I just bought a 1987 300 SDL ... - PeachParts Mercedes-Benz Forum

tstarr · #1 01-11-2003, 11:04 PM

To all,

I just bought a 1987 300 SDL with about 195,000 miles on it. It is very nice, but there are 2 issues with it that I thought I'd ask about.

1) Transmission - hard shifting and it doesn't want to shift into high gear until I back off on the "gas". It stays in 3rd until it gets well past 3000 RPM and won't shift unless I back off on it, then it shifts up and I can go on from there. Lower gear shifts are pretty rough, as well.
2) There is an "idiot" light on the dash with a picture of a radiator on it. The light goes on intermittently even though the temperature on the gauge is fine.

Other than that, the car runs great, doesn't burn oil, all electrical, heat and A/C work like a champ. Any ideas on the above? I'm actually having a similar transmission problem with my 1982 300SD (which will now go to my 17 year old son), so insight may be valuable on both.

Thanks for any info you can give me.

- Ted

HGV · #2 01-11-2003, 11:51 PM

Not an expert on transmissions, someone will chime in, but my tranny was shifting hard and it was the gadget the is attached to the injection pump that controls shifting. Mine was changed and made everthing fine.

The idiot light on the dash that looks like a radiator means to put water in the system. Take a looke at the level in the plastic tank on the passanger side wheel well in the engine bay. Check it cold and see if it needs water. If it does not, it could be the that the sensor is bad. Not uncommon.

Good luck and enjoy the car. Do a search for problem area, One piece of advice, never and I mean never, let the car overheat. Not even once or for a short time time.

Henry

tstarr · #3 01-12-2003, 12:10 AM

HGV,

I'll take a look. I wonder if that part is the vacuum modulator. It would make sense.
I hear you on the overheating. That's the one thing I did hear prior to looking at this. I guess it's the aluminum head. The temperature was well within limits and the PO said he carried a coolant mixture in the trunk just to make absolutely sure that he didn't get stuck. He didn't have any problems with it, but I did like the attention to prevention.

- Ted

rwthomas1 · #4 01-12-2003, 01:00 AM

I think this is how you do it: Get a vacuum gauge and hook it into the line that goes to the vacuum modulator on the trans with a "T" fitting. At idle you should see about 10in of vacuum. When the engine speed is increased the gauge should drop progressively to 0in vacuum at high rpm. This will tell you if the correct vacuum signal is reaching the trans. If all seems okay try adjusting the bowden cable and the vacuum modulator. Experiment with each and see what happens. RT

#5 01-12-2003, 03:18 AM

Sounds like you need to turn the bowden cable IN (clockwise) a couple of turns. Turning it CW makes it shift faster, CCW drags out the shifts.

tstarr · #6 01-12-2003, 10:13 AM

Thanks for the info! I'll take a look at it when the temperature comes up a bit. The car is pretty darned sweet and I'm looking forward to having the "big ride" - even bigger than the SD. If something relatively simple like this fixes I owe you guys a martini (I've switched from beer). The seller and I both were factoring in "worst case" of a transmission rebuild and I was able to get a real deal on the car.

- Ted

CSchmidt · #7 01-12-2003, 07:07 PM

Tstarr,

I also have an '87 SDL (for about a year now). The trans was shifting fine, but when the temp here in NC dipped below 30 some mornings I had the same symptom of not shifter from 2nd to 3rd for the first run up to speed. After that it is normal. Is yours fine after the first run through?

Question to the forum. there was a post a little while back saying while cold, the trans changes shift patterns. Would this be considered normal? Did the '87 transmissions have this feature?

Chuck

psfred · #8 01-12-2003, 08:29 PM

Bowden cable should be all the way out without tension on the spring at closed throttle -- it will "retract" into the housing as the throttle is opened.

The hard shifts are because the vac lines to the tranny shift control transducer are shot (its the blue thing that looks like a horn on the left fender). Replace all the hoses.

Also, check the vac lines to the air recirc valve and EGR transducers -- they are the ones that go to the right side of the engine from the 5-way T at the front. If one (or both) transducers are leaking, plug the lines until you replace the transducer -- the vac leak will make the tranny shift HARD, and also make the climate control work funny.

Check the vac at the line marked "trans" on the blue transducer -- it should be 14" or so at idle with throttle closed, and drop off as throttle is opened. You will have to determine the reason for low vac -- I've given you the two most likely above.

That W126 with the 603 is a SWEET car!

Oh, and there is a 50C switch to shift the tranny softer below that engine temp. Won't change shift point, though. Change the tranny fluid and put synthetic in it.

Peter

tstarr · #9 01-12-2003, 10:24 PM

CSchmidt & psfred,

I'll do the vacuum debugging after I actually get the car and the weather supports it. I just put a deposit on the car and will finish paying for it tomorrow, with any luck.
The climate control appears to work fine, and the shifting continues to be hard even after the car is well warmed up. But all of this is based on one test drive, albeit a pretty long one.
This is a totally sweet car. I have been wanting to get one of these for a while now, and the occasion of passing the 300SD baton to my 17 year old son was the perfect time. This one was on e-bay and I found out that the seller lived about 5 miles from me here in Rockville. Apparently I was the only serious bidder. The car is beautiful, with great paint, interior well above average, and engine has had regular service. So I now have the car I've been wanting for some time. Woo woo!
I do plan to run synthetic in the transmission and engine. I switched my 300SD to Amsoil and have been happy with it. Very, very nice ride and now I can take the entire family out with lots of room for everyone.

Anyway, I'm long winded. I'll take your advice and look it over before taking it to a mechanic. They're pretty tough to get scheduled here in the DC area.

- Ted

mplafleur · #10 01-13-2003, 09:06 AM

Peter,

Is there a 50 deg switch on my 190D? (m602) The reason I ask, is that I have an extremely long delay in my 2-3 shift when my engine temp is below 60 deg as shown on my coolant gauge. As soon as the temp reaches 60, the shift is great.

I've come to the conclusion that the tranny is fine, but that I have a vacuum problem.

sixto · #11 01-13-2003, 10:43 AM

Quote:

Originally posted by tstarr
I wonder if that part is the vacuum modulator.

From the shop manual, the part that's attached to the IP is the vacuum control valve, the round part behind the ABS unit is the vacuum amplifier, the small part beside the vacuum amplifier is the vacuum amplifier switchover valve, and the part attached to the transmission is the vacuum unit. Most folks call the last part the vacuum modulator.

FWIW, some SDLs have a reservoir hooked to the vacuum amplifier. I don't know where it is but you can follow the big black vacuum hose that splits from the VAC attachment on the vacuum amplifier. I checked that it held vacuum and left it at that.

To add to what has been recommended, you might check that the kickdown switch under the gas pedal isn't stuck. It sends a signal to the back end of the transmission (the only wire back there) so you can check that there isn't a continuous signal into the transmission.

Sixto
91 300SE
87 300SDL
83 300SD

CSchmidt · #12 01-13-2003, 09:48 PM

Folks,

A bit more history. A while after I got the car the vacuum system developed a problem, no additional fuel under higher rpm/turbo mode. The trans had pretty hard shifts, but never delayed shifts when cold.

Now the weather turns a bit warmer, and a good independent shop I go to fixes the vacuum problem. Back to zoom zoom zoom. The trans now shifts much smoother. Not sure if they adjusted the trans modulator "dial" to smooth the shifts.

Weather now gets chilly, below 30 in the am. The trans shifts 1-2 just fine. The 2-3 shift holds out until about 3000 rpm. Leaving my driveway, I go about 300 yards then slow to go around a corner. In warm weather it would shift to 3rd by 2500 rpm, now in cold weather it doesn't. I slow to go around the corner and now it shifts fine up to 3rd at about 2500 rpm. It is fine the rest of the day.

So is this pretty "normal" for chilly weather? I'm about due for a trans fluid change, maybe time for some synthetic. The car has about 235K on it now.

Thanks,
Chuck

#13 01-13-2003, 09:57 PM

At WOT (wide open throttle) all my shift points are at "redline" or about 4500rpm.

With normal driving my shift points are just perfect, 2500-3000rpm.

If I am slowly crawling in traffic, my shift points are around 3000rpm as well, and stay in gear as long as possible, I think it's the nature of the beast.

psfred · #14 01-13-2003, 10:53 PM

Turbodiesel:

At light throttle you should be in 4th at 25 mph, I usually get a double shift 2-3-4 at that speed. If it always winds out like that, your bowden cable is out of adjustment.

Michael:

I suspect the 190 has the same system -- look for a leak around the switchover valve (if there is one) conneced to the vac system for the tranny. I don't think you have a vac amplifier unless you have a turbo, though. Mineral oil tranny fluid can do this too, though.....

Peter

#15 01-14-2003, 12:35 AM

Maybe my RPM's are slighly off from memory, I know the car feels perfect though, even if not factory spec, I like how it shifts.