Help! 92 300e 2.6 mechanical Q's
 

Hello All...
I recently acquired a 92 300e 2.6 w/ 120k Miles... The car was a Palm Springs car, and has appeared to have synthetic oil most of its life (under the oil-fill cap, the metal has virtually no sludge whatsoever!).. i have some questions about this car, that hopefully maybe someone can voice their opinions on...:


1st issue:.. Air does not come out of the Center vents. The dealer whom i bought this from has an independant (not an MB specialist) mechanic that he goes through, and his mechanic's opinion is that there is a sort of "valve" that needs to be replaced- and that its located wayy in the back of the dash (and its a apprx. $900 (!) repair).?? does this sound right? I must mention that air does blow fine out of the side vents, and the switch assembly does seem to be working properly. This symptom happens reguardless of the temperature setting... $900 seems like an AWFUL lot to get this problem taken care of.. The dealer said they'd be willing pay roughly half of the bill, *if its not that expensive*... Should I consider taking this to a independant MB shop in town (instead of the dealer's "regular" mech.)? heck,i'd possibly like to tackle this myself, if its not *too* hard for the DIY'er.. ..Any opinions??

2) car has a *slightly* uneven idle.. almost like there's a baby/tiny intermittant miss in the engine. Not excessive, just barely noticeable. I replaced the Spark Plugs w/ Bosch HCDC-9 (btw- should I have used the heaver-duty "0" model plug?).. I did notice that the plug wires have some heat-stress marks on the wire insulation.. I suspect these to be the Original wires. Do the Wires usually start to lose their efficiency by this point in time? Should I also consider replacing Dist. Cap/Rotor?(I am guessing the car still has its' originals)... I did run a bottle of Techron cleaner, which helped a little bit.

3)The trans seems to have an occasional firm shift from 1st-2nd gear.. (not bad, just that it kinda softly "snaps" into 2nd).. Is this just a common trait of this transmission? Does changing the ATF to Synthetic help in some cases? (i've heard mixed reports).. Other than the 1-2 thing, it seems to shift great. My guess is that it could use a fluid change anyway, if synthetic might possibly help, i might give it a shot..

4)Every once in a while (and seemingly only in the mornings- 45 degrees or so btw), i will hear & feel a slight "clunk" from (i'm guessing here).. the rear of the vehicle, after i have shifted into Drive gear (after reversing out of the driveway)...Could this be a bushing/flex disc issue possibly.. ?? As soon as the clunk noise stops, the car moves forward fine. seems like the noise/clunk happens first though, before i can start moving. Weird! For the rest of the day, the car is fine- no clunk.. just that initial one in the morning.

5) Lastly.. I just got the oil changed to Chevron DELO 400 15w40. However, the place that did the oil change seemed to put a little too much oil in the car.. its approx 0.25 inch above the full mark on the dipstick. I'm not sure if i like that..Is this bad? Also since the oil change, I notice in the mornings, their is now valvetrain noise for the first 2 seconds -a light "tapping"..which soon disappears..which did not seem to appear w/ the old oil in the car (which, btw from all indicactions was Synthetic, and at the proper oil level).. could having too much oil in the crankcase cause this? Or, Being dino oil and/or at the wrong viscosity? i'm stumped!

Thanks for any and all help, you guys are wonderful!!!

Miles
1992 300e 2.6.. 120k Miles

Regarding your last question Miles, yes too much oil is damaging to your engine also. Overfilling for one will eventually damage your catalytic coverter, and the increased oil quanity can cause foaming in the crankcase which is not a good thing. They put the level marks there for a reason - I'm surprised the shop overfilled!

Depending on what wieght of oil was used previously, you could be hearing valve noise on cold startup while the thicker oil takes marginally longer to work it's way into all the passages...



About you first question: I have heard that valves, and such relating to climate control can be very expensive because of the labor invloved in taking the entire dash apart - that may indeed be what you're in for if you want that fixed :(


Good luck on your other inquiries!

Regards,
- Ryan

hmm.. i think i am going to drain a little of the oil out of the car tomorrow.. i just don't feel right with it being overfilled... Thanks for the info!..

anybody else have any suggestions on the other topics?? :) Thanks so much guys for all of your help!

-miles

I believe the valve that needs to be replaced is the "mono valve", and I'm not sure if $900 is the proper going rate, but I do know that the valve is very cheap, and the price of the job will be almost all labor.

The dash has to come out, and thus very labor intensive. For example, the evaporators sometimes go out on these cars, and it is buried under the dash, and the job is 22.5 hours shop labor.

If you're going to go through the trouble to do this, there are other things you ought to replace when you get in there, like the vacuum elements for both the center vent and the recirc air one, too.

Regarding your second question about a slightly poor idle, many things could cause this.

I don't think the wires have a high failure rate. The original wires (if yours are original) are made of solid copper (not a copper / silicon blend) and are fairly expensive, as far as wires go, and seem to last quite a long time. There is no replacement interval for spark plug wires.

What people usually do is replace the resistor boots or ends of the wires, and they are about $7.00 each. You can check these connectors for intermittent short circuit.

Regarding your spark plugs, make sure they are the original copper core, non-resistor type. Also, the gap might be too small. Check to see that the gap is 0.8 mm (.032 in.).

If you have no record of replacement of the cap and rotor, it won't hurt to change these with the plugs. They are cheap and easy to do for a DIY'er.

I don't know if it'll fix your slight miss at idle, though.

How does your car run when cold at start up? You could also have a problem with your EGR system.

i thought the mono valve was something that has to do with the heater???? Anyway, there is a vacuum operated diaphram that most likely has a leak, and yes, unfortunately, it is in the back of the dash. You have to pull the entire dash(not fun, i know from experiance) to replace it. I would also not be suprised if you had moisture forming on the outside of your windshield with the a/c on due to this. To have this repair done, 900 sounds a little high but not un realistic.
R

Regarding your 3rd question about the hard 1st to 2nd gear upshift - just feel lucky that your car starts out in first gear.

The biggest complaint about these W124's is that they have poor acceleration. All pre '92 W124's start out in second gear. 1992 is the first year of first gear start, and it was a big improvement. The rear end gears are also better spaced apart, and you get a higher 4th gear for freeway cruising.

I think all transmissions shift with authority from 1st to 2nd gear, so yours could be fine. I do know that this can be adjusted. There is an adjustment in the bowden cable (which I've never done), as well as a vacuum modulator on the transmission that can be adjusted to make the shift firmer or softer. The adjustment for this has been posted before, so you can try a search. I'm sure M.B. DOC and Stevebfl have commented on this.

Also, just know that when cold, your car has an upshift delay valve that is there for smog reduction purposes. It delays the shift from 2nd to 3rd gear, and holds the car in 2nd gear to a higher rpm, until the catalytic converter warms up.

Yeah, monovalve could be the wrong term, but whatever it's called, it's still a vacuum operated valve / diaphram that has a leak, or is stuck open.

Regarding your 4th question about the rear end clunk, it could be a worn out flex plate.

These cars have a driveline that has flexible rubber discs at both ends, and a center U-joint with a support bearing. The front usually wears out, and should be examined anyway considering the car has 120,000 miles.

Your differential mounts could also be broken.

Hey Miles81, don't even think about trying to replace a leaking vacuum element unless you're an experienced MB tech! Believe me when I say you'll regret it. The first thing you need to do is correctly diagnose the problem. While the most likely cause of your complaint is a leaking element, it's not the only thing that could do it. The switch-over valve unit ( located behind the carpet on the right side of the transmission "hump" ) could be faulty. This is also the place where ALL of the elements can be checked for leaks. For the rough idle, check the distributor cap and rotor and a compression test would be a good idea( I'm assuming it's a 103 motor ). For the trans shift, the bowden pressure cable should be adjusted correctly and the modulating pressure can be adjusted. My advice is to take the car to an MB dealer and have it looked over. This shouldn't cost much. With accurate information you can go back to the guy you bought the car from and maybe work something out. You'll enjoy your car much more if everything works the way it's supposed to, and the only way to assure that is by trusting the experts who deal with MB vehicles every day. Good luck

The mechanic may be referring to the vacuum switchover valve. It's about a $90 dollar part. It is back in the dashboard somewhere. I thought it was behind the glovebox, but it may be back by the blower motor.

UPDATE
 

Hey Guys.. Thanks for all the help so far!!, over the weekend, i drained out the excess oil, and adjusted the Bowden cable to the trans-.. the car shifts much better now! its almost likea different car! I am going to see if i can get the clunking noise issue looked at this week... BTW- how much $$ does a flex-disc job usually run?

-Miles

92 300e 2.6

Mine was done at the MB dealer at the 120,000 miles major service.

When I get home, I'll look at the invoice and see what's on the invoice.