Shimming your LSD

PDF Write up how to shim diff (it is for FC but will work same for FB)

Step 1:

Jack the rear of the ol' beasty up nice and high so you have plenty of room to move around. Make sure you put some Metallica on to get you in the right mood for it - none of this Reload crap, some Master of Puppets or Ride the Lightning!

Step 2:

Drain Diff oil. There is a plug on the bottom of the diff housing that you can use to drain it into a suitable container. Make sure you do the drain plug back up tight so you don't forget about it later. It's a good idea to wipe the metallic sludge off the magnet with a rag (you'll see what I mean). Also, if you want to re-use the oil, drain it into a clean container. It is a good idea to change it though. I'm not sure on how much oil it takes exactly but you just have to refill it until it starts comming back out of the checker plug, located about halfway up the diff housing.

Step 3:

Make sure handbrake is on firmly. Loosen the 4 bolts holding the driveshaft to the diff flange. If you can't reach them all put the gearbox in neutral, remove the handbrake and rotate driveshaft to suit then repeat.

Step 4:

Once you have loosened the 4 driveshaft bolts, its time to tackle the half shaft flanges. on either side of the diff there will be a flange bolted to the housing, assuming you removed all the brakes, you should be able to pop the axle out of the tubes, you may need a slide hammer to affix to the axle flanges, pop both axles out until you feel them disengage the diff splines

Step 5:

Now we're ready to remove everything. Before you do this make sure all the little housing bolts are removed that you're cracked off.Then it just takes a bit of dicking around to get it out.

Now, with a bit of luck (and maybe a jack too) you have the diff infront of you. It's quite a heavy f**ker yea?

Step 6:

there are 2 bolts either side, undo these and remove the bearing caps (again remember which way around and what side these go on). You will then see some bearings and spacers and things beside the diff head on either side. Lever the crownwheel out with a big bar and make sure u keep all the bearings etc in the correct order and sides (a vivid is handy for marking everything with terms like "inside, outside, left, right etc).

Step 7:

Now you have an oily diff head funky lookin' thing sittin there. There are several (about 10?) large bolts holding the crown wheel on. They are FUCKING tight!!!!! I'd recommend a decent vice and large powerbar or something - alternatively a pneumatic gun will work. Once the crownwheel's off, you'l see 2 large phillips screws. Remove these and off comes the viscous center. You'll see once u pull it off a washer sitting on a flat surface. That's your original preload shim - See below for a rough indication of what it looks like in new form.

lay everything out in order.Here is the entire differential assembely in the order its assembled.You can see the spider at the center,spider gears,the side gears,thrust blocks and case halves.The LSD discs go between the thrust blocks and case halves.

Here are the drive portions of the diff within the carrier unit.The outer case,thrust blocks and drive discs all have corresponding tabs that lock together and rotate them as a unit.

Here are the driven portions that are part of each axle shaft.The side gear is splined to the axle and the driven LSD discs have tabs that engage the side gear which makes them all spin as a unit.

Here you can see the ramps on the thrust blocks and the spider.If you look close,youll see that one side of the spider has heavier wear and the other has lighter wear.This is also visible on the bottom ramp of the thrust block.The heavy side wear is input torque from the engine and the light wear side is caused by coasting torque from the wheels.The wear marks can help you to determine which side is which should you misplace the thrust blocks or get the spider flipped over backwards.

Step 1 is to determine the clearance you have inside the case for the LSD core. It can be anywhere from 0 to .20MM standard clearance with a maximum gap of 1.0MM.

First measure the thickness(not the height) of each cone spring and record it.Then measure the width of the LSD unit with all the discs installed...measure to the outer side of each end disc and be sure to hold everything tightly together.I took 4 measurements from all around the discs and averaged them.Heres what I got.....

The carrier case inside width will not change or wear because the point where the factory measures it is behind the cone springs,and they do not move relative to the carrier,so no wear is possible.The carrier width is 84.0MM, so you take your LSD core width,add the width of the cone springs and them subtract that number from 84.0MM.......I got .11MM total clearance,which means that each cone spring is within .055MM of being totally crushed flat when the LSD is assembled.....that about as much preload as can be obtained provided that the cone springs are in new condition.

involves measuring the LSD core with the copper thrust washers installed.Too much clearance will induce slop in the spider gears since they are beveled and gain lash as they spread apart from each other.The thrust washers bear against the side gears and put them into contact with the spider gears.

They do no affect the LSD preload tension as I incorrectly stated when REVHEAD mentioned machining the cases.Thicker LSD drive discs are availible for taking up excess play in the previous proceedure.For this part of the assembely,if the tolerances are outside of spec,you can get thicker thrust washers to close up the slop in the spiders/side gears.

First measure the width of the LSD unit including the thrust washers.I took several measurements and backed them up by measuring the LSD assembely and the washers seperately and then adding the 3 values.I averaged them all for a width of 87.81MM.

The factory spec is 88.2MM. You then subtract your measurment from that number and get your clearance.....mine was .39MM of clearance.The factory spec range is .16 to .42MM so Im within spec,although a tad loose.No biggie, since the max allowable clearance is .80MM which I am far from.Oversize thrust washers can be used to take up the wear or you can install better or buy new spider gears to get rid of the slop without the thicker washers.

Now for assembely.........

First lay the right side thrust washer and cone spring inside the carrier case.Then stack the 4 LSD discs starting with an outside spline disc and ending with an inside spline disc.This will give you the maximum friction surfaces allowable with 4 LSD discs on each side.

Then install the thrust block over the discs.I found it easier to first alighn the driven discs with a side gear before installing the thrust block.

Then,install the side gear into the block,engaging the gear's splines with the driven discs.Then you can drop the spider and spider gears into the block and engage all the gears together.

Your now halfway there.Just install the other side gear,thrust block and 4 LSD plates,starting with an inside spline disc and ending with an outside spline disc.

Now install the other cone spring and thrust washer on the pack.

Once the end cap is in place,line up the ID marks on the circumference of each and loosely screw in the 4 little phillips screw that hold the case together.Before tightening,check that the thrust washers and cone springs are centered and alighned with everything.They can move around a little,but its unlikely they will gwet out of place.But still,better to be sure.

Then snug up the screws and you are done!

Now the original plan was to double that thickness and put more load on the viscous center, somewhat 'reviving' it to how a LSD should be. If you're me however (you wish!), 1 extra shim just isn't enough for drifting (it is great for everyday driving however). So go on, be a devil and chuck 2 extra ones in there if its mainly for the dr- ifting.

This is what I posted about them on another thread, be your own judge about how many extra to put in:

Add 1 new one to the existing one (total of 2) if you want a decent predictable lsd for driving that spins up 2 wheels with ease. Comparable say to a BRAND NEW viscous diff (i.e. not worn out, you've probably never driven on one).

Add 2 extra preload shims to the existing one (total of 3) if you want a very solid diff that's very tight but not quite locked (comparable to say a kaaz 1.5 way mechanical).

Add 4 extra preload shims to the existing one (total of 5) if you're a crazy c*** and see if it actually works.

Step 8:

Do everything in reverse, make sure you listen to Metallica again!

**VERY IMPORTANT NOTE:**

some high temp silicone to seal it before u bolt it up so it doesn't leak everywhere.

Just a little more info on the shim - It costs aroundabout $17ish including freight from japan. Usually about a 10 working day wait, usually less. You'll need to order this from your local mazda Authorised Dealer. You could also rob one from another lsd but not worth the hassle of pulling 1 apart.

i Personally like to take an extra worn friction plate and install it into the diff as a super thick shim. or you can make shims by taking the friction plate and tracing it on sheet metal and installing. old brake clean cans work great for this.



Content is not my information, and i do not have the original source, if this is yours please contact me so i can cite you and give you credit.