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#1
08-14-2012, 01:05 PM
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hard clunk every shift. 1991 300d 257k
Like it says every time I shift a gear it clunks really hard and sounds like something is hitting the back floor board's weather I'm taking it easy or driving it hard its the same
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86 300sdl 224k sold 1991 300d 257k 
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#2
08-14-2012, 01:18 PM
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Check your flex discs along the driveshaft for wear. Also inspect your differential, see how much play is in it. How hard does your transmission shift?
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TC Current stable: - 2004 Mazda RALLYWANKEL - 2007 Saturn sky redline - 2004 Explorer...under surgery. Past: 135i, GTI, 300E, 300SD, 300SD, Stealth
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#3
08-14-2012, 01:28 PM
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Sorry forgot to put I just replaced the trans mount both flex disc and carrier bearing. It shifts so hard it peels out and sounds like a hammer is hitting it underneath
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86 300sdl 224k sold 1991 300d 257k
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#5
08-14-2012, 03:06 PM
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Quote:
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86 300sdl 224k sold 1991 300d 257k
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#7
08-14-2012, 04:24 PM
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x2 on the clicking, my bet is on the diff. My 300SD was extremely firm shifting (pulled vac line) and clunked gear to gear sometimes as well. Short answer - probably the differential however the real problem is the transmission shifting that hard.
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TC Current stable: - 2004 Mazda RALLYWANKEL - 2007 Saturn sky redline - 2004 Explorer...under surgery. Past: 135i, GTI, 300E, 300SD, 300SD, Stealth
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#8
08-14-2012, 05:23 PM
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My hard shifting might not have been the same as yours but I'll throw my 2 cents in anyway.
Is your throttle linkage adjusted properly? Mine wasn't, as evidenced by the little rotating bearing being half-way through the curved bracket slot with the throttle completely closed. I adjusted that back to the beginning and it helped shift firmness a lot. Also, turned the ALDA screw 1.5 turns CCW and that helped quite a bit too.
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#9
08-14-2012, 10:06 PM
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x2 on no vacuum signal to the transmission. Can you tap a vacuum gauge into the line from the blue thing by the glow relay to the transmission modulator? Shift quality should improve with more throttle. At WOT there isn't much of a vacuum signal to the modulator. IIRC the spec is 0.
Sixto 87 300D^2
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#10
08-14-2012, 11:37 PM
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Quote:
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86 300sdl 224k sold 1991 300d 257k
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#11
08-15-2012, 12:13 AM
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The line to tap is the one atop the round blue thing marked TRA. It comes off the blue thing, elbows towards the engine, goes through a green cylinder then tucks into a sheath. IIRC it's a black line to the transmission modulator.
Sixto 87 300D^2
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#12
08-15-2012, 01:24 AM
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just an fyi when my trans had 0 vac going to it , it shifted just as you describe. felt like i was getting rear-ended when it shifted, tires would chirp, etc.
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1981 NA 300D 310k miles
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#13
08-15-2012, 07:24 PM
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Transmission flaring or clunking? VCV DIY - Benzworld.org - Mercedes-Benz Discussion Forum
This thing is the first part of the vacuum getting to the transmission. A small adjustment goes a long way for changing how hard or soft the transmission shifts. I adjusted mine 1/8th turn, no more hard shifts. Hard shifts are really bad for the drive train, too soft of shifts (flaring) are bad for your transmission. Just look at how much the valve moves (it's connected the the throttle, that's how the valve it actuated), so when you take the valve off the car you can simulate it by hand. You can adjust it on the car but it's a lot harder. To verify how it's working you can suck on where the vacuum tube (where the hose attaches) as you move the lever on the vcv. This is all assuming you have good vacuum going to the vcv. After the vcv there is another vacuum modulator at the transmission that can be adjusted but the vcv is the main valve for vacuum to the transmission.
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1985 300TD 1981 Scirocco 1.6D conv 1986 Golf 1.6D 2003 Golf TDI Last edited by sgnimj96; 08-15-2012 at 07:50 PM.
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#14
01-25-2014, 02:05 AM
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The clunking trans shifts are a vac leak. they pop up every once in a while. get a vac gauge to track it down from the vac pump.
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1991 300 D 2.5 Turbo, 220k also in the family: 1981 240 D 185k 1991 350 SD 185k 2006 S 500 2005 SLK 350
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#15
01-25-2014, 08:49 AM
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Here is your answer
Quote:
On a 1991 300d with 257k miles...... I would bet one or more of these items has failed: 90% odds it is the first and second item, but the others need to be inspected.. These are rear differential mounts, known for clunking when they fail. Rubber mounting, x2 per vehicle MB# 1243527765 Pelican Parts - Automotive Parts and Accessories - Porsche & BMW TEST These are FRONT differential mounts, known for clunking when they fail. Rubber mounting, x2 per vehicle MB# 1243511342 Pelican Parts - Automotive Parts and Accessories - Porsche & BMW TEST These are rear knuckle lower mounts, known for sloppy rear and clunking when they are profoundly bad. Joint, x2 per vehicle MB# 2203520227 Pelican Parts - Automotive Parts and Accessories - Porsche & BMW TEST These are the rear multi links keeping the knuckle in dynamic alignment, known for sloppy rear and clunking when they are profoundly bad. Suspension kit rear multi link Suspension kit rear multi link Home-made $15 W124 rear knuckle - LCA Bushing Tool Home Made Special Tools, This is where members can share how they made special tools 124 carrier bushing R&R Mercedes W124 Rear Suspension Guide .
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ASE Master Mechanic https://whunter.carrd.co/ Prototype R&D/testing: Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician. Noise Vibration and Harshness (NVH). Dynamometer. Heat exchanger durability. HV-A/C Climate Control. Vehicle build. Fleet Durability Technical Quality Auditor. Automotive Technical Writer 1985 300SD 1983 300D 2003 Volvo V70 https://www.boldegoist.com/ Last edited by whunter; 01-25-2014 at 09:32 AM.
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