Main.TrailIndexPage | Suspension | Subframe Mounts

Subframe Mounts

This component is part of Suspension.

Definition

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Function

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Maintenance

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  • How to fix / change

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I just read an article where a DIY guy documented and photographed the replacement of sub-frame mounts on his 280 SEL. It sounded pretty straightforward, no special tools. I would like to perform this and much more, but I am new to suspension and steering repairs. Basically, all the suspension rubber, mounts, and shock absorbers on the front and rear ends have to be replaced. Considering I have a Haynes manual and an MB Service Manual to look at, would this be something an intelligent and patient man could accomplish?

I am in the same spot as you are. So far, I have replaced the differential mount (which made a gigantic difference in the ride quality, (for the good)), another rubber piece in the rear (I'm not sure how to describe it - it was a bushing that was rubber in between two concentric tubes), and the rubber in the hardtop above the windshield. I know there is more rubber to replace - anything that was rubber is worn out on my car, and I'm replacing it as fast as I can afford it. The engine mounts were replaced before I bought the car. My mechanic says that all the suspension-to-body rubber has been replaced on my car. As far as I'm concerned, you can not go wrong replacing anything that is rubber. The more that you replace, the better your car will ride. It all needs replacement, as it all has a short lifetime.

Frank: main difficulty in replacing sub-frame mounts is making enough clearance to insert the new mounts. This can be accomplished using a porta-power, long pry bar, or simply removing all parts that attach the subframe to the body. If you have a fan shroud, it may need to be loosened or removed to allow the engine to drop lower.

Yesterday on my way to work I was driving merrily along (luckily not on the freeway) when I heard a loud bang and the left front suspension collapsed. After I had come to a stop and upon further inspection, I saw that the lower wishbone had snapped off, taking out the shock and assortes linkages and bushings in the process. My mechanic had never seen anything like it in his 20 years of working on MB. The wishbone itself (not the bushings or mounts) has snapped. Now I'm anxiously awaiting the assessment of the collateral damage and cost. Surprisingly, even though the front left tire was banged hard against the inner fender, there is no body damage - thanks MB for using such thick-gauge steel. Note that all this happened despite regular chassis lubrication. My car currently has non-original oversized wire-wheels on it and the PO had to put spacers into the springs in order to keep the wheels from rubbing against the fenders - do you think that this messed up the suspension enough to put so much stress on the wishbone? That's the only explanation I could think of.

Frank: what kind of wheels were on it? Wheels with more offset than original could have contributed to the failure. Also, I think the control arms on later cars were made of heavier metal.

Here is a warning which I think could be very relevant. The front suspension mountings on all these cars are 99% of the time shot and it is extremely wise to actually support the front axle all the time and never let it hang on its own from the car. If this is not done and the suspension rubbers break apart, the front axle will come down. The motor rests on it and everything will come down, resulting in substantial damage and a flat mechanic (!). This has happened to me once on a 230 S sedan. As I lowered the jack, I suddenly heard a tearing noise and the axle came down substantially. The airfilter housing was damaged as the motor lowered and tore it, the break hoses where damaged and the fuel pipe was torn. I was quite lucky because the jack was still in place. I have since checked and replaced these on all my cars because they were all shot. Interesting is that once lowered to the ground, the axle seats itself back to its proper position and nothing is visible. The axle won't come out completely because it is attached to the steering etc. but it certainly makes a lot of damage and it is really scary. These rubber mounts sit on both sides basically on top of the front springs and they are attached from the engine compartment with 4 bolts and one large centre bolt. They are not visible. You can sort of check the condition by carefully lowering the front axle when the car is on stands and observing both sides on top of the front springs. If you see that the whole axle and rubber is coming down, stop and get new rubbers.

The motor mounts are $30 each from Star Quality (#211-006), and it takes about 1.5 hours. Worth every dime if they're worn.

I replaced all my mounts over the winter and yeaterday my tranny started to tap against the metal tunnel. At first I thought it was the exhaust system (recently installed) but I found out it was the rubber spacer on top of the long bolt that holds the tranny mount in place. If you replace your tranny mount buy the rubber spacer also or it will get torn up by the new tranny mount, it's beyond me why a parts supplier would not recommend replacement when you change the mount (since that little piece of rubber is almost 40 yrs old too!), I guess it's kind of like the rubber gasket thats not included in the oil filter kit that they don't tell you about.

When I put my car on a lift, lifting from four points on the underside of the body, and lift the car up, the engine sags forward (or down) until the bolt that attaches the fan comes to rest against the radiator (leaving a small indentation. On the wheels, the fan center bolt is about 1" away from the radiator. I forgot that this happened the other day and tried to start the car while it was up on the lift. Talk about a loud screeching noise. I imagine that this is not "normal". Is it that the engine mounts are worn, or something more sinister. There is NO rust on the car, but the body does flex somewhat. As I am lifting the car, the engine just stays in the same place until the fan bolt contacts the radiator. Hmmmm...

I suspect that the transmission mount is broken which allowed the engine/ transmission to move in the direction you described. The transmission mount is located at the rear of the transmission and above the plate with all of the bolts in it. I would check this out next.

My guess is that the front sub-frame mounts are somehow at fault, allowing the entire sub-frame w/engine attached to sag lower when the car is on the lift(and allowing the full weight of the sub-frame to be "suspended" by these mounting points. That's my $.02.

Tom Hanson says: sounds like bad subframe mounts to me.

Bernt Damm: That is because the subframe mounts are shot. This is dangerous as the whole front subframe comes down and is only held in place but the brake hoses, the torsion bar and sometimes the shocks. I have seen substantial damage caused like that to fuel lines, brake hoses air filters etc. Check by lifting car under body slowly and observing the subframe rubbers from the top. If their bolts do not come up with the vehicle, you must replace them or never lift your car under the body like that until you do.

Walter Klatt: Your subframe mounts are not holding anymore. These are rubber mounts that go between the frame and the front crossmember of your car. The entire engine rests on the subframe and the body rests right onto the subframe and is cushioned by a pair of rubber mounts. When you lift your car you can see the front wheels are further down than they should be. Check the subframe mounts and there should be your problem.

Original poster: it didn't seem normal. I am busily cruising around the net looking for subframe mounts. I also am going to do the engine mounts as well as the transmission mounts. Does anyone know if the 230SL has a rear engine mount as well? And can I replace all of these parts without removing the engine or transmission.

The 230 SL has 2 engine mounts and in the rear, the mount is for the transmission. Yes, you can replace all three without removing the engine and transmission.

I replaced my subframe mounts over the weekend. It took about 6 hours and when I was replacing the drivers side mount the bolt off of the PS unit dented (the radiator was mounted too close to the engine) and then caused a leak in the radiator.

I'm in the process of replacing the rear motor mount (on the rear of the transmission) in my 230SL. I could use some advice on the order of assembly. From the BBB, the order appears to be:

  1. Bolt the mount to the large plate underneath.
  2. Bolt the plate to the body, at least loosely.
  3. (Somehow!!) bolt the mount to the bracket on the rear of the transmission.

The problem is step 3 -- it seems impossible to reach these two bolts once the plate is in place. Before I break my wrists trying, is there another order which works better?

In fact, I believe this is the "correct" way to do the job. There are access holes in the large plate, and if one had twelve inch double-jointed fingers and possibly a special tool, it would be possible to reach the aforementioned bolts through the plate. I found a less elegant but easier way which may be of help to others. The problem with reversing the order -- fasten mount to transmission bracket, then bolt the plate on below it -- is that the bellows, fitted washer, etc., which fit on the bottom of the mount above the plate all fall off before one can get the plate on. I got around that by using masking tape to fasten this stuff on temporarily -- long enough to get the plate on. There is enough access to get the masking tape off afterward.

Bernt Damm: it is easiest to unbolt the whole bracket with the 4 nuts from the transmission. They can easily be accessed with a socket from the rear through the bracket. Just support the transmission with some blocks or a jack. Once off, try to take the bolt through the mounting out. These are often seized and need lots of persuasion. Then replace the mount, the rubber covers and the bolt. Put some anti-corrosion paste onto the bolt thread. Fit everything back and adjust. Not really difficult.

George Davis: Chris, I thought the bellows should be pulled up onto the metal part of the mount, so that's what I did, and added a nylon tie-wrap just for extra holding power. I may have hallucinated this, but I think my service manual shows the bellows pulled over the metal. I also sealed the top of the mount to the mounting plate (with Permatex No. 2, I think) to keep oil from seeping in. This way it isn't loose and won't fall off. Assembly was in this order: attach mount to mount bracket, attach bracket to transmission, put bolt and washers into the plate and get the bolt started, this holds the plate up and makes reinstallation of the plate bolts a little easier. I found I could remove and replace the plate without moving the exhaust by using a wobbly ratchet extension.

Walter Klatt: wait a minute here, does the BBB say where the support plate is positioned? Well, you can install the mount to the tranny first and then to the support plate. You can do this without the double jointed contortion acrobatics, by simply lowering the entire engine and tranny as you let the lift down a bit (engine will tilt to the back as the tranny is lowered). You will gain a lot of room to manueovre here as I did. My hands are big beefy ones, imagine the opening in the dashboard for the radio-these hands can't fit in there. Also might want to remove the muffler donuts and drop the muffler-while still attached to the manifold-to relieve the tension buildup when tilting the engine assy.

Cees: I'm about to replace my motor and transmission mounts. The only thing I am not clear on is exactly where to jack up the engine. Several sources say not to do it under the oil pan but don't say where it should be done instead. I would appreciate other people's input and also how much time other shade-tree mechanics like myself have had to spend doing all three mounts.

Walter Klatt: Cees, It should take a shade tree mechanic about half hour per front motor mounts and at least and hour if not 2 for the rear one. The motor should be jacked up with a lift and a section of lumber (2 x 4) that wider than the oil pan. Place the large flat area onto the pan surface anywhere and then the jack squarely under the lumber in the middle and lift away. You should be thankful you're not replacing the motor mounts on a 6.3- I've heard lots of horror stories on how tough they are-needing to remove the manifolds, exhaust pipes, etc.

I have a question for those people that have replaced the transmission mount. The kit included two rubber washers - one thick and one thin, almost like a gasket. The parts breakdown I have shows these parts in the kit, but does not show where they go - above or below the plate. I placed the thick washer above the plate between the fitted metal washer and the mounting plate, and the other underneath between the thick metal washer and the plate, but this doesn't look right.
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