New to Me 1991 300D Concerns - PeachParts Mercedes-Benz Forum

Bengoshi2000 · #1 11-06-2017, 10:27 AM

Greetings all,

Just a bit of history first... 3 weeks ago I picked up a 1991 300D with 113,000 documented miles from the son-in-law of the original owner. It spent the first twenty years of its life allegedly garaged and driven only on weekends. The last six years it was driven more or less daily, but it's clear it was parked under a tree and washed infrequently. Owner claimed he changed the oil himself every 3k miles.

I've been driving it daily since purchase. Initially it had some nasty nailing going on that sounded like a ball-peen hammer. I'm in the process of running a couple tankfulls of B70 biodiesel through it. That, with a couple of Italian Tune Ups, the nailing is significantly diminished, idle has smoothed out and it's a bit quicker off the line. Of course the fuel filters are now dirty... I'll be changing both frequently until the small prefilters are running clear fuel. (And yes, I know what running biodiesel will do to the rubber lines... I've replaced the fuel lines on my former 300D and my current 02 Golf TDI... so I know the drill and will do the same on this car).

The concerns I have now are as follows:

1) Noticeable metallic clink when going into reverse. I can hear it going into drive, but it's nowhere near as loud. Sounds like it's coming from the transmission mount or the front flex disk. No odd vibrations noticed, but I do hear a faint rattle (when driving with the windows down) that doesn't coincide with bumps in the road (this sounds like rattling dice). I got under the car in the rain Saturday only to find that the W124 has a sneeze guard over the entire underbody... so I didn't eyeball the front flex disk or the tranny mount. It was on ramps, in park, with the emergency brake engaged so I couldn't really move the driveshaft either. Everything looked fine at the differential end... the flex disk there appears new... no cracks or splits and the rubber is still pliable. No play or noises in the half shafts. I know, I need to get back under it and take the sneeze guards off.

2) Minor low-speed shifting issues. Occasionally, the transmission shifts hard. When it happens I'm either accelerating very slowly or allowing the engine to slow the car and the transmission downshifts. Also, on low to moderate acceleration, the 1-2 and the 2-3 shifts will stack... i.e. one right after the other. There's no consistency as to whether the car is warmed up or not. I would say that 3 out of 5 times I'm moving slowly I get the hard and stacked shift (and they usually happen together). Normal acceleration - a nice smooth shift... barely noticeable. Hard acceleration - a nice crisp shift, but not jarring.

3) Minor turbo lurch. I don't know if that's the right term. But under a moderate to heavy acceleration I can feel the turbo cut in... 2600 rpm. Not really jarring, but it's clear the car pulls much harder after 2600 rpm.

4) AC. I bought the car knowing it was having issues with the AC. It's still R12. I've got to get enough R12 into the system (with some dye) so the compressor will engage and I can scout the leaks.

These are the only driving issues I'm having with the car (other than the volume won't work on the Becker Radio, the antenna is stuck halfway up and the paint needs some serious correction/polish, might need an idler pulley for the accessory belt, needs a thermostat... just normal maintenance stuff).

I'm going to try to get a sound sample up of the clinking noise.

I've spent the last two weeks reading posts here and haven't run across these exact issues, so I'm very interested in your opinions on where to look.

Peace,
Norm

jake12tech · #2 11-06-2017, 10:45 AM

1): check the flex discs. Any cracks replace it.

2): vacuum leak.

3): that's called turbo lag. It doesn't spool until 1900rpm. That "kick" is lag.

4): sounds like you have it all figured out.

Diseasel300 · #3 11-06-2017, 11:10 AM

The "clink" noise your'e hearing, is it when the transmission finally engages or is it when you're moving the gear lever? If it's when you're moving the gear lever you need shifter bushings under the car. Do this before they crap out completely and leave you hunting through gears to get the thing to start!

The turbo should spool somewhere ~2000 RPM. If you're spooling late and spooling hard, you may need to reseal your ALDA. Mine was pretty unrefined and violent when the turbo built boost before I resealed the ALDA. Now you can start noticing turbo boost ~1700 RPM with full boost by 2000 RPM. The refinement is significant.

The rough shifting is likely due to vacuum leaks as said above. Go through the entire vacuum system under the hood and replace all your rubber connectors. That'll probably get you pretty close. Another thing not to overlook is fluid/filter. If you have no record of it being changed, do it. Manky old fluid and a clogged up filter will cause all sorts of roughness.

Bengoshi2000 · #4 11-06-2017, 03:00 PM

Diseasel,

The "clink" is when it finally engages. The shifter itself goes into each position firmly with no sound and no slop. Here's a link to a sound file on dropbox. It doesn't sound nearly as intimidating in this recording:

https://www.dropbox.com/s/c94g2lb4cdbb4ih/Transmission.m4a?dl=0

I'll start reading the Alan ALDA threads and see what to do... thanks for the pointer.

I have a record that the transmission fluid and filter were changed sometime during the waning years of the Clinton Administration... so it's probably due. What type of ATF plays nice in these tranny's (other than the M-B stuff made of Unicorn Tears)?

Peace,
Norm

Diseasel300 · #5 11-06-2017, 03:34 PM

Sounds like flex disk or U-joint for the clanking. With a noise like that you can probably see it happen if you have a helper operating the transmission while you look underneath.

The ALDA is fairly easy to reseal. Check if it will hold vacuum. If it does, it's still sealed and probably has something else as your issue. If it doesn't hold vacuum, or if it was like mine and you can't even pump it up, resealing it with new O-rings will make a BIG difference. There's a thread on this forum from earlier this year that deals with the O-rings and gives sizes.

ATF is anything that's compatible with Dexron II/III. I did mine this weekend and used the Valvoline Max-Life synthetic and the difference it made over the mineral oil based fluid is profound. Much smoother and so much more refined. If it's been 20 years since the fluid was changed, it would be worth it just to drain and refill with something cheap, drive around for a while to let the detergents do their job, then drain and refill again in 5-10K miles with some good stuff and see where that gets you.

vstech · #6 11-06-2017, 03:52 PM

Ugh...

Diff gearing slop will do this...

Flex disc will do this...

Center u-joint will do this...

Loose center nut on diff or trans will do it.

Bengoshi2000 · #7 11-10-2017, 11:27 AM

I removed all of the sneeze guards and got under the car today. Had the spouse unit engage and disengage reverse gear.** Sounded like the "clank" noise was coming from the carrier bearing/ujoint area. Removed the heat shield aaaand no play in either one. I could jiggle the driveshaft and the "clank" had moved back up front near the transmission. Lo and behold, the front flex disk was loose and could be jiggled. I got in closer and could see where the bolt mounts are separating from the rubber. The rubber itself is hard as a rock yet no visible splits/cracks. Too bad my parts order won't be in today.

So, is there no draincock on the radiator? I need to replace the tstat...

**WARNING... be sure your spouse unit hasn't recently taken out a Million $$ life insurance policy before attempting this diagnosis.

Diseasel300 · #8 11-10-2017, 01:35 PM

Definitely fix that flex disk before it leaves you stranded or tears up your car!

The draincock on the radiator is probably like the later W126's. Look at the support tray under the radiator. It should have a blue plastic plug with a phillips head located through a hole in the tray.

Mxfrank · #9 11-10-2017, 02:38 PM

Or it might be like the 201’s, draincick accessed by a trap door in the bumper.

Bengoshi2000 · #10 11-10-2017, 02:55 PM

I ordered a front flex disk and a transmission mount this past Monday, thinking it would arrive today... forgot the Federal Holiday part of 4 business days in transit...

But yep, I've seen photos of a Benz "post flex disk detonation" and she won't be back on the road until that's replaced. In fact, I'm shook that I've just been driving it merrily along in blissful ignorance.

Mxfrank · #11 11-10-2017, 07:42 PM

Also check the rear disk if the front is bad.

vstech · #12 11-10-2017, 08:21 PM

And the center mount and bearing...