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 Rb20 Gearbox On Sr20 In S13? - can it be done  

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RS2KB-rad
  • RS2KB-rad
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  • Joined: 29-October 06
  • Posts: 54
  • From: Brisbane
Post #1 post 6th October 2008 - 09:55 PM
Hey there,

The gearbox in my 1993 sr20det 180sx decided it was time to give up the ghost last week. I have been looking around at options for what to do..

I have read that the rb20 gearbox is the same internally as the ca/sr box and that the bell housing on each of them is interchangeable.. I also gather that it is possible to install a sr20 box on an rb20 by using the sr bell housing. I'd like to know few whether the same principle applies the other way?

1. With sr20 bell housing on an rb20 box in an s13?
2. Does anyone know if it will fit in the stock manual tunnel of an s13 and is it the same overall length?
3. Can the stock s13 driveshaft be used or would the rb20 input shaft need to be adapted, 4. Is the Speedo drive the same?
5. Are the gear ratios the same in all of aforementioned gearboxes, would they differ between rb20, rb20det, Skyline, Cefiro, Laurels etc ?

the reason I ask is the rb20 boxes seem to be cheaper than sr20 ones and it would be good to know if this can be done, making it easier to source a replacement box..

Thanks in advance guys..

Cheers,
Brad
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mongrel_cae71
Post #2

ratios are different
don't know about the tail shaft(splines are the same but I'd say its abit short)
It will fit in a s13 trans tunnel
and the front cases are interchangable.
problem is that the rb box is designed to be behind a longer 6cylinder motor, which means if you swap the cases and fit it up to a SR, your gear stick will sit almost ontop of you radio(about 5-6 inchs forward)

RS2KB-rad
Post #3

QUOTE(mongrel_cae71 @ Oct 7 2008, 05:08 PM) [snapback]1282971693[/snapback]

ratios are different
don't know about the tail shaft(splines are the same but I'd say its abit short)
It will fit in a s13 trans tunnel
and the front cases are interchangable.
problem is that the rb box is designed to be behind a longer 6cylinder motor, which means if you swap the cases and fit it up to a SR, your gear stick will sit almost ontop of you radio(about 5-6 inchs forward)


Ok so length would likely be the issue? mongrel_cae71 do you think this would still be the case with the sr bellhousing, ie are the two boxes the same length from where the bellhousing bolts to the box, to the rear seal? Also would the input shaft be the same length?

SR Box

RB Box
mongrel_cae71
Post #4

the RB box (from the sandwich plate to the selector) is shorter than the SR/CA box same measurements(CA and SR share the same dimensions)
I am under the impression that the sandwich plate to the rear seal is shorter too, though i have never actually checked.
Use RB gearboxs with CA/SR front housings to mount SR's/CA's into AE86's/AE71's as standard SR/CA boxes put the gearstick through the centre floor brace and handbrake. RB box puts the selector through the original tunnel hole(only just)
input shafts are the same length between all three boxes.
for reference, the RB20det box is no stronger than a SR/CA box(gear and shaft sizes), the only difference is overall length and that the RB has double syncro assembilies in the first three forward gears

RS2KB-rad
Post #5

Thanks for your help mate, I'm aware that it's not advantageous to have an rb20 box in terms of strength, I've just seen a few with a cheaper price tag than the SR ones (these prices could reflect quality though, who knows). If I can ill find an rb20 box and measure it up and compare it to mine to see if the swap can be done.

Cheers,
Brad

iamhappy46
Post #6

Only difference in gear ratios is 2nd gear, with the RB20 one being longer geared(more speed from same engine rpm). All others are identical

RS2KB-rad
Post #7

QUOTE(iamhappy46 @ Oct 8 2008, 10:02 PM) [snapback]1282978026[/snapback]

Only difference in gear ratios is 2nd gear, with the RB20 one being longer geared(more speed from same engine rpm). All others are identical


Ok, thankyou for the information. You wouldn't happen to know anything about the physical dimesnions of the box would you? Thanks mate.

Cheers,
Brad

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