1971 300SEL 6.3 rear diff,Identification

[MAF]

I went to a charity auction a few years ago, and bought a 109 - 300 SEL 6.3.
When I bought it, I could put it in gear,and hear grinding from the rear end, but no forward, or reverse movement.
I took it in to a good shop, and got a repair estimate of 3000.00.
I parked it.
Two weeks ago, my prize appeared at a local wrecking yard.It was a 6.3, that someone had given up on their restoration project.It still had the rear end, and I struck a deal to buy it.It was finally delivered , and I went to a friends shop to begin the installation.
The diff in my car has the special oil tag,but has smallish non-vented disc brakes.It appears as the diff in the Mercedes parts diagram, and has the tag, but is not the same as the diff from the yard car.The friend estimates the ratio at 3.23,(or so).
The diff from the yard car has no special oil tag, but does have larger vented rotors,but has a large,(36MM), eye cast into the top of the center carrier housing,and approx 2.70 gear ratio.
On the car , there is no attaching point for the eye.In the Benz diagram, the eye does not appear.
On the left side, at the bottom of the side cover,but cast into the center pumpkin, below the cover, it says 6.9,on the rear currently in the car.
Any feedback will be much appreciated, I am confused.
Thanks Mark

[Pooka]

I am going way back in my memory here, but I think the original rear brakes on the 6.3 were unvented, and all 6.3 cars came from the factory with the limited slip diff.

It sounds like the one you bought was installed by a previous owner who either could not find or could not afford a real 6.3 diff.

Anything is possible and it could have been order from the factory that way.

If I were you I would get the fuel pump and the self-leveling valves off of this car as they are worth quite a bit. The distributor and the water pump are also unique to this car as are the rear doors.

The air-compressor/power steering pump is also something nice to have as are the stainless door sills.

Pooka

[MAF]

The car in the yard is fairly well stripped.All that you mention is gone with the exception of the rear doors.
Will /should my car run, with the wires off the electric fuel pump in the rear left?
Funny , but my car is missing the sill plates,the fuel pump cover is loose, the wires disconnected, and my Nardi steering wheel is missing, after being at the diagnosis shop.
I would think that the culprit was a random theft, but the Nardi was replaced with a stock steering wheel, and horn ring, and there is a fuel pump in the car, although disconnected.
I thought it interesting that you mentioned these .Someone knew what to get.
Thanks again, for your reply.

[wbain5280]

The early car's discs were vented and the later ones solid. You need to post your question on the M100 forum.

http://www.m-100.cc/forum/default.asp

They are the experts.

[ja17]

Hello,

It sounds like the diff from your parts car is from another MB car. The large "eye" cast into the top of the diff casting is for a transverse coil spring used in these non-air suspension cars. The 3.27 ratio was the 4.5 V-8 sedans of the time. Some 3.5 air suspension sedans also had the 3.27 rear diff with non vented disc brakes, this may be the best guess. If so the differential casting itself is a bit smaller than the original. The original 6.3 diff used around a 2.60 ratio.

6.3s had an appitite for rear differentials with their 450 ft/lbs of torque!

[mercmad6.3]

There are two different diff ratios for the 6.3 but both equate to 2.86-1 . Different teeth counts on pinion and crown wheels does this. There is no external difference in the left hand side of the housing from a 3.5(4.5) and 6.3 ,both Must have the oil cooler tube .The outer end of the tube on a steel spring car is different to a air suspension car in that the caliper moves on bushings to counter act lifting to prevent diving under braking. The left hand swinging side is the same from all W110 right through to the last W109 in 1972(apart from the aforesaid caliper mount.) . there are no different size housings,all are the same dimensions. Axles and sliding joints interchange between all the models ,so if you are lucky and you have just broken a sliding joint,use one from a W110,it will not have suffered from the same abuse a 6.3 hands out.
Vented discs were only used on the earliest 6.3's and discontinued in early 1969. There's nothing special there,they are just Front discs with a spacer between the caliper halves to make it wider to fit on the disc. There is however a proportioning valve in the line to the rear brakes. this is mounted under the floor above the diff head. If you want to go to non vented discs,you need to change the master cylinder to a post 1970 type and remove this valve .The vented discs never seem to get hot enough to warrent using them.
Limited slip Diffs Were NOT standard,the first 6.3's only had open drive but many were converted because owners had problems with traction in the wet or simply negotiating steep drive ways.
Most LSD's are only identifiable by the tag ( Sperrdifferntial etc on it) screwed to the housing,but if it was a dealer installed LSD it won't have that,sometimes it's written on the housing in such cases. It's important that the diff come apart for inspection anyway because of the strain imposed on it so thats the best time to check if it has clutches in there and you can check the ratio's thoroughly. You can bolt in a used diff without checking it,but because of the torque of a 6.3 it's a foolish move.
BTW.$3000 is cheap for a diff rebuild,a crown wheel and pinion is $5000 and both outer bearings are $220-$240 each.

The diff from the scrap yard is the 2.7 one? and has vented discs? then it's the correct part for your car. With a 3.23 in a 6.3 you get rocket like takeoff but lousy economy and and top speed is really low.
As Warren says below,a too high idle speed will destroy a sliding joint in the diff,a 6.3 develops 900nm of torque in 3rd and reverse is many times this. Add to this, the idle at 800-1000 rpm and a broken diff soon appears.

[wbain5280]

Pictures would help too.

Joe, I've been reading in the M-100 6.3 forum that some mechanics have adjusted the idle a little higher than it's supposed to be, 600-700 rpm. When adjusted high, the engine generated a significant amount of torque causing differential problems, like the sliding joint gets damaged.

Also, if his rear axle is from a 4.5, there is no rear brake torque compensation and no sway bar hookups. This makes the car dangerous to drive.

[MAF]

I was in a bind, and had the mechanics,(only), rack tied up, and was forced to use the donor rear axle.
It appears all of the sway bar/torsion bar mounts are correct, and in place.I have not seen the car yet,but it is back on the ground, and he pushed it out,as the correct diff oil was not known.I ordered the correct oil ,(for the limited slip rear),from the Mercedes dealer here,hoping that it would work for either the LSD, or conventional rear.
I contacted the wrecking yard, to get the serial number on the donor car, to verify, hopefully through the dealer, that it was in fact, a 6.3, and what year,and if it was LSD.
He called back , saying the previous owner had removed all of the serial plates, but that he had checked with his favorite independent shop, and the guy said to use the "heavy hypoid grade".
The two rods , on the valves, in the rear - for the air suspension, have some rather interesting bends in them, and I am wondering if they started life straight?
The other problem is the bags were full, when he removed the old rear end, and now the car sits high , in the rear.
These current guys are in over their heads,(as am I), but at least I am sure no more of the car will disappear at this shop.
Are there any precautions I should take, in consideration of the rear bellows, or will they take care of themselves, after the car starts?
The car sat fairly well, and the positioning valve seemed to work , for the brief time I ran it , to air up, to get in the shop.
After reading on the 100 forum, I had the guy drain the fuel tank, and put in 5 gallons of 91, and one fourth quart of transmission fluid.
I changed the oil,(drained the cooler too), put in a new Dealer filter, and ordered a fuel filter, to be installed Monday, with the LSD oil.I used 10/30, it is 38 for a high Monday.
I very much THANK YOU ALL for your guidance/ expertise.
Anything I forgot?

[MAF]

Sorry, one other thing I forgot to say.
The broken part, in the rear diff, was identified as part number 112 350 06 13
It was said to cost 920.00.This, and a new axle boot, are the only problems with the rear that was in the car.I have saved, and will carefully store,(inside) the old rear, as I will probably fix it , and save for future use.
That part replacement, (and probably a new boot), were the only repairs to be made, for the 3000.00.
Is that the "sliding joint"?

[mercmad6.3]

Do not use heavy Hypoid oil in a LSD . it will destroy the clutches in no time. Use only the approved mercedes LSD oil . It's seriously expensive but cheaper than a diff rebuild.
Yes,it sounds like the sliding joint Broke and keeping the extra diff is a very good Idea.
There is only one link on the diff for the air valve. Do you mean the sheet metal arms which connect the diff to the torsion/sway bar? .Just hammer them straight if they are bent.
If the rear is sticking up ,what position is the button for the height control in? It should be pushed fully home and the main valve nder the hood should have the slot in the round disc lined up with the hole in the valve body. If that is OK,it sounds as though the valve which controls rear height is not adjusted correctly.
You should really consider asking more questions on the M-100 site .It's free to join the site and being an actual member of the club gives you a lot of access to better parts prices .In fact you should mention it to your mechanic,several owners have their own mechanics ask qustions on the site to sort out niggling issues with injection and suspension problems.

[MAF]

Upon your first suggestion, I went to the 100 site, and applied for membership.I filled out everything, and submitted, but have not heard back.
So ,I cannot post.
I spent hours , combing the site looking at diff pictures, posts, and any available info, but am handicapped by not being able to post.
Is the LSD fluid suitable for a conventional diff, as well?There is no tag, so it is either a dealer installed LSD, or a conventional.
The two bent control rods, are at the lower points, near the axles, on both sides, and not the main control valve , at the top, that you refer to.
I assumed that they worked the axles independently, as in turns.I am going from memory, as they are closed, and I have not been there since Friday.
When I got the car back , from the first shop, the main control rod,(in the rear- under the car), was disconnected.
The other two rods are the same diameter as the main valve,with ball and socket ends, and are about the size of Solex carb linkage rods.As I recall , only about 6 inches long.
Thanks, and good on ya!

[mercmad6.3]

The LSD oil will work OK .
The rods you are refering too sound to me like the anti lift/dive links which must be bolted to a point in the floor and each side of the diff. The access is gained through removing the rear seat bottom. Theres rubber bushes on the top and bottom of the rods. If they are bent they can be straightened easily enough.
The car was probably sitting high because the link to the sway bar wasn't connected properly.
You sit the car on the deck and using a jack ,lift the car until it looks OK,the wheels on the rear should be vertical.
Then..look at the valve,it has an arm with a 5mm hole.
This hole must line up with a hole in the valve body. Using a WOOD dowel (not a drill or other steel rod!!) fix the arm in this position,
Then ,loosen the arm on the sway/torsion bar.
it should be parallel to the valves arm. You then alter the length of the rod to suit. tighten the arm on the torsion bar and remove the dowel and the valve is now set to adjust the ride height by itself.

The M-100 site has a security problem aty the moment caused by Porno site owners trying post spam. I think it's been locked until the moderators can figure a way to stop them .

[MAF]

I picked up the special order LSD fluid, that I had ordered through the dealer.I am a little concerned, it says 001-989-17-03-10 Transm.oil
On the bottle it says Universal Hypoid gear oil SAE 85W- 90
It is official Benz package,(gray bottle,blue and silver label),but it just does not sound correct, according to our conversation.
It was certainly expensive enough,25.00 per quart list, 20.00 cost.
Any feedback appreciated.Merry Christmas!!

[Arthur Dalton]

Metal tag on differential - translation pls.

[wbain5280]

Those small arms at the farthest part of the axle are brake torque reaction arms. They attach to bearings to which the rear calipers are mounted. During braking, the torque generated is transfered to the short arm and then to the chassis. This downward force compensates for the rear end lift and on heavy braking causes the rear to squat, and since the front end has no anti-dive, the whole car squates on braking.

Those bearings to which the rear calipers and the arms are mounted have grease points and must be greased as must the swing axle joint. The outer grease points are often overlooked causing problems.

The M-100 group will approve your membership soon so please be patient. If you would like, I can post your questions for you.