There are a few ways to do this. I generally do a bit of homework, but I just could not be bothered this time with what fits what, and such as there was too much noob talk and all that crap surrounding this one - this time.
I do know I could have bought an E39 M5 diff and worked with that, but they are rare, and expensive if you can find one in Irl, or have one shipped from the Uk.
I did buy an E34 M5 diff as I know the M5 rear cover fits those.
Thats not saying Im going to buy an M5 rear over, as I may cnc one out of billet, but we shall see.
An E34 diff is also cheaps as chips, and it seems theres a few about.
I didnt measure flange sizes, or drive length(mines a step trans) or worry about any of that yet.
My plan is to see how I go, and document what I find.
Ill aim the build in two ways.
One way, with a sensible how you can do this job with oem parts and list sizes of stuff.
The other way, and the way Ill probably go about it, because I generally make things, is to make what I need here. I can cast, and have lathes/cnc mill so it should be easy.
One thing everyone will have to make, or get made is the bracket at pinion to mount to chassis. Not sure what thats going to look like yet, but Ill figure it.
Why am I doing this.
Because I want to. And because wheel spin while pushing hard on corners is driving me mad. If you have traction on, it kills engine, if its off, it kills your general go in life, and your tyre life.
Another thing Im doing is moving traction control switch to steering wheel.
Because I made up paddle shift, all my slip ribbon wires are taken, so Ill have to do it wirelessly.
Ill be dong that after I fit diff.
Main concerns at the minute are, final drive ratio - they look to be the same which is good. Just need to double check mine in the morning.
Second concern, is the from bracket ill have to fab. This is critical as it controls the nose down angle of the diff if looked at from the side. If this is wrong its not good. (will go into that later)
Anyhow...did a bit of dirty work the last few hours and tore apart diff, ill let the pictures do the talking.
One or two things, the connector is for the speedo in the e34, and the diff ratio is on the bit of paper, could just make it out off old diff tag.
Gave it all a rough clean too before pulling cover. Its getting all new seals, and paint etc, so Ill be 'surgically' cleaning everything at a later date.
Flanges coming off, these hold the oil seals, and the taper bearing shell, the bearings look fairly ok, so Ill think if I want to change or not when I clean and inspect fully, It is also behind these flanges that spacer shims go to set bearing pre-load, and mesh correctly,
Opening lsd, its is of the clutch type, and not torsen, thankfully. Ive run a torsen in the past, and dont ever want one again.
Bearing unit off, and getting into discs and spacers
As you can see, the clutch disc on one side is worn, as is the cup that it runs on. Ill have to skim this cup to get back to a good surface. Ill also be renewing the spacers and friction discs with new ones.
Because Ill be grinding(blanchard) or milling the poor surface, ill have to regain that lost material with a shim under the belleville(dished) washer to keep preload on clutch packs as it would have n=been when new.
Other than that, its all in great condition, both with the bearings, and tooth mesh wear patterns, so Im pretty happy.
The friction face was a bit scored as you saw above.
Couple of passes on the cnc with a cup wheel removed almost a tenth of a mm to get the surface back to good again,
z axis reading almost a tenth when retracted,
Both faces blued and rubbed off surface plate, all looks good,
Ordered new friction discs, and star spacers. Star spacers are oversize in thickness to make up for material ground off above.
Getting a free e39 diff tomorrow, ill be using this to get my location point/mockup for the new front hanger Ill have to make to mount E34 diff, to E39 carrier, since I cant take my car off the road to do this.
Im making a cover for the E34 M5 diff as mentioned. The original cover wont mount to subframe, so given the price off Bmw(380euro) Ill mill my own.
Below is where I started mapping the holes for the new cover. They are pretty important that they are right in the new milled part, so that it bolts up to diff clean.
You could measure the holes with a calipers, and a divider and plot on paper, but having the cnc makes this easier, and more exact.
Ill try explain how its done incase anyone is interested, or thinking of dipping a toe into cnc land soon.
I remember being the same years ago, thinking cncs were mental, and impossible,- but they are actually pretty simple when you get to know them.
Bolted diff to table square.
Fitted a 12mm round over bit. Set mill in center of case approximately and zero'd all axis.
The pictures are a bit crap as Im just getting to know new phone.
Anyone doing this lsd conversion can skip this step and go buy an E39 M5 diff cover off Bmw like a normal person would.
Bolted to table,
All axis zero'd approx in the middle of diff,
New drawing opened, where the cursor is, where x and y lines meet, is 0,0 and since I zero'd all axis, thats now where the bit is too, on the table,
The correct number of circles(holes) are drawn in in roughly the correct position,
The mill is now moved with the jog buttons to all the hole locations on the diff and their coordinates noted, and transferred to drawing. Once you transfer, the circle moves to a new location where the actual hole is on the diff, and where the bit is sitting, this is done for all holes, 'mapping' them exactly onto the new part drawing - as below,
Bit moved to hole position,
Note coordinates, ignoring the z thats the up and down,
Over to drawing, select that circle,
Click coordinates box, and fill in the coordinates from mill screen above,
Circle moves to new position,
This is done with all holes, and all datum points I needed,
Completed hole locations, now on new drawing,
Onto finding the axle center line. Straight edge held to edge of holes, and touched off with pointer in mill,
Y position noted on mill, and then transferred to drawing,
Since the inner diameter of flange hole(!) is 100mm, taking 50mm off that measurement and drawing another line give me the center line of shafts.
There are more accurate ways of doing this with a dial gauge, but its accurate enough considering where it is,
Then more of the same, finding the other datum points, and case edges,
Thats the basic outline down now, complete with hard measurements of where it needs to bolt to.
The rest, is pretty easy, I need to yet draw in the two hanger points(see E39 diff below) And put some proper shapes and profiles on the drawing before I can mill,
You can see the complete E39 diff below(smaller that M5 diff) and also the difference in the rear covers - the E34 M5 cover is 25mm higher than my diff/cover - which is why I need to make another one!
The billet cover will look something like the one below, but taller to cover the diff I just mapped above.
Its actually easier to do all this, than describe it, LOL,
Ive been away from hands on car stuff for a while, so this seemed a nice little project to tip away at. Granted, the 525i hasnt got that much power to make full use of it, but in time I plan to build a charger for it, so Im laying the foundations for that too,
Did a bit more drawing, almost done, hope to make a lot of chips later!
Ill throw up a 3d image later to give a better Idea of how it will look. The drawing below is not the final, there was some minor changes before cutting,
On the table, ready for roughing, roughing was done with a 40mm insert face mill, then the finish pass done with a 10mm cutter to get the corners out.
All work after that was with a 10mm bit. The great thing with aluminum is that you can cut it pretty much as fast as the machine will go with ease - so its fairly quick.
Drilling holes, you'd normally drill holes before final surface is reached because the swarf that comes up from bit can scratch finished surface,
1st level reached, if you look close, you can see a 12mm wide slot top left. This was cut first, and allows coolant to drain from pocket. Since the billet overhangs table front and rear, this is vital for coolant management, the four holes in the center of part are drilled through, and act as drains also,
Ill throw up the finish drawing later, hope to get the topside, and most of the rear done this evening.
Ok, didnt get much time at this since, but I am now ready to turn it over,
Rounding over edges,
Its hard to see all profiles while on table, you can now see the sections where the carbon fiber panels will be. Fitting panels like this means you can profile out the inner sections, rather than machining them all out to form a thin aluminum wall.
The outline cut is done with a different hss cutter, and cut dry for best chip evacuation,
The main cover is now only held to block with a few holding tabs, you will see these in the next bit,
The jig plate for the other side, the block locates exactly on it with dowels, and is bolted down,
Roughing out the pockets,
Done, and off the table, a little bit of de-burring, and its ready to go,
Just need to drill through the top and bottom bolt holes as they were drilled 1mm shy to stop coolant flowing out of them.
Next up is the fill plug, and the composite panels, and of course the case breather, the mounting to car bosses also have to be faced at correct height and angle.
Not sure how I ran across this but glad I did. Had to join here to say you this is awesome machine work. I have had a E34 M5 LSD in my E39 528i for a couple yrs now but my mount(s) are no where near as elegant as yours. Thanks for posting....looking forward to updates.
Hello and welcome in that case, and glad you found it in the abyss
Normal readers who just want to do the swap can start reading again soon as Ill be back to ''just making the unit fit'' basics shortly.
In any case the front mount will have to be fabbed, so Ill probably do that in mild steel and not with cnc so anybody could make one. Ill post all dimensions.
Lsd rebuild kit landed. Its a normal kit, plus a slightly thicker disc pictured at top to make up for the refaced cups.
Eared discs are case hardened and ground 4340/En24 steel.
Friction discs are also 4340/En24, sandblasted, and then given the thermal Spray process. The deposited material used in the process is usually molybdenum and is around .1mm thick. Molys can withstand very high temperatures without expanding or softening so it is an ideal coating for the job in hand. Due to the surface finish left by the spray process it is also ideal for holding oil.
Onto the diff cover, I did a lot of tests a long time ago on etching aluminium alloy. Ill be etching the entire cover once its finished, both to clean, and to provide an even surface, and also a key for bonding in CF panels.
I did a quick test yesterday on how the aluminum looks when etched with sodium hydroxide(caustic soda) The test was done on the parts I profiled out to form pocket in diff cover. You can see the uniform etched surface and the differences below in the before and after (poor) photo.
Im undecided yet as to if Ill anodize, epoxy coat, or just leave in etched state. There may be some salt spray from the road in that area, but this Aluminum is one of the best in this situation. Ill see.
Had a look in freezer and had just enough prepreg to make panels. I have those setup now to make a 3mm thick panel, ready to machine the inserts from. More later.
I do a lot of different stuff with my job, so I like to pull in as much as I can in the line of info when doing my own bits, so hopefully others can use info too,
Got diff back together,
Got the rear cover finished. Had to angle mill the mounting bosses as with the Bmw cover. The entire diff is fixed at a slight angle from straight ahead. This is to to put a slight angle on drive shaft inner cvs, and also main drive shaft end cv joint. If they were mounted straight, the balls in the cvs would stay fixed, and always touch the same point in their cages. A slight angle imposed on them causes the balls to rotate, and touch different parts of the cages as they spin, creating even wear. A big mistake in making your own car, or designing a driveline, is setting up everything inline, and then finding stuff is wearing fast - this is the reason. The same can be seen in a fwd car, the engine is canted at an angle always, to help with cv ball rotation.
I bolted down original Bmw cover, and adjusted fixture plate to get correct angle. Bolted that off, and bolted on the cnc'd cover and machined bosses at same height and angle, as below,
You can see the mounting bosses now, the angle is quite something,
Thought about breather, and what I could use. Enter, a boiler jet. The rear of a boiler jet has a cute filter screwed in,
Filter screwed out,
Cover bored, tapped, and counterbored,
Another cover will locate in counterbore to keep heavy stuff off, and inside a small splash plate will mount on the carbon fiber fixing bolts,
Ready for etching,
Etching, solution is about a cup of sodium hydroxide(caustic soda) in a gallon of water, left for 3hrs ish, or when its all etched. panel mounting threads are not cut at this time, container is HDPE.
Because the sodium hydroxide etches just the aluminum, the copper stays. I could have scrubbed off this, but its hard get everywhere, so I gave it a dip in a nitric acid solution. Nitric does the opposite, etches copper, and not aluminum, so you can get back to status quo again, and end up with a clean surface.
You can kind of see the copper here,
In nitric, all done,
The glare is gone, and it now sits with a satin finish perfect for bonding,
Got the boss machined for the fill plug, this mounts in carbon, and also tags into one of the panel mount screws,
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