sagging springs tire wear how to
 

I have searched and read plenty but there was not a one-stop thread
on how to check for sagging springs and how they contribute to inside edge tire wear on rear tires.

So my first question:

How tall should the springs measure to at rest, out of the car ?
Is this a false sense of security , meaning even at rest if at acceptable
length can the spring have lost some energy and is it prone to sagging
when put under load ?

How to measure the car for proper height and to determine if the springs are likely needing to be replaced due to sagging.
Doing this measurement with the springs in the car .
Where to measure, how high should it be. I have stock size 195/70/14
tires that are new (if that matters).

My 300SD has just crossed 400,000 miles. The last two sets of tires
lasted half life with inside edge wear.
After two alignments the problem persists.
I suspect that sagging rear end has caused negative camber.
So much so that it cannot be adjusted out, and I do not want to adjust
it out, I would prefer to replace worn parts and restore car to proper spec
and get even tire tread wear.

I have read some really good posts discussing the potential for worn rubber
bushings, differential mount, body bushings at rear sub-frame, and
rear bearings - all being contributing factors in the inside edge rear tire wear.

This weekend I will remove the springs and measure them.
I thought about using coil spring spacers instead of doing a complete spring
replacement - would like to hear comments using less expensive spacers
to simply bring the height back. (will fix camber, but not change comfort).

My Bilstein HD shocks have 200,000 on them and will go in to Bilstein for warranty evaluation. Not sure if that affects inside edge tire wear or not.

What I have been reading, springs won't cause tire wear......what is causing your issue is likely the rear subframe mounts.....

To start off - Instead of thinking about spring height - think about camber. The wheel should be more or less be vertical. (0 degrees) You can check this with a builder's spirit level with your car on a level surface.

You can check the uncompressed length of the coil spring by finding the part number and cross referencing this number with the specifications in the FSM.

As cooljay says - most of the soggy bottom is caused by a sagging differential mount and the sub frame mounts.

Three areas to look at before messing with the springs.

Rear differential mount - slight change in height but mostly noticed when changing from fwd to reverse.
Subframe mounts - slightly more change in height but not much.
Trailing arm bushings - definite change in height if they are worn as much as mine were. Hard to tell how bad they are until they are unbolted and lowered. New ones, wow what a difference! From what you describe as tire wear, I would definitely be looking at these!

PS there is nothing to align in the rear of these cars. If some sold you a 4 wheel alignment....

X2 on this ne, where are the adjustments on the rear?

With 200K on the Shocks, time for new one`s.

After I replaced the trailing Arm Bushings and the Sub Frame bushings and Diff mount on the 85 300D, it really tightened up the rear end. Totally different car.

Charlie

Just in case this subject of rear suspension adjustment comes up - it is worth noting that the original suspension does not have adjustment. You can, however, buy eccentric trailing arm bushings that will give you a bit of adjustment. Fastlane used to sell them. I would not want to sit down and scratch my nuts trying to figure out how it would work though - it would be a right royal pain in the arse to do as the trailing arm mounts are at a 60 degree(?) angle to direction of wheel travel; the height of the sub frame plays a part; those bushings are difficult to reach with the sub frame in position; you'd be playing up down up down with the car...

...I think I'd rather do the worse job on a W123 ever - homokinetic axle re-booting...