RB20 Transmission Rebuild Help

[Rustys14]

I've found myself in a bit of a situation and wanted to post up here to see if anyone has any insite on which rebuild kit to use.

Backstory: I'm working on an S1 RB25 swapped coupe that I just picked up and currently have the motor out to paint the bay and do a bit of cleanup. The motor came from an automatic R33 so the previous owner used an RB20 transmission (RP71C #2) with the swap. The issue is that they did not install a pilot bushing which has caused the input shaft bearing to go out. The transmission also has a slight grind going into 4th gear that I would like to get sorted as well so I figured I would rebuild the transmission while I have everything apart.

Here is where I'm running into an issue. The only rebuild kit I can find for an RB20 transmission is from an eBay seller in the UK and he wants over $600 once I factor in shipping. Normally I wouldn't be opposed to paying this, but that is super steep for a bearing and syncro kit and at that point I would be better off sourcing a new gearbox.

I can tell that the eBay picture is lifted directly from the Cobra Transmission website so I assume he is buying one of their kits and selling at it at a huge markup (their RP71C kits are around $150). The issue is that Nissan made several versions of the RP71C over the years and there are multiple options on the Cobra site. I know a 240sx bearing kit will work with the RB20 transmission, but the syncros have me stumped. As far as I can tell, my transmission uses the 3 piece second gear syncro from the newer versions of the 71C, but uses the larger 3rd and 4th gear syncros from the earlier models so the syncros in the 240sx kit won't work. Does anyone know or have a link to which kit I should use? I reached out to Cobra a few days ago and am waiting on a response, but there are a few events I want to drive next month so I'm in a bit of a time crunch and was hoping someone on here would know so I can get everything ordered.

[Rustys14]

Update: I received a response from Cobra that they don't sell a syncro kit that will work for my application anymore. Does anyone know of any other sources for RB20 syncros? They don't seem to be available through Nissan anymore.

[Ashchetum]

I actually have a rebuild kit, I'll PM you

[Kingtal0n]

I thought the RB20 and sr20 trans was very similar or the same?

I also remember a transmission from an RB25 laurel (4-door) that definetely has sr20 transmission parts inside it

I have an automatic from an RB20 R32 I just pulled out for a powerglide...

[Rustys14]

Originally Posted by Ashchetum

I actually have a rebuild kit, I'll PM you

Awesome, I just replied

Originally Posted by Kingtal0n

I thought the RB20 and sr20 trans was very similar or the same?

I also remember a transmission from an RB25 laurel (4-door) that definetely has sr20 transmission parts inside it

I have an automatic from an RB20 R32 I just pulled out for a powerglide...

They are very similar. As far as I can tell the bearings and seals are identical in the RB20, SR & KA transmissions, but comparing them the 2nd, 3rd and 4th gear syncronizers aren't compatable. I believe the syncros are the main difference aside from the RB casing being about 4 inches shorter in overall length.

Replacing the box with a new RB25 box (or something more stout) from Nissan has crossed my mind since they're easy to source and not all that expensive considering its a brand new OEM transmission. But then I'm down the rabbit hole of needing a new driveshaft, trans mount and having to modify my harness which I'd like to avoid. I don't plan on making more power than the RB20 box can handle so sticking with it makes the most sense from a time/money standpoint if I'm able to source the parts to rebuild it.