86 300SDL New Owner, New Questions! LOOK!
 

I posted problems I had with my new 86 Mercedes 300SDL and I have a few problems and some general questions.

1. What are the RPMS I should expect to see at highway speeds (70mph is about 3000RPM on my Benz)?

2. My heater works great but the problem is, the heat only come out the lower vents (floor vents). I get regular air if not cool air coming out the upper vents (this is also the case with the rear air).

3. The temp control seems to take a little while to adjust to a new setting...is this normal?

4. Is it normal for a Benz tranny to slightly slip? It really is slight.

5. Is is normal to be able to change gears (from park to reverse and so on) with the key off and out of the ignition?

6. How easy is it to fix the mirror motor...my mirrors only go side to side and only on the pax side...even if I switch it to the DS, it still adjusts the PS.

7. Someone did a poor job of putting the CD player in and messed up the center console before I bought it...how do I go about putting it back together?

Thanks for looking, any other tips about restoring the interior would be greatly appreciated!

1) I'll check and give you the exact number
2) sounds like a vacuum problem
3) it does take a short time to adjust to a new setting
4) not sure on this one
5) not sure if it's normal, but you can do it in mine
6) I would take spray contact to the switch. so far, that has cured my heatrest and seat switches
7) describe the problem a little more........

While it's very hard to diagnose with one liners here are some suggestions that you can continue and use the search function on the forum.

2. Vacuum Pods, CCU, Air Circulation Switch

4. It should not slip - most common problems are vacuum leaks, Transmission Modulator needs adjustment, Kickdown (Bowden Cable) needs adjustment.

5. Yes

7. If you are asking how the wood can be refinished there is a good thread on that here on the forum.

Where are you at Putty? I am in Chatt, TN This week.

Alright, heres a little more detail...the center console seems to be bulging out in the middle and on the sides...like its not tucking into the upholstery properly. The little cup/tray doesnt stick/clip down, the ashtray pulls straight out when you pull on it and the wood paneled shifter piece moves freely...I try to find a way that it might snap in place but it just doesnt...If I push inward on both sides of the console, it looks normal...when I release, it bulges out. Weird eh?

Welcome to the forum.

You've got an extensive set of issues there and it's difficult to address the details of each in a single thread. We usually devote our attention to a single issue and work it until it's resolved. Once you post a group of issues, only general responses will be garnered in most cases.

Here's a set of general responses to get you started:

1. 3000 rpm at 70 mph is normal.

2. This condition is usually caused by faulty vacuum pods. The vehicle should close it's dash vents when in heating mode. If it does not, there is a leak in the system and/or specific vacuum pods are faulty. The main characteristic of this issue is defrost on........all the time.

3. Leave the temp wheel alone. Set it in one position and forget it. If you must move it.........move it in very tiny increments........otherwise the unit will go into "ballistic mode"...........and you'll go ballistic soon after.

4. You'll need to define "slightly slip".

5. The mirrors are usually replaced if the motors don't function properly.

6. Additional details required as to the condition and position of the console.
It's held by a single screw at the back end below the carpeting in the coin tray.

I move the temp wheel on the climate control all the time and it never has an issue. Maybe because my headunit has been rebuilt?:confused:

These cars lack shifter locks, you can move it anywhere you want without the key or pressing the brake. So keep little kids out of them!

Hello all...Need some advice please, I am looking to buy a 1991 SDL, when I do find one,

WHAT should I check for ??
WHAT Questions should I ask the seller ??
WHAT is right price for a good SDL ?? Thank all in advance.

Don't buy one. The risk of catastrophic engine failure on that engine is about 30%. It's not worth the risk.

Use the search function and look up the term Rod Bender. :eek: Enough said.........

Buy a 1986-87 300SDL.

Hmmm, a more in-depth divulgence of tranny slippage? I recently replaced my tranny filter with a WIX filter from OReilly...they have always been great filters for all other vehicles. It was a direct drop in. I put in new tranny fluid and it seemed like it didnt take the 6 quarts they recommended...it was closer to 4 and it still says Im over...but no seals have blown yet. Anyways, that aside...the slippage usually happened between 3 and 4. It was minor slippage but enough to get irritated and question your investment. The new filter seems to help but when the tranny is warm and the car is in traffic, I get that very slight slip between 3 and 4...anybody? Ooooh, another question...what is this vacuum that I should be looking at...and how?

and in reply to buying a nineties model SDL...DONT DO IT! Even though Im new to the Mercedes owners group I know about those engines! I had a very long talk with a mercedes mechanic and he discussed rods breaking or poking through and "ovaling" of the cylinders...this can all be fixed but not without extensive engine work by yourself or someone else...either one will cost a good deal of money. Like stated earier, 30% chance may be below majority but if someone handed you a box of candy and told you that 30% of them were filled with arsenic, would you eat one?

Run away, they are rod benders. The overall engine risks are too great with those to even bother with them. They had a design flaw.

I also have a 1986 300sdl. An absolutely wonderful car!! I had some slippage between 3 and 4th gear also. My slippage occurred when the car was cold, and then slowed down in slippage when the car was at operating temperature.
My culprit was a device called the Temperature and boost pressure dependent vacuum control system. The softness of the shifts in the tranny depend on the vaccum applied to the vaccum modulator on the automatic transmission.

When the engine is cold there is a temp switch that controls a vacuum amplifier switchover valve. This valve SOFTENS the shifting of the transmission when the engine is cold. Softening the shifts can equate to slippage.
When the car reaches 50 degrees celsius in water temperature this opens the ground from that temp sensor switch and now there is a decrease in vacuum going to the modulator at the tranny and the shifts become more firm. hence less slippage.

Experiment: disconnect a vacuum line under the hood of the car and drive the car. Loss of total vacuum and the shift will be very hard and firm, like the shifts are banging. Reconnect the vacuum line and watch the shifts get softer.

I disconnected the electrical plug from my vaccum amplifier switchover valve and now my cars shifts are a little harder and I have no slippage whe.n the car is cold.

John

Heat only comes out through the bottom and side vents, as well as from ducts under the front seats for the rear seat passengers. The center vents and the rear passenger vents only blow vented or cold air. The defroster also blows out hot air, but only on the windshield and through the smaller upper side vents.

If they haven't already, the vacuum actuators controlling the flaps will fail - there's only so much give in 20+ year old rubber. Most can be repaired using a diaphram repair kit. The one controlling the center vents is most likely to go, and hardest to get. For that I got the replacement through Phil for ~$35.


Yes - although starting in '89 (?) the W126s finally got that feature. I considering adding it to my SDL, which can be done easily by getting the parts from a donor car and routing the cables. That's low on my list, though.

First, the mirror control on the console only controls the P/S mirror. The driver's side mirror is controlled manually. The first thing I would do is to verify if the switch is in good working order. It may even be as simple as blowing air into it to get rid of the junk that collected in there. When I did that on mine, I was surprised at the size of some of the chunkules that blew out.

For the mirror itself, you can pry off the mirror from the unit using a plastic wedge and doing so CAREFULLY. It's possible to lubricate some of the visible moving parts. If you have an extra $350, the best thing is to purchase a new mirror, or at least a used one from eBay, junk yards, &c.

Finally, congratulations on purchasing an SDL. Many on this site say they are no good compared to the older OM61x motors. However, in the big scheme, the 603 has significantly more power and is smoother and quieter. The only thing to beware of is the infamous cracked head issue. If your coolant lines are soft about 12 hours after driving, you're golden. Just make sure you never, ever overheat the engine. A while back, a survey on this site indicated about 1 in five people had this issue, and I believe all of them stated the engine had overheated at some point.

I've also found this forum answers about 90% of my questions when I do searches, which is why I have so few posts. From this, you'll learn everything you need about the SDL.

Good luck,

Casey

Heater issue in 86 SDL
 

I bought this 85 SDL six months ago and it's been running well. I've read all of the threads on CCU's, but I can't figure out what's going on with this thing.
Symptoms: Defrost heat is always on. Not bad in winter, sucks in the summer. No other buttons work on the CCU. After 30 minutes of driving everything will turn on and the blower, heat, vents, etc. work fine. Sometimes the fan will have a heartbeat. On, off, on, off. This is after 20 minutes or so, usually.

What I've done: checked blower--it works great hooked up to the battery directly. Replaced porquepine, blower regulator. Removed CCU and resoldered loose soldering (couln't see any problems). Replaced fuses. Chanted strange words.

Does this sound like I need to replace the CCU? It's already been done at least once in the last 320,000 miles.

Brian Carlton, are you out there?

My mechanic friend says it's the blower, even though the thing works when hooked up to direct current. He says it's the commutators that are bad. I don't want to buy a new blower or CCU if I can help it because I don't know when this car will die completely, and I can survive with cold feet.

Thanks.

Keep the friend.........ditch the mechanic.

You have all the symptoms of a CCU that needs to be replaced. Intermittent action of various features and no action of others is certainly indicative of the CCU.

However, are you confident that the vacuum pods are all working correctly?

If you have more than one problem, it's not easy to diagnose over the wires.............

The blower is blowing. It's not the blower.

There are three controllers in your HVAC system. The push button unit (CCU); the Temperature Control Module (TCM), over by the passengers right knee; and the Blower Speed Module.

Your problem could be with the push button unit or the temperature control unit. If either aren't working, you will get heat from the the defrost as the default mode.

The TCM gets input from the CCU temperature wheel and the temperature sensor in the cabin (also from the airbox and the block) and decides when to open the coolant valve. The TCM also is the module that actually turns on several of the vacuum pods. Replacing this module fixed the "hot defrost always on" on one of my SD's.

That's certainly a possibility as well. Have you ever found a method to test that module?

How would one go about checking the vacuum pods? Do I access the TCM the same way I got to the blower regulator and blower, or is there another access point from the engine? I suppose I could just try getting a rebuilt or new CCU, but I'd like to eliminate the problems might cost less before breaking out the cash for a CCU. The rest of the car vacuum system seems to work fine, as far as I know.

The best way to check all the pods is to access the set of vacuum switchover valves. These are sitting in a vertical column right next to the CCU and radio. You access them by removing the passenger kick panel, removing the passenger carpeting, and carefully removing the carpeted transmission tunnel piece on the passenger side. You'll see the six electric switchover valves in a vertical row. Remove the top screw to gain some access and you can pull the horizontal hose off each of the valves.

Connect the horizontal hose to a Mityvac and pump it up. Any pod that does not hold vacuum must be rebuilt or replaced. I've got the sequence of which valves to what tasks, so, if you do the checks, just make a note as to which valves have properly working pods and which do not.

It's very common for the dual diaphragm pods to fail. There are three of them.........the defrost pod, and the two main air door pods.