For you L series guys, Check this transmission out

[rayaapp2]

 

I picked this up this past weekend. Its a 5spd RB20det transmission.

The backing plate is for the L series. The Starter, and both bottom bolts including the lower left dowel are correct. The top bolt holes and locating dowel are close but no cigar for a direct bolt up. With a simple drill press though they could be corrected(slotted or whatever) to accomedate the L series block. The only thing I do not know is angle of the dangle. Where will the shifter be in relation to the old L series shifter. Both engines lean the same direction towards the right side.

 

Ive kinda suspected that the transmissions were close, but not that close.

 

Its not that far of a leap to use the RB25det transmission for a high HP L series turbo build if the lean angle is correct enough.

 

thought I would share my findings. Anyone know anything about a swap like this? Could be a nice alternative to swapping out the KA bell housings as the RB20 transmissions cost about the same and are also fairly abundant through engine importers like Venus Auto or what have you.

Edited October 5, 2011 by rayaapp2

[duragg]

That front bearing cover plate looks aweful familar..

[rayaapp2]

Right!

 

Its the same transmission they used(with exception of gear ratios) on SR, CA, KA, and other RWD late 80's through mid 90's engines. Nissan just change the bell housing to accommodate each application.

Its gonna be some time before I pull my transmission from my 240Z. If anyone is really curious they are welcome to drag their L series transmission over here and see what the difference is.

 

I have an extra block around that can be used as well.

 

Ray

[ovenfood]

its a yes and no sort of thing. I cannot remember of the top of my head at bed time all the combos but the box fits so will a CA box although both boxes are not at the wrong angle looking front to back the L leans like \ and the RB and CA like / I have also heard of people getting a RB20 and an L series and swapping the bell housing but I did not look into that much so I can't help much...

[Tony D]

Should be of no surprise, the RB20 was the generational replacement for the L-Series in the model lineup in 1983/84. Same cars, just different engine/tranny.

[rejracer]

Ray,

The transmission is a FS5W71C. The L series Bell housing is swappable with the KA / V6 (VG?) / RB20 bellhousing as ovenfood indicated. I got the same transmission but from a NA 1987 300zx, and plan on following Nigels writeup when the funds become available. The machine work required on the L series bellhousing is the following:

 

1. Bore the counter shaft hole to 62mm so it will accept the FS5W71C bearing. (or swap out and use the FSxW71B bearing but that's weaker.)

2. Take about 3mm off the face area around the counter shaft bearing to clear the cluster gear.

3. Enlarge the 1-2 shift rod hole to ~16mm.

4. IF you are using a 4spd bell housing you will need to relocate the reverse switch.

 

Nigel did an excellent writeup on this.

 

Nigels FS5W71C writeup. Edit: Another person doing the same mod.

Edit: Nigels writeup can be found here: Clicky Look in his Albums

 

Now if what you are saying is it's as easy as drilling holes, that makes it much simpler. Do the RB20 and RB25 bell housings have the same bolt pattern? Too bad the the bell housings are not swappable between the RB20 (Fs5w71c) and RB25 (Fs5r30a).

Edited October 6, 2011 by rejracer

[Nelsonian]

I am wondering if it is absolutely necessary to go the route of swapping out the smaller bearing for the larger 71c bearing. I have been told by others that it wasn't. I have looked at that great write up by Nigel, with intentions of installing an s14 5speed from a 98' black top front clip, with a early 280z bellhousing. Hopefully not jacking the thread, just looking for opinions on this step.

[rejracer]

You can use the 71B bearing, it's just weaker, and you need a bearing puller. Considering the countershaft bearing is a very common failure on the 71B boxes, it makes sense to swap it out.

 

If Ray's idea works out, it makes all the mods I described unnecessary.

[cygnusx1]

I ran an early 80's 200SX trans 5-spd in my Z for many years. It has a really low 1st gear. Good for tire smoke. I just had to install my original four speed bell housing.

[Tony D]

I would agree, one of the primary reasons to swap to the later transmission is strength--the gears are wider.

To leave the early bearing in there defeats the purpose of the swap. You put in stronger gears to handle more torque, then overload a 'weak point bearing' from a transmission which is rated for much lower torque/horsepower.

 

Short term, it works...but long term?

 

FYI in Japan they cut down the shift fork to fit the earlier tranny, rather than bore-up the casing. I guess they want as much aluminum die-cast supporting the rods as possible. And THAT takes some doing as you have to disassemble the clusters to some extent to remove the rod, chuck it in a lathe, cut the end down, and then reinstall it!

 

Then again, I suppose their logic is 'while it's apart, overhaul it' and therefore turning down the rod is simply another step while the thing is all the way down.

[rejracer]

When I do mods I think of serviceability. If the trans were to fail, I want the least to do to get it up back up and running. Splitting a case can be done in a pinch while on the road with minimal tools. Swapping out a shift rod would be a problem. Perhaps I just put too much thought into these things. Although turning down the rod would result in a lighter transmission by about an ounce or so? If the Japanese do that mod for weight, perhaps they put too much thought into this too! Although I would have to ask why did the engineers enlarge the shaft to begin with, I would assume is they have had a number of them bend during hard shifting? I suppose machining it at the end is not going to weaken it as much as if it were reduced diameter in the center.

 

I guess my logic is to modify the bits that don't break, so when it comes to replacement, there's minimal parts swappage going on.

 

What Ray is talking about and what Nigel did only modify the front case. I don't know of an easier way to get an upgraded transmission in for so few dollars. The while your at it also comes into mind because the front case must still be modified by doing a face cut to clear the thicker cluster gear. It makes sense to bore out 2 additional holes.

 

I have 150 invested in the trans, will have ~150 in machine work, 250 on a drive line. So for 600ish out the door it's a pretty good swap in my opinion. If Ray's idea works this mod could be done for 450 or so, and that's assuming you have a new drive line made. Do the drilling yourself and use a early drive line and this thing could be in your car for just the cost of the transmission, which I am estimating to be in the 200 range.

[Tony D]

Are you serious? Are you seriously saying the shift rod in these transmissions is a point of failure. Well, I've been into and out of them since about 1984 and I have YET to see a rod cause a failure. The roll pins through the rod yeah. And with a machined case, there is logic (as I stated) about leaving as much meat in that area as possible. I just mentioned it as 'that is what I saw them doing in Japan' and they've been doing this swap for quite few more years than we have on this side of the pond. I don't see why they would machine the case and NOT bore up the shift rod. It does seem easier to me to do it that way. But 'serviceability'---that's a moot point in this discussion. If you are seriously considering failure points, the CASING and BEARING come FAR before 'sliding back and forth shifting rod'!

 

Casings I've seen split, gears break, but MOST OFTEN: BEARINGS FAIL.

 

The largest reason these transmissions STOP you on the roadside is a BEARING. A synchro that goes bad will not make a bit of difference on the road. Bungee the thing in gear and drive on (been there, done that, TWICE.)

 

But the bearing comes apart, and that shaft deflects? You start rapidly grinding gears to nothing.

 

If you are saying you do this swap at the roadside, I call bullshite. Unless you got the premachined casing sitting in the back of the car when it happens, this is NOT a 'roadside swap.' Seriously, roadside maintenance? When was the last time you rebuilt a Datsun Transmission on the roadside?

 

That's way out there as far as I'm concerned. Not a factor.

 

EITHER modification path is a ONE SHOT deal. Once the machine work is done, you're finished forever.

 

If you don't change the bearing, you have a failure prone part left inside. A part which you already have to swap from one tranny to another (or buy new.)

 

For me there is no big difference in the shift rods. If you are rebuilding the thing, it's up to the person doing it. I guess there is an argument to be made that cutting down the rods makes for a stronger front casing.

 

But if you are going through the trouble to do the swap, the larger bearing is compatible and designed for the torque handling capability of the transmission. I'm all for quick and dirty swaps...but there is a point where it doesn't have a payback.

 

I feel this is one of those instances. I have half a dozen of those five speeds with THAT bearing failed sitting in my container. It's the prime motivation to have gotten a couple of the later trannies in the first place. Stronger. Less apt to fail. Same serviceability, but with a better shifter.

 

I just never thought someone would claim the reason not to use the bearing was because they might have to do this on the roadside one day. I got news, THAT ain't gonna happen!

[Tony D]

" Although I would have to ask why did the engineers enlarge the shaft to begin with, I would assume is they have had a number of them bend during hard shifting?"

 

I missed that, but deflection may be a reason to upsize the rod. Turning down the ends of an immovable pilot point will not have any effect on this function. I would not say 'bend' as that implied they took a set. I would probably say the more correct word would be 'deflect' which made shifting harder. And with the IMPROVED shift linkage in the tailshaft, more force can be applied.

 

Again, turning down the pilot end really isn't a factor. Look at the Clutch Input end of the tranny to see the exact same turning-down of a critical input device. And everybody does it!

 

This all involves the front case, I don't know where you get the idea you cut the whole thing down, just where it pilots into the end. Then you don't have to drill anything and the factory alignment of the rods is preserved...

 

Remember, I'm not the guy talking about prospectively using a hand-drill on the operation. You want to bind the shift rod, misalign those holes a mm or two when the drill skips around a bit. See how nicely they shift then. By turning down the shaft, that potential fail in aftermarket machining is eliminated. And it IS a REAL concern. Any monkey can run a lathe. Center-Finding the hole and then competently redrilling it or machining it oversize DOES take SOME skill in machine work.

[280z"Vador"]

This thread is coming interesting since I have an rb20det tranny at home and my Z need a transmission upgrade

 

Well the problem is that I know many GT-S R32 user that always broke theirs rb20 trannies and upgrade to an rb25 instead... I mean, the RB20 is a 2.0 liter without "many" torq and can pass through theses trannies like butter so what about a 2.8 liter turbo with mods (more torq/hp here)? I'm not sure if an KA/CA/RB tranny is a kind of an upgrade in term of solidity... Well gears are larger for sure but is this enought to old the numbers of a slightly modded l28et?

 

EDIT: I'm worried about the gears more than the bearings since my 3 l28 trannies that I went through this year was due to exploded gears inside and not bearings issues (2 times the fifth gear though)...

 

EDIT of an EDIT: Is the internals of a RB20 is more like the s13 tranny? If so, I think my problem would be corrected by a s14 tranny since gears are wider?

Edited October 7, 2011 by 280z"Vador"

[Tony D]

Generally the KA Tranny is acknowledged to survive to 400HP, while the original L-Series won't last long if you are constantly using 300+.

For over 400, the Z32 Tranny seems to be the adapted choice.

 

You have to be careful with 'exploded gears' as a diagnosis. Is this due to countershaft flexing, bearing failure, or shock-loading. You can break ANYTHING with shock-loading. I've broken low-mileage L-Series Trannies with a stock L26 because the bearing retainer let fly and the gears moved allowing high loads on the face to shatter them. Many times gears are broken because bearings allow improper alignment and the face contact of the gears change---add to that a shock load and it APPEARS the gears are at issue, but in reality it's bearing failure or other flexing of the case/components.

 

I don't know what happened with your fifth gear, but the round nut backs off on those allowing failure.

 

I spend a lot of time at work analyzing broken gears, twisted shafts, broken stuff of all types. To a casual observer, one cause may make sense, while in reality the failure is something completely and seemingly unrelated. When you see a broken component ask yourself "WHY" Five times on each answer you give yourself. If you can't answer it all five times...you're likely overlooking something!

[280z"Vador"]

Hi Tony, thanks for the detailled answer! Well the first tranny that I broke was due to the gears at the front of the tranny, the 2 last was because of the fifth gear...

 

"I don't know what happened with your fifth gear, but the round nut backs off on those allowing failure."

 

Well in one of them, this is actually what was the problem! When I did open the tranny, I saw that the nut was completly lose and unscrewed. On the other one, I just don't know what happened but bearings was in good shape. When I broke a tranny, be sure that I look inside to see what is the problem (It's how we learn anyway)

 

I should be ok with the KA tranny, I don't plan making more than 280whp

 

Generally the KA Tranny is acknowledged to survive to 400HP, while the original L-Series won't last long if you are constantly using 300+.

For over 400, the Z32 Tranny seems to be the adapted choice.

 

You have to be careful with 'exploded gears' as a diagnosis. Is this due to countershaft flexing, bearing failure, or shock-loading. You can break ANYTHING with shock-loading. I've broken low-mileage L-Series Trannies with a stock L26 because the bearing retainer let fly and the gears moved allowing high loads on the face to shatter them. Many times gears are broken because bearings allow improper alignment and the face contact of the gears change---add to that a shock load and it APPEARS the gears are at issue, but in reality it's bearing failure or other flexing of the case/components.

 

I don't know what happened with your fifth gear, but the round nut backs off on those allowing failure.

 

I spend a lot of time at work analyzing broken gears, twisted shafts, broken stuff of all types. To a casual observer, one cause may make sense, while in reality the failure is something completely and seemingly unrelated. When you see a broken component ask yourself "WHY" Five times on each answer you give yourself. If you can't answer it all five times...you're likely overlooking something!

Edited October 8, 2011 by 280z"Vador"

[Nelsonian]

A big thanks for the advice on running the larger more stout bearing. I will take heed of this info and go that route with my s14 trans.

[rejracer]

Tony,

I am not saying the shift rod is a point of failure, nor does it matter if the rod is turned down or the hole enlarged from a reliability standpoint. Yes it is deflection that I was thinking of. I can see why you could get that from my last post as it wasn't clear. When I said: "I guess my logic is to modify the bits that don't break, so when it comes to replacement, there's minimal parts swappage going on. " was in reference to making the case larger to fit the stronger bearing as well as not having to r&r a modified shift rod.

 

I wasn't knocking what you were saying about what they do in Japan. Just explaining what I see as pro's and con's of how this swap is done in the long run from a serviceability standpoint.

 

My comment about roadside is basically if this swap is done, and then the new box fails, how much work is it to get new internals in and it buttoned up. If I were to source a new or used transmission to get the car on the road, while on a trip, then the modified shift rod is just one more custom part to be R&R'd. I would not want to deal with roll pins and detents. And yes I would tear the cases down to swap out the internals on the side of the road if I had to. Granted "on the side of the road" I probably would not attempt it there, but safe place where you can work on it, assuming bare minimum tools are available, parts house, and I could source a trans on the cheap. You know as well as I how easy these boxes are to split apart. Now R&R of the trans is another story. I would not want to do any type of service without my tools and garage, but when broke down out of town, you've got the choice of pay to have it hauled home, to the nearest garage, or fix it there.

 

When I said: "Perhaps I just put too much thought into these things." It's not an understatement. I know I think about the worst case scenario too much considering it's a modified street car, but I still think about long term serviceability when deciding on what to do and how to do it.

 

Going back on topic, Ray's idea has merit. If the bell housing can be modified, it's a one shot deal. If the trans fails, pull the trans, and swap any compatible FS5W71C internals and button it back up. Same concept, just using different method of modifying a bell housing.

 

Lastly the drilling I was referring to is drilling the holes for the new bell housing pattern as Ray had said in the original post, not the shift rod. The only critical holes on the bell housing are where the locating dowels are. The other holes are more of getting them in the neighborhood.

 

For what it's worth there is a machine shop that will do the bell housing mods I described for around 100 bucks after shipping it's closer to 150. I think the mods that Ray is describing would be even simpler and cheaper. If you were to take the 2 bell housings down to any competent machine shop, they could make a pattern fairly easy. Which would make drilling them using a drill press fairly straight forward.

[Tony D]

"If I were to source a new or used transmission to get the car on the road, while on a trip, then the modified shift rod is just one more custom part to be R&R'd."

 

EXACTLY why you should machine the casing for the larger bearing, and poke the rod holes bigger at the same time. If you source a new or used transmission, you simply pull off your existing bellhousing and DIRECTLY fit it to the front of the new unit and reinstall.

 

If you do NOT machine for the larger bearing, then you have a bearing you have to change on the roadside as well!

 

Yes, Ray's poke a few holes approach may open an alternate tranny for use... But I don't see RB 20 Trannies floating around all that much.

 

I don't know of a single machine shop that would 'drill' those shift rod holes on a press, either. It's all Bridgeport work, and in todays shops, NC-Precision Bridgeport work.

 

Hell, at my HOUSE it's Bridgeport work!

[rejracer]

Tony, the RB20 trans is just a FS5W71C. Ray's mod is just a means of not having to pic apart a 71b box to be used as a bellhousing doner. Once it's been machined, any compatible Fs571c can be used as a doner for internals. I am aware of the 300zx, 240sx and some 2wd trucks that use this. Granted the Rb20 boxes are not as common, but at least it's another option.

 

I already have a trashed 71b box, so I'm going to modify it, and not attempt the RB20 route. If I had not already picked up a box on the cheap the RB20 path would be a more appealing option.

 

I'm somewhat scratching my head on this on. I'm getting the impression your trying to convince me to use the larger bearing, which is what I've been saying all along, as well as punching out the 1-2 shift rod hole.