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Car Forum / Mercedes-Benz Cars / September 20051992 300D transmission questions...
Hey all, I've noticed a few things about the 300D I just bought that I'd like to ask about to see if they're normal or not: 1) I occasionally hear an intermittent "ticking" noise that seems to be coming from under the rear seat area. It appears to increase and decrease in frequency with the rate of speed. (i.e. the faster the car is going, the faster the ticking is). It comes and goes without any directly attributable cause. 2) Occasionally "sharp" shifting. The transmission seems to always want to shift at precisely the points when I'm letting off the gas pedal for various reasons. This tends to cause particularly sharp shifts, as I think the transmission is getting confused by my letting off the gas right as it shifts. Assuming the vehicle starts out in first gear, then shifts to second, then to third, and so on, the shift from second to third is usually sharper while first-to-second and third-to-fourth is quite smooth. Again, this isn't consistent, and the car usually shifts smoothly between all gears with no problem. Also note that I spent the last two years driving a CVT-transmission-equipped Honda, so I didn't even have to deal with any shifting, so I might just be more sensitive to it. I had a mechanic examine and test-drive the vehicle before I purchased it, and they gave it a clean bill of health, so I'm not terribly worried. Still, as I'm not fully certain of what "normal" is on the car, and since it has 198k miles, I'd like to confirm that everything's working normally and that there's no problems.  SignaturePete Stephenson HeyPete.com Occasionally "sharp" shifting. Normal, these hydraulic transmissions shift more firmly than the new electronic boxes and certainly more firmly than a CVT variable ratio transmission. Look for a vacuum leak when ALL the shifts snap your neck! I occasionally hear an intermittent "ticking" noise that seems to be coming from under the rear seat area. I'd suspect a rear axle CV joint after inspecting both rear tires to exclude them. The car's miles point me to that suspicion. Axles can be bought remanufactured, if that's the problem. > Normal, these hydraulic transmissions shift more firmly than the new > electronic boxes and certainly more firmly than a CVT variable ratio > transmission. Hmm. All right. It just seemed a bit unusual. They mostly seem to happen at relatively low rates of speed (<30mph) with mild acceleration. Hopefully it's not a problem. No metallic noises are heard, just a firm shift. I'm spoiled by the CVT. :) > Look for a vacuum leak when ALL the shifts snap your neck! Will do. > >I occasionally hear an intermittent "ticking" noise that seems to be > >coming from under the rear seat area. > > I'd suspect a rear axle CV joint after inspecting both rear tires to > exclude them. The car's miles point me to that suspicion. Axles can > be bought remanufactured, if that's the problem. The tires and rims are essentially brand-new, with less than a thousand miles on them. I'll look at the CV joints, but I doubt I'd know what to do with one of them. The mechanic notes that the boots and everything are secured properly. It's difficult to isolate the sound from inside the vehicle, but it sounds as if it may be located more centerline than off near one of the wheels (and do the rear wheels even have CV joints, as they aren't really designed to turn like the front wheels?). Again, the problem is intermittent. Oh, I also got to experience my first hill-climbing excursion with the turbodiesel today. I have no doubt it can climb nearly any hill on this continent with a road on it, but it sure as heck won't climb them quickly. Acceleration on a modest grade is quite lacking, even with a turbo and operating about 50 feet above sea level (I could see the ocean from the road). Not a major problem, as I don't climb many hills, but it was nice to see the effects of slopes on the speed of the vehicle. SignaturePete Stephenson HeyPete.com CV joints give a lot of warning before failure so just drive it. A diesel is essentially a constant speed engine (thus its economy) so you see why one needs to charge hills at their bottom or be in the truck lane for their duration! > CV joints give a lot of warning before failure so just drive it. What sort of warning should I be on the lookout for, just in case? I hear that they're very over-engineered and require practically no maintenance. > A diesel is essentially a constant speed engine (thus its economy) so > you see why one needs to charge hills at their bottom or be in the truck > lane for their duration! Indeed. SignaturePete Stephenson HeyPete.com > > A diesel is essentially a constant speed engine (thus its economy) so > > you see why one needs to charge hills at their bottom or be in the truck [quoted text clipped - 5 lines] > Pete Stephenson > HeyPete.com Indeed not. A truck engine or stationary engine is a constant speed engine. A Benz diesel car engine has a wide rpm range and a significent spread between maximum torque and maximum power. Chas Hurst The warning will be boring - just slightly more noise, eventually a CV joint will start clunking. That's when you must take it for repair. I may have had to charge hills in my 79 300D but never in my 95 E300D. > I may have had to charge hills in my 79 300D but never in my 95 E300D. Nor I in my '91 300D 2.5. I was really surprised at how much power the car had when I test-drove it, compared to my turbo W123s. it's kind of neat having an oddball (for California) model, too. Geoff Signature"Am I crazy, or is it hot in here?" -- Charles Manson > Nor I in my '91 300D 2.5. I was really surprised at how much power > the car had when I test-drove it, compared to my turbo W123s. it's > kind of neat having an oddball (for California) model, too. Ah, I seem to have determined the problem with the hard shifting. It was related to me having problems retracting the rear headrests. It seems that I bumped some of the vacuum lines around, and had reconnected them improperly. As the engine communicates with the transmission via vacuum, it wasn't able to communicate properly, and the shifting was very hard. I've since re-connected them in the proper manner, and it now shifts smoothly, consistently, and properly. SignaturePete Stephenson HeyPete.com > Ah, I seem to have determined the problem with the hard shifting. > It was related to me having problems retracting the rear headrests. I can understand how inadvertently disconnecting a vacuum line might cause hard shifting, since I've had a similar experience (an inattentive mechanic knocked a vacuum line loose while opening the air cleaner housing). But where exactly do the rear headrests enter into it? Geoff Signature"Am I crazy, or is it hot in here?" -- Charles Manson > I can understand how inadvertently disconnecting a vacuum line > might cause hard shifting, since I've had a similar experience > (an inattentive mechanic knocked a vacuum line loose while > opening the air cleaner housing). But where exactly do the > rear headrests enter into it? The rear headrests are also vacuum-operated. Specifically, they lock in the upwards position, but a vacuum "signal" is needed to release them back to their stowed position. By dislodging several vacuum tubes and mis-connecting them, this had the dual consequences of hard shifting and inoperative rear headrests. SignaturePete Stephenson HeyPete.com > The rear headrests are also vacuum-operated. Ah, I didn't know that. I'd had the impression that they were released electrically. I guess that explains the delay in their dropping when I press the switch. Never gave it much thought. Geoff Signature"Am I crazy, or is it hot in here?" -- Charles Manson > Ah, I didn't know that. I'd had the impression that they were > released electrically. I guess that explains the delay in > their dropping when I press the switch. Never gave it much > thought. I never knew that either...just discovered it here the other day on this newsgroup, remembered that I goofed up the lines, and put two and two together. SignaturePete Stephenson HeyPete.com |
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