From: Peter Mathew [petermat@one.net.au] Sent: Sunday, February 13, 2000 8:00 PM To: 928 Subject: [928] Cruise Control retraction Hi All, I guess around 18 months ago I sent a post reporting that the roller costa ride resulting from me setting my Cruise Control had been fixed by the replacement of the two comparator chips on the control board. Which indeed it did up until about a month ago. When the CC ceased to operate at all. Following the standard tests, the fault appeared to be in the control unit again. Under magnified examination I found about 6 suspect solder joints. Once again my CC was functioning perfectly. I started to think about the comparator replacement, having time on my hands at the moment, I dug out the original chips and swapped them with the "new" chips from 18 months ago. Low and behold the old chips work fine! My conclusion is that my PC board was ( and maybe still is) riddled with dry joints,time will tell if I have got them all. So for now I believe that if you are having trouble with your CC and have isolated the problem to the control board, and you have the expertise, try critically examining ALL solder joints on the board. I'm sorry if others have tried the comparator fix and found it did not work for them, but beleive me initially (18months) it appeared to be my fix. Peter Mathew From: bounce-928-18649@rennlist.org [mailto:bounce-928-18649@rennlist.org]On Behalf Of dpbecker Sent: July 03, 2000 9:57 PM To: 928 Subject: [928] R&R of cruise control unit Hello collective, I'm planning on removing my cruise control unit on my 87 to have it re-built..........but I don't know how. I've checked the tips, nada. Has anyone done this on a S4 and willing to type me through it? Any help would be appreciated. Take care, Dan 87 black/black , 5 speed w/RMB From: Randy Page [randy.page@pagetechnology.com] Sent: Monday, July 03, 2000 10:11 PM To: 928 Subject: [928] RE: R&R of cruise control unit Dan, I have had every piece of the cruise control system out on my 87. When you say the cruise control unit, I assume you mean the electronic brain. Below are the instructions for removing it: 1) Remove the carpeted panel on the passenger side of the center console. You may need to remove the knick-knack tray (or at least loosen it) to get it out. 2) The cruise control brain is located in the center console right next to the fire wall (about 6" or so from the back of the stereo head unit.) It's a silver aluminum box about 5" X 4" X 1". It will be held in place by a single bolt you can get to from the passenger side. 3) To make things easier, you may want to disconnect a few of the wire bundles running between you and the cruise unit. There are several with connectors you can easily disconnect. This will give you more working room. 4) Once you get the single bolt out, you can pull the unit out, but it will be a little tight. 5) Once you have it out, disconnect the 12 (I think it's 12) pin connector on the back. 6) Send the unit off for repair, and cross your fingers that was the problem!!! If you have any more questions, please feel free to ask. Good luck! Randy 87 S4 Auto Black/Black -----Original Message----- From: Peter Mathew [mailto:petermat@one.net.au] Sent: Friday, March 10, 2000 3:04 AM To: 928 Subject: [928] Cruise Control-George Murphy Eureka!! Just located this summary of cruise controls uses on MB's They use the same VDO unit as used in 928's. The author is well known to some of us as the guy who will fix your control unit for $150 US. I was especially interested in item 4 which has been my experience. Peter Mathew. '81 928SEuro Auto, Hellblaumetallic TROUBLESHOOTING YOUR CRUISE CONTROL by George Murphy The factory-installed cruise control provided on Mercedes-Benz automobiles works very well for the first 4 to 5 years of operation. It is rock steady up hill and down and really a leg saver on long trips. But with time, the components in the system age and begin to cause trouble. The first indication can be intermittent loss of control or even total failure. In this article I will cover common problems I have encountered in the 8 years I have owned my 1978 300D and the experience of other owners who have contacted me with cruise control (CC) problems. NOTE: The repair technique outlined below for the printed circuit board has been successful in about 2/3 of the cases I have encountered - but it is worth a try before replacing this outrageously expensive device. There are three major components in the CC system: the control unit, the transducer, and the throttle servo unit. Control Unit: this device compares the actual speed of the car and the selected speed. In the event of a deviation from the selected speed the control unit sends pertinent control signals to the vacuum- or electrically- actuated throttle servo unit until the actual and selected speeds are again in agreement. Transducer: a speed sensor mounted on the speedometer cable (early version) or on the speedometer (later version). The transducer sends the actual speed signal to the Control unit. Throttle servo unit: (early version) a vacuum-actuated servo which positions the engine throttle to attain the selected speed. Later versions utilize an electric servomotor. In order to trouble-shoot the system, you should have a digital volt-ohm meter, some test leads with alligator clips, plus straight and Phillips-head screwdrivers, metric wrenches, and a trouble light. But first of all, check the obvious - is the fuse blown? 1. Locate the throttle servo unit in the engine compartment. The vacuum unit is similar to that shown in Figure 1. Check the vacuum and vent lines - replace the small rubber hose couplings if they are cracked. Age and heat can cause deterioration of these rubber parts - as well as other couplings under the hood (and throughout the car). The electric unit looks like a small metal box with a linkage connected to the throttle. Check that the linkage is secure. 2. (Vacuum units only) Pull the 2-pole connector from the throttle servo unit. Connect an ohmmeter to the servo unit pins. The resistance should be between 10 and 22 ohms; if not, replace the throttle servo unit. 3. (Vacuum units only) Follow the actuating cable from the servo to the engine throttle linkage. Check that the end of the actuating cable is just touching the throttle lever with the least possible free play, but not exerting any force on it (otherwise the engine idle could be increased). If the end of the actuating cable is not touching the linkage, turn the adjusting nut (Figure 2) in such a manner that the end of the actuating cable just touches the throttle linkage. CAUTION: on diesels, turn the idle speed adjuster knob completely to the right and hold the emergency stop lever (on the throttle linkage) all the way to its stop before adjusting the nut. This adjustment assures that the vacuum-operated throttle servo unit is operating in the middle of its range, which gives the best control and response. 4. To check the speed transducer, remove the left hand cover under the instrument panel. On early models the transducer is located in line with the speedometer cable. On later models, it is a small black box about 1" square mounted on the back of the speedometer head. (You may have to push the instrument cluster out of the dashboard to reach the back side of the speedometer). Unplug the 2-pole connector from the transducer. Connect an ohmmeter to the transducer. Early models should read 50 to 106 ohms; later versions should read 650 to 1370 ohms. If these values are not attained, replace the transducer. If the above steps do not solve your CC problem, then the control unit could be at fault. In order to do any repair on the control unit, you will need a soldering iron of not more than 25 watts, plus a small amount of fine resin core solder wire. (These can be obtained at Radio Shack for a few dollars) 1. Remove the left hand cover under the instrument panel. The control unit is contained in an aluminum box about 1" by 4" by 7" and is secured by a single bolt to the brake pedal bearing bracket. Remove the bolt, unplug the electrical coupling from the unit, and remove the unit from the car. 2. Carefully bend back the crimps on the aluminum housing so the printed circuit board can be withdrawn from the box. 3. Inspect both sides of the printed circuit board for burned or melted components. If there are any, the unit will have to be replaced. If the board does not show any obvious signs of overheating, it may be repairable. 4. Look at the two sides of the printed circuit board - mounted on the component side are various transistors, diodes, and integrated circuits; and on the "foil" side is a confusing pattern of thin copper foil "wires" soldered to the wire leads of the various parts on the opposite side. The control unit generally fails whenever one or more of the soldered connections on the foil side become loose due to vibration or heat. If you are very careful, it is possible to resolder these connections and get the unit working again. For this task, you will need a steady hand and the 25 watt soldering iron (and possibly a magnifying glass to inspect your work). 5. Solidly position the printed circuit board foil side up in a well lighted work area. Starting at one end of the board, carefully apply heat with the tip of the soldering iron to each solder joint on the board. CAUTION: Apply only enough heat to cause the solder around the connecting wire or lug to momentarily melt, then remove the soldering iron and allow the soldered joint to "freeze". Make sure no solder flowed to an adjacent connection or you will have a short circuit. You may add a small amount of solder if the joint appears to be lacking enough for a good connection. The solid state devices cannot tolerate excessive heat, so use care with the soldering iron. 6. After you have resoldered each connection on the board, closely inspect for solder "bridges" between connections which can cause a short circuit. The connections may appear slightly discolored from your resoldering efforts, but no harm should occur if you were careful with the heat. 7. Replace the printed circuit board in its housing and carefully recrimp the sides of the box. Reinstall the unit in the car and make sure all connections are secure. Be sure to check the fuse for the unit in the fuse enclosure. 8. IMPORTANT If you are not sure, check that the brake light bulb in each tail light unit of your car is an original equipment OSRAM or BOSCH bulb. DO NOT USE U.S. TYPE 1157 BULBS - THEY CAN DAMAGE THE CONTROL UNIT BEYOND REPAIR! The correct bulbs are available from your M-B parts supplier. 9. Take the car out for a road test and actuate the CC in accordance with the owners manual to make sure it works properly. Good luck! G. Murphy From: Jim Stadter [jstadter@austin.inri.com] Sent: Thursday, August 24, 2000 10:23 AM To: 928 Subject: [928] Re: speed control unit for the cruise control jjburg wrote: > > Please help I am looking for the speed control unit for the cruise control > for my 87 928 s4 automatic trans... > If anyone has a source please forward this info onto me Thank You jjb mwhite wrote: > Here is a past post about George Murphy, who is a well-known rebuilder > of the units. > Unfortunately I don't have his (KY) address at hand. Here's the info. George is highly recommended on the Mercedes list. George Murphy Performance Analysis Co. 1345 Oak Ridge Turnpike, Suite 258 Oak Ridge, TN 37830 USA MC/Visa 423-482-9175 9am to 5pm ET Fax 423-482-9175 anytime george_murphy@compuserve.com -- Jim Stadter '83 928 S 5-speed (U.S. spec) '88 928 S4 5-speed Lone Star Region PCA (Austin) 928 Owners Club (http://www.928oc.org) From: Wally Plumley [wplumley@bellsouth.net] Sent: Monday, November 06, 2000 4:01 PM To: 928 Subject: [928] Re: Cruise Control Surging At 10:42 AM 11/6/00, John wrote: >Hi All, >Been having a problem with my 84 US auto in that the cruise control surges. > That is when the speed starts to fall off, the cruise control kind of over >does it or aggressively accelerates the car to about 2 mph over the set >speed before releleasing the throttle. I've searched the archives and it >appears the most common cruise control failures are a flat out failure to >engage or failure to hold speed. There was one such case in the archives >of surging (symptons were more extreme that what I'm experiencing) and that >required the comparators to be replaced. Vacuum system seems to be in >pretty good shape and I'm not having any problems with any vacuum related >accessories (HVAC etc.) but intend to give that area a closer check >anyhow. >Since this is an automatic, could there be a possibility of a torque >converter problem or a needed tranny adjustment? Also, I've worked on some >US built controllers that have adjustments for surging - is there any such >adjustment on the VDO unit? Since vacuum problems are so common, you might try eliminating the possibility. Temporarily disconnect the check valve and four-way vacuum connector, and hook the cruise control line directly to the fitting on the brake booster, and see if it makes a difference. If the cruise control works properly, you have a leaking vacuum actuator in the HVAC. If there is no difference, you may have a controller problem. Wally Plumley 028 Specialists www.928gt.com From: Ken Postma [postmak@qwest.net] Sent: Tuesday, December 26, 2000 4:49 PM To: 928 Subject: [928] Went for a curise .. control (longish, 90% more than I started writing.) I had ignored the 928 for a few weeks. It's been cold and a little messy here in Colo. When they sand the roads, some of the grains are about the size of a quarter! No, not a story about the rocks. (This is sort of a ramble about fixing my cruise control, by the way.) I'd been away from the list for several days too, my computer died and I ended up rebuilding it over a week or two. So I was catching up on some of the posts and reflecting on the "garage locked" 928s in the North east, and decided the paints not perfect anyway ..and the roads are fairly clean ..and I did buy the car to drive ..and a snow storm was supposed to be approaching the Rockies ..and I had a little more xmas shopping to do. So out to the shark I go, the car starts right up, obviously eager to go! A stop by the station for a splash of fresh gas and onto the hiway south to town. Now I must admit, I ,like some others wish I had more power. And no, I did not get the supercharger kit for Christmas.;o( I do live at 7000' and am told this causes about a 20% drop in power. But, this is a power loss felt by every other car here also. It had only been 3 or 4 weeks since I had driven the 928 last, But it is a joy to accelerate onto the hiway merging easily rather than struggling to attain the speed limit. In toasty, warm, heated seat comfort, ...from my most recent repair. It's been 3 years of ownership now. I wouldn't trade it and I'm not planning to sell anytime soon. If I do, I want a 90 or newer, or the blower on my 86.5!!! I've spent a little over 4 grand (Shhhhh, don't tell my SO) fixing the things that were wrong or went wrong. Nothing major mind you. But to fix up / keep up these cars is not cheap. I'm not complaining, but the list recommendation of a $2,000 min repair budget for the first year, is a good one. (I do miss Gene O'Rourke and his view of the world, would've been nice to have had a martini with him.) I can't help but think of the story of the miata, was it, that slid backwards into the Florida state patrol following the entrance ramp!?!!? or the old lady that threatened to buy the police dept and fire the officer at the scene of her backing into several expensive cars and wanting to drive away after causing 1/2 a million in damage ;o) Sorry for the ramble, back to the story. So after finding my spot in traffic, I decided to baseline my last, original repair list item. The cruise control has never maintained the set speed. You can tell it's activated and helping but can't hold the speed. Set the cruise at 75 and right away it's just creeping down, regardless of uphill or down. So I decide it's time to try to fix this last item from my original list. Jeez, 3 years I know, gimme a break. It's only the cruise control, I didn't buy this car for the cruise control! I had read that a common fix was to resolder the circuit board and this was a pretty reliable fix. So I decided to find out. I do have an extensive, if not faded electronics background. (I'm building a fuel injector tester in my spare time.) So by removing only the passenger side, center console cover the cruise control unit comes out just fine. Oh, I did check all of the other function per the manuals 2 years ago. I removed the cover, removed the circuit board and resoldered all of the connections. This does take a while, by the way. Today, I plugged the control unit back into the car and went for a drive. I'll be, It worked, the cruise control holds speed just fine now. So why did I wait 3 years?? Time, as I tell Jason, It's all about available time and desire. I still don't know when I'll ever use the cruise control. I tend to use the throttle to much!! But it's fixed now. Merry Christmas, and Happy New Year. Ken Postma '86.5 928S Auto Out with the old and in with the new (Problems)