Bought 84 300SD (long) - PeachParts Mercedes-Benz Forum

ToddM300SD · #1 10-27-2011, 11:26 AM

Well, I ended up buying the 84 300SD (thought it was an 83). Price was right. It certainly moves much better once you pass 2.5k RPM. Trans shifts very smoothly. The ride is amazing. It just soaks up bumps. The steering box has a ton of play, but I'll get to that eventually. I can reach down to where the steering wheel shaft enters the box and twist the shaft with my hand from side to side, w/o the output links moving. Does the steering box have a wear adjustment or is it just worn?

Lot of issues to tackle. Two things right now that I need to look into ASAP (besides the obvious tune-up items) -- no blower (I do feel heat) and no dash lighting. I messed around with the rheostat (after a search), and I got lighting for a brief moment. As soon as I tried to turn up the rheostat to max illumination, lighting was gone. The good news is everything lit up. Windows, gear indicator, climate control and switches in console. I'm going to pull the gages out and either jumper the rheostat or grab another one (I found a 420SEL in a U-pull.).

As for the blower, I need to search more and start checking connections. Is there a separate fuse on the firewall? I thought I read that somewhere. Also, I have located a fuse diagram (on this site), but it doesn't include identification of the relays. Where can I get that? The fuse cover is missing all ID info.

What is the connector on the passenger side vertical floorboard? If you remove the carpet, it's right where you would place your feet with your legs extended (12 pin?). It was disconnected and nothing changed when I connected it. Also, I found a 4-pin female connector (two brown, blk, green) just above the steering column behind the dash. Anyone know where that goes? Given the length, it looks like it connects to the back of the dash somewhere. I'm sure there's more.

Thanks to everyone on this board for persuading me to purchase this car. Even with all the little problems (and there's a bunch!), it still seems like a bargain.

Todd

kerry · #2 10-27-2011, 11:35 AM

Worn brushes are a common cause of no-blower. Lots of threads on how to pull the blower out and replace the brushes with ones bought at Ace Hardware. Of course check your fuses first and check for voltage at the blower before replacing the brushes.

mbzjag8090 · #3 10-27-2011, 12:04 PM

The blower is easy to replace. Pull the carpet panel beneath the passenger side dash. There should be three screws near the glove box door and two more, including one plastic one, further down in the recess. Then remove the three screws that hold the blower cover on after disconnecting the pins. Then three more screws to remove the blower.

The 12 pin on the passenger side floorboard is for the alarm system. It is usually disconnected because of one of two issues: (1) the 1984 alarm sometimes has a mind of its own or (2) you must have the pins connected from the door handles for the system to work properly. If door handles have been changed (usually due to lock tumblers jamming) then it might not be connected for that reason. If you've got a single key for all locks and if the handles are connected (check this by taking driver and pass. door panels off...then look to see if white 2 pin connector is attached behind the handle) then you could plug up the 12 pin and see how reliable the alarm is. But when mechanics would replace the handles sometimes they would cut off the white 2 pin all together and disconnect the alarm.

The only 4 pin I know of behind the dash is for the cruise control stalk switch. It should connect to its other half right above where the blinker/combo switch is plugged in.

mbzjag8090 · #4 10-27-2011, 03:45 PM

Come to think of it...the cruise switch might be a 6 pin connector. Cannot remember...but it does sound like the cruise switch.

The later models have the blower fuse on the firewall. I do not believe the 1984 models have a separate fuse, although you should check the combo fuse in the box.

toomany MBZ · #5 10-27-2011, 04:37 PM

If you can, apply power to the blower motor. Oftentimes, the push button unit has issues and the message to the blower is not sent.

t walgamuth · #6 10-28-2011, 06:20 AM

ON top of the steering box is an adjuster. It is about a ten mm threaded rod with an allen head of maybe six mm. There is a locking nut around it that is about nineteen mm.

With the front wheels straight on loosen the lock nut and rotate the allen counterclockwise until you begin to feel some resistance then back off about an eighth of a turn. Test the feel of the steering then lock it down.

Really does not take much longer than that. Be sure to clean out the allen before trying to move it and use penetrating oil to get it all started but it is a really easy task and these boxes will usually allow satisfactory adjustment even with over three hundred thousand miles on them.

ToddM300SD · #7 10-28-2011, 09:15 AM

Pulled the instrument panel yesterday. The rheostat is shot (big surprise!). The winding literally popped out as I was removing the left side of the cluster. Yanked the rheostat and made a jumper out of two female bullet connectors attached directly to the circuit board.

The unidentified 4-pin connected to the outside temp display. It still doesn't work. Is that indicative of a bad display unit or temp sensor under hood?

Thank You for the advice on tightening up the steering box. I haven't felt that much free-play since the days of 70's and 80's american full-size cars with their pinky-finger power steering.

Taillights/antenna are leaking rain water into the trunk (I pulled out all of the carpet and tire/tools. New seals are $35/each?!!! Anyone used clear silicone or black RTV to make their own seals? I'd rather spend $70 on tune-up stuff.

HVAC troubleshooting starts today. I'll report back with my findings.

Todd

ngarover · #8 10-28-2011, 10:20 AM

If it's not a show car then I see no issue with black rtv. We use it all the time on the rover seals around the rear quarter glass thats notoriously prone to cracking and leaking... Even new seals don't last more than a year it seems. You can make the black rtv look nice with little effort and it lasts.

Johnt49 · #9 10-28-2011, 03:50 PM

DO NOT use silicone, unless it is low acid silicone specially designed for automobile window installation. It has a high acid content that will destroy the body sheet metal over time. Try getting some black latex sealer from a hardware or big box store & run a bead on either side of the old gasket. Mine have been in for over 4 years now & not a drop has leaked in.

ToddM300SD · #10 10-29-2011, 10:50 AM

Removed and cleaned up the tailights. Latex sealant worked great on driver's side, but passenger lens cracked during disassembly -- back to the junkyard. I did manage to find a working outside temp gauge and blower motor. ACC seems to work -- I was shocked. Heat is warm, not "hot", but that varies with engine temperature.

Which brings up another question: The temp gauge sits around 60 in the city, working it's way up to 80 on the highway (ambient: 38F). Do these cars run cool in the winter? If the engine thermostat is working correctly (I will check it), is there any need to partially block the radiator to get hotter heat OR do I need to check the mixing flap first? The "temp wheel" adjusts the temperature leaving the vents, it just doesn't get hot enough when turned to the highest heat setting.

Bring on the snow -- I want to try some diesel donuts!

Todd

300sdToronto · #11 10-29-2011, 11:02 AM

Welcome to the club. I love driving my SD>

Your engine operating temp sounds a bit low. Mine runs around 80C pretty much all year round. And that includes driving in -20C ambient!

When you run out of urgent repairs maybe it's time to look at a new thermostat? A coolant change will be a good idea at the same time if you don't know when it was last done.

Your warm rather than hot heat may be related to the low operating temp. I can make my cabin uncomfrtably hot even in the depths of winter. The cabin climate system was as many posts on here as Wikipedia! A good topic for a rainy winter's night.

Good luck!

vstech · #12 10-29-2011, 11:45 AM

x2 the SD never sits much below 80C even when cold outside. either your thermostat is stuck open, missing, or it's got a lot of holes drilled in it...