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  #1  
Old 02-08-2007, 07:18 PM
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Join Date: Sep 2003
Location: NY
Posts: 88
1990 300E m103 clunk when shifting

I just bought this car used and thinking about changing the fluid. When I move the shifter, from reverse to drive, park to drive, etc., the transmission clunks and shifts very hard. I noticed the car doesnt do this when it's cold in the morning. Other than that, the tranny shifts firmly and does not slip. Anybody familiar with this symptom? If the tranny's on its way out, I wont even bother with service. Please help.

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  #2  
Old 02-08-2007, 08:08 PM
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Join Date: Jul 2003
Location: Montreal, Quebec
Posts: 508
Could be a tired flex disk (most likely front).
have it checked a.s.a.p.. it if fails completely while driving at highway speed, a second mortgage on the house will probably be in order to fix it..
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  #3  
Old 02-08-2007, 08:17 PM
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thanks
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  #4  
Old 02-09-2007, 01:15 AM
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Location: Bradenton, FL
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Quote:
Originally Posted by onesixthree View Post
I just bought this car used and thinking about changing the fluid. When I move the shifter, from reverse to drive, park to drive, etc., the transmission clunks and shifts very hard. I noticed the car doesnt do this when it's cold in the morning. Other than that, the tranny shifts firmly and does not slip. Anybody familiar with this symptom? If the tranny's on its way out, I wont even bother with service. Please help.
onesixthree,

This sounds more like vacuum to me. Check the vacuum line to the modulator on the transmission and the modulator itself. If vacuum present/in spec, modulator can be adjusted to smooth out shifting. I've taken for granted that you've checked the fluid, and records, if any, indicate that its the proper fluid for your car. If at all unsure about the fluid, have the trans and torque convertor drained, new filter, and fill with proper fluid. If not familiar with the process, if it were my car, I would only use a transmission shop that other owners of your type car recommend. A well qualified specialist can do the vacuum check and modulator adjustment in about 10 minutes. Enjoy your new to you car!

Bob
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  #5  
Old 02-09-2007, 02:44 AM
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Join Date: Oct 2004
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Also, check the tranny mount. I had a very bad clunk once... turned out the tranny mount was ripped in half... that clunk was the tranny slamming against the floorboard.
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  #6  
Old 02-09-2007, 05:43 AM
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Join Date: Aug 2006
Location: Los Angeles, CA
Posts: 172
trans mount and vac modulator

I'm having same issue with my m103 in a 1988 300CE. Seems like the transmission is shifting in a big delay mode. could just be the modulator is in need of adjustment or the vac lines need replacing. The trans mount is in need of replacing due to motor oil on it over the last 18 years.
My trans problem started with a short delay when going from second to third and now it's getting to the reverse gear too. Reverse is hard and I can feel the driveshaft picking up the power transfer late and when it does it's not smooth.
I'll get the modulator vac line looked at and also replace the trans mount to see if that helps, it should.

The shifter itself seems fine, it's definitely at the modulator. I dont think its the gear valves themselves. The delay I'm talking about is when after shifting the actual shift takes longer than it shound and when it does finally shift a second later its jerky and the motor is working overtime.

Recently changed the trans fluid and motor oil and all filters. Replaced the fuel relay and checked the plugs. Replaced 02 sensor with the expensive model. Been running only chevron with techron supreme for 6 months. Replaced exhaust with stock center resonator and custom 3" pipe to rear muffler. Just passed CA smog.

Sorry for hijacking this thread.

Thanks
Jason
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  #7  
Old 02-09-2007, 06:57 AM
LarryBible
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Don't overlook the differential mounts. There are two at the rear of the differential that mount the diff to the subframe. These are bad about going out and tough to change. You will need to make or buy a puller. Do not try to drive them out with a hammer and drift, it will destroy the sheet metal subframe.

They are at the lower rear of the differential and you can see if they are loose by looking at them.

Good luck,
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  #8  
Old 02-09-2007, 09:57 AM
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Quote:
Originally Posted by onesixthree View Post
When I move the shifter, from reverse to drive, park to drive, etc., the transmission clunks
I noticed that on my '92 300E. Replaced front and rear flex disks 2 yrs ago and have not observed any clunking since then. Shifts very smooth with Mobil 1 ATF even with temperatures in the single digits (Farenheit) this week.
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  #9  
Old 02-21-2007, 12:59 PM
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Join Date: Oct 2002
Location: Texas
Posts: 303
VACUUM
Simple test: attach a mityvac directly to the modulator: it's a round plug attached to the driver side of the transmission that has a vacuum(plastic line) going to the engine.

Then pull vacumm between 5-7 in. (you need a long vacuum line so you can hold on to the mityvac while inside the car- autozone has them for 10ft for $4)..

While pulling vacumm at the modulator, start the car and go thru all the shift issues you were having and see if it dissapears. If it does, Modulator is working .YOU HAVE A VACUUM LEAK! If for some reason, you can't sustain vacuum at the modulator, that means the modulator is leaking..if you have to pump it every 30sec-1 min to sustain 5 inches, you should be ok. The mityvac is the best $30 dollar investmant you'll ever make. Keep us informed

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