Gearing swap in d series trans, rt4wd, and LSD options

scootersteve

Hey guys,

Long time lurker first time owner. A little info:

First honda at 13yrs of age, 1987 Honda elite, still have it! Next was a 1995 civic hatch. Pretty much stock with cold air, cat back, full eibach suspension, nippon racing 15" with toyo proxes T1S all around. Really fun car! Next, 1999 Civic hatch, built D16 vtec, high compression pistons, new rods, heavily worked over head, high lift cams, full ITB setup, complete dyno tune with hondata, skunk 2 FULL suspension, urethane bushings, fresh and upgraded fuel system and ignition system, seem welded body, custom plexy rear windows, CF hood and rear lip, JDM front and rear spoiler, LED blinker/tail light upgrade with HID projector headlights, nippon racing c3 in bronze, toyo proxes T1R, stock trans with LSD and full gearing swap (5th gear topped out at 122mph). Quite a few other little heres/theres but in the end we netted 171 at the wheels and with the gearing swap it was incredibly quick!!! Never made a trip down the strip but as a daily driver and circuit racer found it to outrun many an S2000, turbo B series etc. Down fall... Less gearing so the fun was over in seconds and only 120 +- MPH.

Today I own a 2000 Toyota Echo with a celica gts 1.8 swap. stupid quick for a stock motor in a tine car! I have had this one for about 3yrs as is and already have a buyer which is good because I am now in the market for a rt4wd wagon! I have absolutely fallen in love! I have a d16 vtec with various rods/piston combos sitting around, a few stock wrx turbos, various injectors, and a bit of close ratio gears from the 99 hatch setup sitting around.

So, this brings me to why I am here today:
After searching this forum for the past 3 hrs I have not really found my answer, or at least, clearly. I want to know if I can exchange gears from other d series trans into the d series rt4wd tranny. It seams that the 89 and on cars have standard d series clutches and splines so maybe also the same gears? I know the final drive is pretty awesome but I would like to make my gear change very close as it was in my 99 hatch. Well, at least have the option to play with gearing and so on.

I figure a front LSD, rear JDM LSD, urethane bushings, built drive/propeller shafts, and so on will allow for a conservative and reliable 220whp. I think this would be the ultimate little honda "anywhere" car. Kinda a rally setup is what I will shoot for. Mud flaps, brush bar, under carriage guards and fully covered in bed liner, brake upgrades, better wheels and tires to suite, mounted spare tire at rear, etc. etc. etc. You know this is now an obsession!

Really guys, I looked for ever and if you're going to keyboard kill me I can't say I will be too amused... Please, for the sake of me asking, if there are already posts on this just send the link. I say in advance you are smarter than I, have a keener eye, can search in ways I just cant and you are the honda king. I just want to join this spread out crew of diamond in the rough cars all over these 50 states and along the way, show off some naughty pics as she comes together.

Thanks in advance to all who offer answers in the interest of helping a project in motion.

Stephen

stampern

The impression I've gotten for the reading I've done is that the front differential won't work with any of the d series lsd's out there. The d series lsd's will fit in the rear diff though. As for the gears, I believe they are different, but never seen anybody confirm it.

udubrx7

^^ What he said. I don't know about the gears being different though..... as far as I can tell they look pretty similar to the other d-series transmissions except for the SL gear/shaft and the transfer case section.

This is the rt4wd transmission exploded.

scootersteve

Hmm, yeah. I mean without seeing it in person aside from the chart it does look very similar. The output shaft and gear ring set is what seems the most different. I still think with some mods LSD can work. I have looked at a few pictures and diagrams, and appears that things could work. Why it doesnt I dont know. But I will go to town on that issue for sure.

udubrx7

The diff looks the same as all the other open ones I've seen in D-series transmissions, but it has a transfer drive gear on it which I think is held to the final drive gear and differential by 12 bolts which go through all three of those pieces. Sounds like you need to get your hands on a cheap OBX lsd for a d-series, and see if you can make it work with the transfer drive gear and final drive gear. Good luck!

http://www.hondapartsnow.com/online/Pag ... fferential

scootersteve

Guess what, GOT ONE! I pulled it from the trans I got this motor and other stuff from out of a totaled car. The rear end was total carnage. I knew the kid who owned it and have all the papers from the build as well as the break in procedure notes and miles on the build. This whole system has a whopping 1091 miles on it! Thanks for that input BTW. It looks pretty good so far. Boy, you guys are already giving me the giggles about this whole thing.

turbo_teg

the talk has always been that only thing u can do for the front diff is a phantom grip and like stated above a d-series front LSD works in the rear with some mods. ive got the lsd just need a phantom or i might just make one....

udubrx7

Looking at the diagram of the stock 2wd open diff, it looks like there are only 10 bolts that go through the final drive gear into the differential case, same on the OBX. So that is probably where you will run into problems, also who knows about the spacing of that transfer drive gear. You may have to make a spacer/adapter, and maybe drill some new holes here or there. Or maybe it just won't work at all.... I'd be curious why though.

heres a stock 1990 crx si 5spd open diff

Jaker

The OBX fits the rear diff housing perfectly. The only issue you will have is the ring gear bolts. The OEM Wagon rear diff has blind holes where the bolts go right through and thread into the ring gear, whereas the OBX diff has threaded holes, as the ring gear is the part with the blind holes in the FWD transmission. Other than that, all you need to do is get some rear diff bearings (they're tapered bearings) and get the diff properly shimmed for both bearing preload as well as proper pinion/ring gear mesh.

I have a huge pile of both RT4WD gears as well as FWD D series gears here, and if I get a moment, I'll compare some of them to see how compatible they might be.

udubrx7

What about using an obx lsd as the diff for the front wheels on an RT? Any idea why that is supposedly not possible? That's what I was trying to get at.

Jaker

Well judging from the link/photo posted above with the parts breakdown of the front diff, there are 12 bolts on the ring gears/diff so to mount the OBX one would have to weld most of the holes shut (8 of them) on the OBX , re-machine the ring gear flange flat/true/square and drill new holes (10 of them). I have not had the chance to check ring gear flange offsets, etc... to see if it's even close to lining up. Not a priority for me, as I have no need for a front LSD.

leWolf

hey, really hope you get further than i did, I lack the ability to swap gears myself and all the shops in town are way overpriced to do it. I wanted to know if i could swap the ZC trans gears into an dx trans, or if a 93 SI trans gear set will swap into a 88 dx trans.

udubrx7

AlexanderleWolf wrote:

hey, really hope you get further than i did, I lack the ability to swap gears myself and all the shops in town are way overpriced to do it. I wanted to know if i could swap the ZC trans gears into an dx trans, or if a 93 SI trans gear set will swap into a 88 dx trans.

Well unless you want to get REALLY complicated and do stuff like swapping out 5th gear etc. you really don't need to worry about all of those gears. Not 100% sure about the ZC but I know that ALL of the 1-5 gears and shafts on the 89-91 5spd civic transmissions are exactly the same. The 88's have the same gears, but the spline # on the shaft is different. You're probably thinking about final drive ratios right? To change the final drive all you really need to do is use the ring gear off of the differential (or the whole differential in some cases) of the transmission which has the final drive that you want and put it in your transmission. Your problem is that the DX transmission has 35mm diff bearings, and there is a counter-bore in the transmission housing which is 35mm.......the Si transmission has 40mm differential bearings. So you can't just take the diff out of an si transmission and put it in your car. Long story long, buy an Si transmission, then see if you want to change the final drive. It'll be cheaper and easier for you in the long run.

Jaker

Some of that is not correct. The final drive swap includes changing the mainshaft (or countershaft, I always mix up those terms) as well as the ring gear. It's like changing the ring and pinion on the rear end of a Ford of Chev muscle car. They're a set. It does not matter what size bearings you have. Keep your existing diff, and just change the ring gear. Remember that the ring gear bolts are left hand thread (wrong way thread).

I have done lots of gear swapping in the 88-91 transmissions. The best setup I ever ended up with was in my 89 hatch Street Modified autocross car. I had the ZC 1st to 5th, and the JDM Integra ZXi (RT4WD Integra) 4.4375:1 final drive. That shit ripped. Sure, 75mph in 5th was 4,000rpm, but the car, along with the optional JDM Civic LSD (O.S. Giken, same diff as the ITR, but sized for the Civic L3 tranny) and the supercharged D series in a 1,900lb car was an absolute blast! Oh, had a 7 1/2lb flywheel too!

Pretty much all the 1988-1991 Civic FWD gears can be mixed and matched. I do know that some of the EG and EK D series gears can also be swapped, but I have no experience with those, so can't offer any advice.

turbo_teg

jaker im sending u my lsd and my diff so it gets done right. let me know what u would want to do this if u would want to do it at all. ill do anythig but setting up gears has always scared me for some reason.

udubrx7

Thanks for the correction. I also didn't mention that the HF 1-5 gears are different. The ZC 1-5 gear ratios are 3.250 1.944 1.346 1.033 0.878 with a final drive ratio of 3.888, I'm sure those gears with the 4.437 FD was pretty epic, especially with the supercharger!

Looking at a table of the gear ratios...... even if they would fit, it looks like it wouldn't really be worth the effort to use the 92-95 si 1-5 gears unless you happen to have your tranny split apart and happen to have those gears sitting next to you.

http://www.knology.net/~jediklc/gearratiosdseries.htm

Haydz

Just to add, the JDM Integra ZXi is not RT4WD. It is FWD and uses the same gearbox as the JDM Shuttle 56i. I have one of the gearboxes in my garage.

leWolf

yeah I have about 5 transmissions that all seem to have some issues somewhere and that is why I was playing the mix and match game. I'll just chunk them and move on.

Jaker

Thanks Haydz. I guess the "net" is full of misinformation. There was a RT4WD ZXi starting with the 3rd gen DC chassis, but as applies to this discussion, the ZXi gears we are talking about come from a FWD transmission.

Matt, I didn't do the shimming myself. I trusted the "experts". I took it to a place called Gears and Rears. I did the initial grinding of 2 ring gear bolt holes just to prove the concept, and then had a machine shop open up the other 8 holes.

Alexander, if any of the transmissions your going to "chunk" is RT4WD, I'll gladly pay shipping and take it off your hands.

turbo_teg

ahh i see no prob i have a buddy that can help me do it.

leWolf

naw, hydro si trans with bad input shaft bearing, and so on.

turbo_teg

anyone ever think of trying to use an integra LSD for the front diff on the RT trannies? cuz even if u got a d-series diff to work the axles are the same spline count as 90-00 integras as our RT's. I think im gunna just do the phantom grip i just dont know whick model of car i need to order it for.....

udubrx7

No idea about the LSD....

http://store.phantomgrip.com/catalog/pr ... 40df319097

Phantom Grip Part No. PGHO1334 is for the 4wd wagon. But if you want to be really cool you can get the one for a '66-'70 Honda S800, because the part number is PGHO1337

Jaker

Teg diff won't work. 10 ring gear bolts. Wagon RT4WD front ring gears are 12 bolt. If you wanna do some welding and re-drilling, it might work, but then you have to worry about the offset of the ring gear flange.

turbo_teg

thanx mang

turbo_teg

ahh were u discussing that above jaker? i read the whole post again and started going cross eyed with all the talk

shenrie

udubrx7 wrote:

Not 100% sure about the ZC but I know that ALL of the 1-5 gears and shafts on the 89-91 5spd civic transmissions are exactly the same.

Is this confirmed information? Im having troubles finding gearsets for my rt tranny, but if this is correct, you just made my day.

udubrx7

Notice that i said "on the 5spd transmissions." I don't know about the RT's tranny.

shenrie

Dang. Thanks for the clarification.

Been looking around the quicklinks, but cant find the RT gear ratios. Is this info available?

Jaker

viewtopic.php?f=7&t=4893&p=53882&hilit=ratios#p53882

Bottom of the page!

shenrie

^^^ thank you Jaker!!! Now off to comapre with other d trannies.

Any ideas on where to purchase gearsets from for the RT?