What and were is the rack damper - PeachParts Mercedes-Benz Forum

my126benz · #1 01-20-2006, 03:27 PM

I understand that the rack dampener can go bad and cause excessive vibration. What and were is it on a 83 300 SD Thanks

dannym · #2 01-20-2006, 03:37 PM

The search button is your friend.

Rack Damper photos

Danny

Pete Burton · #3 01-20-2006, 03:38 PM

On the back side of the injection pump, near the oil filter housing. Old ones are frequently beat. Do a search on adjustment and sources.

meltedpanda · #4 01-20-2006, 03:49 PM

The rack damper
bolt is designed to
damp the vibration that are inherent in that engine when
EVERYTHING is running perfectly The original bolt (on
the back of the injection pump) had a relatively weak spring
and it fatigued making proper adjustment impossible. A new
bolt (GOLD in color - old one was "silver") with a much
stronger spring was designed ( '84-'85) . This is a very important update and the
adjustment of the rack damper bolt is very critical. It
should just barely make contact and damp the shake (when
EVERYTHING is running correctly and the engine is WELL
warmed up) then loosen it 'til it shakes - then tighten 'til
it just stops shaking. Then tighten it down. Search for other ideas , but I have found it is all a feel thing and the engine MUST be warm

my126benz · #5 01-20-2006, 04:34 PM

Thanks for the info. Ive learned alot about these cars but not about this bolt.

Hit Man X · #6 01-20-2006, 04:35 PM

Also helps a great deal in cold starting/idle too.

Brian Carlton · #7 01-20-2006, 05:37 PM

Quote:

Originally Posted by meltedpanda

..........but I have found it is all a feel thing and the engine MUST be warm

.........and........try not to burn yourself in the process.

meltedpanda · #8 01-20-2006, 08:14 PM

yup forgot that part

MB-Owner-in-ind · #9 01-20-2006, 08:14 PM

I know it might sound unusual but I never did find the bolt on a '79 SD. I found it on the other cars I have but not on that one. I wonder if there are cars that don't have one?

#10 01-21-2006, 04:22 PM

The rack dampner bolt must also not be screwed in too far otherwise when you rev the engine and let off the accel with no load it will droop below idle speed and most likely stall.

You are basically shooting for the point at which the vibration JUST stops...then leave it there and tighten down.

Do all of the adjustment/tightning while the engine is running...that way you know if you screwed something up. Also rev the engine in-between adjustments to see if you have it on or not. Imagine you are adjusting a carburator

Brian Carlton · #11 01-21-2006, 04:58 PM

Quote:

Originally Posted by Brandon314159

The rack dampner bolt must also not be screwed in too far otherwise when you rev the engine and let off the accel with no load it will droop below idle speed and most likely stall.

Any thoughts as to whether the bolt can affect a very cold (15°F.) idle. The SD "hunts" a bit for a minute or two when it's brutally cold.

I hadn't given the bolt a thought until you mentioned it.

#12 01-21-2006, 05:03 PM

Quote:

Originally Posted by Brian Carlton

Any thoughts as to whether the bolt can affect a very cold (15°F.) idle. The SD "hunts" a bit for a minute or two when it's brutally cold.

I hadn't given the bolt a thought until you mentioned it.

If it doesn't hunt or show odd vibrations when warm...the rack dampner cannot do anything to help this without affecting your warm idle too.

My educated guess would be that the oil in the IP is so thick that the mechanicals are not operating quickly/smoothy and thus it will hunt a little until everything is warmed up.

Mine does this as well...and idles smoothy when warm. You can try and see if the bolt is a little too far in but my guess is that the engine is just cold and shivering heh.

Brian Carlton · #13 01-21-2006, 05:50 PM

Quote:

Originally Posted by Brandon314159

If it doesn't hunt or show odd vibrations when warm...the rack dampner cannot do anything to help this without affecting your warm idle too.

My educated guess would be that the oil in the IP is so thick that the mechanicals are not operating quickly/smoothy and thus it will hunt a little until everything is warmed up.

Mine does this as well...and idles smoothy when warm. You can try and see if the bolt is a little too far in but my guess is that the engine is just cold and shivering heh.

Well, it's synthetic oil, so I doubt that's the culprit.

The "situation" has developed since I did the head replacement. Probably just a coincidence, but, I don't ever remember the SD doing any hunting when cold. However, usually, when it's that cold, it would crank for a 5-10 seconds and start with a grumble and a pile of smoke. Now, it kicks over in one second, with no extra fuel in the cylinders. So, comparisons may be meaningless.

Hit Man X · #14 01-21-2006, 05:51 PM

Well I'll relay my experince also if it will help -

Before adjusting the bolt, my SD would idle VERY low when cold. Temps from the mid 50s on down. So low infact I had to have the foot on the throttle until the SD would warm up a bit.

After the adjustment, it'll start and idle down into the 40s (hasn't gotten colder here recently than that, I was out in shorts and a T-shirt yesterday!).

The adjustment took me maybe 10-15min. Just throw on a thick glove to resist getting burned. I used my fingers in a backward "C" shape around the oil cooler line. That's it.

SD's bolt was VERY tight in there before adjustment. 2-3 full turns too tight.

Brian Carlton · #15 01-21-2006, 06:56 PM

Quote:

Originally Posted by Hit Man X

SD's bolt was VERY tight in there before adjustment. 2-3 full turns too tight.

Thanks. I might just back it off one full turn, when cold, and see how it does. I'd need real cold temps to check it and we've not got them for awhile.