Mercedes-Benz Forum banner

79 450SL Differential Replacement

6K views 16 replies 8 participants last post by  Ken K (73 450SL) 
#1 ·
I need to replace the differential in my 79 450SL because of extreme wear of teh ring and pinion gears. I have a replacement unit from a used car ready to install.

I would like to be able to change the diff without messing with loosening the axles at the wheels, and hopefully not having to drop the exhaust system (which is new and painstakingly welded!). A local MB mechanic mentioned if I put the car on a rack and dropped the diff (after removing the axle clips inside the diff) the axles would slip out as the diff dropped down.

I would appreciate any opinions on this project.
 
#2 ·
Where there's a will, there's a way.
I think you are asking for trouble though.
 
#8 ·
What do I think?

I think that you think that I know something.

I've got my own problems that I currently can not solve.

But thanks for thinking of me. :)


Firstly....the MB manual will give you guidance. There are few steps that you can deviate from....in other words...few short cuts.

I'm not sure how your axles are installed exactly....but I can picture the geometry of dropping the diff with the potential of the axles falling out.

It's the going back in part that will probably give you grief.
 
#5 ·
The problem might be accessing the 4 nuts on top of the rear subframe that hold the differential housing in place. I don't know if there's enough room to do that without dropping the subframe down at least partially. Removing the axles from the differential is more of a bear then messing with them at the wheels IMHO. Drop the rear shocks out, remove the sway bar links, remove the exhaust hangers and support with longer coat hanger wire to give yourself some room, remove the rear diff mount, pull the axles, remove or loosen the subframe bolts, and slowly lower the subframe down just enough and maybe, just maybe you can then access the nuts on top to make the swap.:thumbsup:

Maybe there's an easier way? I don't know.
 
#9 ·
Ive done the whole 107 rear end and I would certainly not do it in any other method than the factory manual suggests - which is the quickest simplest method.

as for needing some 'special tool' once you remove the bolt (providing it doesn't snap off on you) then all you have to worry about is getting the spline out of the hub. a spray of wd-40 on the splines, a suitably large brass drift and a 4lb mallet will achieve this reasonably efficiently.
The only time the special tool is really useful is when youre removing the hub from the bearing, which is an asshole of a job.
 
#11 ·
A local MB mechanic mentioned if I put the car on a rack and dropped the diff (after removing the axle clips inside the diff) the axles would slip out as the diff dropped down.
Your local mech. is correct. You may still need to remove or lower the exhaust system. You will need a transmission lift or other suitable apparatus to raise and lower the diff. You can also move the diff. from side to side while lowering in order to get the splines out of the diff. housing.

However, removing the shafts completely will give you an opportunity to have them rebuilt or replaced. At 35 years they probably need some attention.
 
#12 ·
Thanks for the info, Steve. A friend who has a big garage is going to "loan" me a lift to do the work, and has a transmission jack. I think now that that is the way I am going to try. If I have a problem, I can always revert to the standard method, now that I will have a lift available. The axles have been worked on in the recent past, so I will probably just need to replace the axle seals in the diff.

You may be able to answer another question - the manual says to use new self-locking nuts that hold the diff in place. Is that necessary? If so, a repair kit costs about $65 with the nuts, and the seals are about $40 a piece, so I am looking at sinking another $140 or so in the rear end.

I had an interesting discussion with an old friend who worked as a mechanic at a used car place several years ago. He said that when they got a vehicle in that had a lot of rear end noise, they would just put a lot of sawdust and extra-heavy lube in the diff! He said that would quiet anything but the very worst situation for a while!

One reason I did not want to address the exhaust removal is I just had a new muffler and cat put in and, since nothing would fit (aftermarket!) the muffler shop had to install two small pipes (the muffler pipes were about a foot and a half too short - makes me think they thought we had resonators on the car), they welded everything from the cat back. The cat pipes had to be expanded a little to fit the exhaust pipes and they clamped the _ell out of them! But, whatever. If I have to, I'll just cut the pipes to the muffler off and have the muffler shop weld 'em back!
 
#13 ·
You may be able to answer another question - the manual says to use new self-locking nuts that hold the diff in place. Is that necessary? If so, a repair kit costs about $65 with the nuts, and the seals are about $40 a piece, so I am looking at sinking another $140 or so in the rear end.
Yep - get the kit - or the equivalent. They're just big nylocks. You may also want to replace the differential mount. The diff. attaches by four heavy bolts to the rear subframe. There's also a diff. mount attached to the rear cover and a body cross member.
 
#15 ·
On the early subframe 4-bolt differential housings it will be a pretty interesting task. on the late 126 housings, it is pretty straightforward, albeit requiring a little persuasion with a pry-bar.

Having done the job before, and trying to do it the way the OP states, I'm not going to say any more. I did indicate in another related thread (trailing arms) the most straightforward way is to do it by the book.
But, to each their own.
 
#17 ·
Just finished swapping my diffy for one I got from Pick-n-Pull several years back.
It had been "clunking" on up and down shifts,
Took 8-9 hours over 2 days. Heavy duty stuff.
The 4 upper bolts were a real pain, 1/2 shaft had maybe 2mm of clearance when removing.
No need to drop the subframe, but ya gotta remove both sets of o-rings on the exhaust system and remove a rear brake line.
Didn't need to pull the other one from the wheel hub
Getting the 4 allen hex bolts reattached on the rear mount was impossible.
Finally used some longer 10.9 grade bolts
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top