That was how I first looked at the situation and even came to that conclusion earlier on in the thread. But once I tought about it more, and played with some of my daughter's legos, I realised that the issue was further complicated since the axle was free to spin relative to the differential. This led me to beleive that the trailing arm bushing position has a dependent positional relationship to that of the forward/back tilt of the differential, which is independent of horizontal nature of the axles, meaning that the positional nature of trailing arm bushing is a function of two variables, namely the up/down axle positions (x) and the forward/back tilt of the differential (y). It could be that (y) is of significantly less importance to the bushing positioning compared to (x) and that the FSM assumes that the most obvious position for technicians to setup (x) is with (y) relatively parallel with the ground.


If the original Mercedes engineers were as particular as I am, they may have determined the horizontal position of the axles based on the median of the vehicle's anticpiated life expectancy. If they determined the vehicle had a typical service life of 20 years, they may have assumed the spring and bushing sag ride height at 10 years and found the axles to be horizontal in this situation. It is also possible that they took the ride height when all suspension components were new and noticed that the ideal axle position was, say, +5 degrees, but felt the difference between 5 deg. and horizontal positioning was negligable.

The trailing arm bushings I removed seemed fine as well. I only elected to swap them because I was changing the springs, spring pads, sub-frame bushings, diff. mount, front suspension components, etc. My sub-frame bushings were cracking, as was my old diff. mount. I have a '79 though.

I'm afraid that in 20 years, our comparison may not be of much value since I no longer drive this vehicle much after obtaining collector status licence plates. 1000 km per year max.

Do you know what type of lube to use on the centre sleeve bushings on either end of the drive shaft? FSM says to lube it, but I could not find the page in the online CD which specifies the lube type.

I wouldn't be surprised if the measurement was way off. I was unable to take the measurement with the vehicle on its wheels. This measurement was taken while jacking up the diff. until the sub-frame reached the underbody. This is all while the chassis is supposed on 4 jack stands. Consequently, I measured again and noted the diff. pinion pointed 4 degrees upwards from the ground. It is very unlikely that my 4 jack stands are leveled at the vehicle's normal ride height.

If someone has one of these cheap magnetic angle finders, like that shown in the photo, could you place it on the rear section of your drive line and check the angle? I do not plan on measuring this until I reinstall my drive shaft, which is waiting for new flex discs.

I see what you are trying to achieve but I think you misunderstand how the design works.

The angle of the differential is dependent on the ride height of the car - that might not be correct - it is most likely that even if you could get everyone to measure their differential angles you would find quite a large degree of variation between the results. At best you'd get a ball park figure but that is in no way as meticulous as the design made by Mercedes.

Mercedes give specifications in fractions of degrees - you are considering angles that are at least ten times as big.

The only way to work out if the subframe and the rear mount on the differential is not sagging too far is to measure the angles between each joint in the drive line.

The method is to measure the angle at the gearbox / transmission - then the front section of the propshaft - then the rear section of the propshaft and then the differential. Special tools / attachments are meant to be used to make sure a reliable angle is measured for each part. The difference between each measured angle either side of each joint in the drive line is then calculated and compared with the specifications as determined by (meticulous) Mercedes.

The point of this exercise is to check whether the drive line is straight - if it is not - the single universal joint will induce vibration.

I don't see this as at all relevant. (If you mean: position of TA bushings is dependent upon forward/back tilt of the differential) I'd have to say no. Once the subframe and diff are mounted in car, the diff is rigid - ±only the infinitesimal give in the bushings. Again, I'd have to say no. The position of the TA bushings is entirely dependent on the axle position with respect to the differential, and on nothing else. No. Yes. No.I don't see this at all. I think the angles you are wrestling with are intended, collectively, to be a template for understanding the system as a whole, for use with the entire assembly out of the car. They provide a frame of reference for relating all the components in space. I'm sure there is someone, somewhere, who's done this project in a shop, with the entire assembly on a stand of some sort, for whom all those angles were a useful tool. I think you're way over-geometr-izing this.

So you would have no problem letting your diff./subframe tilt down, say 30 degrees, making the two axles horizontal (with diff. still at 30 degrees), and torquing the trailing arm bushing bolts?

I cannot see it not having an impact on the normal ride orientation of these bushings. I would prefer to level off the diff., make the axles horizontal, then torque.

You know what I probably wouldn't do that because it isn't convenient but so long as the differential is RIGIDLY attached to the sub frame it doesn't matter - the angle you are measuring is not relevant. Like I said before you could do this task anywhere you choose - it is independent of the chassis and the differential angle.