S15 diff

[McCoy]

Finally... finally got around to installing the new S15 HLSD that I got last April while in Japan

I was quite surprised how easy it was to drop the diff. In the two hours my son was taking a nap on Sunday I was able to drop the diff and get to the point of swapping over the ring gears. The biggest challange was finding the biggest crow bar I had to remove the stock open diff and get physical with it. I used MT-90 for the diff fluid and it's sitting under the car ready to go back up... probably be done tonight after the son is asleep.

I won't go to much into the details of the install since it's well covered on various websites. I used Kent's writeup on the sr20forum, here

My trusty little helper... red, couldn't have done it without him .


Hand carried this all the way back from Japan... wife shook her head everytime she saw it.


Can anyone guess when the last time the diff fluid was changed out. This stuff stunk the whole house up

[Epstein]

A diff that sludgy would stink up a yard on a windy day! By the way, your house is probably ruined now. Better find a new one.

Did you use the special bolts with 13mm collars, or did you just stick the old 12mm bolts back in?

[McCoy]

I used the 12mm bolts, if I would have thought far enough ahead I would have bought a set on ebay when they pop up every once in a while.

Hopefully the house will not stink as bad tonight, I bagged up everything that was touched by the sludge and tossed it in the outgoing garbage . I think I can still smell in on my hands though

[Your Mom]

I got the 13mm bolts off of tom style on ebay. got them in less than a week from japan. You should be ok unless your doing some serious drag racing.

[WilloW]

Have you guys ever heard of people using these to install the S15 HLSD? A while back I was told to use these.

[Your Mom]

yep those are the bolts were talking about. They are very special bolts with a 13mm shank and 12mm tread. I called arp to see if they had any or would make them. they said it would cost me more to make them than the 85 it cost me to get them on ebay. and i tryed multiple hardware stores, i just got weird looks.

so most people just use the 12mm bolts that come off the stock diffs.

[e1_griego]

I still haven't heard of any problems with people using the 12mm bolts.

The helical in my car is some nissan oddball--it's a nissan diff, but uses 29 spline shafts and the regular 12mm bolts. But I would have used the same ones, regardless.

Alex

[Def]

I'm running on almost 3 years on the stock 12mm bolts in my S15 HLSD. Just put the ring gear in the position it'd be if it torques all the way forward and you'll be fine. There is enough of a safety factor on the bolts that the reduction in bearing area is not an issue.

$80 or whatever for some bolts is a little steep for what they are IMO.

[Def]

Alternatively you could make some 13mm OD 12mm ID sleeves to fit around the stock bolts, but I still think it's not needed.

[Epstein]

Those are the Nismo bolts I used as well. I was just inside that diff swapping it into a 4.083 gear. I had my KAAZ in there before. My garage and hands reek of gear oil. Especially when you open a clutch diff with friction modifier in it. Blech.

I'm not about to find out the hard way that 13mm shaft bolts are necessary as I'm doing high speed trips down the interstate. Those $65 bolts are peace of mind. Hey, Def. If you can make some sleeves with 0.5mm wall thickness, more power to ya! A buddy of mine machined up some 12mm OD, 10mm ID sleeves to put a late-model diff into his old S30 long-nose gear/housing.

[McCoy]

Came home to the worst stank inside the house... guess I should have bagged the old open diff and cleaned out the oil pan some more last night

The car is back on the ground and I'm heading out for a test drive... if you don't here from me by midnight, then call the police... I'm probably on the side of the road somewhere

[McCoy]

OK... that was FUN! I always wanted to know what a 2nd gear pull felt like without tire spin, now I know . Also the turn I took coming back off the hwy into town at 3rd gear under WOT was just as fun... I never liked this turn in the 240 due to the back end stepping out when trying to accelerate through the turn.

[e1_griego]

Yeah, open diff > helical is a rad upgrade

I def get wheelspin though lol.

Alex

[knate]

Another alternative is to use Ford starter bushings.. I do not know the years and engines, but if you ask a shop that rebuilds starters to look at a 351 starter bushing you can check to be sure that is it.

Here is my post from another forum:

Some people putting the S15 unit in just bolt in with no problems even with some slop in there, but I didn't want to take any chances.

I was going to have some machined, but I found an easy source for them. I used 12mm ID 13mm OD starter bushings (I believe it is from a Ford starter, I do not have a part number). I just went to a shop that repaired starters and they found what I needed.

They are too long, so they can be cut into two pieces. I used a pipe cutter, which made it very easy. I just had a long 12mm bolt to keep the bushing round and wrapped some tape on there to keep it from spinning. Then make sure you deburr them. They cost about $2 a piece, so only around $10 total if you cut them in half.



Perfect fit!

[McCoy]

Knate - nice DIY bushings there. If I had more downtime, I would have probably done something like this. You could probably get these at McMaster-Carr pretty easily, and maybe even in the right length.

As for a review on the S15 Diff, I'd say it was a heck of a big improvement over the stock open differential! I ran the first session this last friday at 11-12 psi with the T28 then turned it down to 9-10psi just to keep myself from getting into trouble. Last year I couldn't use any boost past the apex or fear of kicking the car out, which I did every lap as it was and I wasn't really enjoying it that much after a while. This year, even in colder weather I could go full throttle in the 3rd gear turns and had to modulate some in the tighter 2nd gear turns. If I did get the back end to kick out some, it was more than easy enough to stay in the throttle and let the car pull its self straight again and don't remember once having the pucker factor. The best part is that you don't even feel that it's there, that's how it should be IMHO.

I can't wait till the next track day when I get to use the 275 RA-1's on a dry day to see how much faster I can get through the turns