ITR LSD Install
By: B20luda

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MC's note: swim1's old ITR LSD install write-up is at the bottom, and yes B20luda's is contradictory. Instead of machining down his ITR LSD he had to shim it with a large shim. However B20aluda works at a Honda dealership and did the install himself so his info is the most accurate. swim1's is being left here "Just in case" someone installs one that does need to be shaved down.

LSD install guide


1. TQ wrench click type and a 1/4in beam type
2. Hondabond sealant (from Honda)
3. a good manual that has good tranny pictures etc.
4. coarse file or a dremel
5. bearing race installer ( if U buy new diff bearings which U should as the stock ones will have to be reused and they usually get ruined when taken off the old diff, I suggest getting new ones from also U may not need to get a bearing race installer as U can use the old races to install the new ones..
6. brass hammer or something similar

7. snap ring pliers

8. general hand tools

9. feeler gages
10. some type of tool that will grasp the inside of the differential so U can turn the diff with a beam type TQ wrench ( I used a special tool from my work it wasn't made for it but I made it work..
)U will have to be creative at this point.. I'm sure there is a tool..but I'm not sure what its called and I'm sure U could get it from the Acura dealer remember what diff your working with not what car..

THIS IS FOR THE D2A4 trannies the ring gear on the 88-89 is different the swap is still possible its just the ring gear has a different bolt pattern and WONT bolt to the ITR diff. so U will need a D2A4 ring gear..

OK first things first U may want to just clean the tranny up real good that will assist in keeping your work area cleaner and keep dirt OUT of your tranny. OK after that's done Follow the manual step by step to split the half's of the tranny, once that's all apart.. follow the manuals instructions on removing the main and countershafts.. once both shafts are out U will have full access to the diff. remove the diff, U will see the bearing races installed in both sides of the case.. these will have to be removed U can remove them with a brass hammer by hitting the axle side of the race (U will hit the diff shim first just be careful with it U may want to use a piece of pipe to spread the load over the shim), once removed (U should have the new bearing installed on the Type R diff by now) U will have access to the diff shims, NOTE: only 1 side of the case has selectable shims and if I remember right its the clutch side that's selectable. now here's the hard part...the Type R diff seems to be slightly smaller and will require a bigger shim than what Honda can provide..U have 2 choices at this point..stack the shims or have a custom one made.. I had a custom one made my buddy just happens to be a upcoming machinist so he made some for me.. I don't see the harm in stacking them but in the HONDA manual it says not to so I didn't.. we will comes back to this later...
Now case modification..this is easy the diff will hit the case right where it protrudes out thru the case where the axle comes into the diff. ( modification needs to be done to the NON clutch side of the case not sure what's that's install the diff in the case to get a better idea of what I'm talking about..NOTE: when U put it in there without the custom shim it will hit in other areas NOT to worry it wont once the proper shim is installed. using a file or a dremel just remove some material..DO NOT remove material where the bearing race/shim sits.. U shouldn't have to remove much to get it to clear..
OK back to the shims..its hard to get the extra amount of clearance measured, to get the right shim thickness, this is what I did.. I installed the type R diff in the case with bearings installed and all..put the cases back together and toque the bolts now with that done U need to manually push the shim from the outside of the tranny against the bearing on the diff...once your sure its firmly placed against it take a feeler gage and measure the clearance between the case and the shim..once U get that clearance add it to the size of the current shim in the Trans..(factory shim sizes can be found in the manual) once U get the total clearance added up add a couple thousands to get preload on the bearing itself...( at this point this is not accurate the idea is to get some kinda of bearing preload to measure so U can see weather it need to be increased or decreased in my case I needed to increase it.. every lil bit about .02 will increase preload by 1-3 in lbs .. so don't go over board..

now to measure bearing preload..with the shims installed and the case Toqued to specs use the tool I described in the tool list.. and put the TQ wrench on the tool and watch the gage on the TQ wrench as U turn it ..what we want is the START TURN TQ..NOT THE TQ REQUIRED TO KEEP MOVING IT ONCE IT HAS ALREADY MOVED.. the procedure is also in the manual so U can follow that if I'm unclear.. now if U don't have the proper TQ U will need to adjust the shim accordingly.. Please this is the most important step in the whole process if this is wrong then your bearings will go to shit.. I put mine on the tighter side of the clearance just because they were new bearings and I wanted some room to allow them to break in..mine were at 19in LBS also this beam type TQ wrench is very hard to find luckily my next door neighbor had the one out of all people so I used his.
that is pretty much it..each shim diameter will be different so giving u mine will be of no use. THIS is a BIG modification so please don't attempt it if u have never taken a tranny apart before as u WILL fuck it up.. there may be some details I'm missing feel free to ask questions and this post my be subject to editing.. so CK back for details this is also a lil unorganized so bear with me just read it this is a last min thing..hope this helps a lot of u ...Mitch







By: swin1

Yes things are looking good for us 3rd genners nowadays swin1 at has confirmed ITR LSD's work with our tranny's with slight modification!


I, all knowing, bow before me! Seriously, I installed a Type-R LSD in my B21 transmission last November, so yes, I know what you 3rd gen owners have to do. Let me first begin with an introduction to our cars and why we might want to go certain routes when modifying them as opposed to others. First of all, our cars are cheap, I'm sure for most of you if you had good money to spend you would have bought a newer Prelude, and I hope that's the only choice you would have, as Preludes are the s**t, and remember that before getting all down on how difficult it is to modify them. I went through various periods where I wanted to sell my car because it didn't have the potential I thought, but finally decided to keep it. Anyway, back to modifying our cars. Unfortunately, there is a bunch of crap out there that will fit our cars from other Honda's we just don't know about, which totally sucks, and trust me if I knew about some of this stuff before I would have saved some money, but in the end, I already have. Now with the LSD, there are a few reasons why you want one:
1. biases power, so that in certain low traction situations you get optimal grip possible with both wheels. I'm sure most of you know that, maybe I'm wasting my time, but maybe not. You want this advantage in an LSD because above all else it actually makes the car much safer to drive. I didn't install the LSD to give me better track times in Autocross, I've never autocrossed or gone to the drag strip, and I don't intend to, I'm just driving this car around as a nice road car. But in the snow, it has made a huge difference, and swinging around corners there is pretty much no squeel or loss of traction in dry or wet, sweet!
2. There are a few different types of LSD's available, I'm sure most of you know about those so I won't go into it. Quaife I believe makes a gear-type, just like Honda's LSD's! The Type-R LSD is a great unit, the best I think for our cars. It so happens that pretty much any recent Honda LSD will fit in our cars, with some minor modifications, you are going to want to have a transmission shop do the install if you've never worked on a transmission before, trust me, I tried doing it myself and got a couple gears bound up and it got stuck in reverse!
Installing an LSD will cost money anyway you go about it, for the most reliable setup, go with a Honda LSD, I got mine from a seller on eBay called Japandy who is constantly selling ITR and CTR LSD's left and right. You can get a good one from $220 - $300. For it to work in our cars one side needs to be machined so it will fit in the case, I tried installing it without machining it and although it seems to fit when you put the case back on, it won't work!! Make sure you use the bearings from the original differential, as the bearings (if you get them) from the LSD won't work. With B20 transmissions, you will need to modify the ring gear, as the holes don't line up. I have provided a picture so you can see what you need to do. In the end, and going along with the fact that we drive cheaper preludes, this is the best way to go in my opinion.
In conclusion, there are other mods you can perform in money saving ways, I will eventually make a simple webpage showing what I have done to my car, my other proud achievement is FREE modification to my control arms to adjust camber for my eibach springs. Now, although you might have lower springs installed, you can still do this mod, but that's another story...