Strange Transmission/Shifting Shudder - PeachParts Mercedes-Benz Forum

pawoSD · #1 04-20-2005, 02:29 PM

What is the cause of a 1982 300SD occassionally shuddering when slowing down in the few mph preceeding the 4th to 3rd gear downshift? Is this a vacuum issue? or a tranny mount issue....or something, its somewhat annoying, and I'd like to figure out how to eliminate it. The car usually just does a good o'l "clunk" downshift, but sometimes it feels like its having a hard time doing so, and shudders the car for a second while downshifting. It didn't used to do this, it'd just do the normal clunk, the shuddering part is more recent, probably a few months ago it began. What is strange is that if I slow down slowly, it doesn't happen, and a large part of the time it doesn't do it at all, slowing down quickly or slowly...if I manually downshift to 3 with the selector at around 20-25mph while slowing down it doesn't either, or if I just leave it in S it doesn't either. The shudder usually occurs from 21mph to 17mph, where it downshifts (when driving in D). Any ideas?

pawoSD · #2 04-20-2005, 09:56 PM

Anyone? Bump?

#3 04-20-2005, 11:03 PM

Bump bump..

pawoSD · #4 05-04-2005, 02:40 AM

Alrighty, I am resurrecting this thread because my car still does this, even after having changed motor mounts and such on my last project. One thing that has never been changed (to my knowledge) is the tranny mount. Should I replace this (see first thread for problem description) to aleivate this issue? The part is cheap, so I will readily change it if it will help something, in fact I may just change it anyways.
Is it very difficult to change this mount? Any tips or warnings? I was wondering if perhaps this downshift issue could be related to a vacuum problem? Strange thing is that it shifts perfectly fine when accelerating, albeit a small shudder into 4th occassionally (probably wear-related, its original) It shifts great and holds them out farther and such depending on throttle. Its just begining to be really annoying when I slow down and the car shudders like that, its like something is loose, allowing it to do so. Always happens around the 4 to 3 drop between 18 and 16mph.....strangely enough, if I slow down gradually it does not do it at all, and even sometimes when I slow down faster, it won't do it....just the majority of the time. Any ideas/help on this one?

pawoSD · #5 05-04-2005, 12:05 PM

Anyone????????

I couldn't find anything on this particular problem on the searches I did. Besides this shudder there is no other vibration or shuddering when driving at all...so I don't suspect shaft bearing problems or anything.....

Veloce300DT · #6 05-04-2005, 01:21 PM

I have experienced the exact same thing with my 300DT, but it only happens when I am slowing down between the same speeds for the first time in the morning at the stop sign nearest to my house. It doesnt do it all the time. I always let the car warm up to normal operating temp. before I drive it for the first time every day, but I would assumee thhat the transmission hasnt warmed up simply because it has only been put in reverse, and drive one time, and shifted up through the gears once before this shudder happens. Once it happens, it doesnt happen again for the rest of the day.

My engine and tranny mounts are relatively new. I do have some vibration at other speeds that is leading me to think I have drive train isssues- flex discs etc. probably need to be checked.

Anybody have an ideas to our shudder problems?

pawoSD · #7 10-16-2005, 12:37 AM

I shall re-tell my tale of the shuddering problem on my 300SD:

I have had a problem (for the last 12k-ish miles) where when I slow down between 20 and 15mph my car will produce a pretty significant "shuddering" feeling. The feeling is not present in the brake pedal. It does not occur if one coasts to a stop without using the brakes. Does not occur until the car is to operating temp (stops perfectly smooth when cold/below 60C or so) but once its at temp its there every time I stop. Dealership inspected the whole car three weeks ago when I had brought it in to have the flex discs and carrier assembly/bearing replaced. They said all that was just fine, but that the carrier bolt (the huge one) was LOOSE

so they tighened that all up for me and dial-gauged all of the brake rotors, determined the rears were quite warped/had runout. Front ones were said to be fine. I replaced those rotors yesterday, as well as the parking brake shoes. Calipers looked good and the pistons move freely/no leaks. Plus all the brake fluid was super-flushed/replaced less than 7 months ago, as well as ALL flex lines.

The shuddering remained after my new brakes were installed just as it was there before. Brakes feel better though and have slighly better stopping power (organic PBR deluxe pads this time vs. OEM ones before). No brake squeal/squeaking anymore when slowing. Shudder begins on-cue at 20mph, continues till 17/16mph-ish, then in the instant the tranny "drops" from 4th gear to 3rd, it vanishes. This leads me to believe it is a tranny problem, not brakes or flex discs etc....if 4th gear is bypassed, (driving in "S") slowing while in 3rd gear still produces the shudder quiver, though less often than when in "D". The tranny also shudders/quivers slightly in a similar way when shifting to 4th gear when accelerating in the 47-56mph range, below or above that it does a firm/smooth shift. Other gears all shift great. Braking is liquid smooth at any speed outside of that 15-20mph range, be it 5mph or 80mph. This lets me know a brake prob is highly unlikely.

Any ideas what could be causing this shudder??? Tranny Vac Issue?

Tranny and Engine mounts are all nearly new.

Please help me, I have spent way too much $$ and way too much time on this prob for it to still be there.

#8 10-16-2005, 06:35 PM

Have you changed your tranny filter (if you mentioned it..sorry I didn't real all of the posts you put up

)

Is the tranny getting good vac? Linkage all adjusted well?

Mine can do this too but its when I disconnect the vac to the tranny. Makes "hard downshifts" and they are sorta weird and clunky. Also check out the driveline/differential.

pawoSD · #9 10-16-2005, 06:40 PM

Driveline was inspected by a tech at the dealer and found to be good except the carrier bolt was loose, they tended to that. Everything else is fine, brakes are great, I also suspect the tranny. I do suspect a vacuum problem, likely those little "valve finger" things in that airbox on top of the valve cover. For instance, it shifts at the normal increments, and generally firmly, but adjusting my modulator does not result in harder shifts, no change at all. So I am wondering if I have vac probs. Our 83 has no downshift clunk when slowing, and shifts perfectly and quite firm (I adjusted it firmer and it responded to the adjustment) so I presume its vac stuff in that regard is in better shape.

Tomorrow morning I am draining out all my Dexron and changing the filter, then refilling completely with 7qts of Mobil 1 synthetic ATF

We'll see how that improves things as well. Then at 1 pm the stealer is going to adjust my valves....which are now at 18.5k since last being adjusted, but its still running smooth and fairly powerful. (some loss of power and increase in smoke has been noted in the last 3-4k though)

#10 10-16-2005, 11:52 PM

Check the vacuum and change the transmission fluid. I've noticed that my transmission is shifting a bit oddly recently. The fluid is also starting to get dirty. Time to have it changed.

I get a shudder when I accelerate sometimes, but it's usually in 1st or 2nd gear. It was really bad when I first bought the car, but that was a turn driveshaft mount or something that my indy replaced... all is well now (well, 95% anyway).

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