RB25 trans on a KA "waking the dead"

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driftedoffroad
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RB25 trans on a KA "waking the dead"

Post by driftedoffroad »

So I am looking for an alternative to the z32 swap and it seems like it could go either way with the RB25 tranny as per this thread:

viewtopic.php?t=26084&highlight=rb25+trans

So just wondering has anyone found a definitive answer on whether this tranny will fit and what modification or swapping is necessary?
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Post by Alonso »

there is a difference. I think the input shaft is longer.

I read about it on hybridz. Search there.
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Post by duncan351 »

I just personally took the backing plates from an RB25 Engine and KA motor. There are only two holes that don't line up at the top of the motor. One of the holes is an alignment tit. This can be pulled out of the block. The other whole is close enough that the hole can be enlarged or just leave it if you want since its only one bolt The rest of the holes including bottom one are the same. :D I'm already running an RB26 clutch on my KA now with my KA tranny. So there's no issue with the input shaft. I've actually seen this before but never really understood why this doesn't happen. Here's more confirmation. I have a customer at my shop right now with a RB25 engine swap mated to a KA automatic Transmission. So yes its bolts right up.
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Post by Pancho G. »

http://www.gtfactory.jp/cms/e107_plugin ... hp?152.150

Guess this is a good first post. either way its a nice way to go. Its halfway down.
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Post by nis240 »

Looks like an easy swap, The only place that you may also have to mod is the starter if the holes dont line up, you would just cut the loop off the KA block and us an RB starter because they actually bolt directly to the tranny.

The other thing is that you dont have many choices for short shifters with the RB25 tranny, that is the one thing i miss on the KA my B&M Shifter. Other than that i beleive that the RB25 Tranny has the same internals as a Z32.


As for RB20 tranny, its the same as a KA tranny.
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Post by ispentallmymoneyontires »

As for RB20 tranny, its the same as a KA tranny.
huh? do they make trans upgrade kits for the RB20 that fit in the KA?

and let me get this straight, the RB25 tranny mates right up to the KA block?
are they significantly stronger than the KA?

:cheers: ?
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Post by Kfred »

ispentallmymoneyontires wrote:
As for RB20 tranny, its the same as a KA tranny.
huh? do they make trans upgrade kits for the RB20 that fit in the KA?

and let me get this straight, the RB25 tranny mates right up to the KA block?
are they significantly stronger than the KA?

:cheers: ?
According to what Duncan said, the rb25det transmission might work. My only concern would be with what Alonso said about the input shaft being longer. I'm sure the clutch disk will still be on the splines, what i would be worried about is the splines pressing against the crankshaft due to the input shaft being too long.

This seems like it might work, but the bad thing is that these transmissions aren't plentiful stateside and importers want $800 for them. I'd rather just pay $1400 for a z32 transmission and installation kit (internally identical) and beable to replace them for $300-$400 if needed. If you can find an rb20det tranny for $500 or so, this would be a great option if it will work.
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Post by killab18 »

well with that link to Powered by Max build.

they said, it works. shows a pic of which hole needs to be egged out. Also says the splines are the same as the KA clutch.

and needs a custom driveshaft.

so good thing is no need for a bell housing adapter plate. You can still use ka clutch and any conbination of clutches we use for the ka (white bunny, rb20/350z) still usable.

they didnt mention anything about the input shaft being too long but i dont know if they checked that.

but yea finding a rb25 tranny is a problem. but if someone local has one it would be a cost effective alternative.

If someone has a rb25 maybe take some measurements on how far past the bell housing the shaft comes.

do the same for a z32 if someone has one

and the same for the ka if someone has one.

i think that will give us the answer pretty quickly.
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Post by nissanfanatic »

The OS Giken upgrade for the SR will work in the KA trans, as the gearbox is the same AFAIK. Although, I think the KA trans is pretty strong as I have flat shifted a lot on mine and haven't broken it. Some strange things have happened on my current trans though. It pops out of 5th a lot and it got stuck in second for about five minutes. Oh well, it's old and slutty, so that is to be expected.

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Post by Kfred »

I twisted my output shaft with only like 330ft lbs of torque, and nitto 555rs (poo drag radials).

I'll have to keep a look out for an rb25 trans for a decent price. If i can get one for $500ish I'd try it out and let you guys know.
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Post by driftfiend »

i found thr 89 300zx trans(5 speed) bolt up to the ka or u could get a t5 borg warner trans from a 1984-83 300zx/1982-83 280zx or jus take the internals from them and install it into the ka trans
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Post by Alonso »

Those t5s aren't any better than stock.
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Post by basic »

the t5 in the 82-83 280zx were in the turbo cars. There's some speculation that it's the same tranny in several mustangs from the 80s as well with a different bell housing. I couldnt' find any concrete evidence of that though.

I do have an idea for a shifter though, but it's a topic for a different thread..
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Post by Alonso »

Mazworx kit all the way
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Post by Kfred »

I almost bought an rb25 bellhousing yesterday. I think if you use the rb bellhousing and 300zx transmission the shifter is going to be in the back seat.

Let us know how it works out, hopefully the shifter isn't as far back as i expect.
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Post by Alonso »

I didnt like how far back the mazworx kit positioned the shifter.

the xcessive kit claims to place the shifter near stock location using their custom bracket and linkage, and they use adapters and spacers so no machine work is required on the housing.

I know I'll end up making/modifying the shifter linkage and bracket as necessary, I aint skeered lol
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Post by Kfred »

If you can score a late 88-89iirc z31 turbo trans, you would be in business. The rb bellhousing bolts on to it and the shifter isn't remote like the z32s. I actually think it might be identicle to a rb25trans except for the gear ratios.

Also check out some late 80's early 90s vg30 d21s and pathfinders look to have the same trans as the 89 z31 turbo.

I have been researching this alot lately lol. Let me know if you find anything out.
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Post by Alonso »

Salvage yards near me want 350-450 for the pathfinder/truck transmissions. Ill stick to the z32 for now as I've seen them go for a bit less plus I have one already. Paid 125 for it :)

The z31 trannies are alot harder to find in my area unfortunately
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Post by vestro »

does anyone know where the shifter placement is on this setup? i might have the oppertunity to get a cheap one stateside and may consider this as an option due to not having funds for a z32 setup right now.
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Post by Alonso »

Idk but my jdm ITR shift knob shipped out
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Post by 240tuned91 »

u can machine a l littel bit of the input shaft in the trans off? or will that rhwo a balance off and make vibration,
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Post by Lucient »

Alonso wrote:I just purchased an rb26 bellhousing. When it comes in ill have a closer look at this...
Did you test fit the bellhousing yet?
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Post by Alonso »

Went with a gsr tranny
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Post by vestro »

any updates alonso? been think of doing this alot now......
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Post by Alonso »

I hit vtec daily
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Post by vestro »

awesomesauce. btw were you able to get any measurements on the z32 bell housing length by chance? if the are the same then this can end up being a overall cheaper alternative.
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Post by Alonso »

Honda
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