well i haven't seen a FD lsd into turboII casing swap write up so i figured i would lay some info for you guys. i know there is a miata lsd write up but it doesn't show you how to set the clearances and other confusing tasks involved with setting backlash. this write up is not how to take the differential assembly out of the car or how to rebuild the entire lsd. This only shows you how I swapped in a fd lsd carrier into my 87 turbo casing. i purchased my lsd from ebay( insert hisses here). make sure it is in fact a legit fd torsen lsd or you're fooked. i have included some close up pics of the torsen so you can distinguish between a lsd from something else. you don't need a lot of tools to get this done, but if you don't have basic mechanical knowledge you probably should not attempt this because it involves technical and diagnostic skills that newbs to cars would not have. if you don't know how to get the differential out of the car, you can get yourself into a big mess if you mess up. i am working on a spare turbo diff, i suggest for first timers to do the same. here are some necessities, the diff of course, a dial indicator( and how to use it), and gear marking compound(which can be purchased from summit or local gm dealer.) if you don't have these stop now. always plan ahead so you won't get stuck cuz you don't have something. i also purchased new carrier bearings, axle seals, and competition diff bushings( i figured while i'm there). you don't necessarily need new bearing as the fd bearings are the same as fc bearings, just make sure they are in good shape.

 

well if you have all necessary parts to continue then let's go. first pic is a close up of the part number on the torsen, there could be slight variations and still be from an fd. there were manual and automatics, both with different part numbers.

next pic is of the turboII diff out of the housing. ring gear and bearings removed. you will probably want new bearings if you don't have a puller. makes things easier as the old bearings tend to break when you use a puller.

next pic is the turboII diff opened up. i took the adjuster locking plates off and marked where they used to be. make sure you wipe the gear oil off before you mark it or it will just smear off. now is a good time to look carefully at how everything goes together, and mark the bearing caps as well. i marked one cap from upper to lower with a single line so when the two halves are put together it forms one line. after marking everything needed you should put everything in little baggies and label them. i lost the locking plates.

here is a shot of the aluminum casing in the parts washer. i like clean parts! you can use brakeclean also, whatever you can get. by the way parts washer solvent ***** up the rubber axle seals. after cleaning you can install new bushings iff you want or paint the housing like i did.

 

here is the FD lsd with new bearings pressed on. you might need a press for the bearings. most shops can do it for you for a fee( like i said think ahead). you should have the bearings pressed onto the new diff before you start tearing things apart, not when you have the diff out of the car and you realize you need a press. when the time comes you should swap the ring gear over to the torsen and torque the bolts to factory spec. a little tip: the ring gear might be a little tight coming off the old diff. just tap it evenly on opposite sides and it should fall off. another little tip don't try to catch it like i did and cruch your fingers! the ring gear has some weight to it and it will drop suddenly. you should also put something under it so it doesn't get marred or nicked. you should put the lsd into a vise to torque the ring gear bolts down.

next is a side by side comparison of the torsen and turboII carriers. make sure they are the same diameters. it should measure a little under 8" across.

i also cleaned the pinion housing. scrape off as much rust as you can, and paint if you want to. i used POR15..some tuff ****. and you can paint it over rust, completely seals it. never rust again, and it looks nicer. i didn't paint near the bolt holes because if that stuff hardens on the hole the bolts might not sit flush. the housing might be unevenly torqued causing a leak. there aint no way i'm taking it apart for a leak.( do it right the first time) also get some rtv or hondabond for when it's time to reseal the two halves. i'm gonna use some nissan silicone because i can swipe it for free.

 

To clarify, this only works with the Turbo II differential. NA differentials need not apply. Am I correct?

 

first pic. bearing cap removed. hopefully you remembered to mark them. only two bolts holding them down. you might need to tap them with a small hammer, on opposite sides to get them off.

second pic. upper bearing cap. here you can see it's threaded on part of it, it matches the lower bearing cap. so you basically can't put it backwards. the threads is how the adjusters go in or out to set tension or preload on the bearings.

third pic. bearing cap on with the adjuster backed out a few threads. when reassembling make sure the adjuster turns in somewhat smooth, or it is cross threaded. it might feel tight but it should still turn.

fourth pic. carrier removed. notice the pinion gear is offset to one side. the lsd can't be installed any other way. also when you are adjusting backlash picture which way the diff is going. if you reference the picture, when you turn the adjusters so that the carrier goes closer to the pinion gear the backlash decreases. when you turn the adjusters so the the carrier gets further away from the pinion the backlash increases. basically backlash is how much play is between the pinion gear and the ring gear.

 

[QUOTE=micaheli;7367728]To clarify, this only works with the Turbo II differential. NA differentials need not apply. Am I correct?[/

sort of. this applies to NA's if using the miata torsen. the turboII diff can only fit the FD.

 

[quote=pistones;7367784]Yeah, I realize that.. just clarifying for everybody else. Thanks! Good write-up!

 

next you will need to find a way to mount the pinion housing. it is fricken heavy. i rigged up something cuz i was rushing. basically you can't just stand it up on the pinion flange, it will put pressure on the gears. after mounting the housing insert the carrier with the bearings. then place the caps into place. they should seat flush and all the way down. you don't need to tighten the bolts at this time. make sure the marks you made before are lining up.

now hand start the adjusters. they should be somewhat easy to turn by hand the it will get a little tough. if you can't start it by hand check the bearing cap alignment. then you can turn them in some more with a prybar or the proper tool. we gangsta here so we use what we gots. the adjuster should also be even going in, looking from above it should be straight. turn in the adjusters so the diff is almost centered. it doesn't have to be exact but just try to count how many turns it goes in and the other side should be the same. stop when the carrier is not flopping around anymore.

 

how is this better than the t2 diff?

 

this is better for most turboII owners because most stock diff are worn to **** and fd diff's are pretty cheap. plus i like how torsen's are more progressive. i can't really compare to a new turboII diff because i have never had one, and they are expensive. i am also not looking to make 500 whp so strength is not a concern. fd diff's handle enough for me. i'm also into auto-x so i would like the progressive nature better.

 

i will finish the last parts of this write up in a little bit.

 

the t2 is viscous not torsen diff. IIRC.

Just pulled from miata.net:

http://forum.miata.net/vb/showthread.php?t=165274

Not sure on why its better either, but then again I only have experience with viscous type and open type.

edit: er quote:

RE RE edit: not viscous....clutch type. thats what i meant.

 

sorry to correct you but i have an 87' turboII which comes with a clutch type. which at 140k miles it is safe to assume it is worn. the S5 89-91 turboII comes with viscous. the miata comes with a torsen but won't fit the turbo diff. that's why i am using an FD(3rd gen) TORSEN lsd. it is better to me ok. it will never wear out. i don't ever have to rebuild it since it will be seeing the track often. ask people who have the FD conversion, they will agree. it's not about being better or worse. it suits my application and my budget.

 

now time to check backlash. remember that weird looking tool? yea it's time for the dial indicator. it comes with a magnetic base to mount it and some rods and clamps to align it to whatever you're measuring. first mark four teeth on the ring gear at the 12 o' clock, 6 o'clock, 3 o' clock, and 9 o'clock positions. basically you want to measure at four different spots because not every tooth is identical to the next. you want the tip if the dial to be perpendicular to the gear tooth, like in the pic. you can just move the ring gear until it rotates to the tooth you want to measure.
to get a backlash reading you want the tooth to contact the gear and compress the dial a little, then you grab the ring gear and gently rock it back and forth. but not so much that you are spinning the gear. just so you hear the gears knocking against each other. that is the amount of backlash from the pinion to the ring gear. now check your reading. it should be beyween .0035 and .0043 of an inch. i am only using u.s. scale because my dial reads in inches. luckily my backlash was at .0039. now here was the confusing part for me. i thought i needed to change a bunch of things, but since i was only swapping out the carrier and i did nothing to the pinion the backlash should be close if you put everything back to the marks you made. again you are just rocking the ring gear very slightly, only a few millimeters.the pinion flange should not be rotating at all, if so you are rocking it too hard. now you must check the other three points. they should all be within specs.
remember if the backlash is too loose you want to bring the ring gear closer to the pinion. so if you have it set up like the empty diff picture, you want the ring gear to move to the right. to do that the left adjuster turns in clockwise and the right adjuster turns counterclockwise. turn both adjusters an equal amount, one rotation at a time so you don't lose count. if it is too tight and you can't feel any play when you rock the gear you want to bring the gear further away. just adjust it slow and keep checking until you come within specs.

 

after you have made sure your backlash is correct. it is a good idea to check your work by making sure the gear wear pattern is correct and i also made marks on the adjusters so i know where i was. apply some gear marking compound onto a few teeth, like three or four using the supplied brush. and do it on another part of the ring gear so it is spaced out. make sure you apply it evenly across the face and back of the tooth. there are two sides per tooth. so now it has four teeth marked space and four more teeth. now you are going to need both hands or a buddy to help you. one hand grabs the pinion flange and the other hand grabs the ring gear. you only want to give a little resistance at the pinion flange with your hand. kind of like if the drive shaft was connected. the ring gear hand is rotating the ring gear a few complete rotations without smudging the marking compound.
now what you are looking at the pattern the gears have made. you can see the marking compound has compressed through the pinion gear and left an indentation in the middle of the tooth. you want it to contact at least 1/3rd of the middle of the tooth. there are many variations of the wear pattern and they all mean something different, but what we want is as close to the middle as possible.
if it isn't in the middle you might get some groaning of the gears, and excessive wear to the ring and pinion. since the pinion gear was never removed the pinion height was never changed so the wear pattern should be close to perfect. after verifying the wear pattern is correct wipe off the marking compound and rotate the pinion flange a few times. make sure all the bolts are tight and you have the lock plates in the adjusters. apply sealant to the differential housing and seal it up. let it cure and fill with gear oil, torsen lsd's don't require any friction modifiers so just about any gear oil will do.
pray you did a good job and install back in the car for a test run. you want to pay close attention for gear whine. since the torsen is used there is NO BREAK IN time. (sweet!) just go beat the **** out of it.

now you have a diff that won't wear out and is a little more predictable than a worn clutch type.

 

this lsd is so good here i am spanking a ford gt! of course he had no idea we were racing.

 

good stuff :P

 

Pistones, nice writeup and photos. Unless I missed it, you never mentioned how you set the side bearing preload. On the NA differential, a large micrometer is used to set the specified distance between end caps. Also, since you reused the same R&P set, you saved yourself a lot of work by not needing to set the pinion depth.

BTW, do you notice any differences between the TII LSD and TORSEN?

Hot_Dog
90 RX7 GXL

 

the torsen is not really noticeable. it just works without you noticing the lock up. on the other hand my old worn TII would understeer hard and then suddenly catch, then the tires spin. very annoying! i wish i had a new turboII to compare it to, and see which one i like better. i do have my old TII that i can rebuild but i'll wait to do that some other time.
i haven't had a chance to really flog it at the track yet but i will keep interested parties posted.
Find the zero preload position. First make sure that you have plenty of backlash (.010 - .025) because you don't want to be tightening the side adjusters if the gears are in contact. Tighten the pinion side adjusting nut until it is snug and then tighten the ring gear side adjuster until it is snug. Turn the ring gear: It should be noticeably tight. Then back off the pinion adjuster just until the point where the nut turns more freely. Next back off the ring gear side adjuster 4 holes or "clicks". Install the dial indicator to indicate off of the outer bearing race on the ring gear side as shown in the picture below. hope that clears up a few things. unfortunately the FSM does not indicate a bearing preload specification.

 

This is how my gear contact looks like when the backlash is correct, what am I doing wrong?

The ring gear is from the stock diff and the pinion have not been removed just like your's, but my gear contact is almost the opposite of your's.

I did this torsen swap 2 years ago, I have not driven it much but the diff have always been making this whining noise and I kind of knew it was because of the incorrect gear contact because I did not check that when I put it together (stupid, i know), I did however set the backlash and bearing preload correct so I dont really see why it didn't work.

What do I need to do now, move the pinion closer or farther away from the diff or replace both the ring and and the pinion gears?

The last picture is of the gears that I painted, the other two is of the gears that was naked.

 

Found another write up with a good picture and it makes alot more sense, maybe my contact isn't as bad as I first thougt?

http://www.pirate4x4.com/tech/billav...4b_Gear_Setup/

 

your contact pattern isn't that bad. that write up was very detailed and informative. if you look at the section with the possible patterns, you will see that your pattern is close but off enough to cause noise. the convex side pattern looks good while the concave side looks a little high. that is where the noise is coming from. your pattern on the concave side is too high on the tooth and also backlash needs to be decreased. i ended up doing mine twice because of noise. the pattern indicated that the pinion depth is slightly off, but i recommend that you leave that alone. it is not that far off. i recommend just readjusting the backlash to center the pattern on the coast side. also clean off the ring gear and don't use so much gear compound. just a few teeth 90 degrees from each set is fine. the noise is during coast correct?
i am by no means an expert but i managed to get it working properly with no noise. i wish somebody could do an in depth write up on how to fully rebuild and set up rear gears like the link you posted. we need more FC dedicated info, and while my write up was better than nothing it was lacking in some areas.

 

if you have more questions you can PM me