The owners manual for my 1970 2800cs says my car has a ZF Lok-O-Magic disc type limited slip differential. With the car on a lift, if you spin one rear wheel by hand, the opposite rear wheel does not move. Do I have a non functioning slip differential or an open non slip differential? Did all 2800cs’ come from the factory with limited slip differentials? The attached picture shows the numbers on the differential casing. Do they identify what type of differential I have? Thanks for your help. Dale
2800 CS differential or not?
- Thread starter Dales
- Start date
The S indicates LSD
Wladek
Well-Known Member
It might be an LSD with worn parts inside (dog ears/friction discs/tension springs plates).
11:38 = 3.45 ratio = 2800cs
If it was just a working non-LSD diff your opposite wheel should spin other direction while hand spinning of the first one.
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Time for a burn out in front of your least favorite neighbors house.
count the stripes…
count the stripes…
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Yes, the differentials need a certain amount of torque before they will lock.
Thanks to everyone for your help. So I have a nonfunctional LSD. The S= LSD. The 11 38 = 1:3.45 ratio = 2800cs. Does anyone know what the 3 stands for or if every 2800cs left the factory with a LSD? The car is on the lift getting other mechanical work done, so I can’t aggravate my neighbor with a burn out. Thanks again, Dale.
If you divide 38 by 11 you get 3:45. This is the ratio of the number of teeth on the pinion gear (11) to the number of teeth on the ring gear (38).
BMW did ship differentials with 0% lockup. If you look inside the top hole, you can see the carrier, but when disassembled, they have spacers instead of clutch plates and they do not lock up. The one I have does not have an S on it.
Again, without a road test, I would not conclude that the one you have is not a limited slip dif.
BMW did ship differentials with 0% lockup. If you look inside the top hole, you can see the carrier, but when disassembled, they have spacers instead of clutch plates and they do not lock up. The one I have does not have an S on it.
Again, without a road test, I would not conclude that the one you have is not a limited slip dif.
Are they really diffs with the limited slip but with no "S" mark" stamped?
Are there differentials with the oil cooler (external) but without and lsd. I was wondering if such configuration would made any sense in practice.
Are there differentials with the oil cooler (external) but without and lsd. I was wondering if such configuration would made any sense in practice.
You may well find that it is an LSD. If it is built with no pre-load the wheels will turn independently of each other. This was the case with older 2002 diffs......
Fritzie
Well-Known Member
Check this by opening the top mounted aluminium breather plate. I don’t know if you can do that with the differential under your car. Maybe with a mirror?
Mine differential has a small “s”, not the big S or painted.
Mine differential has a small “s”, not the big S or painted.
And, in addition to the image above with the green text; if you open the vent cap, you can spin the internals and a sequence of numbers & letters will appear. They indicate how the LSD left the factory (it could have been rebuild, changing the lock % ratio for instance). here's a pic of my LSD unit:
Oldbmwcoupes
Well-Known Member
Erik, does that indicate a 25% lock?
Wladek
Well-Known Member
Don't get me wrong, but you have wrong thinking of LSD work.
When both wheels are loosen - mechanism is locked & both wheels should spin in the same direction.
In good working diff - for example LSD 25% mean that until torque reach ca. 5mkp (difference between the wheels) - mechanism could not slip.
That's why LSD mechanism have preload/tension springs inside along with dog ears & friction discs, that keep it locked up to specific torque.
That's why when for example there is no grip on the road (rain/snow/sand etc.) both wheels with working LSD will spin in the same direction, same speed, same force & that's why LSD is needed for the drifting.
LSD 40% = ca. 15mkp (force difference between wheels) until one of the wheels start to slip (will start to work as open diff).
LSD 0% = 0 mkp, so no force is needed, that's why it's called open. That mean when there will be any difference in force between wheels, all power immediately will go on the wheel with less grip.
Race/track cars have even higher lock %, because most of time they are on dry high grip asphalt & need higher forces until one of the wheels start the "correction" function.
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yep. If it was produced as a 40% lock diff it'll have 'S40' stamped there.
I think it's "S" as the German word "Sperre" means "lock" in English.
The 25% diffs in our cars, also 2002s use Belville springs to set preload, and can be bench tested with a torque wrench by immobilising one flange as described in the blue books. The 40% diffs are of a different design, no Belville springs, no preload no bench test. The wheels can move independently of each other unless torque is applied to the pinion. The test BMW used was to place a roller stand under one wheel and if the car could be driven off the stand, the diff is good. A dirt road burnout is the best way to see if a 40% diff is locking up or not. The lack or amount of preload changes the turn in characteristic of the car, something race car tuners play with but not really noticeable for most of us.
Wladek, for the S40 differential, Ohmess is correct.
As Ian explained, the S40 does not have Belleville springs to pre-tension the clutches, as the S25 does.
The S40 will only develop lock when a certain level of torque is applied to the differential.
Wladek
Well-Known Member
You are right gentlemens - S40 have no tension springs, sorry for inconvenience. 
I’d be interested on clarification on this, my diff housing also has the small s stamped in the same place!
Diff is on car so not able to look inside.
Oldbmwcoupes
Well-Known Member
Correct me if I’m wrong. But are you saying that some side-loader differentials in the e9 cars have lsd but it’s not visible because there is no external reservoir and tube as you would see on cars like the m90 M 535i, and the early euro 635 csi? If so, it will be worth looking at my diffs for a hopeful lsd surprise. I. Reality, I don’t drive them hard enough to worry about it. It’s just cool to have