My car's been clunking when shifting, both up and down, from 1st to 2nd, or from 2nd to 1st. It doesn't do it all the time, but enough that it bothers me.

I'd previously changed the transmission mount, so that is out of the equation. I've looked around for any vac hoses that are bad and replaced whatever seemed bad. The hose connectors all appear to be in good shape.

Any other suggestions?

jeff 1991 300d, 186k

Have you checked driveshaft bearing and flex disks ?

__________________
1999 w140, quit voting to old, and to old to fight, a god damned veteran

I had one flex disc repaired probably 10 years ago, but seems to me there is a front and rear one, is that correct?

I've never checked the driveshaft bearing.

I always think vacuum with those kinds of symptoms. Seems like there are a lot of possibilities. One of the reasons I like the wastegate actuator swap....removes so much of the vacuum system.

__________________
14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 154k miles
06 E320 CDI "Rutherford", Black on Tan, 172k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 142k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

^ Agreed, check the amount of vacuum going to the transmission.

Low or no vacuum will cause hard shifts.

__________________
83 SD

84 CD

Your VCV is probably shot.

It's the thing mounted on the IP that regulates vacuum to the tranny to mimic what a gas engine does with a throttle body vacuum take-off. WHich you don't have in a diesel. So the VCV fakes a gas engine response to throttle position. (Rack position or your right foot pedal).

Your tranny is slamming gears thinking you're flooring the pedal and wanting hard fast shifts when in fact you are pussy footing around.
This misinformation is due to a vacuum leak in the VCV, which is meant to bleed more vac the harder you press the pedal.

__________________
Cheers!
Scott McPhee

1987 300D

Technically low or no vacuum will cause hard downshifts. The tranny is designed to upshift smoothly with zero vacuum; that is why the vac goes to zero immediately at WOT (wide open throttle).

Also check for good operation of the blue UFO.

__________________
Cheers!
Scott McPhee

1987 300D

What about the differential mounts? When mine were bad, I got a hard clunk on those same shifts, even though the trans wasn't shifting that hard. Though you could tell the sound was from the rear. Worth a look maybe.

__________________
1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

Rear Subframe bushes dead? Causing a clunk.

__________________
E300TD year 2000. RUSTY SOLD
cost a fortune to maintain on the road
but run well on WVO
Second Merc died due to corrosion ( NOT rust) How can mercedes get away with that for so long?
Third lasted a month then went away...
Fourth now... Corroded too...

So clunk in the rear isn't the differential itself but an issue with a mount or mounts?

My clunk is worse when cold, so that would make sense.

Thank you so very much!

__________________
Current fleet:

1985 Mercedes-Benz 280TE - Waiting for heart surgery.

1985 Mercedes-Benz 300TDT - Rear ended 23 September 2016 and now looking for a new home.

1979 Mercedes-Benz 300TD - Parted out.

1964 Volkswgen Beetle - Vater's since September 1968 and undergoing a restoration.

1971 Volkswagen Sunroof Squareback with F.I. - in need of full restoration.

1971 Volkswagen Squareback automatic with F.I. - Vacationing with her caretaker until he is in better health.

You did make sure the ATF was at the proper level, right?

Does the w124 have a vacuum regulated tranny? I thought that went out with the w123

You sure? Unless OEM there is a decent chance of failure. URO being the worst, but MTC and Meyle make horrible mounts too. Just something to keep in mind.

__________________
1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

Did you get it fixed?