Rear Axle Carrier Pivot - The Swing Axle Parts

[Tomnistuff]

Since my right axle is out to replace the seals, I decided to replace the slightly leaking split bellows.  Since the axle is just hanging from the carrier with a cross bar tied across the top of the differential to keep the axles from sagging, I noticed that the right axle has some fore/aft play relative to the left axle and differential.  That tells me that the bushings on which the swing axle swings are probably worn.  I checked the EPC to see how complicated and expensive the parts are before I drop the axle and take it apart.

Chilton's, Haynes, The Technical Manual and the Big Blue Book say nothing about the carrier pin to pin bushing to swing axle tolerances so I decided to ask the experts here,  In the EPC, there are many sizes of shims and washers for fore/aft fitting of the swing axle to the differential along the pin axis.  There are also many diameters of sleeve bushings for radial fitting of the swing axle bores to the carrier pin to the differential bores.  How do I decide what shims and sleeves to buy when I don't even know how tight the pin is supposed to fit in the bores and how tight the swing axle bores are supposed to straddle the differential pivot bore?

When the transverse spring, the rear control arms, the rear springs and the shock absorbers are all installed, I doubt that it would be possible to determine manually whether those bushings are worn.  The control arms prevent fore and aft movement and the combination of the weight of the car on the wheels along with the "separating force" of the cross spring would prevent radial movement of the pivot joint.  It might cause clicking on acceleration and braking.  Because mine was almost completely disassembled, the clearance in the pivot joint was obvious and feels quite large.  How tight should that pivot joint be?

The parts that I will need to buy will be the "Correct" size of parts 13a, 13b, 11a and 11b in the two sketches below (Copied and expanded from Haynes p140 - sorry Haynes).  If the pin is worn, I'll need that too and probably the sleeved rubber pin bushing that the whole thing hangs on.  I can replace obviously worn parts and measure the bores and shafts, but I need the desired clearances to know which parts to buy.

Does anyone have documentation of the specs?

If no one can help with the numbers, I guess I can just fit it to a couple of thousandths and keep it well lubed.

Tom Kizer

[George Des]

Tom,

Can't answer the questions regarding the specs but I can tell you that this is a job that takes some time and ingenuity in fitting the parts back toegther properly. Take lots of pictures as you are taking it apart as there is a specific order and direction for the shims and oring seals that is easy to forget if not well documented. The installation of the pin can be troublesome and I found that it was necesssary to use some dry ice to shrink it before installing it. Do not pound on the end of the pin to fit it. it will mushroom fairly easily making the fitting of the shims and large washers impossible. I also recall I used an adjustable reamer to enlarge the bushings just slightly enough to get a snug fit. If you are going this far in disassembly, do youself a big favor and ditch the split boot in favor of the solid boot. Hope this helps.

George

[Tomnistuff]

George,

I understand the Haynes manual`s instructions to "drive" out the pin using a pipe as a drift, since there is no other way to get a handle on it once all the clamp bolts are loosened, but I would never have thought that anything would be press-fitted in place.  My experience with bushings is that they are never press-fitted to the shaft on which they rotate.  I can understand that the sleeves might be lightly pressed into the right swing-axle housing, which already has bushings, but I would not have thought that the pin would be pressed into anything.  I thought that's why they designed in the tapered bolt key - to keep the shaft from moving once in place.

Until I know exactly what's going on inside that pivot joint, I'm not going to take anything apart.  I swung the right axle tube fore and aft to check the clearance in the pivots.  It appears that the total travel of the axle tube at the brake flange is about 3 mm.  Since the axle tube is 26 inches long and the span between the pivot pin bushings is 6 inches, that means that the clearance in each of the two bushings is about 0.35 mm (0.014 inches).  It also feels like the joint is completely dry.  I feel no grease resistance in the joint.

OK!  Here's an update.  I just went into the garage and grabbed my grease gun.  Three hand pumps with my mini-gun in each pivot bushing grease fitting made a big difference.  I can no longer make the end of the axle tube move fore and aft in the car relative to the other axle tube and differential.  By the time the compensating spring, the rear control arms, the springs and the shocks are installed, the system is going to be quite perfect, I think.  I'm just going to leave it alone.

For sure, unless I detect a problem driving it, I'm going to just keep it greased and pretend it's perfect.  If I subsequently find a problem, I'll take it to a highly respected Mercedes mechanic who used to work for the Mercedes Dealer and did all the old models.  In fact, he wrenches on all the old models for the dealer.  I don't want to start something that I can't finish.

If anyone sees any really big flaws in what I have decided to do, please let me know.

Tom Kizer

[George Des]

Tom,

I need to look at the diagram again to refresh my memory exactly of where there was a press fit on this, but I believe that the pin has two places where there are removable bearing surfaces that ride inside the bushings and this is where the press fit took place. It has been a while since I did this job and it entailed replacing all the differential bearings, the crush sleeve, and the rubber boot. I did this on a spare rear end I have and it was a long job with lots of frustration so your idea of going to someone who has done this before will save you lots of aggravation especially if your car is non operative while you try to work through this.

George

[tel76]

Tom,
You have just made a very good decision,i have today completed the fitting of a new rubber boot  together with replacing the spacers and thrust washers( I did not change the bronze bushes) i ordered from MB the same diamension of spacer and thrust washers that i removed,the pin is a push fit in the axle and should not require much persuasion ie main tool.
If and when you do undertake this job have a dry run and build it up first without the sealing rings so that you get the correct end float in the axle tube,strip it down again and have a cup of tea/coffee before you start the final build as fitting the seals/O rings is a bxxxxrd of a job.
This is the second one i have done in the last two years and i can say it is up there with the most frustrating jobs on the car. :'(

[Tomnistuff]

As I said in my last post (reply #2), I decided to keep the axle carrier pivot pin greased and leave it alone.  But as I was preparing to continue with the right axle seals and put the axle shaft back in, I noticed that the carrier post, the part that goes up into the trunk and hangs from the mount, was up against the front of the hole in the trunk and that the inboard seat of the compensating spring (the horizontal one) was up against the cross-member that the front of the fuel tank bolts to in the back.  This was guaranteed to make lots of noise.

There is a locating dimension for the carrier on the carrier bushing relative to the front of the pinion shaft flange that is supposed to position the axle fore and aft in the car.  It is dimension “a” and is provided on page 35-0/1 of the Big Blue Book, but there is no sketch.  On page 139 of the Haynes Manual, the dimension “a” is given as 158 ± 1 mm and is clearly shown in a sketch as the dimension from a straight-edge laid against the pinion shaft flange to the front surface of the carrier post, about and inch below the lower clamp plate at the top of the carrier post.

I conclude that it is important to get this dimension right, because it controls the fore and aft position of the pivot shaft bolt when positioning the axle using the rear axle centering “TOOL” that has been discussed so much and that is shown in the Driveshaft and Rear Axle / Rear Axle Section of the Technical Manual.  It’s also probably impossible to adjust it after the axle is hanging from the carrier mount.

I had to drop the axle from the car because 1) the weight of the axle hanging on the pivot shaft bushing caused the carrier bushing to compress at the top front and bottom rear, throwing off the plane of the pinion shaft flange and 2) because the measurement point on the carrier post is up inside the hole of the body and therefore inaccessible.  I dropped the axle (not literally) to measure dimension “a” and found it too big by 20 mm.  It’s possible that my body restorer moved something when he removed the axle to put the body on a rotisserie, but it doesn’t matter anyway.  It needed to be fixed.

To correct dimension “a”, the pivot shaft does not have to be moved, but the carrier must be moved on the carrier bushing.  That requires loosening the two pinch bolts on the carrier so the carrier (6 above) can slide on the outer sleeve of the carrier bushing (5 above).  I did one other thing to provide, hopefully, a few more years of life to that carrier bushing.  I also loosened the single pinch bolt (4) at the front of the pivot shaft.  Then while holding the carrier post approximately vertical, I used a pipe wrench (located on the outer sleeve about where the number 5 is in the above sketch) to rotate the carrier bushing 180 degrees inside the carrier and around the pivot bolt.  That will put the rubber that is normally in compression, in tension and that which is normally in tension, in compression.  Then I positioned the carrier post dimension “a” from the pinion shaft flange and tightened all the bolts.  Make sure that the inner sleeve of the carrier bushing is still up against the washer (8a above).  It took a bit of hammering to move the carrier on the bushing sleeve but within reason.  If it works like I think, I won’t have to align the axle fore and aft – only horizontally using the locating strut.

I appreciate the advice provided in the above posts and am happy that I did not have to remove the pivot shaft and replace all the bushings.  By the way, I’m also happy I did not have to replace the carrier bushing  – the best price I found was for what I think was an aftermarket bushing in Europe at 86 Euro.  Most all other sources were from $300 to 380 Euro.  This is worse than restoring Ferraris.

Tom Kizer

[mbzse]

 .../... There is a locating dimension for the carrier on the carrier bushing relative to the front of the pinion shaft flange that is supposed to position the axle fore and aft in the car.  It is dimension “a” and is provided on page 35-0/1 of the Big Blue Book, but there is no sketch.../...

Tom, did you examine the rubber in the carrier bushing. Usually this is much worn if it has not been exchanged on a 40+ years old car, and is the prime component to renew. Look at when R Hagenow moves the carrier arm with his hand; 1:58 into this video:
http://www.youtube.com/watch?v=6clvgZBP2tk

The sketch from the M-B workshop manual can be seen in this posting: http://www.sl113.org/forums/index.php?topic=9060.0 
Some more info may be found here:  http://www.sl113.org/forums/index.php?topic=12503.0

/Hans in Sweden
.

[tel76]

Looking at the video it appears that the pinch bolt at the front has not been tightened and the metalastic bushing at the front is turning in the diff oil seal housing front cover,it appears that the front cover is worn.

[Tomnistuff]

Hans, yes, I examined the rubber in the carrier bushing, at least by feel.  With what seems to be similar effort as is applied in the Hagenow video, my carrier post flexes about one degree rotationally and not at all fore and aft.  I say “flexes” because there is not the sound or feel of relative movement like in the video.  In the video, I suspect that there is some sliding of the carrier on the outer sleeve (carrier pinch bolts loose) or inner sleeve on the pivot pin (tel76’s hypothesis of front pinch bolt loose or housing worn) or outer sleeve on the inner sleeve due to deteriorated rubber.  That noise has to be coming from relative movement somewhere, not just rubber flexing.  Mine feels like I would expect a new one to feel - tight and stiff.

Before reinstalling the axle in the car, I need to remember to re-loosen the carrier pinch bolts and adjust the angle between the carrier post and the left axle tube to ninety degrees (nominal camber = 0 deg. +/- 30 min.) so that the carrier bushing rubber will not be torsionally pre-loaded with the car just sitting.

Once again, I screwed up.  Normally I search the BBB, Haynes, Chilton, Tech Manual, the DIY sites and the SL113 Forum posts before posting problems and/or solutions.  This time I forgot to search the Forum.  Thanks for reminding me.  I checked the first four but forgot the forum search.  Eventually, if not already, there will be accumulated enough posted material to justify an Axle Carrier amendment to the great axle stuff that’s already in the TM.

Eric, you may be right about the front pinch bolt in the video, but I think that fore and aft flexibility has to be coming from the deteriorated rubber in bushing.  It does not appear to me that the sleeve is sliding fore and aft on the pivot pin or that the carrier is sliding fore and aft on the outer bushing sleeve.  It appears to me to be a fore and aft angular movement - air where rubber ought to be?

You guys are very generous with your knowledge.  Thanks.  I love this site.

Tom Kizer