1979 300SD Engine Mounts

[Mergyver]

Started work on replacing the mounts. They appear to have collapsed completely, I wonder if they were ever changed before. Tried loosening the single bolt that goes up through the mounts and attaches to the arms on the side of the engine. Both bolts are frozen solid. Does anyone have any clever ways of loosening these? I am thinking of taking an impact wrench to them but I am a little worried about stripping them.

What do you guys think?

[Squiggle Dog]

Maybe fit an Allen wrench or socket on the end of the bolt and smack it several times with heavy hammer.

[daantjie]

Heavy soak overnight with PB Blaster.  Maybe try some heat with a torch too. Multiple cycles might do the trick.

[OLDGOLD]

Seafoam Deep Creep

[Alec300SD]

Ideally, soak with favorite penetrant the day before.
Clean the Allen bolt recess very well.
Position car with front wheels on ramps and rear wheels chocked.

Get under car.
Smack the Allen socket into place with a big hammer (seats tool and helps break corrosion).
Attach extension and breaker bar to Allen socket.

Under the car on your back, align left hand and left hip directly underneath Allen bolt.
Brace feet against  undercarriage.

Grasp breaker bar at socket extension with left hand (and push upwards) to provide a stable counterhold.
Grasp handle of breaker bar with right hand and tug CCW to break the Allen bolt  free.

If it is stubborn, try to slightly tighten the Allen bolt (to break corrosion) and then reattempt removing the Allen bolt.


BTW, I pulled an upper oil pan from a 1980 300SD at the Oakland PNP on Labor Day,
This required removing the Allen bolts from the motor mounts (and  many, many other bolts)
before raising the engine with a hoist (jacks are forbidden).
I had no penetrant or breaker bar with me.
A 27mm combination wrench on the handle of the 3/8 ratchet wrench worked as a makeshift breaker bar.

[Mergyver]

thanks for the tips guys. I didn't think the penetrating oil would work because the bolt is upside down and I can't get to the threads due to collapsed mounts. I will give it a try though.

Alec, it looks like you have done this a few times. not sure I have ever seen a more detailed description. I am going to get a longer breaker bar today and give it another go.

Thanks

[avantbenz]

I'm planning on doing this within a few weeks and not looking forward to the job.

The only advice I've heard that is applicable that hasn't already been mentioned is that once the allen socket is well seated in the bolt head make sure you give it a good snap as opposed to slowly muscling it.

[Mergyver]

Not sure how to give it a snap without an impact wrench. I guess I could put pressure on a breaker bar and have a friend hit it with a hammer?

Right now I am thinking if I do get some movement with a breaker bar I will go back and forth (loosen - tighten) to try and break up some of the corrosion.

I did try a low power impact wrench last night. It was not able to move the bolt but I am hopping that the vibrations created by the constant impact broke some of the corrosion loose. Will find out tonight.

[Alec300SD]

Slip a long pipe (jack handle) over the handle of your breaker bar to gain more mechanical advantage.
Might need a helper to pull the pipe while you hold the socket in the Allen bolt.

[rumb]

I have found that impact and shock hitting can cause damage more often than not.  Long leverage on your breaker bar will cause less damage to the bolt head.  as mentioned add length to your breaker bar. make sure to pound the allen into the bolt and make sure it is seated.

[Mergyver]

Thanks Alec and Rumb. I just got the two mounts out. I took your advice, bought myself a 1/2 inch drive hex wrench socket so I could attach a longer breaker bar. After a few hammer whacks and adding enough pressure they did come loose and back out nice and easy.

I was amazed at the condition of the mounts. The right side hade collapsed so far that the metal cover was bent down in the middle from the engine mount arms. The left side actually came out in pieces. The rubber that connected the middle of the mount to the out outer bracket that bolts to the frame had completely deteriorated. The metal middle portion of the mount that bolts to the engine arm was completely disconnected from the frame portion of the mount.


The bolts are in pretty good shape. I will clean them up before they go back in.  Do you guys know whether it makes sense to put anti sieze or thread lock on the primary bolts that attach to the arms?

[Alec300SD]

The FSM calls for dry assembly. http://handbook.w116.org/Engine/617/22-211.pdf

Loctite will make future disassembly more difficult, and aid in preventing corrosion from reaching the threads.
Anti-seize will make future disassembly easier, and aid in preventing corrosion from reaching the threads.

If you use the right tightening torque (70 Nm) then there should be no need for Loctite.
Anti-seize on the threads may allow the bolt to vibrate loose, as dry assembly torque is usually less than wet assembly torque.

Note:  the bolts I removed (to pull the upper oil pan) had split ring lock washers, but these are not shown in the FSM pdf above...
I'll check the EPC tonight.

If your main concern is preventing corrosion from getting to the threads,
then give the exposed Allen bolt head a good spritz of Lanocote spray (after you torque it in place).

[Mergyver]

I am focused more on preventing corrosion in the threads. I will look at the Lanocote spray. I have never used that before.

Interestingly my main bolts( the ones that thread into the arms) had split lock washers on them.

[avantbenz]

Sigh, I am in the same boat you were before you got the bolts unstuck. The passenger side mount bolt came out easily enough but my driver side mount bolt seems frozen. I've taken all the advice with the exception of heat cycling. I have a piece of pipe to lengthen the breaker bar and had multiple cycles of PB Blaster and trying to tighten / break to loosen any corrosion present. I've taken the hammer to make sure the hex bit is firmly seated.

Still at it - trying to get this done before the sun sets. Mergyver's success gives me hope...

Edit: 18 inch 1/2 drive breaker bar with a 6 inch extension worked perfectly on the first try. 

[Mergyver]

I just finished replacing both engine mounts and engine shocks. While I was under there I replaced the bushings on the shifter linkage which had completely disappeared.

As a reminder the right hand mount had completely collapsed, the rubber in the left hand mount had hardened and crumbled into pieces.

I can officially testify that 300SD's work 1,000% better when the engine is actually attached to the frame. The car went from shaking like a paint mixer to running like a new Mercedes. Absolutely beautiful and worth every minute of effort.

To make things even better I can now shift by moving the shifter next to the letter (i.e. P,R,N,D,S,L). As opposed to before where I would put my foot on the brake and move the shifter untill the car jolted in the direction I want. Thank you bushings. To replace the bushings I used the Mercedessource bushing kit. It literally turned it into a 10 minute job.

I was thinking that the transmission mount should be replaced but I could not tell if it was bad. Does anyone have any pointers on how to tell if they need replacement