Rear wheel alignment - leaning in at top >

[FRITZ68]

I was following my wife this afternoon behind her 1968 280SL, and noticed (from behind her car) that the rear wheels were angling in at the top, and out at the bottom - more than I have ever noticed on any car.  We just installed a new set of tires and am wondering if this will wear out the tires, or cause other problems.  Is there any type of rear wheel alignment or anything that I am missing?  Need some advice.  Thanks,

Fritz

[w113dude]

Hi Fritz,

it's your compensating spring or the rubber mount on the rear axle, If you have a heavy load in your trunk will look like that too, If you don't then a new spring or a rubber mount or both will bring it back to original. Most likely its the rubber mount,  this is the piece on the floor in you trunk covered with a plastic dome.

[FRITZ68]

Thanks a lot for the info.  I removed the plastic cover held in place with two small screws (always wondered what  it was) and will be calling Miller's this morning for the needed parts.  I guess I should start first with the rubber mount (whatever it is - my book is at work and I am still at home this morning).

Fritz

[FRITZ68]

I googled this part and it seems like it might be a major job to install.  So far all I have done is remove the plastic cover held in place with the two screws.  Does anyone have any hints or ideas on how or where to start?   We have a lift in our shop.  Are there any special tools required?

Thanks, Fritz

[w113dude]

Fritz,

It really isn't a big job, If i remember it correctly it's held in by for bolts and a large center bolt holding the rear end to the frame, first jack up the diff, so that it doesn't drop, undo the large center bolt then slowly bring it down enough so that rubber mount can be changed , take the four small bolts out replace with new one, lift the diff, place the large bolt in and you are done.

[FRITZ68]

Wow - I was hoping that it could be changed from the top, so will order a new part tomorrow AM and  install it when it arrives.  My wife drives this car, so want it to be right - THANKS!

Fritz

[w113dude]

Fritz,

Nearly all of the work is done from the top, you are just lowering the differential a few inches so that the rubber mount can be replaced.

[FRITZ68]

Status Report - Today the new rubber/metal mount on top of the rear axle arrived from Miller's and we installed it today in our shop - an easy job - the bolts were not rusted and easily removed and the installation went smoothly.  The old part didn't look bad at all, and I am almost sorry that we replaced it, but was hoping for an improvement.

However, the results were not what was expected!   After installing the new part, the inward lean at the top of the tires not only did not improve, it worsened.
Prior to the insallation, using a carpenter square, the inward tilt measured about 1 inch at the 24" top of the square (measured between the outside edge of the square to the sidewall of the tire.  After the installation, it measured 1-1/4 inches out of plumb.  We cannot understand the reason for such a change and are hoping for the reason that this occured. 

I have a repair manual and we found the compensating spring which runs parallel to the ground, but we did not do anything as yet.  Is there an adjustment of that spring?

Any idea for this and also any idea of what step is next?  I am thinking that the compensating spring should be replaced, but it could also be the rear springs, although the car does not seem to sit low in the back.  See attached picture taken a few weeks ago at work.  I do not exactly understand the purpose for the rubber mount, but since the old one looked about the same as the new, why did the lean change?   Also I do not exactly understand the reason for the compensating spring, but am thinking that if there is no adjusment, we should order a new one and install it next?  Before doing so, am in hopes that I can get some input on this.   Any ideas on this subject will be greatly appreciated.

Thanks,

Fritz

[FRITZ68]

Here is another picture taken of car on our lift  - no lean at all - looks normal.  I am now wondering if the compensating spring broke, or the attachment broke or came out of place, or out of adjustment as it seemed to happen suddenly while my wife was driving the car home.  I noticed the lean while driving behind her, and we then ordered and installed the center rubber mount without success.  We will put the car on our lift tomorrow to take a better look, but for now the car cannot be driven, as the inside of the tire (at top) is rubbing against the inside of the fender well.


Fritz

[w113dude]

Fritz,

I have seen some drivers adding rubber shims to the compensating spring that will give it a bit of a lift, but at this point you may want to consider changing the spring with new rubbers, if it has never been changed might be time for it, as for the rear springs, when you put it on the lift should be easy to see if they are broken, but from what I can see in the picture looks to be the compensating spring that is too low. The fact that without any load your spread outwards is a sure sign. but make sure your rear springs are in good shape before going this route.

I have a few old MBs, they all have this in common, the rear wheels tend to stay slightly inward at the bottom without passengers and extra weight, so that when you have passengers or extra weight in the rear the compensating spring will make up for it and level it out, and if the load is too heavy it goes the other way around with lower part of the wheels spreading outward.

Hope this helps.

[FRITZ68]

Thanks w113 dude,

I forgot to mention in the picture of the car on the lift at work in my 2nd post (with rear wheels fairly straight) was BEFORE all this started, but after car was painted.  I do not have the car on the lift today, but I can say for certain that if I took a picture today, the car would not be sitting with the rear wheels looking fairly straight. What I still cannot possibly understand is the fact that after installing the center rubber mount it got worse.  When following the car, it looks as if the rear wheels were going to fall off.  I can hardly wait to get the car on our lift to check the spring - hoping for something simple.  I will be calling Miller's for availability of a new spring, or at least new spring rubbers.

Yesterday, my mechanic raised the car with a floor jack from the center of the rear end and set it back down and it looked perfect.  Then he backed up the car about 10' and we heard a loud snap and the rear wheels both leaned in at the top again.  I am thinking that when this happened, the compensating spring was snapping back into place.  We looked under the car and could see where the inside of the tire had been rubbing on the inside of the fenders.

Fritz

[w113dude]

Did you or your mechanic tighten the large center bolt all the way when you changed the rubber mount? I have a feeling you did not pull dif, arm up all the way, check that first.

[FRITZ68]

You may have hit on something simple - hopefully so. My mechanic installed the new rubber mount yesterday (Wed), and as I said, the inward lean at top of tires was worse then before when he was finished.  He is not at work on Friday and I plan to take a good look at this myself.  We have a shop with lift, floor jack and all the necessary tools.  While it might not be likely that something was missed, anything is possible, and in this case might even be probable.  I prefer to do this myself this time to be doubly sure that nothing was missed.

So tomorrow, I plan to start all over on this, but as I was not there when the first installation was made, am asking for some detailed (step-by step) advice for someone who has never done this before.

First, I remove the metal cover over the center 5 bolt assembly.   Then as I understand it, I jack up the differential with a floor jack.  Then in 8th grade language, can you give me the step-by-step instructions from that point?  Do I first remove the 4 bolts, then tighten the large center bolt all the way with the differential in the far up position with our floor jack and hen tighten the 4 bolts?  After doing this, then lower the differential with the floor jack?

I really need some help on this and am in hopes that this can be explained in simple terms.   After tightening/reinstalling this part, if no change, I will then put the car on our lift and chedk the compensatiing spring and bushings.

Thanks and hoping for some good luck tomorrow.

Fritz

[w113dude]

Fritz,

Don't remove any thing yet, It is also possible that it is not sitting right in place, that long "J" shape arm attached to your differential needs to sit in place this could explain that clunk noise that you heard after installation. Fist place a car jack right below the differential, start lifting a bit at a time and keep looking at the center large bolt in the center of your rubber mount if you see the large bolt moving upwards a bit that would mean needs to be tightened more, lift enough so the rear wheels just start lifting off the ground then go ahead and tighten it all the way.

[FRITZ68]

Wednesday afternoon after realizing that the situation worsened (wheels leaned even further in at the top after installing the new center mound), my mechanic jacked up the car by the differential, and as the car was raised, the wheels straightened out. However we had the trunk closed and the small metal cap installed so at the time, did not look at the center bolt.   When he then set the car back on the ground, the wheels looked just fine, but as soon as car was backed up about 10 ft. we heard a loud click and the wheels were leaning in again.  We then put the car back into our garage, hoping to obtain help on this forum (thank you w113dude)!  My mechanic is good, but his knowledge of Mercedes is minimal, as is mine, but we are learning, as have two nice Mercedes  (this '68 280SL with automatic, and a near mint low mileage '62 220 SEb 2dr hard top with stick shift).

As soon as I go to work today, I plan to do the following - let me know if this is the recommended procedure:

I will first remove the small metal cover over the center new rubber mount and leave trunk open.
I will not loosen the 4 bolts holding the center rubber mount in place. I assume these are to be left alone for the tightening process only.
I will then lift the car with a floor jack with jack under the differential and observe the position of the center bolt (to see if it moves up).
I will tighten this bolt if it lifts up as car is raised.
I will eventually raise car until rear wheels are off the ground and will further tighten the center bolt if needed.

Let me know if I missed anything and thank you very much for the analysis and advice.  I will report my findings on this forum later this evening and am  in hopes that this solves the issue.  If not, I will put the car on our lift next week and carefully check the compensating spring, mounting brackets and rubber bushings.  Millers has a new spring in stock if needed and has bushings in 18mm thick or 21mm thick for about $12 each and it was mentioned that in some caes a metal spacer plate can be machined for additional thickness if needed (if using the old spring). We have a machine shop at work and can handle making such a spacer if necessary.

Fritz

[jameshoward]

Fritz,

A few thoughts from someone who knows the rear axle better than I would like. I suppose that the car brakes properly and that the wheel nuts are tight.

It is odd that your cars wheels are 'leaning' the wrong way. You mention the compensating spring. You should look at it to see if it's okay. That said, I'd find it very hard to believe it could be broken. If original, it's a sonofabitch of a spring. Really long and really strong. It's also a complete bastard to remove. I failed at this task several times and have never been able to do it with the axle in. Your spring rubbers could be shot, but I doubt very much that they alone would make the difference to the telemetry you describe. It maybe that the mount that holds the spring in place may have come unbolted (there are two bolts) but the pressure from the spring on the bracket would make it unlikely that this would come undone. I suppose that the axle does have a spring and not a damper? A quick look will tell you.

I'm not sure I subscribe to the idea that it's the centre mount, because if it was weak wouldn't it present the opposite problem, ie wheels in at the bottom? This might explain why the new mount made the situation worse.

I think you should check the road springs and shocks. Take a look at my thread about the 4,08 to 3,46 axle swap. It has quite a few pics in it that may help.

[FRITZ68]

Thanks James Howard,

I just returned from work and here is what we found:  By lifting up the rear differential, and using a long extension we were able to tighten the top large bolt one turn, but it made no difference of any kind in the angle of the rear wheels. Not having a new compensating spring (as an experiment), we did the following:  We cut 1/2" thick by 1-1/2" wide by about 3" long shims and spread open the compensating spring and wedged them between the coils of the spring. It took four (4) of these to get the wheels lined up properly and the car now sits just about right, with wheels perpendicular to the ground (no lean).  Of course this was not a permanent fix at all, but by adding shims between the coils, we increased the outward "push" on the spring, which temporarily fixed the lean issue.  This also seems to indicate that we definitely need a new compensating spring, which will be ordered next week, along with new rubber ends.  The ends are made in 18 mm  and 21 mm thicknesses, and Kevin at Miller's said that with a new spring, he recommends the 18mm size. 

I am thinking that this spring might be a bear to remove and install and perhaps we should consider taking the car to a spring shop for the installation, as it looks as if it could be dangerous.  If anyone else has any comments, please let me know.  Also of note is that my previous picture of the car on our lift with tires not leaning in at top may have been made after we removed the rear wheels for undercoating the inner fender wells, so until the car was driven, they looked OK.  Once driven, the car settles in and the outward top tilt appears immediately.  Since we have not driven this car over 100 miles since date of purchase, we were not aware of the problem until I followed my wife home one night.

Your theory on the reason that the new center mount probably made the situation worse agrees with our observations today when we took a good look while car was on the lift.  The mount that holds ths spring is perfect and tightly bolted in place - we checked that today.  The road springs may be just a little weak, but we added two small coil lifters to each (another experiment) and this did not do anything for the inward lean at the top of tires.

Back to the drawing board............

Fritz

[mbzse]

.../...I am thinking that this spring might be a bear to remove and install.../...

By means of the self-made tool descibed here, it is quite doable, even with the rear axle in the car (see reply No1)
http://www.sl113.org/forums/index.php?topic=10465.msg69460#msg69460
/Hans in Sweden

[wwheeler]

I used the same tool that Hans showed on my W111 and it worked perfectly. Don't scrimp on the plate thickness. I think 1/4" would be absolute minimum and 3/8" preferable. The limiting factor is how thick can you get between the coils. Use fat fender washers as in the picture under the nuts to help spread the load out. I forget what size all thread I used but 1/2 is minimum and 5/8 to 3/4 preferred. Might consider using grade 5 or 8 high strength all thread and nuts. That spring has a lot of load!   

[jameshoward]

Like Hans said, that tool is in my view the best way to remove the spring, and it's not hassle free. You have to be patient. 1/4 plate is ok, but I'd go for quite thick studding. The stuff I used was probably about 3/8 and it got quite chewed up. Note that the spring is very long. Make sure you use some washer between the nuts and the plate, obviously. I found a flexible ratchet spanner very useful. Start the work with the car supported on axle stands as close to the wheels as possible so the spring is naturally compressed by the weight of the car. Additional weight in the boot will help. (I climbed in at one point). Release the right hand shock absorber at the bottom (on the axle). Once the spring is sufficiently compressed you can remove the right axle stand from the tube (by jacking the car on the chassis and maybe with another jack to slowly lower the right tube gradually letting pressure off the road spring). This should leave the compensating spring compressed and in place. You can then decompress the spring. Just be aware that re-compressing the spring is a pain because it will want to bend in a certain direction whereas you want it to curve to get it to fit back onto the end bracket. Finally, when you remove the right hand shock, the axle will be able to fall freely. There is a risk here of the right axle tube being damaged in that the casting can crack. With the shock removed and the axle swinging free, you must carefully control the movement of the right axle tube. Keep an eye on the road spring, also, as it may want to shift position as the pressure is taken off it. You may want to undo the trailing arm on the right. You'll just need to see how you get on with the compensating spring.

Enjoy!

[FRITZ68]

Thanks for such a complete explanation.  I am wondering if it might be safer and better to have a spring company handle this?   They are more experienced in matters such as this I think.  We are not looking forward to such a job and am glad that all of the risks involved were explained so thoroughly.

Fritz

[zoegrlh]

Fritz,
You should also look at your axle springs.  They too have rubber shims at different MM sizes.  You can add thicker  shims to the axle springs, and this will move the rear end upwards, by doing so the caster (inward slant at top of wheel) corrects.  My feeling is that your conpensating spring is most likely fine.  These springs are hard to loose their strength.  I replaced my rear axle springs a few years ago and this made my caster correct it self.  Might want to check this.  Axle springs are much easer to remove, and rubber shims are still available from MB.
Bob

[FRITZ68]

Fritz,
You should also look at your axle springs.  They too have rubber shims at different MM sizes.  You can add thicker  shims to the axle springs, and this will move the rear end upwards, by doing so the caster (inward slant at top of wheel) corrects.  My feeling is that your conpensating spring is most likely fine.  These springs are hard to loose their strength.  I replaced my rear axle springs a few years ago and this made my caster correct it self.  Might want to check this.  Axle springs are much easer to remove, and rubber shims are still available from MB.
Bob

That is what my son has been suggesting right from the start and he is a good mechanic - rear springs!  We will check into this next week before ordering in anything.  After reading the instructions on the compensating spring, I was not looking forward to that installation at all.  It may be possible for us to do some tinkering to figure out if the rear springs are weak.  We spent months on this car (mechanical, interior, paint, some plating, and wanted a nice little car for my wife to drive.  So far every time she has driven it. something new comes up.  Hoping to finally get it in shape for the summer.

Fritz

[jameshoward]

Fritz,

Watch this. It will help. http://www.youtube.com/watch?v=olXCAagF5yI

You don't need a specialist to remove the comp spring as the tools have been identified below. It's just a pain of a job to do, so you pays your money, etc, etc.

There are a few techniques for removing the road springs, and if you haven't done it before, it's probably not a great idea to do it on your own. A knowledgeable friend helped me and now I've very comfortable taking them on and off. If your son is a mechanic he will, of course, know what to do.

I already suggested that you look at the road springs. The you tube video will give you all the info you need on rubber spacers, and then you can take a look at yours and report back on what you find.

Good luck.

[FRITZ68]

Today we successfully removed the compensating spring, using a setup as shown on this forum.  Here are the specs of ths spring uncompressed on our bench: 13-5/8" long by 3-5/8" outside diameter and 12 coils almost 1/2" thick.  The one end of the spring had two small red painted marks. 

We then placed it in a fixture, and using an all-thread and two metal plates, compressed it to about 9" so that it can be reinstalled, which allows about 9-1/2" spacing.  I can tell you that compressing this spring further might not be possible.  The original rubber spacers look decent, although not perfect. We were planning on banding the compressed spring before inserting it back into the car, and after attaching in place, removing the bands.  The spring looks good and seems to be very strong.  We are leaning towards adding a small round shim at each end to give it a little more push and reinstalling it.  

Any ideas on how thick to make these shims?  W were thinking about 3/8" to 1/2" thick each. I do not feel that this spring itself needs replaced, although it is not easy to determine.   

The two rear coil springs may need replaced (not sure as yet), but we want to first install the compensating spring to see where we are at.  So far we added 4 of the small spring inserts to give the rear coils a lift.  I called Millers today and was quoted a price of $259 each for new rear springs!   

So we plan to handle this one step at a time - first add the compensating spring with metal shims at each end and install it.  Then see the results.  If still too much lean, will probably add more spring inserts in the rear coils to see if the wheels line up.  If this does the trick, we will then be ordering new rear springs.  Eventually hope to get it right.   '

This all was an unexpected experience, as until I followed the car, we were not aware of the problem. 

Fritz