W123 Mercedes VDO Tempomat Cruise Control Actuator Replacement

The Mercedes-Benz VDO W123 Tempomat cruise control is now going on 42 years of service for the first years of production. Or perhaps it is no longer in service due to mechanical failure. 

These units, based on the research I have done, are pretty robust and are serving a good long time. That said, my 1981 240D with the bellows style VDO Tempomat actuator has been baking under the hood in the desert for many years and is finally not holding proper vacuum. 

Mercedes W123 VDO Tempomat cruise

NOTE: Before you get a new actuator, they are $640, make sure it is not the amplifier (the brains) under the driver side dash or a vacuum leak elsewhere. The amplifier is subject to intense heat and vibration and they do get fickle with age. Several symptoms of a amplifier going bad is being able to increase your speed using the cruise control lever but not being able to set that speed once you let go. Other scenarios include the cruise control cutting out while engaged. 

I have already replaced my control unit with a remanufactured unit several months back as new units are not available from Mercedes.

Once the cruise control began working, I realized it had probably not been used in many years and the actuator began to malfunction after several trips on the highway. The symptoms: Once the speed was set, it would steadily lose it a few miles per hour every several seconds. Either the Tempomat was losing vacuum due to a dry rotting bellows or the internal vacuum/vent switch was not engaging properly.  Either way, in my case, it was time for a new unit as I knew I did not have any vacuum leaks.

NOTE: It is also important to note that the cruise control actuator is to be hooked up to the 2/3 way yellow and gray vacuum check valve (some check valve used for the door locks) which draws vacuum from the vacuum reservoir tank located in the trunk above the gas tank. Make sure this is not leaking or it will cause problems with your cruise control among other problems.

REPLACING THE VDO TEMPOMAT CRUISE CONTROL ACTUATOR

The replacement of the actuator is not complicated at all, but one that will require a great deal of finesse to remove the bowden cable, if you wish to save the cable. While there are a number of NOS actuators available from Mercedes, there are evidently only two bowden cables remaining in the global Mercedes stock. 

While the cable is not fragile, all the plastic clips that are necessary to keep the cable in place are! If you break any of these clips the cable will not function.

STEP 1
Disconnect the vacuum, and vent lines along with the electrical plug. Now is the time to make sure no vacuum hoses or rubber connectors are failing.

Disconnect the three plugs show in the photo. The gray nut for the vent line is plastic!

STEP 2
Remove the nut holding the actuator in the bracket.

STEP 3
Carefully release the bowden cable from the throttle linkage (valve cover area). Remember, the plastic clips are very brittle and are ready to crumble. Gently using needle nose pliers will work well.

STEP 4
Unscrew the plastic threaded adjusting "nut" and once again using the needle nose pliers release the next section of the bowden cable.

STEP 5
Push the cable toward the actuator to give a bit of slack to remove the next clip. This clip is awkward to remove and is too ready to fall apart. Go slow and gentle.

STEP 6
Unscrew the three screws at the actuator retaining plate for the bowden cable. Give yourself enough slack for room to work. 

STEP 7
Release bowden cable from cover

STEP 8
With the cable removed, the installation process is the reverse. 

STEP 9
The following steps are for the W123 second generation diesel models only! To adjust earlier models, W115 and W123, please refer to the Mercedes Service Manual.

Adjust the cable. If the cable is not properly adjusted according to the Mercedes service manual the cruise control will not function properly. Make the following check and adjust cable length as necessary with the plastic threaded adjusting "nut": Press and hold the emergency stop lever (diesel) in the off position and check the slack of the cable.

Mercedes R107 450SL Bumpers – U.S. Market Cars

In the early 1970's the U.S. Department of Transportation required upgraded bumpers to accept a 5 mph "tap" without any significant damage. As many will remember, these bumpers were pretty ugly and extended the length of the car significantly. 

Mounted on twin shocks, with rubber corners, rubber block overriders and rubber impact strips, they have now taken on a certain retro charm. 

Disassembling the bumper for restoration or repair is not complicated and is well worth it if you are wanting to do your car right. 

STEP 1
Both the front and rear bumper are held in place by two shocks mounted to the body of the car and by two mounting brackets on each side of the driver and passenger fenders (front and back). Start by detaching the side brackets. Next, simply remove the shock bolts and remove the bumper. NOTE: The bumpers are fairly heavy and awkward. I would recommend making this a two person job to avoid damaging the car or the bumper. 

STEP 2
Once the bumper(s) have been removed it is time for disassembly. My stainless steel caps were fairly dinged up, but purchasing new ones will cost you a considerable amount. With that knowledge at hand, I decided to have the old caps restored. You can either take the caps to a metal polishing shop who will beat out the dents and polish or, should you have the skill and tools to remove the dents it will save you a good bit of money. I chose the latter as I have metal working experience and once dent free, took the caps to be polished. I would recommend not attempting to polish at home unless you have professional equipment. Getting the mirror finish can not be achieved with consumer grade tools.

STEP 3
Next, remove the turn signal units to avoid any damage to them. Should you need one or two they are still available, as are just the lenses. The OEM unit is ULO and can be obtained from AutohausAZ

STEP 4
Now remove the shocks from the bumper. Remove the 4 bolts and extract shock along with two brackets and 2 rubber buffers.

STEP 5
With the shocks removed, the retaining nut for the overriders will be exposed—remove.

STEP 6
Remove the rubber bumper end caps by removing the 3 nuts and bolts. 

STEP 7
Now remove the rubber impact strip inserts. The front bumper will slide out, while the rear bumper will require the removal of one overrider/shock bracket to remove the impact strip.

STEP 8
At this stage the stainless steel bumper caps are now ready to be removed. Work carefully when removing to avoid bending the metal. Slightly lift up each tab to loosen the cap. Gently pry off cap from the back side (not the front lip). The tabs do not need to be opened up very much to get the cap off. 

Be mindful that you will be working around a rubber gasket and soft rubber sponge strip used to eliminate water and vibration.

With the bumper now disassembled and while the caps are off getting worked on, now is the time to clean and prep the bumpers. 

As you will see, the lower portion of the bumper is factory painted with a "rocker panel" stone guard. SEM makes a very good product for this application - Part No. 39793. Make sure to scrape, sand and clean very well before reapplying a new coating. Spray in even long strokes and do not apply in heavy coats. 

At this stage and once the bumper is dry for a good 24 hours at 75°F, the bumper can be reassembled and installed. Again, I would recommend this as a two person job.

W123 Valve Train Noise After Oil Change

If you own a W123 Mercedes diesel and have heard what appears to be valve train clatter, ticking, clicking, tapping, your choice of words, it may very well be the timing chain tensioner. 

Since 2015 my 1981 Mercedes 240D has clattered on start up following an oil change. This apparent valve train noise however subsided the moment the system pressurized, roughly 5-7 seconds. According to Mercedes the 5-7 seconds it took to pressurize was perfectly normal but the clattering was not. Ironically no one pointed to the tensioner as a possible problem.

Understand, the W123 diesels, whether 240 or 300 series engines, do not have hydraulic lifters so there should be nothing to "tick, clatter or tap". The one thing that is hydraulic is the timing chain tensioner.

Changing the timing chain tensioner is not hard and will also potentially restore your timing by a touch, reduce a considerable amount of noise from the engine bay and the biggest thing of all, save other components from being destroyed!

STEP 1
Drain radiator. If you have not changed the coolant in the past 2-3 years, now is the time to service the cooling system. Do a complete flush with new Mercedes coolant. FYI, why do I recommend Mercedes coolant, simple they have proprietary additives that keep the system in good shape for the duration of the 2-3 years it is in the system. Other coolants I have tired have not maintained their clarity on changing as the Mercedes brand has. 

STEP 2
Remove the thermostat housing assembly from the head. You will only need to disconnect the short coolant hose shown below. Check this hose for any dry rot and replace if necessary. NOTE: A considerable amount of coolant will flow out when disconnecting.
In addition, I would highly recommend to replace the two bolts holding the thermostat assembly to the head. They pass through the water jacket and will most likely be rotting. Mercedes has them for about $6 ea. Worth the price to not have a broken bolt the next time you have to get into the system.

This is also good time to replace the thermostat if you need a new one.

STEP 3
Remove the 2 bolts and one exhaust manifold nut. NOTE: more than likely this tensioner will be stuck in place and will need to be pried off the side of the head, but if it still has any "spring" left it will pop out. 

STEP 4
At this stage you can disassemble and see if you can rebuild the unit. Mercedes has the spring but no longer make several other key components in the system that will more than likely need replacing. I went by way of a new tensioner as I need two parts that were no longer available. 

Mercedes-Benz still has the tensioner available for about $330. Febi a German OEM supplier also has them for about $75. I am a big fan of all OEM but in this case I could not see a difference in construction and went with the Febi. Time will tell.

STEP 5
Clean the area around the tensioner hole making sure not to introduce any dirt into the engine. 

STEP 6
Place gasket on end of new tensioner and mount. The new tensioner will have much more resistance and will require you to compress it while installing the bolts. 

STEP 7
Reinstall cooling system components, and refill system with coolant. Do not use the old coolant. 

STEP 8 
Run car and listen for any unusual sounds. Check coolant level after engine has cooled. 

Removing Mercedes R107 450SL Dashboard Vents

After 43 years, the heat and A/C vents are filthy and not moving freely as they did from the factory. While the dashboard is out and being prepped for refinishing I decided to remove the five ball vents for a good cleaning. Here is how to do this with ease. 

The vents are held to the dashboard by a large "wave" washer and two built in clips. 

To remove the vent nozzle depress one of the plastic tabs and gently lift up on that side to keep it from snapping back in place. Repeat the process with the other tab and gently separate the two halves. For the three center vents, a wide flat screwdriver worked great. The end vents however, did not have the room needed for the screwdriver and so I used a paint can opener which worked excellently. 

Next, take a very small screwdriver and gently pry wave washer over tabs and carefully press remaining assembly through the front of the dashboard. 

Once the vent assembly has been removed, it can be cleaned. I use Dawn liquid dish detergent and a soft toothbrush and warm water. The results could not be better. NOTE: Remember the plastics are old and brittle. Be very careful and don't force anything—unless money is no object. 

The vent assembly looked and worked like new after cleaning and reassembly. It's worth the time and effort.

DO NOT grease or lubricate any part in the vent assembly. It was not done from the factory and should not be done now as any lubricant will attract a considerable amount of dirt in the vent. If the vents don't feel buttery smooth, know they weren't when the car was new either. 

The process of installation is the reverse.

Mercedes R107 450SL High Quality Aftermarket Tail Light Lenses & Seals

Depending on where your Mercedes has spent most of its life, the tail light lenses might very well be cracking or simply dull and or discolored. The rubber weather seal is a whole other story.

Since November 2017, I have been on the SL Shop waiting list for the first round of aftermarket Mercedes R107 tail light lenses and it was worth the wait. Admittedly, I was a bit skeptical, but seeing is believing and this is an excellent reproduction. The lenses appear to be a very good quality and the fit is just as the originals. As with any product, time will tell if they are as excellent as the originals. The colors are very deep and rich which is often a shortcoming on aftermarket lenses. 

With the lenses I also purchased the weather seals from the SL Shop. These seals have a perfect fit and first rate quality in addition to feeling every bit as good as the Mercedes weather seals for a fraction of the cost. Again, another several decades will be the true test, but for now it couldn't get any better.

The SL Shop, located in the UK, has provided me with numerous parts thus far for the R017 restoration. I am not only very pleased with all of the parts, but am just as delighted with their dedication to customer service. While I source many of my parts directly from Mercedes, I will continue to purchase from the SL Shop on excessively priced parts or aftermarket parts no longer available from Mercedes.

The following images show the original 43 year old Mercedes taillight along with the new after market version. NOTE: When reinstalling, DO NOT over tighten as the lens assembly can crack. The bolts are to be snug, not tight. In addition, do not force any of the parts together. They fit very snugly and should be eased back in place.

The M-B original has faded over the years from being parked in the desert for 8+ years, but remains in remarkable condition.

Every detail is expertly replicated

Assembly as it came out of car before cleaning for reinstallation.

W123 Transmission Vacuum Diagram & Shift Issues

If your W123 diesel has shift issues, there is a very good chance that the transmission is just fine. 

There are several things to check, and most of them are vacuum related. Any part of the vacuum system that is failing can and will cause disruption to the transmissions ability to shift properly

SYMPTOMS:

Transmission quickly progresses through gears (1-4) from a stop and does so a bit sloppily. Or perhaps there is flaring between particular shifts. Or perhaps, the transmission is not wanting to shift at all or shifts very late.

These symptoms should be checked at once to avoid potential damage to the transmission. The following check list will help determine what might be going wrong.

CHECK LIST:

Transmission Fluid: Drive car for at least 15 min. to make sure engine and transmission are at full operating temperature. Check fluid level with gear selector in "N". Do not use "P" as you will not get an accurate reading. NEVER OVER FILL the transmission.

Vacuum System: Must be in perfect working order. Even the smallest leak can cause havoc on how the transmission shifts. If need be, isolate the leaking sections by disconnecting them and capping off at the location. Remember, if the vacuum is to high the transmission will want to shift to quickly, if the vacuum is to low, the transmission will not want to shift at all. The transmission vacuum system for the Mercedes 240D is as follows:

The VCV and Transmission vacuum modulator are no longer available from Mercedes-Benz.

Main Vacuum Circuit Components

Change over valve (located on top of valve cover) This part breaks regularly!
Vacuum control valve (VCV)
Vacuum modulator (located at side of transmission)
Vacuum Dashpot (check valve) green in color

ADJUSTMENTS:

If your transmission fluid is at a proper level the next step is to ensure your vacuum system is in perfect working order along with the throttle linkage being properly adjusted

Once you are sure the fluid, vacuum and linkage are in good working order, the next step is to adjust the VCV valve. 

HOW TO ADJUST THE VAVLE:

1. Loosen the VCV valve retaining bolts (no need to remove)

When bolt has been loosened, screws and hose removed, gently remove cover.

2. Remove side cover

3. Using a wrench, turn the nut on the end of the spring counter clockwise if your transmission is shifting early and clockwise if shifting late. NOTE: To make this adjustment you MUST hold the throttle linkage in the closed position while turning the nut. It is also important NOT turn the the adjusting nut more than a few millimeters at a time. If you over adjust, your transmission will not shift out of first gear. 

Leave the cover off while test-driving the car to make it easier to make adjustments while you are on the road.

If this adjustment still leaves your transmission shifting a bit late or early the next step is to adjust the transmission vacuum modulator which we will cover in a subsequent article. 

Mercedes Vacuum Diagram

I developed the following digram for the 1975 R107 Mercedes-Benz 450SL so I would have a complete guide should anything go wrong after the car is put back together. This digram does not show the engine vacuum. 

LEAK DETECTION:

When diagnosing leaks in the Mercedes vacuum system, a vacuum pump with gauge is mandatory or should you have a smoke machine on hand, that would be the ultimate way to go. 

First, start by checking the vacuum tanks for leaks. One is located directly under the front fender on the passenger side above the wheel (LHD). This tank supplies vacuum to the central locking system and cruise control. The other tank is located behind a panel to the left of the emergency brake. This one hold vacuum for the climate control. 

Unscrew plastic panel and slide away to expose tank. To remove tank and panel, e-brake assembly must be removed.

Passenger side U.S. model

The vacuum tank for the climate control should not have any issue with deterioration other than the rubber grommet that seals the tank where the vacuum line enters. This part is still available through Mercedes.

The central locking vacuum tank however is susceptible to damage and deterioration as it is open to the elements just above the front wheel. Both the tank and grommet are still available from Mercedes.

A good test to perform to insure proper vacuum is maintained, is to pump up the tank down to 10 mHg. Make certain that your connections are leak free and your gauge is good. The tank should hold vacuum for at least 48 hours without any loss of vacuum. Conduct this test on both tanks. I personally would not recommend using the smoke machine to test the vacuum tanks. 

Finding leaks in the system is not complicated, but time consuming. Most often it is the rubber connectors that dry rot and begin to leak. If you have the original system, it is best to test each section of vacuum line by disconnecting, capping and testing one section at a time. The digram will show how the system is divided up throughout the car.

Vacuum leaks are also very prevalent at the diaphragm type locking modules. At 40+ years, the rubber diaphragms are quite crispy and will likely leak. These include the heater tap, fresh air flaps at cowl, passenger side door, fuel flap, and trunk. The passenger side door lock, and trunk lock on earlier 450SL's are no longer available from Mercedes.

Other points of leakage are the driver door lock master vacuum switch and the vacuum switch at the A/C switch. Both switches are identical in function but are designed differently. Both are available from Mercedes.

Vacuum for A/C Switch is still available through Mercedes-Benz

The final potential point of a vacuum leak is the Ford-Philco cruise control unit. The cruise control unit is most likely under the dash behind the glove box on a U.S. car.

It is also wise to change out any check valves. They are located under the hood at the fire wall driver side. Original check valves are black and green while the new ones are blue and black. These are unmetered.