I've got a bad idle shake that is much worse when the engine is hot (like just getting off the highway) than on a cold start.
It's an 82 300sd so it has the old damper bolt.

It's got good compression, just did a diesel purge, haven't done a valve adjustment or changed the motor mounts yet.

I found a brand new bolt for pretty cheap and I'd like to just swap out the old one as I think it will solve the problem.
However some folks suggest changing the motor mounts and doing a valve adjustment before changing the damper bolt.

Why is this?
I can't imagine anything going wrong except tightening it too much and having a hard problem with cold starts...

The damper bolt is half the price of changing the motor mounts and engine shock, the rubber on the mounts seem to be in good enough shape (not gooey or cracking). I'd rather replace the damper bolt now and do the mounts later on than end up having to do both right away.
I do plan on doing a valve adjustment, but don't see why that would really change the picture.

A rack damper adjustment cannot cure collapsed engine mounts. Therefore, your observation of the engine will be severely compromised and effecting a positive outcome with the bolt will be difficult.

You might get some improvement............might not. But, any results that you get are invalid if the mounts are compressed flat.

So, if you do change the bolt, refrain from commenting on the results as they are basically worthless until the mounts are changed.

Motor mounts and valves that need adjusting can cause the engine to shake significantly. The valve clearances on these engine get tighter over time, which leaves the valves not closing entirely. This leads to reduced compression. If you have some valves sealing properly and others not you get uneven compression which will cause rough idle. Properly adjusted valves can help idle a lot if they are way out of spec. I'd highly suggest at least adjusting the valves if you haven't in the recent past. It's cheap and easy if you've got the wrenches. If you don't you can find another member that does and get a hand. If you want to come visit me we can do it.

You certainly won't do harm by putting in a new rack bolt, but you may not get the results you are looking for if the mounts are bad and the valves are out of spec.

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I just made some wrenches last week, probably going to do the valve adjustment on Friday.

This is a real bad shake. Way worse than my wagon which definitely has lower compression and also needs new motor mounts.

If the valves are tight, will the idle shaking be worse when the engine is hot vs cold?

Valve adjustment is critical, motor mounts are a normal wear item. A rocking motor and shaking felt in the car typically points to motor mounts. The simple fact that you are uncertain as to valve adjustment status might indicate that the valves need adjustment.

Best of luck.

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83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.

When I had the Hot Idle Shake I bought a new Rack Damper Screw but adjusting it did not help much; rebuilding the Injectors and adjusting the Valves took away 85% of the shake.
Replacing all the mounts and taking care of a small Air leak too away most of the rest.
At the end of it the Rack Damper Screw was able to work and remove a little more shake.

I believe Rack Damper Screw is there to remove a little shake on Engines with everthing else in spec.

I also believe an Engine that shakes a lot because the Injectors are shot and the Valves need adjusting shortens the life of the Motor and Transmission mount and may be one of the reasons the Crankshaft Damper shakes itself loose.

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84 300D, 82 Volvo 244Gl Diesel

Adjusted the valves, the cold idle is a little bit smoother but the hot idle isn't any better.

Going to do the motor mounts & shock and the tranny mount tomorrow. I guess I'll wait on the rack damper.

Also, now there's a knock that I swear wasn't there before. It did have some slight knocking when I first got it and after I did a diesel purge it smoothed it out.

This sounds louder. Is there something I could have done wrong with the valve adjustment? Not tightening the locknuts enough or?

It sounds very much like an injector knock to me, but it seems strange that it's worse after adjusting the valves. I took a video to see what folks think:
300sd 002.MOV - YouTube

You can adjust the Rack Damper at any point you want to; you may be lucky and that is all that is needed.
I was just saying that in my Case I expected a lot from the Damper and found out it is not a cure for larger problems.

If the Valve adjustment helped up the Compression the knock could be from more Fuel burning.

Try loosening one Fuel Injection hard Line nut (and tighten it back up and move down to the next Injector) at a time and see if you can locate which Cylinder that knock is coming from.

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84 300D, 82 Volvo 244Gl Diesel

Is the old style rack damper even adjustable? Everything I've read says to just replace it if you have the older style.

More fuel burning can cause a knock? New one to me!

I was actually going to try that injector test, but I was super exhausted b/c my new used jack that I just bought (low-pro Napa 4.5 ton!) got stuck and wouldn't lower, while it was holding up the whole front end by the cross member! Finally got it down after trying lots of different methods.

Yes. In theory, at least.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

The Damper adjustment is limited to the travel on the spring loaded plunger in the middle of it.

See the DIY section to find out the undesirable effects of turning it in too far.

The newer one has a stronger spring inside.

Also I noticed that my Old Damper was worn some on the Plunger end.

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84 300D, 82 Volvo 244Gl Diesel

My 82 shakes only during hot idle, rock solid smooth when cold. Replaced the motor mounts and shocks/shock mounts with all OE equipment from MB. Didnt change it.

Valves were adjusted, compression good, etc.

Sometimes it just is something else, be it the rack damper (OP, have you played with the original one yet to see if it made any difference?), air in the lines, etc.

Ive adjusted the rack damper before and never got the shake to go away completely. It isnt bag but it is noticeable and I want it perfect. No telling if it is the solution for many of these shaking situations though...

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

If you have the Stock Bosch Injectors Nozzles they are likely worn out and or plugged with Carbon.

The very tip of the Injector Nozzle #12 in the pic; the Pintel (sometimes called the Needle) is drilled with two tiny passages #14 and #15.

When those are plugged it keeps the Idle Fuel from shooting through those passages.
All the Injectors on my Engine and most of the used Injectors that I have pulled from the Junk Yard have had those passages entirely Plugged with Carbon.
When I had that Hot Idle Shake the Valve Adjustment and rebuilding the Injectors (with Monark Nozzles that do not have those little passages) took care of 85% of my shaking.

However, it is better to do all the free or cheap stuff like the Motor and Tranmission mounts before moving on to the Injectors.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

Nope I have rebuilt, popped and balanced injectors from Sean Watts, with Monark nozzles. No change from before and after injector pull.

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

Does the knock in the video sound like the injector nozzles?