rear end swap 4.08 to 3.27

[George Davis]

John,

I replaced the strut bushings a year or so ago, and it hung up the same way.  I had to remove the big nut on the upper end of the strut, pull off the upper bushing and then pull the strut shaft out, downwards toward the diff.  Reassembly was the reverse, basically assembling in place.

Use a good pentrating oil or something on the nut and strut threads to lubricate them as you remove or tighten the nut, it's easy to deform the end with the screwdriver slot.

Good luck!

George Davis
'69 280 SL Euro manual

[n/a]

George,

Thanks a bunch for the tip. I was avoiding unscrewing that nut as I'd already had trouble with it and had deformed the slotted end to a degree. I did put penetrating oil on it last night, just in case. I'll try gripping the bolt with padded Vise Grips to see if I can break the nut free w/o and further distortion of the slot.

John

quote:Originally posted by George Davis

John,

I replaced the strut bushings a year or so ago, and it hung up the same way.  I had to remove the big nut on the upper end of the strut, pull off the upper bushing and then pull the strut shaft out, downwards toward the diff.  Reassembly was the reverse, basically assembling in place.

Use a good pentrating oil or something on the nut and strut threads to lubricate them as you remove or tighten the nut, it's easy to deform the end with the screwdriver slot.

Good luck!

George Davis
'69 280 SL Euro manual

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[n/a]

I was unable to get the outside nut off the locating strut and mangled the threads up pretty good trying.  In frustration, I kept trying to pry the assembly out from different angles with a large screwdriver. It finally popped out and is sitting, fully disassembled, on my bench. Hallelujah!

I’m assuming that the strut rod is supposed to have that bend in it. I’ll get it reassembled this evening.

Now it’s time to get the new hand brake bits installed on the axle. If that goes well, I should be able to lift the axle back into place this weekend.

Or not!

John


John Livingston
Newport News, VA
1968 280SL 4 speed manual

[n/a]

One more thought on the strut:

This is one place that an impact wrench would've saved the day, I think (mine was stolen last winter, alas). A deep 19mm socket and an impact probably would've had that outer nut off in no time (although clearance under there might've been a problem).

I'm attaching my Rube Goldberg solution on the compensating spring. I used spring-lowering clamps I got cheap on ebay to compress it a bit (it's a John Olson progressive spring), and then put a Vise Grip on the pivoting saddle to help me compress it the last bit before sliding the bolt back in place. Looks messy, but it worked pretty well.

John

Download Attachment: comp_spring-sm.jpg
57.24 KB

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[George Davis]

John,

glad you got the strut out.  Mine has a bend in it, too, although I don't know if it's supposed to be bent or not.  I'll consider yours as evidence that the bend is supposed to be there.

George Davis
'69 280 SL Euro manual

[ja17]

Hello John,
I was just looking at your photo. Be careful, when the swing axle is hinged to the full down position, the internal axle assembly is up against and stressing a delicate part of the differential casting. This somewhat delicate lip is under the large rubber boot clamp. I have seen a sudden jolt actually break off the casting! If you feel through the boot at the bottom you will see what I mean. When the axle is installed in the car, the swing axle is prevented from travelling this far by the right rear shock absorber which acts as a limit to its travel.
Anoter person on this list recently discovered that their newly installed differential had accidentially be cracked in this manner and had to find another differential.

Joe Alexander
Blacklick, Ohio

[n/a]

Thanks, Joe. I've been careful about not letting it swing abruptly since I read the cautions on the list. However, that doesn't mean I didn't do something stupid when uncrating it way back when. I'll feel under the boot and see if anything feels broken.

John

quote:Originally posted by ja17

Hello John,
I was just looking at your photo. Be careful, when the swing axle is hinged to the full down position, the internal axle assembly is up against and stressing a delicate part of the differential casting. This somewhat delicate lip is under the large rubber boot clamp. I have seen a sudden jolt actually break off the casting! If you feel through the boot at the bottom you will see what I mean. When the axle is installed in the car, the swing axle is prevented from travelling this far by the right rear shock absorber which acts as a limit to its travel.
Anoter person on this list recently discovered that their newly installed differential had accidentially be cracked in this manner and had to find another differential.

Joe Alexander
Blacklick, Ohio

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[Benz Dr.]

I don't think the strut rod is bent. It should be straight or it was bent a log time ago. Could be why you had trouble getting it out.

Dan Caron
SL Barn

Daniel G Caron

[n/a]

The angle shown in the BBB drawing doesn't eliminate the possibility that it was pre-bent. Looks like a factory job, but I'm sure not the expert. I should've taken a pic before I put it back in! I suspect, though, that the bend will allow it to line up better with the mount on the differential housing.

I hate to jinx myself, but I think the axle assembly is going back in today!

John

quote:Originally posted by Benz Dr.

I don't think the strut rod is bent. It should be straight or it was bent a log time ago. Could be why you had trouble getting it out.

Dan Caron
SL Barn

Daniel G Caron

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[n/a]

I've got the axle-end of the hand brake mechanism working smoothly. I dragged the axle back under the car but probably have to wait until I get another pair of hands to help get it on the hydraulic jack and to help steady it as it's raised.

I was looking at the manual and it said to remove the bump stops and then, once the axle's in place, raise each side up until it hits the body. Is that necessary if the axle has not been disassembled?

I'm attaching a shot of the bend in the strut rod. It's not at the best angle, but you should get the idea. Let me know if it looks different than yours.

Thanks.

John

Download Attachment: strut-rod-bend.jpg
76.55 KB

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[Benz Dr.]

It's bent for sure.

Dan Caron
 SL Barn

Daniel G Caron

[n/a]

Darn! Anyone have a good, straight, used strut rod they want to sell me? The new ones ain't cheap!

John

quote:Originally posted by Benz Dr.

It's bent for sure.

Dan Caron
 SL Barn

Daniel G Caron

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[n/a]

Well, I finally got the new, beautifully-straight strut rod. I put it in last night, with the new rubber bits. The end that attaches to the rear housing pushes up hard against the opening, at about 10:30 (see attachment).  I'm assuming it should be roughly centered in the opening. Any way to fix that? I've got a nice, new rubber grommet to fit over the hole and it won't go the way things are now. I don't see any deformed parts/areas that would cause the rod to be so off center.

Thanks.

John

Download Attachment: strut-rod-offcenter.jpg
64.58 KB

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[George Davis]

John,

If you tightened up the nut on the other end, I'd guess it's just the way those odd bushings squished out.  When you put the whole assembly (diff and connector to diff) together, I suggest loosening the nut first, install the boot, connect it all up to align, and then retighten.

George Davis
'69 280 SL Euro manual

[n/a]

Thanks, George. I'll give that a try.

Any suggestions on how I safely lift the rear back into place? I lowered it with my floor jack. I tried lifting it back the same way, with the jack's lifting plate in the concavity on the underside of the differential, but it was pretty unstable.

We're heading out of town for the three day weekend tomorrow. It may thus be a few days before I reply to any posts.

John

quote:Originally posted by George Davis

John,

If you tightened up the nut on the other end, I'd guess it's just the way those odd bushings squished out.  When you put the whole assembly (diff and connector to diff) together, I suggest loosening the nut first, install the boot, connect it all up to align, and then retighten.

George Davis
'69 280 SL Euro manual

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[n/a]

Time for the four-month update!

I broke down and bought a transmission jack adapter from Harbor Freight. They - as usual - took their sweet time getting it to me, but it was durned cheap (http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=507)
Alas, the saddle hole (!) on my old jack wasn't large enough for the adapter, which requires an opening of 1 1/4". Therefore, I had to buy another jack (Craftsman 3 ton, with stands, for $99). Having the second jack on hand proved handy as I used the old one to lift one axle housing while sliding the new jack & adapter underneath. I needed my son's second pair of hands to steady the axle while doing this, but it all went pretty smoothly.

I'll attach a pic of the axle resting on the jack adapter. I'm just using the flat surface, without the ears and chain. So far, so good! (I keep getting timed out on attaching the image. I'll try doing that separately.)

John

quote:Originally posted by johnlivingston

Thanks, George. I'll give that a try.

Any suggestions on how I safely lift the rear back into place? I lowered it with my floor jack. I tried lifting it back the same way, with the jack's lifting plate in the concavity on the underside of the differential, but it was pretty unstable.

We're heading out of town for the three day weekend tomorrow. It may thus be a few days before I reply to any posts.

John

quote:Originally posted by George Davis

John,

If you tightened up the nut on the other end, I'd guess it's just the way those odd bushings squished out.  When you put the whole assembly (diff and connector to diff) together, I suggest loosening the nut first, install the boot, connect it all up to align, and then retighten.

George Davis
'69 280 SL Euro manual

John Livingston
Newport News, VA
1968 280SL 4 speed manual

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[n/a]

Well, try as I might the image wouldn't upload. I put it on a web page in case you're still curious.

http://www.johnlivingston.com/axle_jack.htm

I'd be tempted to put some sort of sticky surface on the transmission jack adapter surface to help keep things from shifting around. Maybe that sort of thing you line tool drawers with would work.

John

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[TheEngineer]

I installed the compensating spring after the axle was in place - but there are often different ways of doing things.

1969 280SL,Signal Red, A/T, P/S, A/C, Both tops.    Ret. engr.

[n/a]

I think the generally accepted way of doing it is your method. I had a real hard time getting the compensating spring in as none of my compressors worked very well on that size spring. I was afraid that it would be a nightmare getting it back in with the axle in place. Having it fully extended like this is not encouraged, I know, but I have tried to be careful about not over-stressing it. I'm hoping to get it bolted back in sufficiently this morning that I can get some jack stands under the axle ends and lift it back to a more normal position.

John

quote:Originally posted by theengineer

I installed the compensating spring after the axle was in place - but there are often different ways of doing things.

1969 280SL,Signal Red, A/T, P/S, A/C, Both tops.    Ret. engr.

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[n/a]

the transmission adapter and jack combination worked beautifully to lift the axle back in place, while allowing me to move the unit around to keep it centered in the opening. It's now got the main, center bolt back in place. I've jacked up both axle ends enough to take some of the strain off, and I've put in the new shocks. I went with KYB just to try something different. Time to go find the bottom shock bolts and get them torqued in. I'll attach (I hope) a picture showing the adapter and jack a bit more clearly, albeit with a lot of distracting clutter around it.

John

Download Attachment: shocks2.jpg
77.03 KB

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[n/a]

I got the axle alignment jig soldered up (sorry for the lousy joints!) this morning and it looks like the unit is where it should be. I'll try to attach a pic of the jig. It took one five foot stick of half-inch tube to put together.

Anyone have any tips on how to get the locating strut back in place and tightened, keeping my alignment as it now stands? It seems that I have to pretty much have everything back in place before tightening the 19mm outboard nut, but then when I tighten that and compress the bushings, it'll tend to pull the axle toward the passenger side and thus out of alignment.

John

Download Attachment: axle_jig2.jpg
56.31 KB

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[George Davis]

John,

I think you're in for a bit of fun.  The locating strut is adjustable, and that adjustment is what you use to center the axle.  The outboard end of the strut has a screwdriver slot in it for turning it to adjust the length.  You have to loosen the locknut that secures the strut to the lower piece.

BUT, with the outboard nut tight it's quite hard to turn and when I did it, the end of the strut got all bent up where it's slotted.  It's pretty weak there.  So my suggestion is: with the big outboard nut loose, adjust the length of the strut somewhat, then tighten the big outboard nut and snug up the locknut and see where you end up.  Repeat until it's centered, loosening the big nut each time.

I've enjoyed reading your axle replacement saga, and am now convinced that I can live with my 3.92 ratio!

George Davis
'69 280 SL Euro manual

[n/a]

Thanks George, for the words of encouragement (?!). I think I'll take a nap and then try fiddling as you suggest. Luckily I got the  mangling of the slotted end out of my system with the original strut rod.

Don't let my epic novel discourage you; it took me something like 13 years to get my BA!

John

quote:Originally posted by George Davis

John,

I think you're in for a bit of fun.  The locating strut is adjustable, and that adjustment is what you use to center the axle.  The outboard end of the strut has a screwdriver slot in it for turning it to adjust the length.  You have to loosen the locknut that secures the strut to the lower piece.

BUT, with the outboard nut tight it's quite hard to turn and when I did it, the end of the strut got all bent up where it's slotted.  It's pretty weak there.  So my suggestion is: with the big outboard nut loose, adjust the length of the strut somewhat, then tighten the big outboard nut and snug up the locknut and see where you end up.  Repeat until it's centered, loosening the big nut each time.

I've enjoyed reading your axle replacement saga, and am now convinced that I can live with my 3.92 ratio!

George Davis
'69 280 SL Euro manual

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[Benz Dr.]

First of all you have to get the axel square. To do this you need to get the centre pin 90 degrees to the axel shafts so that it sits in the car without any undue stress.
What I do is lay the axel on a level floor and shim up the axel until both axel tubes are level  by using a carpenters square. Then I move the center pin until it's straight up and down. Although it may be out a degree or two it's still a lot closer than by eye. I never actually change the length of the cross strut from its original position as I believe that dimension shouldn't change if the rest of the car is straight. A quick check on an alignment rack should be able to tell you if the rear wheels are within spec.
I'm pretty sure there were tools available from the factory that were used to check the basic geomerty of the chassis but no one would have that now, or at least no dealership would.

Daniel G Caron

[George Des]

John

You and I are running somewhat in parallel here. I just today soldered up the same alignment tool to locate the rear axle. I had re-installed my axle some time ago but hadn't gotten around to doing any of the alignments. The car has not been mobile during this time since I had a host of other things I was woking on including the installtion of an A/C system. I did venture out of the driveway and around the block the other day to check some things out and I could tell that both rear and front alignment needs to be adjusted so now I'm on to that. I did notice from your post that you had lifted your rear axle in w/o the trailing arms attached. I had not considered that and had instead lifted my entire rear axle, trailing arms and all into place in one shot. Got to tell you, locating the bushings on the front end of the trailing arms where they mate with the body was a real pain especially since I did not have the centering cones that MB shows as a tool to aid in doing this. It occurs to me that you may have a much easier time doing this the way you are since you will be able to simply jack the rear of the trailng arm up into position on the rear axle and the mating "slot" will be able to hold it in position while you screw down those two big fittings on either side.


George Des