Rear Diff Swap Question- 126s - PeachParts Mercedes-Benz Forum

Graplr · #1 05-14-2010, 10:14 AM

I think I am going to pull the rear diff from an 85 500 SEL this weekend. I believe it has the 2.47?? I would plan on putting it on my 84 300SD with a 3.07.

I assume since they are both 126s, everything should bolt right in, correct? What all do I need to take with me from the SEL? Obviously I will pull the speedometer, but how much should I take from the rear end?

Can anyone walk me through the best way to take one off as I've never attempted this before.
Thanks!
Ryan

vstech · #2 05-14-2010, 10:57 AM

be sure it's an 85 or older SEL... the 86+ diff will not fit.

daw_two · #3 05-14-2010, 10:59 AM

Here's the order of steps.

Block FRONT wheels so car cannot roll.
loosen lug nuts on both rear wheels
jack car up --- you can prop the car up under the trailing arms if you are not removing them.
take wheels off
undo the driveshaft (flex joint) in front of the rearend.
remove the bolt in the center of each wheel hub.
put jack under the rearend.
There are going to be 4 nuts that hold the rearend up to the rear suspension frame.
There are also going to be 4 bolts that hold the rearend mount to the rear frame crossmember.
you have to remove all 4 nuts and 4bolts --- you want to get these loose but not all the way out until the axles are free
Use a 1/2 inch of pipe and hammer to drive the axles out of the hubs (toward the rearend) -- jacking the rearend UP usually helps.
After axles are free, remove the 4 nuts and 4bolts --- lower rearend with axles attached; cable (odometer?) might be attached to the rearend.
To remove the axles from the rearend --- take off the back cover, pull the C retaining clips from the center (axle end in the pumpkin), then the axles slide out of the rearend; BEWARE of the rearend oil.

You might want to verify the ratio by cleaning the "tag" area --- lower driver's side of the pumpkin when looking from the back of the car --- BEFORE you start the process.

Good Luck.

Graplr · #4 05-14-2010, 11:07 AM

Quote:

Originally Posted by vstech

be sure it's an 85 or older SEL... the 86+ diff will not fit.

Thanks for the reminder.

Graplr · #5 05-14-2010, 11:08 AM

Quote:

Originally Posted by daw_two

Here's the order of steps.

Block FRONT wheels so car cannot roll.
loosen lug nuts on both rear wheels
jack car up --- you can prop the car up under the trailing arms if you are not removing them.
take wheels off
undo the driveshaft (flex joint) in front of the rearend.
remove the bolt in the center of each wheel hub.
put jack under the rearend.
There are going to be 4 nuts that hold the rearend up to the rear suspension frame.
There are also going to be 4 bolts that hold the rearend mount to the rear frame crossmember.
you have to remove all 4 nuts and 4bolts --- you want to get these loose but not all the way out until the axles are free
Use a 1/2 inch of pipe and hammer to drive the axles out of the hubs (toward the rearend) -- jacking the rearend UP usually helps.
After axles are free, remove the 4 nuts and 4bolts --- lower rearend with axles attached; cable (odometer?) might be attached to the rearend.
To remove the axles from the rearend --- take off the back cover, pull the C retaining clips from the center (axle end in the pumpkin), then the axles slide out of the rearend; BEWARE of the rearend oil.

You might want to verify the ratio by cleaning the "tag" area --- lower driver's side of the pumpkin when looking from the back of the car --- BEFORE you start the process.

Good Luck.

Thanks daw, I'll bring your notes with me.

Thanks for the note about checking the rear diff BEFORE I start as well.

cirrusman · #6 05-14-2010, 12:00 PM

How about taking some pics in the process? I'm planning on swapping my diff to something like that on my 300SD as well... I'll be folowing this thread too

rrgrassi · #7 05-14-2010, 12:28 PM

Also make sure you can remove the oil fill plug before any disassembly...

charmalu · #8 05-14-2010, 01:35 PM

I would use a brass drift to knock out the axles from the hub, less chance to ding anything up.

the hub to axle bolt is 13mm

Diff mount is 13mm 4 bolts

Diff mount to Diff 22mm 2 bolts

Diff to sub frame 19mm 4 nuts, use a deep socket and a long pry bar to loosen
nuts. once loose I used a short 3/8" ratchet.

Flex disc, 15mm & 17mm open box, a gear wrench will speed things up once loose. some have a hex bolt. think it is a 8mm?

the gasser w126 use a larger flex disc than the W126 300SD. will have to change it.

In the JY usually they don`t allow a jack. when I have loosened the 4 19mm nuts, sometimes the Diff will hang up and not just drop down. I use an old tire and maybe a pile of old carpets under it. use a long prybar and wiggle it loose, then when it drops down it lands on the carpet instead of the dirt and rocks.

Have fun

Charlie

The Gears · #9 05-15-2010, 03:49 AM

If the axle boots are in good condition why remove the axles from the diff. Swap the whole package axles and all. Don't drain the oil, don't remove the rear door. Save your self a lot of time and you wont have to re seal the rear door. Remove the pass side brake caliper, hang it on a wire. With the diff supported on a floor jack or something slide the unit to the driver side and retract the right axle from the hub. Now slide the whole package to the right, down and out. Careful with the axle angle, don't let them fall.
Leave the exhaust system in place. It will support the axle when pulled from the driver side hub. Also don't mess with the center bearing. lower the diff and pull to the rear away from the flex disk.

Graplr · #10 05-17-2010, 11:44 AM

I ended up NOT pulling the rear diff. Someone had already taken the cluster. That is how rare Mercedes are in the parts yards around here. I may go back and pull it but a new rear diff is just not a priority right now and I don't feel like paying $50 to have something sit around in my garage that I may or may not get to. Thanks for all the info about pulling it.

It was indeed an 84/85 500 SEL. The stamp said 10/84. I looked at the rear diff and saw alot of numbers but nothing that I could dechiper what the gear ratio was??

I ended up pulling both mirrors, both headlight assemblies, the bottom panel trim on the outside of the car from the Mercedes. I spent most of my time pulling stuff for my Suburban. I am trying to get the AC working in it. Well, it works, just leaks somewhere. I pulled a condenser (I wrecked mine taking the hose off), and all the hoses in the engine bay. I spent most of Sunday putting the new stuff on the burb. I got it all together and pulled vacuum for a short bit. I have to get a new low side r134a quick attachment for my gauges as it wouldn't go on. So I'll do that today and check for leaks tonight...I'm keeping my fingers crossed the leaks were in the front, which I suspect they were because some PO had spliced in two filters (front and rear ac lines) and just clamped them in the hoses. I'm hoping this is and the ports are where the leaks were.

pawoSD · #11 05-17-2010, 06:08 PM

The 2.47 in the 300SD is nice. We did the conversion to my dad's SD....can go 80+mph at 2700rpm.

daw_two · #12 05-17-2010, 09:40 PM

Quote:

Originally Posted by Graplr

It was indeed an 84/85 500 SEL. The stamp said 10/84. I looked at the rear diff and saw alot of numbers but nothing that I could dechiper what the gear ratio was??

.

The last 3 digits of the stamp on the driver's side lower corner of the "pumpkin" as viewed from the rear of the car provides the ratio. Here's the picture I took of the silver w126 gasser parts car --- please note, it even has the "period" in there. Image has been rotated for better reading.