DIY: Swapping SR Bell Housing to KA Transmission

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Hijacker
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This tutorial is to help those who have had their SR transmissions go bad on them. KA 5 speeds are a bit more abundant, and aside from a slight change in 5th gear, are identical to the SR trans. The only major obstacle to overcome is that the bell housings bolt to their respective blocks differently.

This tutorial will help you tear the trans down all the way so you can inspect the gears, but I will not supply information on rebuilding the gear sets if yours is having problems.

WARNING! There will be lots of stinky, nasty, and all around obnoxious gear oil. Plan on making a mess.

I did this swap using an S14 manual trans we had. Some of the pictures will differ slightly, but the procedure between an S13 and an S14 transmission should be the same.

You can see the obvious differences in the bolt pattern.

The backsides are identical though.After you have your transmissions disconnected and sitting free, you can start the transplant. This tutorial will cover mating a KA tail shaft housing and gearbox to an SR bell housing.

Remove the gearbox breather tube, throw out bearing, and clutch fork as well as the rubber clutch fork boot. This will give you access to the front cover inside the bell housing. Remove its bolts and pull it off. If it’s giving you trouble, you can work a pry bar in through the clutch fork hole and place it on the clutch fork pivot. A few taps should knock it loose. There’s a shim that is placed on the countershaft bearing. You will need to save that. There is also a big retainer clip around the input shaft bearing. Get a ring spreader and pull it off. A pick can help a ton here too.

There's the nasty nasty ring.

Now get a couple small pieces of 2x4s and set the trans up on them with the bell housing facing down.



Next is to get the tail shaft housing ready to come off. There is a small plate held on by 2 10mm bolts. It prevents you from going into reverse while moving. Note its orientation and pull it off. Next pull the two spring retaining bolts from the shifter housing. Both have springs beneath them, so be careful. You should be able to pull one half of the plunger out. The plunger is in two halves and keeps the gear selector from rotating.

The two parts that need to come off.

Now pull the bolts holding the two halves of the trans together. Take a mallet and knock the housing loose. The ears for the trans mount bracket work well for a spot to hit. Rotate the gear selector as far to the left as possible (towards the driver side). It should pull up easily. If it has resistance, it hasn’t cleared the shift forks and is still hung up on them. I suggest getting a feel for how the forks maneuver around the shifter linkage. I would pull the tail shaft housing off and put it back on so you know how everything should be oriented.



Now you can remove the bell housing from the gears. Lay the unit back on its side with a block of wood propping it. Take your mallet and hit the input shaft to start separating the sandwich plate from the bell housing. It will come with enough persuasion. Just don’t get too mallet happy and accidentally knock the bearings out of the sandwich plate. You could also use a screwdriver or a pry bar as a wedge and separate the sandwich from the bell housing as well. Just be careful not to tear up any of the mating surfaces.

You should be left with this.

Take the time to inspect your gears for unusual wear, wobbly countershafts, or anything else that may stick out to you.

Repeat all of that for your other transmission.

Reassembly is pretty much the reverse of the teardown, just be careful when you’re reattaching the tail shaft housing. It takes some practice to learn how to maneuver the housing on without getting hung up on the shifter forks. You will know if you do get ‘em hung up. They usually knock a fork forward, which you can see from inside the bell housing. Just get a feel for how you took it off.

Make sure to reapply gasket maker to both sides of the sandwich plate, and sometimes a thin layer on the plate inside the bell housing helps too in case your gasket in there got a tear in it.

Now you can drop this trans back into your car!

It is possible to change just the bell housings and leave the tail shaft housings on. Remove the plate and snap ring inside the bell housing and then pull the bolts and knock the bell housing off. Use the input shaft and you should be able to keep from breaking the gasket seal for the tailshaft housing. Reapply gasket maker and put the new bell housing on. Quicker, easier, but you won't know what shape your gearbox is in.

I will try to clarify this and update it so it's more legible as I get more feedback. Please PLEASE don't bug me on AIM about this procedure.


Emperor_Tha
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good job. so what is the difference with the 5th gear? ka is slightly longer gear ratio?

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Hijacker
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KA is a bit taller IIRC. You shoudl be turning less RPMs with 5th gear given the same speed. Since 5th is an OD gear anyways, you don't really lose anything.

Emperor_Tha
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so it would mean better mpg?

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Hijacker
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a slight improvement. The change isn't that dramatic, though.

The SR uses an .838:1 gear ratio and the KA uses a .759:1 gear ratio

So if I'm actually able to keep this straight, which I have difficulty with gear ratios I might add, the KA's gear will allow the engine to turn slower given the same road speed.

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duffman1278
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Just a side not, its DIY, you have DYI. Simple type o

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Hijacker
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Heh. Thanks duff. I must have been typing too fast.

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ILikeMy240sx
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baller write up.

Thanks!

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jdm_master_X
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excellent write up man.

just by chance do you know if this applies to CA18s as well?

Seishuku
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Nice write-up, but there's no need to remove the tail housing... You only have to pull off the bell, it saves a lot of trouble.

And yes, it pretty much applies to all Nissan transmissions, as long as the models match. In this case they are both FS5W71C transmissions, and so is the CA18DET's (all 86.5-88 S12's, all S13, and all S14's got that transmission, as well as a few Z31 and other Z cars, and some trucks).

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Hijacker
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This is the same technique I use for doing old L series transmissions too. Taught to me by an old datsun mechanic.

I recommend taking the tailshaft housing off so you can inspect the gears. Also since you're removing the bolts that hold the sandwich to the tailshaft housing, you can almost guarantee it that the gasket seal will get broke between the sandwich plate and the tailshaft. But that's just the way I do it, which is why I wrote it this way.

I also wrote this more of less to give a fuller understanding of tearing the trans down than to just simply swap bell housings.

EDIT: I edited the how to clarify that this is a walkthrough to help you tear down the transmission and inspect your gearbox. I added the simpler procedure.

Nissan786
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Right on i just finished doing in in my s13 because someone dropped my tranny or somthin happened when it was shipped. long story short it was stuck in first somthing got bent and everything works fine

silvia tech
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Killer write up, good detail and great pictures!

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91RMKS13
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silvia tech wrote:Killer write up, good detail and great pictures!
Werd.

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drft_808
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nice job. should be a sticky. how much stronger is the ka than the sr?

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efrain240sx
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hijacker I have a quick "Q?" : Do you know if the bearings on the input shaft and the ones be low the shaft ( I don't know the name of does ) are the same on the sr & ka bell housing? I ask because my sr trans is making this loud clunking noise all the time. So I got my self a KA trans and I'm going to swap the bell housing over. I don't want to take the chance that the clunking noise is one of does bearings so I want to replace them with new ones. But I don't know if I can use some of a ka trans or if I need to find a place that can get me some for a sr trans. Thanks

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Hijacker
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They're the same. The gearboxes are identical save 5th gear's ratio.

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sr20powerd
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Do any trans have a lower 5 gear than the KA?

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efrain240sx
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kool thanks hijacker

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Hijacker
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sr20powerd wrote:Do any trans have a lower 5 gear than the KA?
I couldn't tell ya to be honest. Although I think anything lower than the KA's would result in some annoying power loss during highway travel. You'd gain a bit in mileage, but not worth having to downshift to 4th to pass anyone.

RAStreet
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Holly crap, I'm glad I found this! My SR tranny is somehow locked into first gear and the shifter is still in neutral. Luckily I kept the KA and transmission, I was actully going to call the junkyard to come pick it up this week. Thank god I found this post or I would still be pulling my hair out and listening to my girlfriend gripe about more money being spent on the car.

Thanks A LOT for posting this!!!!!!

On a side note, does anyone know what is going on with my other tranny? It has me somewhat confused.

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Hijacker
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The shift fork for that gear jumped out of place. Can you put the shifter in first gear?

RAStreet
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Sorry to take so long to get back. To answer your question, no the only gears it will go in are 5th and reverse. And reverse seems to just lock up the transmission. While the car will move forwards in neutral.

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Hijacker
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Sounds like the shift forks are messed up for 1st-2nd and 3rd-4th. The cheapest route would be to swap a KA gearbox onto the SR bellhousing I think.

RAStreet
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Yeah, I'll never get it, It drove fine the whole way to work. But when I went to move it to go home, that's when I noticed it. Oh well, thank God I didn't get rid of that KA yet.

And actually, I'm in the process of changing the tranny out now. Just waiting for my friend to get here so we can actually pull the transmission from the car.

Nissan786
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If it was me i would rebuild the old sr trans so you have a spare.......just one of the just in case things

Emperor_Tha
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So everything in the tailshaft is the same. I lost the pin that goes to the fork where the shifter sits on from my old sr tranny the blew up. I should be able to use the ka pin instead?

Are the sohc and dohc ka tran the same

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PantherRacer
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OK, Changing transmissions in cars with different power levels is a good way to knock off 1/4mi times. For you guys that wanna go fast.But know this, the transmission with more torque in it will decrease your gas mileage, since you will be at a higher RPM in the taller gears.

below statement is just an example:here's the scenario:Nissan has the SR20DE and DET.Now, so the DE can Hang with the DET, it has gearing that will allow it to keep up with the more powerful engine. Gears are the great equalizer for power variances.

So now, say you throw the DE tranny in the DET, you will drop seconds on your 1/4 mile time. but your gas mileage drops since your Revs will be higher in the higher gears. but hey, you'll get where you're going quicker!

This is basically one of the formula that car makers go by. change a couple of teeth in the transmission instead of giving the car more power, and it can hang with the more powerful variants/cars.

Rusker
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Great writeup!

Emperor_Tha
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Is it possible to swap parts from the de to the det like swaping 1st 2 be and 3rd gear?


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