For the past week I've been hearing and feeling a loud clunking noise during each shift...seems to be coming from the differential. Once the car has warmed up the transmission is as smooth as ever. I know it's normal for the shifting to be a little hard and slow when cold but now it's accompanied by this noise for the first 10 - 15 min. I suppose I could just let the car warm up more........ differential bushings? flex couplers? but why only when cold?? thanks for any advice. Bryan 87 300tdt

I had the similiar problem on my 87 300TD. Thought I needed new bushings or a tranny. The first time at Peter Schmidt transmissions, they changed the gadget on the IP tht ontrols shifting. The second time, I had inadvertandly disconnected some vacuum lines in the same vicinity. Both times it fixed the problem. Don't know what the thing is on the IP that controls shifting, but it was about $75. Take a look. I am sure someone else will give you a better explanation. I have never had a rea end go out on my cars. I don't suspect it.


Henry

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63 190d (sold)
69 220D (sold)
69 280SL (sold)
76 BMW 2002 (sold)
86 190E-16v (Demised at Laguna Seca Turn 9)
87 300SDL (sold)
87 300SDL 135k
87 300TD 280k (sold)
95 E320W 211k
95 E320w 111k
05 C320 4matic
06 E320 CDI 90k (Totaled by a texting 19 year old girl in a nissan)
2013 GLK 250 Bluetek 4MATIC

Henry, thanks for the tip. I'll check for any vaccum leaks in the IP area it would be great to only spend 75 bucks to fix what sounds quite expensive.
BTW since you've got the same car....mind taking a look at another current post? "300tdt blower motor shut-off?" just wondering if the fan is working correctly. thanks Bryan

both on an off the throttle and coasting in neutral, a steady clunk
should mention it came along all of a sudden though
this is the result -

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1984 300D Turbo - 231k....totalled 11/30/07 RIP

sorry here was the result below. certainly no harm in checking out the diff.

Attached Thumbnails

 

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1984 300D Turbo - 231k....totalled 11/30/07 RIP

Bryan:

You have a vacuum leak when the 50C switch is indicating cold. There is a switchover valve next to the one for the overboost protection, and some vacuum lines going to the blue vacuum amplifier on the left fender.

Check all the vacuum line rubber connectors for leakage -- by now most of them are rock hard and leaking or soft and sticky and leaking -- I replaced most of mine when I got my 87 300D last summer. Makes a bid difference.

The switchover valve may be bad, too, leaking in stead of just switching the vacuum. Probably a bad rubber connector, though.

You could also have bad bushing on the diff -- causes a terrific bang under the rear seat.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Peter, thanks for the diagnosis.... just wondering if you could be more specific as to the locations of these possible leaks. I'm not familiar yet with the vacuum system as it relates to the transmission. Thanks, Bryan

Bryan:

I've got the vacuum diagrams somewhere (not digital, alas or I'd post them), will dig about tomorrow evening. If it find them I'll let you know. The main part of the vacuum lines is hard plastic. The ends are connected together and to what they operate by short pieces of rubber hose. Some are simple straight bits, others are elbows or multiple connectors. I replace the straight bits with bits of vacuum line -- replace the complex bits with factory parts.

Basically, vacuum is supplied to the control valve on the IP (aluminum box on the side) and to the vacuum amplifier via white plastic lines. The vacuum amplifier looks like a blue plastic car horn with several vacuum lines attached, some on the top and some on the bottom. One line goes to the tranny (marked), one goes to the main supply, one connects to the box on the IP, and the other is connected to the switchover valve, if I remember correctly. The line from the IP box may go to the switchover valve, too, I don't remember.

There are a couple small inserts in the connectors -- these are restriction orifices and must stay where they are or things won't work properly. Look like a plain fitting, don't lose them.

I suspect you will find some of the short rubber connectors are bad, most likely the ones from the switchover valve.

What happens is that the vacuum signal from the IP box is modified when the engine is below 50C to have later, harder shifts -- in your case, excessively hard shifts.

Look for lines pulled off -- there should be two on each switchover valve -- or bad rubber bits. I replaced all the simple rubber bits with standard vacuum line from the autoparts store -- all the ends were oversized and leaking.

Hope this helps!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!