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Discussion Starter · #1 · (Edited)
I posted this once before, but it apparently got deleted somehow. I tracked down the original file on my old computer so I’ll repost. As an update, I have about [60,000 miles as of 9-2011] on this OBX LSD and so far, all is well. It drives around town, corners, freeway, everything just like a normal car – until you punch it and lay down dual black marks, or stab the gas in a corner and it immediately goes where ever the wheels are pointed. Nothing but rave reviews from me. Although I would definitely go through the steps of this rebuild – at least the deburring and Bellville washer replacement – before sticking the unit in the tranny. Anyway, on with the show:
 
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Discussion Starter · #2 ·
Bulletproofing the OBX – (or making it a lot better – that is for sure!)

Well, I have jumped into buying an OBX LSD based on it’s relatively dirt cheap price and the fact that my clutch is toast and this is really one of those projects that is best done while the tranny is out for the clutch replacement anyway. I’ve heard of other people pushing massive amounts of power through them, So I dropped the 3.5 bills for the OBX. Of course, I’ve also heard of people destroying them in a matter of 100’s of miles or hearing clicks and clunks as they drive down the road.

Before it went in, I decided to give it the once-over to make sure it has the best chance of long life in my turbo S. Below are my observations and a few pics of what I did. There is already a great write-up of disassembly and reassembly on a similar B series unit here:

http://honda-tech.com/zerothread/1752849 props to Enzo Speed for taking the time and effort to document this.

Also take note of my special caution on reassembly later in the document. This may explain some of the failures and noises with these units.

So on with my story…
 

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Discussion Starter · #3 · (Edited)
The LSD arrived from ebay in fine condition. Well packaged, and sealed in an oiled plastic bag…likely to prevent corrosion on the long ocean voyage from China. I tore the LSD down to check the Belleville springs as many people seem to have theirs installed incorrectly from the factory. Another scary thing was putting the original washers in a vice to squeeze them down and see if they take any permanent set. They did! One squeeze and they never sprung back! So I ordered a replacement pair.

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Jan-2013 Edit: I ordered a replacement set of washers from McMaster-Carr Supply (mcmaster.com) though it appears I left the part numbers out of this thread originally. It's been so long, I don't have the number or dimensions anymore. However, member Justindrider reports Fastenal P/N 0125786 works as a replacement.
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Plus, I can see right away that there are a few additional things I would like to do. Not the least of which is remove some metal burrs around some of the holes and slots. It is good machining practice to ‘break’ or round over all corners, chamfer all holes and generally make sure the surface is as smooth as possible to prevent premature destruction.



Opening up the LSD we find that some corners are nicely chamfered (rounded over) while others sport a raw, machined edge with plenty of burrs…just ready to chip off and roll around in your tranny for the next 50,000 miles.




I used a dremmel tool with a medium grit paper sanding drum for most work. A cylindrical stone worked great to chamfer the holes and a pointed stone to break the corners of the oval holes at the bottom of the helical gear pockets. The red lines are a sample of the corners I attacked.



After that was done, I threw it in the glass bead blaster for some general surface clean-up. This will also help increase strength by ‘peening’ the surface which makes the part slightly harder on the surface and less prone to cracking.



I also gave a quick sand and polish to the thrust faces of the main axle gears and the Belleville washer retainers… neither of these steps is necessary, but they can’t hurt. This is where some of the main movement and friction will be so we can make it a little smoother
 
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Discussion Starter · #4 ·
Now that everything is clean, deburred and smoothed, I want to do a quick blueprint just to see how those Belleville washers are going to stack up. Basically, the two halves of the LSD housing form a cavity and that cavity is filled up by the two gears that drive the axles plus Belleville springs and their retainers. So if we measure how wide the housing is, subtract out the thickness of the gears and the lips on the Belleville retainers, the remaining distance is what the springs have to take up. So I get:

(Right housing + Left housing) – (Gear 1 + Gear 2 + lip 1 + lip 2) =
(.982 + 1.646) – (.950 + .942 +.167 + .165) =
(2.628) - (2.220) = .412 inch

So it looks like our stack of spring washers needs to take up at least .412 inch – anything else will be the preload on the gears. That works out pretty good because my stack of 6 measures .485 inches tall, so we have about .073 inches of preload on the washers. .073 inches / 6 washers means each washer is deflecting about .012 inch which is close to ½ it’s total travel. You only need enough pre-load to keep the gears from clanking around – this preload does not substantially increase or decrease the slip rate of the LSD.

I also note looking at these numbers that considering just the housing and the gears…(.982 + 1.646) – (.950 + .942 ) = .763 inches. This is OK since the center sleeve for the Belleville washers is .692 inches thick. That leaves about .070 inch. Enough to counter any thermal expansion and still leave some free space.
 

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Discussion Starter · #5 · (Edited)
So here we are – Reassembly. One note of caution here: Unlike Enzo’s B series teardown, the K series has parts that are all interchangeable - that is, both axle gears, all helical planet gears, Belleville retainers, etc are the same size…they “can” fit in either way, but there is a hitch:

If we hold the two axle gears in their proper orientation with the chamfered edge facing out and the notched edge facing in, there are two possible configurations – one where the bevel gears point away from you and one where they point toward you.





If we play the part of the center differential for a second - (pretend you are back in the drivers seat, differential ring gear is on the left side of the housing and forward means the diff rotates out away from you over the top and toward you on the bottom) - holding everything in the proper orientation and imagine turning the gears (hence the axles) forward when engine power is applied, the ‘arrow pointing away’ configuration will thrust the gear outward against the LSD housing when torque is applied (this is good). The ‘arrow pointing toward’ configuration will thrust the gears toward the center of the differential – heavily loading and possibly crushing the small Belleville washer housing (this is bad!) Furthermore, every time you let off the gas, there will be a clunking sound as the gears spring back into place. The axle gears have to be installed in the “arrow pointing away” configuration.





If this isn’t clear, re-read what I just said…this is really important. These gears can easily be installed wrong and will lead to a quick death of your LSD. I have seen at least one instance where an improperly installed gear led to failure:

http://honda-tech.com/zerothread/1381146






Here is my LSD in the same state of disassembly. Note how the axle gear helix in the two pictures (arrows) are mirror images. In my case, engine torque will thrust the axle gear out against the bearing pad in the housing. In non-VTEC’s case, the torque forces the axle gear in and crushes the Belleville washers – and obviously leads to additional destruction!




The last item of the reassembly is the helical gears. These are also thrust loaded when force is transmitted through the differential, and they are thrust loaded in the opposite direction of the axle gears, that is, toward the center of the diff. housing. These can be installed either way around, but looking at mine, some had a really large dimple in the end, and others had a small dimple. We might as well take two seconds and make sure the smaller dimple is on the thrust loaded side, just to make sure the maximum amount of area supports the load.

 

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Discussion Starter · #6 ·
OK – going for the gold…. I like to make sure everything is spotlessly clean, and use a little MTF as pre-lube. No use of starting dry or having crap that is going to roll around in the gears for 50,000 miles.

Set the non ring gear side of the LSD facing up.



Clean, lube and drop in the first axle gear (make sure to note the orientation of the chamfer- facing down, and the helix of the gear – slanting to the right at the top) Also take a second and look at those 24 little splines – all the power your engine makes comes out of the transmission, through those tiny splines and to the wheels. Aren’t you glad you took 20 seconds to chamfer the edges of that gear?!?!



Clean, lube and set in 5 helical planet gears with the small dimple end up. (One set of 5 will drop right in, the other set of 5 will have an opposite twist on the helix and are used for the other axle gear.)



Lube the star shaped Belleville washer collar and drop that in, either side up is fine.



Lube a washer retainer and drop that in with the thick edge down. (refer to Enzo’s post if you’re not clear)

 

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Discussion Starter · #7 ·


Lube and drop in a stack of 6 washers in the )()()( configuration, line up the holes as much as possible. Drop in an appropriate sized drill bit if you wish.



Lube another washer retainer and drop that in, thick edge up (this should form a pocket with the washers inside.




Lube and drop in 5 more helical planet gears, this time with the small dimple end down



Lube and drop in the final axle gear again paying attention to the chamfer which should be ‘up’ this time.



Lube and drop on the upper housing with the ring gear attachment



Now is the time for a quick ‘gut check’ – we measured about .073 inches of preload on the washers earlier, so the two halves should have about .073 inches at the mating line right now….looks good to me.



Drop in the 9 bolts. I went ahead and used some red lock-tite.

Torque in criss-crosses and stars until you get to about 35 pounds. Make sure to keep the drill bit centered in the opening throughout the torque process, this will keep the Bellevilles aligned.



Yay, done and ready for the car!
 

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wow that is a good DIY. How do you know so much about how to assembly that thing and how it works?

anyways that def deserves a +rep... and where can people get access to glass bead blaster or those other tools you talked about? And did you do that sanding and dremel work on the gears too or just the housing? any other parts that need touching up?
 

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Discussion Starter · #13 ·
wow that is a good DIY. How do you know so much about how to assembly that thing and how it works?

anyways that def deserves a +rep... and where can people get access to glass bead blaster or those other tools you talked about? And did you do that sanding and dremel work on the gears too or just the housing? any other parts that need touching up?
Thanks for the rep. I guess the know-how just comes from years of breaking stuff and taking it apart. - it's my job. The bead blaster isn't 100%necessary - you might find a machine shop to do it - but just icing on the cake, really. My gears looked to be in good shape, so I didn't touch them. The housing was where the real work was needed. Of course, if you see other burrs, take them off, too.
 
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Discussion Starter · #14 ·
yay that. can you use wet sanding with sandpaper instead?
For the deburring? I'd have to say no - there are just too many corners and the burrs are too heavy - you just can't get a straight shot to move the sandpaper back and forth to reach in the corners. Some small files might work, but the dremel is the king! You could always take part of the $700 you are saving over a Quaife and buy a $30 dremmel.
 

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Nice write-up and opportunity for the rest of us to see what the inside of LSD looks like. Some day I may even understand how it works!

You mentioned something about preload or proper positioning and how it prevents "gears from rattling around".

I am about to install a used Civic LSD, and if I shake it I can hear the gears move ever so slightly.

Is that something to be concerned about, or is it normal to hear some noise/clanking?
 

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Discussion Starter · #20 ·
The planet gears can move back and forth slightly in their pockets - this is normal. If the sun gears (gears the axle slides into) are rattling, that is not good.
 
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