I see now. Thanks a lot for your help.


From 35-110, "1. Completely remove rear axle together with rear axle carrier (35-010)."

I saw the "remove rear axle", and thought "ok, skip that section, I will leave the axles in". All those sections equates to a lot of reading and tonnes more steps.

I have now relubed my four trailing arm bushings and 2 sub-frame bushings with KY jelly and pressed them in. It was much faster the second time.
The status is now the same as noted previously, except I have not yet re-bolted the trailing arms to the sub-frame.

These are the steps I believe come next. Please correct any step that is incorrect.

1. Re-bolt the 4 trailing arms to the sub-frame, but leave them finger tight.

2. Place a hydraulic jack under the centre of gravity of the differential (with axles, sub-frame, and 2 trailing arms connected). Jack it up until the output shaft of the diff. is at riding height.

3. Remove 4 bungee hangers for exhaust and tie a string around the back of the tail pipe so that the pipe hangs down as much as possible without any resistance. Find a suitable location to attach the other end of the string.

4. Remove the 4 diff. mount bolts (or should I just take off the two larger diff-to-mount bolts instead?)

5. Lower the jack stand to a height that allows access to all 4 trailing arm bolts.

6. Use a second jack (the Jeep's in-car jack) to raise one of the trailing arms until the left axle shaft is horizontal.

7. Use a third jack to raise the other trailing arm until the right axel shaft is horizontal. Note that I do not have a third jack, so I will need to use a jack stand to rest the 1st axle on after it has been jacked up.

8. Use a carpenter's level to ensure everything is horizontal and perpendicular. Use string meaurements to ensure both axles are square.

9. Torque the 4 trailing arm bolts to 89 ft-lbs.

10. Jack up diff. and reattach diff. mount

11. Place coil springs and shocks back in.

12. Bolt sub-frame mounts in. Not sure how I am going to do this yet. I am only familiar with the lift-one-side-at-a-time method.

13. Re-attach e-brake cables at centre coupling.

14. Reinstall callipers, rotors, driveshaft. Set e-brake tension.

15. Proceed to a tonne of other work needed on this car before the weekend ends.

EDIT: to go along with #5, I need to know what the verticle tilt angle is of the diff. output shaft when the vehicle is on all four wheels. This is needed to establish proper ride tilt of the diff/subframe. Since my vehicle is taken apart, I cannot accurately measure this. The best I could do was to angle the diff. up using a jack such that the subframe mounts hit the chassis. Under this condition, I get that the diff. output shaft is tilting 2.5 degrees upward (+-1 deg. - accuracy of the device). Can anyone confirm this? Here is a photo of my setup. Thanks.
Attachment 123473

WOW hmmm OK

The four 13 or 14mm bolts for the differential mount are the best parts to remove. The big bolts that go in to the differential are often buggers to get undone. So do the easy thing!

Forget the string and angle gauges this isn't precise science. This is just automotive mechanics.

Lower the differential so that you can lower the whole subframe - if you need to remove the exhaust then do this at the manifold and drop the whole effing thing out of the way

Then using your MK1 eye ball - or if it is difficult to see use a spirit level - to raise or lower the trailing arms and the sub frame so you can tighten up the trailing arm bolts. As you are working under the car you might find it better to raise the car some more rather than messing about with the trailing arms and the subframe.

You don't have to worry about the angle of the differential with respect to the true horizontal - that's not the point. Imagine looking through wheel hub to see the output shaft of the differential - that's all that is important - a straight line from one hub centre through the centre line of the output shafts of differential to the other wheel hub centre. The sub frame could be at any angle you choose as can the differential to help you tighten those pesky bolts - it doesn't matter only that line of alignment matters.



Then lift the sub frame and trailing arms etc etc etc up into position on the car - alternatively lower the car onto the other bits - which ever is easiest.

Make sure you can see the wood for the trees.

I have found that approximate positioning of the sub frame with jacks is the best you can expect. It is then much quicker to man handle lift and push one corner of the sub frame "triangle" into position - hold it in place with a bolt => do the next corner => do the last - then go round and tighten it all up.

{We'll talk about wheel alignment AFTER you've got the effing thing back toegther!}

I am measuring the differential output on the pinion side, not the axle side in this image. The objective is two-fold. 1) The front-to-back of the differential needs to be at the angle that it would be in while the car is on its wheels. 2) The axles need to be horizontal while the front-to-back of the differential is at its normal position (no angling).

If your front-to-back line of the differential (I'm using the output shaft from the pinion as a measurement) is not at its normal tilt, then even if the axels are horizontal, then the trailing arm bushings will not be at their normal resting position as when the car is on its wheels.

Are these statements correct?

There are probably a multitude of angles the front-to-rear of the diff. can be in, say +-20 degrees, whereby it is still possible to make the axle shafts horizontal. In each case, the trailing arm would be tilted differently on the trailing arm bushing/subframe.

So what did you do to determine that your diff. is tilted in the proper front-to-rear directions? Should the pinion output shaft be completely parallel with the ground? Or angled up or down a bit? And if so, by how much?

I will likely put a jack stand under each of the sub-frame bushings and a jack under the diff. centre and drop the whole assembly down. Then shim up or down the jack stands and diff. to achive the proper angle. Once that is achieved, I'll set the axle shafts horizontal and square.

Unfortunately, the FSM doesn't show a side profile of the diff. to see how they are angling the pinion output shaft relative to the ground.

No!

Please stop thinking about the angle of the dangle on the differential.

Once the trailing arms are fitted to the subframe and so long as the differential is fitted to the subframe that's all that is needed for the next step =>

http://www.peachparts.com/shopforum/...ent-35-110.jpg

Look at the screen shot you posted - the diagram shows the straight line running from one wheel hub to the centre line of the differential to the other wheel hub.

That's it.

It is as simple as that!

You can tighten the trailing arms to the subframe with the differential fitted at any place - New York - Rio - London - Paris - anywhere! The subframe and the trailing arms and the differential do not have to be anywhere near the car for this step.

Thank you for your response.

It does not have to be an angle of dangle. The whole assembly could be resting on a level floor and there will still be some tilt associated with the diff/pinion shaft.

The proximity to the vehicle is unimportant, however my focus is on what the axial tilt of the diff./pinion output shaft should be. Did you have your pinion output shaft horizontal with the floor when you torqued your trailing arm bolts?

Am I correct in deducing from your response that I can have the diff/subframe tilted up or down at any angle, say at a 45 degree angle with respect to the floor, and tighten up the trailing arm bushings so long as the axel shafts are horizontal? I just want to be clear on this point.

I am also deducing from that FSM 3D drawing that the forward/backward tilt of the diff. pinion is parallel with the floor, however I do not know what they are using as a reference point. The diff. is not a symmetric square box, so I am using the pinion output shaft as a reference level.

When I look at that drawing, I can imagine tilting the axel/subframe downward, while still holding the axel shafts horizontal. The twist occurs at the trailing arm bushings, which implies the forward up/down angling of the diff/sub-frame is important and should be fixed in a position that is the natural resting position of the vehicle. What is the angle of the pinion output shaft with respect to the floor in this condition?

Can someone explain if there is something wrong with this logic? I would like my logic to be incorrect. If it is, I can leave the axle assembly on the diff. mount, angle the diff. down just enough to reach the trailing arm bolts, and torque the bolts after leveling off the axle shafts.

In this picture

http://www.peachparts.com/shopforum/...ent-35-110.jpg

The "Z" axis going into the picture and coming right at you would indeed be horizontal or orthogonal to the "X" and the "Y" axis...

...but that's not the point - the differential is fixed by four bolts RIGIDLY to the subframe. The trailing arms are fitted TIGHTLY to the subframe. The trailing arms go up and down and pivot about those TIGHT fixings. All you can do is align the centre of the wheel hub to the centre of the differential output shaft.

That's it.

I know what why don't you drop the subframe - fit the trailing arm and the bolts to hold it in place and see if raising the differential when it is RIGIDLY bolted to the subframe makes any difference at all?

At this stage in the reinstallation process, the bolts are not tight - they are finger tight. The trailing arm does pivot with respect to the subframe. The goal is to find the normal ride position of trailing arm bushings with respect to the subframe. This is why I am inclined to think the pinion angle has some importance. On many vehicles, the pinion is pointed up slightly. It may be that +-5 degrees of tilt on the diff. does not play a substantial role with respect to the amount of pivot on the trailing arm bushings prior to torquing. The uncertainty aspect makes me want to set that pinion angle to within +-5 degrees of horizontal before torquing the trailing arm bushings. This requires more effort on my part but brings peace of mind.

I think you just need to do it. Go and do it - make sure the axles are the same as they are in the first picture of your screen shot and you will be fine

http://www.peachparts.com/shopforum/...ent-35-110.jpg

I will be doing it this afternoon. Everything will be square. I had hoped for a broader range of feedback on this subject, but looks like I am out of luck.

It will be awkward torquing to 89 ft-lbs with the whole assembly held up with jacks and jack stands. I was hoping to leave the diff. mounted to the back of the car, but then I won't get my +-5 degrees. Oh well, maybe I can get my wife to hold the assembly still while my head is under there with the torque wrench.

sweat it not...
 

feipoa, I can add a bit to the range of feedback on this, having just done this job - finished a couple of days ago...

I wouldn't sweat it too much. I think your objective on reassembly of those trailing arms should be simply good enough when positioning them; I wouldn't go too nuts with it. FWIW, I just put mine together with the subframe and diff mount completely unattached to the car.

Then, progressively: Started jacking the diff/subframe assembly up, got the springs in - no spring compressors, btw - then put the rebuilt axles in... Continue jacking, adjust positions, jostle, rinse, repeat, etc. Emphasis on adjusting and jostling...

My read on the FSM procedure you've been using? : It's just (probably) intended to get those bushings roughly at the center of their normal range of play; IE, good enough. I wouldn't over-think it...

As a point of discussion, perhaps? : It does seem a slightly weird design on those trailing arm bushings; that, when installed, the bushing races seem to put quite bit of pressure on their corresponding mount faces. This seems to set up a lot of rotational stress on the internals of the bushing. Or, I've got it entirely wrong, and the bushings begin to rotate freely after a few miles of driving...

As to the ±5° vertical position of the diff (in the sagittal plane), I don't think I'd worry about this at all. As Stretch as pointed out, once that diff is bolted to the subframe, it's essentially rigid. The only play will come from the very little the diff mount and subframe bushings will allow; you've presumably replaced these as part of the project. I can tell you my car feels better than it has in 20+ yrs.

Bolt the diff to subframe, line up axle holes - eyeballing across the diff - and you'll have the trailing arms roughly level. Tighten those bad boys up. You're done.

Really good German Design going on here. More and more clear with any project I do on this car.

I really appreciate your feedback. It is possible that my background has enspired me to be overly particular in this regard. I am accustomed to designing more precise instrumentation.

I do not beleive the bushings begin to rotate freely. I could be wrong, but I beleive they are always under some amount of rubber twist when not resting in their torqued positions.

The +-5 degrees is only for initial torquing to obtain zero bushing twist while the car is at normal ride position (I'm using the pinion angle to establish normal ride position along with the axles being horizontal). The subframe and trailing arms are only rigid once torqued. They move freely before being torqued, which is why I beleive the pinion angle is of importance.

If the trailing arms and subframe are not square to normal ride position, I beleive that the "very little" play which would normally exist will be forced to twist more and wear the bushings out faster. This is in line with what I beleive Whiskeydan was talking about here "Trailing arms in the same resting position as it would be with the weight of the car off the jacks. Failure to do this will result in early trailing arm bushung failure."

This is what I ended up doing...

I left the diff. mount on with the diff. bolted to it under the car. I then tilted up the pinion side of the diff. with a jack to make the diff. as level as possible while still having wrench access to the outer-most trailing arm bolts. I leveled off the axles with jack stands. I measured the pinion angle at 0 degrees to the ground. I estimated the pinion angle is typically at around +2.5 degrees from the ground (pointing up) when the vehicle is on its wheels. I'll measure this angle for certain when I put it back on the ground. So the 2.5 degree mis-match was a satisfactory compromise for me. Otherwise I'd have had to find a way to adjust the angle without the diff. mount on the car as a helping hand. And this would equte to more work, more time, more upset wife.
Attachment 123542

I then torqued the 4 trailing arm bolts to 89 ft-lbs. You can just barely access the back nut of the outer-most trailing arm bushings with a combination wrench with the sub-frame assembly in this position. That was the tricky aspect, but I was able to torque it all down. Time to move on.
Attachment 123543

I think we're in the same boat there - the beauty is that the car projects distract me from all the other stuff for a few hours. Then I get to drive it!

My point on that was that - it seems to me - the geometry is completely fixed once the trailing arm bolts are in place. IE, with the TA rotating in the only plane it can, and the differential mounted to the subframe, the 'subframe aligned position' can be determined by aligning three holes. Seems to me this could be determined irrespective of the assembly's position in space.

All those angles and procedures in the FSM seem to me to be The Party Line; the (shop-based?) Stuttgart Method - because there must be one in the FSM! (But just look at all the home-brewed approaches on this forum to any number of procedures/tools).

This confused me a bit. With weight off the jacks - IE, with TAs in neutral, loaded position, my axles are not quite level - as a function of the spring buffers installed (also new). On the other hand, this neutral position - which I take to be the center of the arms' normal play - seems to me to be precisely the correct angle at which the TA bushings should be torqued. This is the reference position I used.

Let's compare notes on how our TA bushings wear over the next 20 yrs(!) FWIW, the ones I took out looked completely serviceable, having been in the car since '83. True also of the subframe bushings, btw.

I'm glad to read you got the job done - I hope it works out for you.

I've been trying to find the specification for the relative angles between the transmission, each side of the propshaft and the differential. There is a specification for this somewhere for the W123 but I guess it is in WIS. So it is hard to reach.

I have found it for the W201 and the W124 system which is a similar system although the subframe mounting is slightly different (still resiliently supported). The limits for this are a fraction of a degree. Chapter 41-085

I think your assumption of 2.5 degrees is way off. If you consider the drive line design that incorporates a single universal joint there's no way you'd allow your differential to droop that much you'd be getting universal joint induced vibration.