While I change gear from R to D with brake pedal pressed, I hear bang sound as if someone hit the rear door of my car with rubber hammer. This bang is accompanied with lifting of the front of the car.

Randomly, I get such bang at up-shifts.
Yes, it seems random. Sometimes, at very gentle or almost no acceleration, the car bangs at upshift. Sometimes, at similar acceleration, the car upshifts very smoothly.

The cause is not found yet. Any opinion?

1992 300D 2.5 turbo diesel. 252 k miles.
124.128 chassis, 602.962 engine, 722.418 tranny.


Below is recent history regarding transmission.

November 2003.
226546 mile.

Transmission fluid leak.
Removed valve body and intermediate plate to replace
reaction valve and shifter rod O-rings and bushing.
006-997-01-47 seal ring, VL
016-997-36-48 seal ring, TR
(they said the car has original tranny)


April 2004.
231000 mile.

ATF analysis by Blackstone.
ATF has 6000 miles on it.
“Wear levels were very low. Oil in good condition.”


July 2004.
232951 miles.

Cleaned vacuum filter and replaced transmission vacuum line cover.
126-277-00-81


July 2004.
233638 miles.

Clunk when releasing gas pedal.
Replaced flex joints.
124-410-06-05 flexible joint
202-410-05-47 flexible joint

Replaced engine and transmission mounts.
201-240-42-17 mounts
124-240-06-18 mount
201-410-13-15 flexible joint


July 2004.
235156 miles.

Adjusted transmission linkage.


July 2004.
235481 miles.

Vacuum modulator hoding vac but out of adjustment.


December 2004.
241340 miles.

30000 mile service.
(This service should include ATF and filter change.)


June 2005.
250420 miles.

AFT changed (the pan and the converter). Filter not changed. DIY.
Castrol Dexron III/Mercon.
No change in shift feel after ATF change.
ATF sample taken from the pan drain.


July 2005.
242140 miles.

Road tested. Shifting fine at this time. Checked trans fluid level and condition: OK. Slight clunk from reverse to drive. No vacuum line leaks noted. Flex disc OK.


July 2005.
252300 miles.

AFT changed (the pan and the converter). Filter not changed. DIY.
Mobil 1 Synthetic ATF.
Less often than before, but I still experience random bang at upshifts and R->D.


July 2005.

ATF analysis result received from Blackstone.
“ATF has about 10k miles on it. The wear metals were in line with the universal average levels (based on 24k miles oil use run). We suggest not running the next fill any longer than this. We do not see signs of an obvious problem.”

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1992 300D 2.5 turbo diesel. 319 k miles.
124.128 chassis, 602.962 engine, 722.418 tranny.

Sounds like it could be flex discs, trans, diff, or engine mounts are possible too. Differential mount is a good possibility since I don't see that it's been replaced. Also any of the mounts that have been replaced could be loose if they weren't tightened down right.

__________________
1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k

Yes, the diff mounts would be my first guess as well. It's a simple matter of getting under the car and wiggling around until you find what is loose. It's not rocket science at all.

Good luck,

Thanks Larry - you have a way of making the job much more aprroachable and taking the scare out of it for us less experienced guys.

I have the same problem as KTLimg with my W124 and was feeling intimidated at fixing it. Your one sentence has me feeling good about the job again. Thanks

__________________
1983 240D Silver/Blue "Sadie", unknown miles. 100k miles on WVO single tank, converted to 2 tank about 10k miles ago, FPHE, Injector Heaters, Aux Fuel pump. Alcohol/Water injection. Frantz oil bypass filter
1992 300D 2.5 Turbo Green/Tan "Jade" 267K miles Stock.
1992 300D 2.5 tan/tan "Rocky" on 2 tank WVO. Pressure actuated Turbo "rat's nest" surgery completed. 197k miles

These days, my 1992 300D's transmission shifts fine after it is fully warmed up - it takes about 40 minutes -.

Before it is warmed up, 1->2 shift is very hard (the car's front significantly lifts up due to sudden acceleration right after the shift), and the engine revolution momentarily goes up during 2->3 shift.

__________________
1992 300D 2.5 turbo diesel. 319 k miles.
124.128 chassis, 602.962 engine, 722.418 tranny.

You might also get an indication by having someone in the car shift from forward to reverse. At the same time with you down on your hands and knees listening for the indicated source of the noise.