w124 300D Rough Shifting - PeachParts Mercedes-Benz Forum

nvestor88 · #1 05-10-2009, 01:27 PM

theres a slight bang when the cart shifts from first to second, not as bad when it shifts from second to third. car has the original tranny(1990), with 160k. from a stop when i shift into drive theres a slight bang as well. it does not do it as bad if i shift into the lower gears at a standstill. does not happen when i shift into reverse? car has a new flex disc. can it be something besides the transmission? if it is the tranny, would it be considered "DIY", or should it be left to the pros for a swap out? seems rather pricey for these cars. thanks

kerry · #2 05-10-2009, 02:01 PM

Not that familiar with the 124's. However, if it was a 123, it would almost certainly be low vacuum to the transmission. I suspect that is your situation also.

i-osprey · #3 05-10-2009, 04:02 PM

I am having the exact same problem with my '93.

I have 209K on it and counting.

All my other vacuum actuated devices, except the rear headrests, are working properly.

Maybe I have a loose vacuum line to the tranny.

I know that the previous owner used the car to work cattle on West Texas dirt roads. I also have to adjust the emergency brake cable before I can pass inspection. There is also mud caked on the outside of the tranny housing and under the aero plastic panell under the passenger side of the car.

I suspect that with all the scraping around, mud and debris that was bouncing under the car the vacuum line to the tranny may have become slightly dislodged and the emergency brake cable, too.

Diesel911 · #4 05-10-2009, 08:12 PM

Info on tuning transmissions

http://www.continentalimports.com/ser_ic20242.html

On mine I followed another members advice and put in some Lucas Transmission Sealer and Conditioner when I changed the Trans Fluid and Filter; it too away most of the 1-2 harsh shift. (But, only after maiking sure your vacuum situation is OK.)

Brian Carlton · #5 05-11-2009, 12:48 AM

With almost certainty, you've got a vacuum leak somewhere with the original lines. Don't know that specific vehicle, but you'll need to get a Mityvac and start disconnecting various vacuum devices and see which one won't hold vacuum.

Additionally, the gauge will allow you to monitor the vacuum level to the transmission while driving the vehicle.............which will actually provide some data into your issue...........rather than just allowing twenty different members to simply take random guesses at the problem.

JimmyL · #6 05-11-2009, 01:22 AM

My W124 was shifting with a bang just as you describe. It was a vac line loose up under the intake manifold. I don't think yours has the same setup as that exactly, but it is most likely a vac line loose somewhere....

nvestor88 · #7 05-11-2009, 06:19 PM

Quote:

Originally Posted by Brian Carlton

With almost certainty, you've got a vacuum leak somewhere with the original lines. Don't know that specific vehicle, but you'll need to get a Mityvac and start disconnecting various vacuum devices and see which one won't hold vacuum.

Additionally, the gauge will allow you to monitor the vacuum level to the transmission while driving the vehicle.............which will actually provide some data into your issue...........rather than just allowing twenty different members to simply take random guesses at the problem.

thanks for the info. do you think its the transmission? it has the original tranny. seems like the the throttle is not too responsive. also slow pickup.

compress ignite · #8 05-12-2009, 03:09 PM

The Experts here stress, First correcting any power problems (Engine)
BEFORE any Tranny adjustments are attempted.

I bring this up because you've mentioned "Perceived" power difficulties.

VegStew · #9 05-12-2009, 07:02 PM

Quote:

seems like the the throttle is not too responsive. also slow pickup.

The 90 300d has a vacuum actuated wastegate that is controlled by a transducer. That transducer is one of 3 in the egr system. If you are having boost issues (which it sounds like you are) you may have a bad one. Or your egr is malfunctioning, which would cut boost.
I had an issue somewhere in that system that was causing poor acceleration. I switched over to a pressure actuated wastegate and the issue was 90% gone. My overboost protection valve was clogged so i was still getting a slight bogged down feeling on acceleration. Right now that is bypassed. Folks would caution against that as a solution. The car has an amazing amount of power compared to when i first bought it. And the tranny shifts much, much smoother.

Get your self a boost gauge if you havnt already to check your PSI. You should make sure your alda line is clean. If that doesnt fix it you can try bypassing the over boost protection valve to see if that solves your issue. If so, clean/replace etc. If not, you may want to see this thread Wastegate actuator swap for OM602.962?