Motor Mounts, Flex Disc

[JoeyTheB]

My exhuast manifolds are out for cleaning,
and it looks like an easy reach for the motor mounts
on my M117.

What's the procedure for R&R for the motor mounts ?
Car is on ramps at present - hoping it can stay there.
Torque specs ?

Also what's involved with changing the flex disc ?
Do you usually do the tranny mount at the same time ?
Should the "bearing" be replaced too while I'm in there ?

Thanks,
Joe

[JoeyTheB]

just wondering so I know what parts to order.....

thx in advance....

[300SDog]

JTB, if its anything like any other Benz..... you wanna scissor jack the engine with plywood buffer under the pan as you loosen engine mounts. Major problem can be getting grip on 8mm allens from above that get filled with grit. Yep, gotta clean the allen heads before wrenching them. Underneath, you've got 10mm allens (one on each side) that bolt into motor mount arms from below...... but they are usually easy to turn, as beat rubber makes them loose. Btw, the underside 10mm allens are on list of nuts 'n bolts that should be torqued and tightened each couple of years. Go back and tighten them 6 months after installation when new motor mounts have settled.

Unless you strip the upper 8mm allens, the only parts you will need are motor mounts themselves. Tools you need include both socket allens and regular allen wrenches. Its not a bad job for DIY and is probably rated at "4" on degree of difficulty.


Hell yes, itsa good idea to bang out the tranny mount, flex discs and center support bearing at same time. This is very good idea!! And most people would consider subframe mounts also on the list. Yet for most people, engine mounts are easiest driveway repair and driveshaft/tranny gear is not. Good luck on this project and let us know how it turns out.

[JoeyTheB]

240DD -
Good points to consider. I've got a pretty good idea of where
my threshold for taking to the shop is, and it sounds like the tranny/flex disc just might be there.

Subframe mts are definitely on the list,
as are new shocks - just not in the budget yet and there
is GREAT info on this site going into great detail.

PS - I'm a closet 240D fan. Keep looking over local ads.
Afraid if I go look at one and drive it, I'll be coming home with one.

Joe

[JoeyTheB]

Found some help there - posting here if anyone is interested:

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I was only successful in finding the torque for the engine mounts -- 10
mkp (and no conversion table, alas).


My guess would be 30 ft/lbs or so, I don't use a torque wrench, just
tighten well. The nut for the rear mount (on top) will be similar. Make
sure you get the mount in right way round -- there is a notch on the top
plate, or a pair of them. The smaller bolts on the bottom only need
about 20 ft/lbs.


Be prepared to pry the engine side to side when replacing the engine
mounts. I had no trouble with the right side, but had fits with the left
- -- had to pry the engine over about 1/2" to the right to get the bolt
back in even with the taper on the end!


--------------------------------------------

And a long one...

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I don't use torque specs except on connecting rods and head bolts.
torque specs will tell you if the bolt has reached its yield point.
if you can't reach final torque, stop. and replace bolt.
it's stretched thus will fail.
These feel things are what a mechanic calls experience.
torque = twist force, rotation
Bolts and nuts are like "rubber bands" AKA "holding together force"
An innumeral amount of failures after a "mechanic" has done a repair
is due to improper torque.
iteration is the key,
Torque it down then do it again, tomorrow
after the metal has "relaxed"


In general : the bolt type determines the torque.
fine threads get more torque than coarse threads.
Hex heads 13/14/10 mm wrench you may be able to break them
hex head 17 mm wrench = unbreakable
Allen head hex = virtually unbreakable
sneak up on the bolts in a regular pattern until they do not torate anymore.
if torquing into aluminum casting be careful to not "over torque"


engine mounts:
17mm socket on bolt = as much muscle as you can provide
with a 1/2" Craftsman w/12" extention breaker bar 17mm socket


flex disc:
These should hurt your muscles
6 bolts and nuts same as above except use
a box end combo wrench on fwd side nuts.
Grunt and pull a few muscles.


tranny mount:
17mm bolt same as above
general rule:
if a 17mm socket required you can't break anything
and you will max out your muscles


Any suggestions for making the job easier ?
Use thread lube and finger tighten before applying torque


My exhaust maniflolds are out - looks like a good time to do the motor
mounts.
do-um while convenient.
Use new exhaust pipe to manifold bolts and nuts.
Re-torque while hot. Seriously.

[300SDog]

You probably know this already, but on torquing bolts and nuts it's length of ratchet handle thats critical..... old timers like short handle ratchets because shorter handles practically never over-torque - yet something like 16" 1/2 drive brakebar can easily over torque up to 70 or 80 lbs and beyond..... using progressively longer handle ratchets should give good feel for measuring torque. Most people over tighten bolts, thats my observation. 30 lbs to me sounds like full pressure with shorter handled ratchet, or lighter pressure with longer handle. I dunno the 4.5, but have snapped manifold dowels on 220Sb. But the trick of hot-torquing manifold to exhaust pipe collar sounds like good advice.

Older heckflosse cars have list of nuts 'n bolts in owners manual for regular tightening that include subframe bushings, sway bar supports, engine mounts, differential mounts, steering box bolts to fender well and others. And 30 yr. flex disc is one thing you dont wanna have let go...... have heard horror stories of driveshafts snaring emergency brake cable and raising hell when flex disc gets chewed up.

[JoeyTheB]

So how do you remove this thing ?
All bolts loose, but drive shaft still attached.

Isnt the fwd drive shaft on a spine so you can slide it back a bit ?

or must you drop the drive shaft from rear diff ?


Thanks in advance,
Joe

[300SDog]

if you're knockin out both flex discs, try doin the rear one first.... i cant speak for the m117, but front flex disc on the m110 can be pried loose with crowbar by itself - and then you rely on nuts 'n bolts to restore driveshaft to original position..... gotta paint mark position of shaft couplings that meet at flex disc, so they tell me - just in case the driveshaft has been factory ballanced to drivetrain at the tranny.

[psfred]

Joey:

The M117 mounts have a bolt from the top (19mm I think) and two small (8mm) allen bolts that hold the mount to the frame. Easy to reach or without the manifolds on.

You must remove the top mount on the left and the bottom mount on the right engine shock to jack the engine up. I'd do one at a time. Be prepared to pry the engine sideways to get the left side mount bolt in, the engine wants to slide over to the driver's side for some reason.

Tranny mount probably needs replacing too -- drop the crossmember after removing the nut on top. Make sure you get the new mount right way round -- there is a notch in it that fits around a bump on the tranny.

Flex disk requires that you lower the driveshaft -- loosen the clamp nut at the splines a couple turns, not more, then remove the bolts that hold the center bearing carrier. Remove bolts at flex disk and pry the driveshaft front section back until the centering sleeve clears the pilot, then fold down to get it out of the way. DO NOT separate the front section from the rest of the driveshaft unless you have indelibly marked it for correct placement -- the splines are not keyed, and if you miss the original placement, it may vibrate badly.

Peter

[JoeyTheB]

Ok, I finally got the protective sheet metal out of the way,
what do I use to loosen the clamp nut on drive shaft ?

I assume lower the rear wheels so I can get something to turn against - currently in neutral with one wheel off ground.

Someone on the 108 vets list said using a chain wrench from lowes worked pretty well....

Motor Mounts - yes, quite a tug of war. I won by using a 40" 2x4 to pry the engine back into it's proper location. Unfortunately, I did the job b4 I saw your posts on what to loosen - nothing broken, but I bet it sure would have saved some time.

By the way - I see the new mounts were marked with red dots -
does the red go toward front or back - sure hard to tell as the
damn thing looks symmetrical...

Joe

[David Speed]

These are the 'special tools' I used for center bearing replacement.........the adjustable plumber's wrench in the center of the picture is what I used for the 46mm clamp nut on my w123(seems most MBs are similar)........something similar should be available in the US

You should have a close look at the center bearing and mount and consider replacement while you are there

As Peter noted..........be sure to mark the shaft at your first opportunity........just in case it accidently come apart with pulling & jiggling

I marked it with typists correcting fluid in the valley of one of the splines that lined up with a cutout slot.........and be sure to look after your markings........apparently one spline out is enough to cause trouble

David