obx ripoff of a torsen, install

[winfred]

here is a repost from another board of my install of a obx ripoff of a torsen into my e24 shark, i autocrossed it last weekend and it works great with none of the unloading of the inside tire and smoke shows that i was getting with the stock LSD on hard maneuvers, video of first cold run from said event with seals and spacers i am at a little under $500 installed and so far i love it, ill likely try it in my e30 as the diff's are a direct swap but i am not sure if it will do anything for it, i have yet to have the 230k mile factory LSD unload on it as the e30 is a good bit lighter then da shark and doesn't have that big of a weight transfer, when it breaks loose it breaks both loose

ok.....
all da insidie bits


measuring the back lash of the ring gear you will want to set the lash as close to this reading at possible on reassembly, you set it with the shims that are between the diff housing and the two side pieces that have the 6 13mm bolts



those side pieces have the outer races of the bearings that are on either side of the carrier, you will need a puller to get those bearings off the carrier which is the big black one from harbor freight, i tried a snap on of the same size class and it would not grip the bearing at the correct spot to pull it off without damaging it, the puller was just too thick and id rather buy a new cheap puller and grind it if needed (and it wasn't) then fuck up a expensive snap on


and a big two jaw to work with the clamp, but you could use a shop press at the risk of dropping the carrier



you need to heat up the speedo chopper to get it off the carrier and if you are quick drop it right onto the obx carrier, mine once cool was only snug and not tight because they cut the step a waffleswaffleswaffleswaffles hair too small, i didn't try to measure the difference but it will be so small it may come down to manufacturing differences on if yours fits tight, i popped mine a few times with my dc tig, i didn't even add filler and just let it flow together



you will need to grab the one per side snap ring out of the old carrier and put them into the obx, these are what keep the axle drive flanges from sliding out, i had to run my pick around the grooves to clear out a burr or two so the ring could fit clean



nice snug fit on the ring gear as it should be, i used a couple pieces of plastic but wood would work too to protect the ring gear from damage, booger that up and you are fucked



while it is apart inspect the worms and other gears for burrs, about half of mine had little things like this, i used the edge of a fiber wheel on a dremmel at a near flat angle to the surface to knock the defects off (i have been doing this for a long time of various items including to sharpen drill bits, you can fuck up quickly and put a nasty mark on the gear, if you are not comfy use needle files and do it by hand) after cleaning up the burrs i lightly buffed all the obx gears on a bench grinder with a wire wheel just to smooth them a little, i don't have a post buffing pic




i used a fan clutch tool and couple bolts to torque the carrier to 29ftlb, to torque the ring gear i clamped the carrier in a vice (can't remember the torque but i found it online, it is recommended to replace the bolts but i suspect that they come preloaded with locktight and that is why they want new ones, i hit everything with red)


the "large" spacer set, there is a small set and it is a crap shoot what you will need, you gotta measure that back lash and see what it comes out with and measure the spacers with vernier calipers to see where you stand, i took several diffs down looking for spacers to get it together so i wouldn't need to wait a week for them to come from germany and bust out $50-60 for em and found them all to be in the .065 range with only a few thousandths variation (biggest one i found was .070 and smallest was .060) the biggest spacer being .077 in my set (they ran .067 to .077 on couple thousandth steps



all done, in the end i could only go the backlash to .002-.003 which is likely close enough to the .005 it started with, if i couldn't get it closer i would of needed to pull the bearings and file the seats a little to get the bearings to seat deeper as i used the two thickest spacers a .076 and .077 (thicker increases your clearance) i tossed new o-rings and seals into the side pieces for the last time together and sealed up the rear cover with ultra gray sealer and no gasket (been doing it that way for years with no leakers)

get the replacement hardware for the obx from this guy http://rbryant.freeshell.org/obx_washers



if one was so inclined i don't see why you couldn't do this job with the diff in the car but you gotta like being on your back or have a lift, me ill take the other 8 bolts out and put the bastard on the bench

[Danny]

Wow.

[Jean]

winfred - glad you posted it here too :) I've followed your thread on e30tech on this.

[bwh13]

Excellent write up on this.

I went through this last year, although I took mine to the local differential shop and they couldn't get the side clearances correct, even with both packs of new shims. It was either too tight or too loose.

I finally decided to try a different case (have 3) and found one that seemed to fit just fine, although I think they might still be a little tight. I hear a whine on-throttle but it isn't too bad.

I might try to re-shim it if I feel like it later.

[guibo09]

what about carrier bearing pre-load? seams like you ignored this completely...

and why not simply buy new diff bearings? they cost 20$ each.

[winfred]

the preload was dealt with the shims, it started off at .005 and the closest i could get was .003 with the new carrier, so i am the width of a hair off from the 150-200k mile measurements. if i had not been fucked by not having the right size shims on hand i would of had the whole job done in a hour and the undamaged bearings that i have put the last 15k miles on didn't bother me to reuse, the races were clean/smooth and i actually know how to remove the bearings without killing them so $40 more bux in my pocket :D

what about carrier bearing pre-load? seams like you ignored this completely...

and why not simply buy new diff bearings? they cost 20$ each.

[guibo09]

the preload was dealt with the shims, it started off at .005 and the closest i could get was .003 with the new carrier, so i am the width of a hair off from the 150-200k mile measurements. if i had not been fucked by not having the right size shims on hand i would of had the whole job done in a hour and the undamaged bearings that i have put the last 15k miles on didn't bother me to reuse, the races were clean/smooth and i actually know how to remove the bearings without killing them so $40 more bux in my pocket :D

good for the bearings, didnt know they were relatively new.

i still dont see the bearing preload. .003 measurement you are talking about sounds like backlash to me. preload is how tight the carrier fits in the case regardless of the backlash. in other words, if you were to add one .005 shim to each side, you would not change the backlash but you would increase the bearing preload.

this is critical because not enough preload and your carrier would move in the casing causing poor gear meshing and noise while too much preload will make the diff whine and burn through the bearings.

[winfred]

id rather be a .001 or so loose on the bearings then too tight which is kinda hard to measure, once i get a bit more run time on it i may pull the cover and see how it is going but so far so good and if it blows up ill just walk over to the pile of diff's and grab another, i am the guinea pig here for if this diff works or not, if the bearing craps and the diff doesn't.....