S2000 differential busted

Zach Hill · **Posted:** Mon Jun 07, 2010 5:15 pm

Two days ago, I started hearing a faint clicking noise from the rear of my MY02 at slow speeds (< 5mph). The noise varied with speed, but was independent of throttle position, braking, clutch engagement, and gear. I thought it was something like a wheel bearing, and told myself I would take it to the mechanic on Monday, and not drive it too much over the weekend. There was no fluid buildup on the floor of my garage. Last night, on my way home and only a few hundred yards from my apartment, I heard a horrendous CLUNK noise, had 100% power loss, and heard an awful grinding noise until I came to a complete stop, regardless of clutch engagement or gear position. The car wouldn't move and only made grinding noise when engaging the clutch.

Upon inspection, the left axle seal appears to be leaking: http://xak.us/diff.jpg (see discoloration down the side)

My theory is that the seal started leaking, but because it is located so high (in elevation) on the diff, it did not leak at a standstill (i.e. no puddle in my garage), but leaked under load. It lost fluid, and eventually heated up from friction and, well, exploded.

What kills me is that if my theory is true, and I had jacked the car (in 90+F heat) on Saturday and saw the leak, I would have topped the fluid and taken it directly for further inspection and seal replacement, and possibly have avoided now having to replace the diff. :banghead:

It's currently at Jake's Transmission shop on recommendation of a few friends for a diagnostic. I can get a brand new LSD gear unit (I think that's what I need for a rebuild) for about $800, or an OEM pumpkin for $2789 through Honda Performance Development. I have also seen low-mileage AP1 pumpkins on S2KI and S2KCA go for $500-1500. The guy at Jake's said a rebuild would be well over 12+ hours labor @ $75/hour, so that's nearing the cost of an entire pumpkin. Not to mention a new one would be around the cost of two used.

If you have any recommendations, advice on Jake's (and/or Happy Jap's and Performance Chassis, the other two shops I was considering taking it to) or anything else I'd be entirely grateful.

Thanks in advance from a sad autocrosser... :cry:

Karl Shultz · **Posted:** Mon Jun 07, 2010 6:45 pm

Ugh!

Find a used AP2 diff on s2ki.com, and buy it. The AP2 diffs are stronger than the AP1 diffs. As a matter of fact, last time I checked, the AP2 diff is the now-recommended part number if you look up an AP1 diff. I've seen them sell for well less than $1000. I don't know if he's still got it, but here's a guy who was selling one for $500 shipped:

http://www.s2ki.com/forums/index.php?sh ... ry18414308

There are often people parting out wrecked S2000s on s2ki too, so when you see a "Part-out thread," look in there. Check the Carolinas section too, or even post a WTB. I found my backup diff on carolinahondas.com, but it was the first and only time I've ever seen much of anything S2000 related on that site.

JamesShort · **Posted:** Mon Jun 07, 2010 7:13 pm

Damn....I better replace my 'seeping' rear diff seal when I do my new struts/shocks in a few weeks! I've been putting it off for a while now....probably shouldn't take it for granted.

Good luck.

I'd get a whole unit to swap in rather than rebuild....will be cheaper....particularly if you buy someone a 6 pack or two to come over and help you install it.

I'm sure the AP2 diff assembly will be both STR and BSP legal too so you're good to go if you get an AP2 diff (both are 4.10:1 FD).

Zach Hill · **Posted:** Mon Jun 07, 2010 7:18 pm

JamesShort wrote:

I'm sure the AP2 diff assembly will be both STR and BSP legal too so you're good to go if you get an AP2 diff (both are 4.10:1 FD).

This is what I was wondering about! Thanks for clarifying. I also noticed today while doing research that there is a reference from the original AP1 part number to the newer diff part number.

Thanks for the info, James and Karl. I'll continue my search for a used pumpkin. :thumbsup:

JamesShort · **Posted:** Mon Jun 07, 2010 7:24 pm

I've done a few Bimmer diffs, a subaru rear dff and numerous Honda FWD transaxles so I'd be willing to help you tackle this if you want. For whatever used unit you get, mind as well get 2 new seals so you know they are fresh.

JasonWatts · **Posted:** Mon Jun 07, 2010 8:06 pm

I skipped the reading, so shoot me if its already been said.

If you are replacing it, and have the money, get whatever the lates and greatest after market lsd is for the s2k. its STR legal and will put you one step closer to fully prepped.

JamesShort · **Posted:** Mon Jun 07, 2010 8:19 pm

JasonWatts wrote:

I skipped the reading, so shoot me if its already been said.

If you are replacing it, and have the money, get whatever the lates and greatest after market lsd is for the s2k. its STR legal and will put you one step closer to fully prepped.

The R/P ratio has to be the same as stock (ie 4.10:1) and if I'm not mistaken the case has to be the same as stock for STR. The only thing that can change is the LSD unit itself.

JasonWatts · **Posted:** Mon Jun 07, 2010 8:29 pm

STR opend up the rules for Diff's. You can use after market last I heard. Not sure about the R/P ratio.

JamesShort · **Posted:** Mon Jun 07, 2010 8:36 pm

JasonWatts wrote:

STR opend up the rules for Diff's. You can use after market last I heard. Not sure about the R/P ratio.

Yes you can use aftermark LSD units but the unit has to bolt to your stock R/P gears and install into your stock case. My point to Zach was a diff install/rebuild is going to be much more expensive than a stock AP2 full diff unit. There is nothing wrong with the stock S2000 diff unit from an STR perspective. I'd absolutely buy a $800 full AP2 diff pumpkin (almost free install if you do it yourself....not a bad job) than pay $1.5+k for a aftermarket LSD unit and then $500 installation labor into your stock case.

What I think you are referring to is the fact that LSD equipped Miatas go to STR instead of STS and once in STR you can swap in whatever LSD you want, but you have to keep the same case and R/P ratio.

Karl Shultz · **Posted:** Mon Jun 07, 2010 9:08 pm

I should mention, in addition to what I posted above, that there are those folks who claim the AP2 diff isn't any stronger. And I suppose that might be true, especially since AP2s have a delay valve in the clutch hydraulics to take up some of the shock when launching hard. That said, Honda did change the part numbers of some stuff from AP1 to AP2. AP2 diffs seem to fail a lot less regularly, too - I think Jason Saini told me he went through at least two or three on his BS AP1 years ago, and today's tires are stickier.

Donnie or someone else better with rules interpretation would have to verify this, but an AP2 diff might even be BS legal. I checked on hondaautomotiveparts.com for part numbers. Indeed, the same product number is listed for the differential assembly when I put 2002 or 2004 in as the model year. I would imagine that if the factory specified part number is only one part number across all of the cars, the diff should be BS legal. If you care about that.

Anyway. Once you've got the new one, I recommend changing its fluid frequently. I use Lubrication Engineers 1605, and change it roughly twice a year. It's serious overkill, but it's an easy enough job, and even using the esoteric fluid, it only costs me $20 to do it. Besides. I like me some overkill. :lol:

With regards to upgrading the LSD itself - Keith and I have a friend up in St. Louis with a very well put together STR AP2. He's running an OS Giken, and he loves it. Personally, I don't find the standard torsen lacking at all. In fact, we talk about "let the diff do the work for you" all the time with my car.

JamesShort · **Posted:** Mon Jun 07, 2010 9:24 pm

Torsen's don't need any better than ~75w90 extra virgin olive oil to run properly. Just change your diff fluid decently frequently with the cheapest legit branded GL5 lube you can find twice a year and you'll be golden for years and years. If you insist on boutique oils (ie Avon for men) you may be able to let it go longer, but use a UOA to determine this. Many of these boutique lubes shear just as quickly as their lesser priced group 2+/3/4 counterparts.

Karl have you run a UOA on your LE diff oil after 1/2 a year in your diff? I bet it'd be in a state to go straight in someone's engine at that point. 75w90 gear oil is like 10w40 PMCO......drain your diff oil into a clean jug and give it to me and I'll run it in my engine! :lol:

Keith Vail · **Posted:** Mon Jun 07, 2010 9:35 pm

I will +1 everything that Karl has said and I am sorry to see that happen Zach. I change my diff fluid every other oil change because I did it at 10,000 miles and the fluid was fried even using Mobil 1. I am going to switch to the LE stuff that Karl uses.

All the S2000's have the same final drive but the trick is are the AP1 and AP2 diff housings different. If so has Honda superceded the old part with the new? If they haven't then using an AP2 housing in an AP1 is not legal for any class short of SSM or XP. Stupid I know but that is how SCCA wrote the rules. I doubt you would have any issues from anyone locally for doing that though.

Karl Shultz · **Posted:** Mon Jun 07, 2010 9:39 pm

JamesShort wrote:

Torsen's don't need any better than extra virgin olive oil to run properly. Just change your diff fluid decently frequently with the cheapest legit branded GL5 lube you can find twice a year and you'll be golden for years and years. If you insist on boutique oils (ie Avon for men) you may be able to let it go longer, but use a UOA to determine this. Many of these boutique lubes shear just as quickly as their lesser priced group 2+/3/4 counterparts.

Karl have you run a UOA on your LE diff oil after 1/2 a year in your diff? I bet it'd be in a state to go straight in someone's engine at that point. 75w90 gear oil is like 10w40 PMCO......drain your diff oil into a clean jug and give it to me and I'll run it in my engine!

You didn't read the whole post:

Karl Shultz wrote:

Besides. I like me some overkill. :lol:

I enjoy obsessing over my car.

You'd probably think I was delirious if you knew how much I had in my wax collection.

And UOAs cost $30, don't they? They did the last time I did one. Compared to doing UOAs with extra virgin olive oil, I'm money ahead doing it the Avon way. :lol:

JamesShort · **Posted:** Mon Jun 07, 2010 9:49 pm

Keith Vail wrote:

I will +1 everything that Karl has said and I am sorry to see that happen Zach. I change my diff fluid every other oil change because I did it at 10,000 miles and the fluid was fried even using Mobil 1. I am going to switch to the LE stuff that Karl uses.

All the S2000's have the same final drive but the trick is are the AP1 and AP2 diff housings different. If so has Honda superceded the old part with the new? If they haven't then using an AP2 housing in an AP1 is not legal for any class short of SSM or XP. Stupid I know but that is how SCCA wrote the rules. I doubt you would have any issues from anyone locally for doing that though.

Sorry Zach. Keith's comments have blown the AP2 diff out the water... I knew the R/P ratios were the same, but I thought the housings were the same too. Oh well.

Keith, how was your diff fluid fried? Just discolored? At 7500 miles (4000 miles on the fluid) my rear diff fluid was greyish....UOA comes back perfect....still completely in viscosity grade, and friction modifiers and add pack still very strong. Testament to the color means nothing for the lubricant argument.

Karl,

I got your point, I was messing with you. Don't worry my Subie has had 2 "extra s" tranny and diff fills in 9k miles. $15/qt Japanese Fuji Heavy Equipment fluid

. I know it doesn't make sense but I do it anyways.

Zach, In my pursuit for a STX legal 328 I was considering getting a diff unit built for a 325 but setup to put into a 328 open diff case. It was not going to be cheap and there might (probably) would have been some shimming involved so again like a said, you have to weigh the STR/BSP vs SSM legality going to an AP2 diff. So you are best off going for a full AP1 pumpkin as opposed to getting a AP2 gearset/diff unit and having a shop swap it into your stock case.

Karl Shultz · **Posted:** Mon Jun 07, 2010 10:03 pm

I was thinking of the stock class rules allowance for replacement parts, which reads as follows:

[quote=The Rulebook]Alternate components which are normally expendable and considered replacement parts (e.g., engine and wheel bearings, seals, gaskets, filters, belts, bolts, bulbs, batteries, brake rotors, clutch discs, pressure plates, suspension bushings, drivetrain mounts, etc.) may be used provided they are essentially identical to the standard parts (e.g. have the same type, size, hardness, weight, material etc.), are used in the same location, and provide no performance benefit. The allowance for use of such replacements does not include camshafts, differential covers, or ring-and-pinion sets, nor does it authorize the use of piston rings having different configurations (e.g. “Total Seal”) from those of the original.[/quote]

Interesting. I guess the AP2 diff is indeed out. I wonder if a letter has ever been written with regards to manufacturer-specified parts that have been revised over the life of a vehicle, like this case.

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