RB25 Trans behind a KA24DE

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RB25 Trans behind a KA24DE

Postby titec2 » Fri Jul 13, 2007 7:10 am

I ran across an RB25 transmission for a great price and was wondering how close it comes to bolting up to the KA. I know the output shaft is bigger but I don't think that will cause me any problems because I have a Drive shaft Shop drive shaft and I believe that they can make me a new yoke that will fit the RB trans. So how close does it come to bolting up?
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Postby nlzmo400r » Fri Jul 13, 2007 7:58 am

ive never heard of anyone trying this. All of the RB guys I know use RB trannies and all of the KA guys use either KA/SR/VG trannies. You may have to just take measurements and see whats up
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Postby EviltoM » Fri Jul 13, 2007 9:27 am

It wont bolt up, you will need to make a custom adapter, and a custom tranny mount too. From what I have read, the RB25 is the same tranny as the Z32 tranny but with different bellhousing. Can anyone confirm this?
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Postby titec2 » Fri Jul 13, 2007 9:35 am

I was talking to a local guy and he seems to remember that when he looked at this trans set-up that there were only two bolt holes that don't line up. One of the bolt holes in the trans bell housing he said is close enough that you can see 1/2 of the threaded hole in the block through it and the other will require a redrill. Can anyone confirm?
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Postby LocAss24 » Fri Jul 13, 2007 1:50 pm

kings_blend wrote:It wont bolt up, you will need to make a custom adapter, and a custom tranny mount too. From what I have read, the RB25 is the same tranny as the Z32 tranny but with different bellhousing. Can anyone confirm this?

Yup, basically the same tranny as the Z32.
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Postby EviltoM » Fri Jul 13, 2007 1:55 pm

titec2 wrote:I was talking to a local guy and he seems to remember that when he looked at this trans set-up that there were only two bolt holes that don't line up. One of the bolt holes in the trans bell housing he said is close enough that you can see 1/2 of the threaded hole in the block through it and the other will require a redrill. Can anyone confirm?


If that is the case, we would be able to run modified RB26 trannys as well.I just picked up a z32 tranny form a buddy for $60 (best friends discount) and will be making my own adapter and mounts. Hopefully I can start early next month some time to be ready for the track events in september.
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Postby titec2 » Fri Jul 13, 2007 2:05 pm

Seems to me that if I can make this work without an adapter plate it would be a much better/easer way to get the durability of a z32/rb25 trans behind the ka. I talked with the guy form the driveshaft shop and he said that he can supply me with the correct yoke to work with the driveshaft shop drive shaft I already have and fit the rb output shaft. The guy with the rb transmission is going to bring it to my shop week after next and I will let you guys know what it is goint to take to make it work.
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Postby EviltoM » Fri Jul 13, 2007 2:11 pm

Cool! cant wait for the results.
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Postby nlzmo400r » Sat Jul 14, 2007 6:25 am

well if they're the same tranny are the bellhousings swappable? Saying using a z32 bellhousing with the rb25 trans? Can't wait to see the results of your experiment.
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Postby EviltoM » Sat Jul 14, 2007 7:12 am

Ya they are, theres a guy on FA with an rb26 swap in his z32 and he used his original tranny with the RB25 bellhousing.
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Postby 05gsxr750 » Sat Jul 14, 2007 9:24 am

i heard of a guy useing a rb25 bell housing on his sr20det trans for his rb25 car when his trans went out and people local use sr bell on ka trans when there sr tran goes out. not too sure but it might work....there's a guy on ebay selling his rb25det powered coupe right now that has a bad trans in it and he has a sr trans to throw the 25 bell on to make it work.. so im leaning towards yes but i do not know.
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Postby doggunracing » Tue Jul 17, 2007 4:37 pm

These transmissions are pretty different. VG and RB are similar but since Mazworx makes an adapter for the SR/KA to VG, I would say that there's no 'easy' bellhousing swap here.
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Postby ZmasterB » Wed Jul 18, 2007 9:15 am

05gsxr750 wrote:i heard of a guy useing a rb25 bell housing on his sr20det trans for his rb25 car when his trans went out and people local use sr bell on ka trans when there sr tran goes out. not too sure but it might work....there's a guy on ebay selling his rb25det powered coupe right now that has a bad trans in it and he has a sr trans to throw the 25 bell on to make it work.. so im leaning towards yes but i do not know.


That is not possible......RB25 trans are 30A's, same as a Z32, and SR trans are 71C (RB20, CA18, SR20, and KA are all 71C). A 30A bell will not fit on a 71C trans......they are VERY different. What you are saying would be possible if it were using an RB20 bellhousing.....


I'm the "local guy" BTW :) I have put an RB20 bellhousing on a KA block, the dowels line right up, and only 2 bolt holes need to be modified, one of them is extremely close & could be done with a die grinder in a few minutes.

The RB trans' are a little shorter overall than a KA trans, so I'm interested to see how this turns out also.....I think shifter location/driveshaft length may be a problem, but we are gonna find out.
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Postby titec2 » Wed Jul 18, 2007 9:52 pm

Just a small update... The guy what has the RB25 trans also has a Mckinney drive shaft and trans mount as well. He is scheduled to bring the whole set-up to me on the 29th of this month. I am very excited to see where all of the pieces fall. If i could impose on ZmasterB; i would like to have one of his many ka24de transmissions on hand for comparison. What do you think ZmasterB?
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Postby EviltoM » Thu Jul 19, 2007 5:19 am

Isnt the RB20 bellhousing compatible with the RB25/Z32 tranny then? And the McKinney driveshaft and mount are probably for the BR26 swap into an s13 or s14. Hmmm we might have all the parts readily available, we just have to put the pieces of the puzzle together.
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Postby titec2 » Thu Jul 19, 2007 5:56 am

That is what I am hoping. :D
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Postby ZmasterB » Thu Jul 19, 2007 6:15 am

titec2 wrote: If i could impose on ZmasterB; i would like to have one of his many ka24de transmissions on hand for comparison. What do you think ZmasterB?


Yea I think we can rustle one up LOL.


I had forgotten, I have an RB20 trans that is very dead.....but it could be used for measurement purposes, it has the same tailshaft/overall length as the 25 trans.
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Postby ZmasterB » Thu Jul 19, 2007 6:30 am

kings_blend wrote:Isnt the RB20 bellhousing compatible with the RB25/Z32 tranny then? And the McKinney driveshaft and mount are probably for the BR26 swap into an s13 or s14. Hmmm we might have all the parts readily available, we just have to put the pieces of the puzzle together.


Thats what I'm saying, no, the RB25/Z32 trans are 30A's (big), and the RB20's are 71C's (small, same trans as a KA/CA/SR). The bellhousing from a RB20/CA/KA/SR wont fit onto a RB25/Z32 trans.

I have a friend who is working on getting all the AWD stuff from an RB26 to work on a KA......but we'll see how that goes. The trans fits, its that oil pan/front diff thats a toughie :lol:
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Postby EviltoM » Thu Jul 19, 2007 11:46 am

Oh I see. I was just hoping it would be true. Oh well, I guess I'll continue with my plans to make a custom adapter plate.
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Postby Tad_07 » Wed Jan 20, 2010 10:35 am

ZmasterB wrote:Thats what I'm saying, no, the RB25/Z32 trans are 30A's (big), and the RB20's are 71C's (small, same trans as a KA/CA/SR). The bellhousing from a RB20/CA/KA/SR wont fit onto a RB25/Z32 trans.


+1

I have a rb20 swap & the bell housing is just about the only difference btwn the ka, rb, & sr tranny. There are a few internal differences but nothing to give one more strength than the other.

A rb25 or z32 tranny on the other hand are much better, nicoclub as some good info on them
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Postby Alonso » Wed Jan 20, 2010 12:26 pm

Wtf are you doing?

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Postby Dik_fitswell » Wed Jan 20, 2010 1:36 pm

Maybe swap the Ka bell housing on the rb trans. My friend has basically the same thing but reversed, rb bell housing on a ka trans.
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Postby mo_hish » Sun Sep 12, 2010 11:11 pm

titec2 wrote:Seems to me that if I can make this work without an adapter plate it would be a much better/easer way to get the durability of a z32/rb25 trans behind the ka. I talked with the guy form the driveshaft shop and he said that he can supply me with the correct yoke to work with the driveshaft shop drive shaft I already have and fit the rb output shaft. The guy with the rb transmission is going to bring it to my shop week after next and I will let you guys know what it is goint to take to make it work.


Whatever happened to the guy running the rb25? Did he stop by and shed light on this?
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Postby crazys14 » Mon Sep 13, 2010 2:33 pm

it works, it's been done here in san diego a few times now only 2 bolts dont align.

these trannys are very expensive however which makes the z32 really cheaper in the long run if you ever need to replace the trannys.
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Postby mo_hish » Mon Sep 13, 2010 4:57 pm

They seem to be pretty pricey, but the bell housing can be had for like 250. Can't I just grab the rb25/26 bell housing and bolt that up to the z32/pathfinder tranny? I know I'd need a custom driveshaft and I can fab up the mount if need be, but does the shifter come through the regular shifter hole?
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Postby mo_hish » Mon Sep 13, 2010 5:11 pm

Also, I was wondering why we can't just redrill the z32 bellhousing to fit the ka. I mean, were essentially opening up two bolt holes with the rb25/26 or just leaving them be, so why can't I just pick up a z32 tranny and redrill some holes to mate it up with the ka?

Is it that the z32 is shaped differently or something?
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Postby Kfred » Mon Sep 13, 2010 6:39 pm

The z32 bell housing is not even close to matching the ka block. The rb transmissions line up you just have to wallow out two holes.

You can put the rb bell housing on the z32 tranny and bolt it up to a ka, but the shifter will be back pretty far like this. The rb shifter is similar to the ka, while the z32 is remote mount.
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Postby mo_hish » Mon Sep 13, 2010 8:01 pm

http://zilvia.net/f/chat/270726-pics-z3 ... y-s13.html

The placement in those pictures doesnt seem that off, and that's with the adapter pushing it farther. Is the bellhousing going to push it farther back than that?

The comparison pics of the rb25 vs z32 bellhousings here makes it seem like the difference is very little (about 3/4 of the way down the page):
http://www.houston-nissans.com/index.php?topic=953.0
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Postby Driftnasty180sx » Fri Oct 08, 2010 11:42 am

my 2 cents

stock KA / SR trans- i usually break them at 400+ whp.
(please take into consideration that i drift my car and clutch kicking should be factored...well i would think)

Z32 trans with the MAZworks kit- I would say this is your best option. This kit comes with everything you need such as drive shaft and shifter placement.

RB25 trans has the internals as the z32 trans. In order to make the Rb25 trans fit the two top hole need to get drilled out a bit. Then you need the drive shaft made. (since i dont street drive the car i dont care about the speedo)

RB25 Belt housing could fit on the z32 trans but the shifter placement would be wrong and you would still need to made a drive shaft.
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Postby Keegan » Wed Oct 13, 2010 11:23 pm

Parts shop max runs RB25 trans on KA-T in their green/white S14 campaign car. Just opened the holes up.
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Postby AceInHole » Thu Oct 14, 2010 11:31 am

I saw the PSM car and found a steal of a deal on an RB tranny, so I went ahead and bought it. It should be here tomorrow and I'll get started on it next week or so.

What I found across the internets (rumors/ folklore/ etc):

The RB25DE transmission is similar to the RB20 transmission: it's just as weak as the stock SR/KA transmission. I've seen pics of it next to an RB25DET transmission and it's definitely different.

You can swap internals in the RB25DET transmission with a VG transmission, which should make rebuilds easier to do. Both gearsets are notably larger/ sturdier, which is indicated by the entire transmission looking bulkier than the SR/KA tranny. The easiest visiual difference is the RB25DET transmission has a slanted rear shifter plate, while the RB20/ RB25DE transmission has a flat plate similar to the SR/KA.

PPG makes gearsets for both the KA and RB transmissions. They recommend the RB transmission for cars with more than "400 engine horsepower". It's a pretty strong indicator that the RB tranny is going to be a major upgrade. The ultimate would be a PPG gearset in the RB transmission (or a G-Force T5).

The RB tranny is around 20lbs heavier than the KA tranny. Not a huge difference, but piece of mind that my car isn't going to eat 2 trannies a season is worth it, IMO.

The RB25DET transmission is around 3" shorter from the bellhousing to shifter than the KA transmission. It looks like I've got around 1.5" or so to push my engine back, so I'll be attempting to compensate for shifter position (as well as weight balance) by redoing my motor mounts.
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Postby Alonso » Thu Oct 14, 2010 5:20 pm

Damn that's a lot of extra work just to get the shifter to come up thru the hole. With the z32 tranny I just shortened the shifter assembly...
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Postby AceInHole » Fri Oct 15, 2010 7:45 am

I could just make a new shifter that tilts back more, but I'm always looking to improve my car's performance, so setting everything back is a welcome change. I've already dropped the engine an inch to compensate for the Avid mounts, so another cut and weld should be easy.

One thing I never found an answer to with the Z32 tranny: Mazworks appears to clock it differently than Xcessive. Did that affect the shifter position laterally? Also, was the transmission mount parallel?

Transmission just came in:
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Notes:
- It's huge. Way bigger than the KA/SR tranny. Bigger is better, right?
- Slave cylinder is different. The bolts run in-line with the cylinder instead of on opposite sides. Already ordered a new slave and pivot to get that out of the way.
- This tranny didn't come with a shifter. Any recommendations?
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Postby AceInHole » Tue Oct 19, 2010 5:29 pm

Got a chance to compare the RB25DET tranny to the stocker today:

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Took a KA dust cover and lined it up:

Image

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Pretty much what I expected. The starter bolts, and all bolts below the center are lined up pretty perfectly. The 2 bolts up top are slightly off, and there's one bolt that's just way off. Debating doing something about the bolt that's way off (weld a flange to it) and also might go so far as to fill in the two bolts up top before I redrill those, as well as the dowel pin between them. (If need be I can get it on a CNC milling machine)

Notes:
- The KA release bearing, sleeve, and fork all fit perfectly (so far).
- Looks like a KA shifter might work? Didn't get a chance to check but will confirm next time I'm working on it.
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Postby 91white_ka » Tue Oct 19, 2010 6:45 pm

I'm so excited to see what happens here. Good job man.
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Postby k4rr » Tue Dec 28, 2010 2:37 pm

tt
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Postby turbonola » Fri Dec 31, 2010 3:02 am

when i asked this damn question i got no answer. glad to see someone doing this though.
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Postby DjayS12 » Sat Jan 01, 2011 12:02 am

Interesting thread! keep us updated! :)
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Postby MattPowers » Sat Jan 01, 2011 10:30 pm

i did it. i ran rb25 slave cylinder and also rb25 shifter. ka is different. custom mount, drilled the top holes out, always bolted the first 2 side bolt holes in first, starter i just drilled the threaded section out and run the bolts in from the engine side into the tranny where its threaded on the rb. ka/rb clutch is the same. i used an rb25 single plate on my ka tranny and just kept it when i did this. then i ran this setup with an os giken gear setup. then i just switched to a dog box. i never had an issues but i tihnk to drill out the wholes and stuff is kinda janky. i wouldnt do it again. also i had to remove all the dowell pins.
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Postby trk240sx » Tue Jan 18, 2011 9:23 pm

Bump!! Update on this thread. Looks possible with alittle welding and redrilling. Anyone with first hand info?
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