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#1
06-12-2007, 01:15 AM
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Mysterious "thumping" in first and second gear
Here's on that has me scratching my head.
1982 300SD 276,000 miles When starting from a dead stop, if accelerating hard, there is a series of 5 thumps that seem to come from the rear differential at the bottom of first and second gears. If the start from a dead stop is slow, then the thumps are not as noticable, OR nonexistant. My first assumption was that the suspension was tired and the universal joint was striking the bottom of the car, etc. (yes, I've seen this happen on Chevy Caprices from the early 80s) However, on closer examination of the undercarrige, I can not find any evidence to support this theory. Anyone have any insight?
__________________
1982 300SD 300k+ miles 
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#2
06-12-2007, 01:45 AM
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Try examining the driveshaft support bearing.
__________________
'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate Sooner or later every car falls apart, ours does it later! -German Narrator in a MB Promotion Film about the then brand new W123.
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#3
06-12-2007, 08:42 AM
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and check the exhaust pipe support doughnuts. if the pipe is sagging, it can contact several things as the car launches (ha I said launches on a diesel!) really there are so many things on these older cars that deteriorate and cause noise, the only way to find it is to strap yourself under there and watch... not really recommended. could be cv joints, rear dif support bushings, flex disks, transmission mount, motor mounts letting the motor shift positions under hard load, a bowling ball in the spare tire compartment... etc...
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 190D 2.5Turbo 1987 190D 2.5-5SPEED!!!  1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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#4
06-12-2007, 08:50 AM
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Check your axle boots (look for a quationable amount of grease just outside of one of the boots).
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1989 300E 144K
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#5
06-12-2007, 09:18 AM
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I had the same symptom in my W123 300D. Hard acceleration in 1st gear was making a thumping noise but not when I was easy on her. I thought it was a flex disc about to go but it turned out to be the prop shaft center support. The rubber gets old and tears.
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Dave 2002 Audi S6 Avant 1983 300D 1984 300D (sold) 1990 560SEL (sold)
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#7
06-12-2007, 10:26 AM
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Quote:
Right side, about 25 MPH, louder when I am turning left (and putting more weight on the right side.
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NC Benz Fuquay-Varina, NC 1979 300D 1983 300D Turbo 260,000 Miles 1984 300D Turbo 345,000 Miles (sons car) OBK #31 1998 Ford Expedition 5.4l (fer Haulin'!) 145,000 1973 19' SeaRay with 115 Mercury TOWER OF POWER! Club Car Golf Cart 36V Ex toys: 1967 Mustang 289 (First Car) Fiat 124TC 1975 Honda CVCC 1980 Audi 5000 Turbo
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#8
06-24-2007, 10:13 PM
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I was just about to post a very similar question. 84 300 TD with 4 speed manual. In 2nd gear, about 23 mph, more pronounced when going uphill and under load I get the thump. Anyone figured this out yet?
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1981 300TD - SOLD 1981 Euro 300TD 4 sp. parts car 1982 300 SD - SOLD 84 300 TD 4 sp n/a 241K - SOLD
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#9
06-24-2007, 11:43 PM
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I had identical symptoms.. check loose or worn motor mounts. The engine will hop a little under heavy torque.
__________________
'79 300D, Ivory "Gunther" ......going '81 300SD, Metallic Blue Silver, The Grey Ghost.....going '87 300D Turbo ...gone '05 CDI.... gone
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