text (p. 9)
1996 Mercedes-Benz C220
Copyright © 1998 Mitchell Repair Information Company, LLC
Wednesday, January 26, 2000 12:03PM
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
AUTO TRANS DIAGNOSIS - 722 SERIES
Article Text (p. 10)
1996 Mercedes-Benz C220
Copyright © 1998 Mitchell Repair Information Company, LLC
Wednesday, January 26, 2000 12:03PM
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.

[tychain99]

are the headlights supposed to drop when the power to the car is off? I know when my car is turned off and the lights are up, i spin the dial to kill the lights, but they do not retract. If they are supposed to drop even with out the car on, i should check the connections you pointed out

[MPDano]

Originally Posted by tychain99

are the headlights supposed to drop when the power to the car is off? I know when my car is turned off and the lights are up, i spin the dial to kill the lights, but they do not retract. If they are supposed to drop even with out the car on, i should check the connections you pointed out

If the car is on and you have the lights on and up, when you turn the key off, just the lights will go off when you turn your headlight knob. This is normal.

Then with light switch off and the headlights up, turn the car on and the lights will drop back down.

[924CarreraGTP]

MPDano said I should post this to this thread, So here it is.
Porsche 928 electrical short tip!

--------------------------------------------------------------------------------

Many times the overhead interior light can short and drain your battery. You can spend years checking the jumper, cleaning the grounds and pin connectors and never find it.
It is a common problem and you must remove the fuse to the overhead light.
Another thing, doing a draw test and pulling every fuse to find a short is tedious while standing on your head in the 928 floorboard. You are better off getting a clipboard, checking all systems and writing down the ones that don't work. Remove one fuse each day from the nonworking systems until you find the short. I narrowed mine down to the trunk latch, antenna and the interior light. The interior light was the short.
I hope this helps with your Shark ownership.
If you talk to enough people somebody will eventually tell you that the overhead lights short onto the body when the fixtures are rebulbed or due to the tabs bending. Its a common problem but so many people will tell you to check your jumper circuit and grounds only to leave you in the same place. My 928S now holds its battery charge for months on end.

[dtool242]

Not really so much a 'fix' as I am still sorting out what my problem is, and no pictures. Just some general tips for measuring transmission pressures from another thread I posted.

For all the test connections I used a 1/16 NPT to 1/4 tube fitting connector (Swagelok part number B-400-1-1) to which I connected 1/4 poly-flo tubing of sufficient length to route up through the passenger window connected to a gauge in my lap while sitting in the drivers seat.

Operating pressure:
The spec is 16.9 bar (245 psi) so I used a 0-300 psi gauge. This gauge is too small. When the car was idling in park or neutral the pressure is much higher than 300 psi. Luckily the gauge did not have a high peg so the needle wrapped around and was bouncing off the back side of the low peg. I'm guessing it was seeing ~350 psi. With the car in drive the gauge was bouncing between 240 and 250 psi with temporary drops when the car shifted gears and then right back up to the 240 - 250 psi.

Modulating pressure:
The manual tells you to drive at 140 kph (87 mph) to measure modulating pressure. I've seen where other people discuss that they measure and set with it at idle. When I measured I got ~64 psi (4.4 bar) whether it was in idle or driving up to about 70 mph.

Governor pressure:
This one you definately have to drive to measure the pressure as the pressure increases with speed of the car. This is the one that I am currently having problems with. Last night I installed a governor I got from Landseer and was still seeing low governor pressures. So according to the ATSG manual for the transmission http://avtopedia.ru/akpp/722-3%20722-4.pdf (pg 103) the next step for me is to check out the valve body.

One last tip:
I know I said above that I used poly-flo tubing, but DO NOT USE POLY-FLO TUBING! It will certainly stand up to the pressures but the problem is when measuring the modulating or governor pressures, the line will have to run perilously close to the exhaust. After driving a few miles around my neighborhood last night while checking the governor pressure, all of a sudden the pressure went to zero (had been riding 5 - 10 psi) and the car went to first gear and stayed there. I look in the rear view mirror to see a trail of fluid behind me. Fortunately I only had about a 1/4 mile to go to get back into the garage. Seems that the heat from the exhaust softened the hose and it separated from the swaged fitting.

[MPDano]

Sunroof Fix: Most of our Sunroofs fail due to old grease. Here is mine on my 83 928S. All parts were fine but just needed a good cleaning and some lube. I used Silicone Lube Spray.

This past Saturday I got the motivation to fix my Sunroof. It never worked properly since I bought the car. It was kinda open but trying to close it with the switch became impossible. I ended up having to use the little rubber motor clutch and spin it manually about 1000 times to get it to move 1/4".

Anyways took mega pics (of course) to show you how I successfully got my Sunroof to operate 100% and very smoothly.

The Instructions from this website got me motivated and helped a lot in getting me started in the right direction.

Sunroof

Open the Sunroof 3/4 of the way.



Here are where the 3 screws a relocated (this holds the inner cover on)



The 3 Screws (Manny, Moe and Jack)



This is what those 3 screws connect to.



This the Sunroof Tranny (as I call it) that connects to the Motor which on the other side of the screw pictured turns a gear that moves the toothed cable (which is inside a guide tube). That's a serious run-on sentence there boys and girls! The top arrow points to the electrical plug to the motor. I actually removed the Tranny and pushed the switch to make sure my Motor was nice and strong (which it was)



These are the Four 8mm bolts that hold the Sunroof on. You'll find four more bolts on the opposite site.



Eight bolts removed and sunroof removed and off.



This is the Track you want to make sure is nice and clean. I used lots of Simple Green to get this nice and clean.

[MPDano]

These next two pics are the $$ Ticket. This is the toothed cable which moves inside the Guide Tube. Old 30 year old grease really slows this down and binds the whole system. I ended up using Silicone Lubricant (spray) to get these to move nice and smooth. I bought the Silicone Lube at Home Depot. I also used it on all the parts that touch or ride on each other. HUGE Difference!! I did a test when using the switch before the Lube and after. Absolutely awesome!





Clean these bad boys too. I used Brake Cleaner, the Lubed them with Silicone.





Here's the orientation of these pieces.







Thes two bolts were fun to put back in, plus you need to make sure the washers that sit on the "other side" stay in place. Mine stayed in place with thick grease. Be patient here, you' also get your 6 pack ab's after this task.

**Update! Make sure to use Blue Locktite on these bolts since they may back out.



This is a pic of the inside sunroof plate. You will need to get that all that vinyl/leather material back on the plate. I used the same adhesive I used on my Hood Liner.

[MPDano]

Here's a couple pics of the adhesive in place. Your going to let it dry until the white becomes transparent then just press it on.





Here's a video of it all working. I LOVE MY SUNROOF!

[MPDano]

Here is the Silicone Lube I used:

[Danglerb]

Nice work Leo. Sometimes adjusting the interior roof panel can be a REAL PITA.

Harbor Freight sells a gadget for cleaning bike cables. A rubber sleeve clamps over the end of the cable with a hole you can squirt in cleaner that is forced down the cable (towel etc. at the other end to catch the mess), then spray in the lube.

I think I used Wurth HHS 2000, but garage door lube might work well too.

[Landseer]

Thanks for the sunroof description and pictures. And the whole thread, actually!

[dcrasta]

Awesome How to on the Sunroof. Great documentation and pics. Thanks!

[MPDano]

Issue: Low Alternator Output

Possible fix: Replaced Voltage Regulator. Huco Brand and Made in Germany. Purchased from Roger. Make sure all Grounds have been cleaned first.

I trust Roger so no question that this part would not be the issue if I wasn't getting the voltage I need after the install.





Here is the Remanufactured Alternator from Advance Auto. I already suspected the Voltage Regulator even before I put the Alt on as it didn't look new. I also pulled the Part Number off the old Voltage Regulator and it came back as one from China. Piece of Craaap! http://www.alibaba.com/product-gs/452389069/IP2700_12V_autmobile_electrical_voltage_regulator. html





I had to use an Impact Screwdriver to get the two screws off since they were on so tight. Worked like a charm.





Even this didn't look right as soon as I got the Regulator off, here is the before.



Here is the after, I used a very very fine sandpaper to remove the black marks



I used Blue Locktite on the supplied screws to make sure they didn't back out on me.

[MPDano]

Huco Voltage Regulator installed





This is the Volts just after starting. It's a Cold reading



This is with the AC on and Headlights on. Car is still cold



AC Off, Headlights On



Headlights Off



Warm reading. Nothing on



After a 5 mile drive. nothing on



This why you don't trust your Cluster Voltage Gauge. I got 13.5 volts on the jump post and this is what it shows inside.

[MPDano]

Issue: Got Dim Instrument Panel Lights and you've cleaned all grounds and nada changed?

Fix: Remove Pod and then remove Cluster from Pod. Removed the three Large Refractors and three Small Refractors by popping them off with a small screwdriver. Use Brake Cleaner on a Tower to remove all the old Chrome Paint. Find some Chrome Tape from a Hobby Store and cover the areas where there used to be paint. Also put chrome tape on the small refractors.

Remove the three black connector covers and clean lightly the fingers with Brake Cleaner on a Q-Tip. I used an Xacto knife to gently scrape the fingers clean. Slightly tighten all screws and nuts holding the PCB (Printed Circuit Board).

Reassemble and test at night.

[MPDano]

Issue: Got old Brake Booster Vac Lines. Cracked or Rock Hard? Leaking due to this?

Fix: I picked up some 1/2" Heater Hose which is reinforced. Four feet of it to be exact. Picked up eight hose clamps while I was there. Used all my old hose as length templates.

Replaced hoses: Throttle Body to Y at Spider. Small piece from Y to Spider Body. Y to Coupler at Brake Booster. Small piece from Coupler to Brake Booster.

Tested with no leaks or collapsing.

[MPDano]

Issue: A/C Clutch turn on then off. Electrical Buzz in HVAC Controller. System has no leaks and is 134a/R12 Full.

Possible Fix: My Ac worked fine up until 30 days ago. I had my local AC guy check and narrowed the issue to the HVAC Controller. Since I remember seeing a write up on replacing the internal relay, I thought I would give this a go.

I ended up buying all the pieces needed but found out that my internal relay is different. I ended up cleaning all the contact points with Brake Cleaner on a Towel to remove what I saw was oily substance all over the Circuit Board and then using my Dremel with soft brush at low speed on contact points as well.

My internal relay has a plastic removable cover, so I removed it and used a manual soft bristle brush and lightly brushed the contact points. Then I made sure to blow it out to ensure no bristles were left in the relay itself. Closed the relay back up and put the lower cover back to test it.

I started the car up and low and behold, I got arctic cold air again. I made sure to move the nicely newly installed slider back and forth and "NO" more buzzing noise. Somehow just cleaning it up nicely did the trick.



The irreplaceable Relay



Clean these contacts really good, you'll see yours won't be this shiny



Clean these Fingers as well



The top round thing is what the black plastic piece pivots on. You can remove the circlip and the pivot comes out revealing the metal pressure fingers which I also cleaned up. I also bent them slightly down more so it got nice contact with the Board.





Clean these Contacts as well.

[MPDano]

Issue: A/C Clutch turn on then off. Electrical Buzz in HVAC Controller. System has no leaks and is 134a/R12 Full.

Possible Fix: My Ac worked fine up until 30 days ago. I had my local AC guy check and narrowed the issue to the HVAC Controller. Since I remember seeing a write up on replacing the internal relay, I thought I would give this a go.

I ended up buying all the pieces needed but found out that my internal relay is different. I ended up cleaning all the contact points with Brake Cleaner on a Towel to remove what I saw was oily substance all over the Circuit Board and then using my Dremel with soft brush at low speed on contact points as well.

My internal relay has a plastic removable cover, so I removed it and used a manual soft bristle brush and lightly brushed the contact points. Then I made sure to blow it out to ensure no bristles were left in the relay itself. Closed the relay back up and put the lower cover back to test it.

I started the car up and low and behold, I got arctic cold air again. I made sure to move the nicely newly installed slider back and forth and "NO" more buzzing noise. Somehow just cleaning it up nicely did the trick.



The irreplaceable Relay



Clean these contacts really good, you'll see yours won't be this shiny



Clean these Fingers as well



On the underside of this round piece is a clip that holds this black plastic piece on, once the clip is off, you can clean the metal fingers on the underside. I also bent them down a little more to give them better contact pressure.





Last fingers to clean