I have been reading up on doing an rb20 gearbox conversion in my fj20 datto 1600

i gathered that the only mods that are needed are that the rb20 bell housing needs to be slightly modified on the top two bolt holes in order to bolt up to the fj20 block

Can will the fj20 bellhousing bolt up to the rb20 gearbox therefore allowing direct bolt up to the fj20 block??

Is the rb20 box is longer then the fj20 box??.. if so by how much exactly???

Are all 5 speed rb20 boxes the same e.i. turbo and non turbo???

what can you expect to pay for a good nick box??

any other info would be great

cheers

Read my post on boxes. It has the info you need.

Differences bt turbo and non turbo boxes are simply number of synchros. Id personally go for NA since they havent been thrashed like most "t"s. However, you need to check their condition anyhow, you can ruin any box even with 2hp.

Going prices are about 500 for any of the sr rb ca boxes thouth they can be had cheaper.

so how will different synchros affect driving

i have looked through 10 pages of posts and cant find anything about the length of the rb20 GB
i just wanna kno if i have to shorten the tailshaft again

cheers

from what I've read the box is the same overall length with the same splines for the tailshaft, except the crossmember is a bit further forward/back? can someone confirm?

this is what i know about rb boxes due to experiences with them
i just got another rb20 box for my car and when ringing aroud the wreckers i was quoted anywehre form $800 -$650 mainly but i found mine for $450
box length is the same but crossmember is back further about 25mm.
to change the bell housing to the fj one ,
you must machine out the holes for the shifter rails and bottom bearing or use the fj bearing and macine down the plate behind it ,
or when you put the bellhousing in the box will not spin .

also i noticed the rb box has much larger gear selectors than the fj and thats what broke alot of the time with fj boxes because 2nd gear syncro was always sh#t

the rb box is much nicer to shift than the fj box

ive also been told to run a 75-90 synthetic gear oil with the rb box wich i do now

hi graham, the rb20 box with fj bellhousing is exactly the same length and the g/box x member mounts 20mm further foward on the box. hope this helps

cheers for the info..

2 questions

Is the easiest option just too use the existing rb20 bellhousing and get the holes redrilled to suit.. or modify the fj one..??

any benefits..??

and what would the difference in drivablility be between the N/A and turbo box???

cheers

Modify the FJ bellhousing , then it bolts up properly like the factory did it . Slotting/welding the RB bellhousing is a bodge and not how Nissan would have gone about it . To each their own .

cheers DP

so anyone kno if there is a noticable driving difference between N/A and turbo boxes

perhaps just change gears a bit quicker with the N/A box ???

No mater how you go about fitting a RB box to an FJ it will never be as Nissan intended it as it was never done by Nissan.
It is no less bodge to weld the holes in the RB bell housings and re-drill them as to re-machine the FJ bell housing.
It is how ever more assessable to most people and easier to weld and drill over machining.
Either way will work fine as long as it is done correctly.

well that clears things up a bit

cheers for that..

so basically if you weld and redrill and do it right everything should be good,.,.,.

that seams like the easier path to travel

gray one question why are u going the rb20 box and not the rb25? i was told there weak as the fj box?

YES-11S

YES110

really cause thats the first ive ever heard of it..

from my understanding the rb20 box is much stronger then the fj box..

ive been reading many threads on here about guys who have been blowing fj boxes , then upgrading to rb20 and having no dramas..

but obviuosly there is a point at which the rb20 box will have problems itself..

i just think for the power im looking at outputting the fjbox will be marginal and im not really interested in swapping boxes when it blows..

id rather do it right the first time..

as for the rb25 box hahaha im 20 years old full time at uni and getting centrelink.. i think that explains it well enuff...

as they are "unbreakable" to speak that will defo be a future mod in years to come..

na its cool man i was kinda asking the question if i was correct or not.yeh im in the same situation im an apprentice lol

are there any RB20 boxes that are different through the series of cars or are they all the same..

And what skylines did the rb20 engine come out in... only the r31

http://www.network54.com/Forum/166246/thread/1157640898/last-1158649502/Your+box+is+playing+up,+no+worries+plenty+of+options

Read again up there, i cant remember exactly. Im sure all are the same. But you be better off going for NA rb20 and of latest car since they havent been thrashsed as much and as long. NA have less syncrhos though. Up to you. Still as stong as turbo box.

FJ20ET and RB20DET boxes use the same diametre and width gears , the fist four ratios are identical . Front lower bearing and 3-4 syncro hub aside why would you think the RB box is any stronger ? I've had the two in bits side by side , the RB20 box guts even fit the FJ20 casings with a few small mods . If it had been possible to get more strength and durability into the 71 series boxes there would be no RB25 DET gearbox .

Fitting methods , if you modify the FJ bellhousing it bolts up with ALL the std fastenings as the factory intended . Weld /drill method , you lose the top dowel so the bellhousing can NEVER be located as accurately as the factory method allows . In all vehicles its critical to have the gearboxes input gear (first motion shaft) exactly aligned with the pilot bearing in the back of the crankshaft . To do this properly the bellhousing MUST have at least two dowels . If you slot or redrill the holes and remove the top dowel there's a very good chance the gearboxes inputshaft will be slightly off centre which will chew out the pilot bearing and make the box jump out of gears because the first motion shaft binds on this bearing and moves in and out . I cannot understand why there is so much resistance to getting a decent machinist to bore the lower hole out for the larger bearing . Its not dear or even very time consuming . Provided the hole is sized correctly and on the same centre it will work as Nissan intended it to because thats what they do in this situation . I did it once , did it the correct way and never had any problems with it . From an engineering point of view its the only way to do it .

QUOTE "FJ20ET and RB20DET boxes use the same diametre and width gears , the fist four ratios are identical . Front lower bearing and 3-4 syncro hub aside why would you think the RB box is any stronger ?" QUOTE

Why? Because I have seen many FJ20s with RB20 boxes with no problems where they all had problems with the stock boxes.

Also, im pretty sure the RB20 boxes have much larger bearings which is the reason why they are better and stonger. Its not only the gear size that counts. Bearings take the axial load of the torque emplaced upon it, the larger than bearing, the less load and the stronger the box given the constant gear size.

People shouldnt get stuck on RB20 only, SR20 boxes will also do the job equally well.

SR20 box?????

how can this be made to fit..

Why hasnt there been much said of this before tho..

is it stronger??

Relocating the dowel to the corrects position is a given.
You can not seriously sit there and say if you weld and re-drill the holes the gear box will fail. If you are suggesting that, that’s a load of BS.
Re-machining the FJ bell housing will cost around $150 to $200 at most good engineering shops.
Welding and re-drilling the top holes and relocation the dowel will cost around $30 to $60 at any good fabrication shop, if you don’t have a mate that will just do it for you.
Don’t get me wrong. Machining the FJ bell housing is a great idea. We have done it on one of our own cars with a SR20 gear box. But there is nothing wrong with welding the holes and re-drilling them and the dowel position to suit.
Welding and drilling is a good option for guys that are building there cars to a tight budget.

Would I do it to my own car? “Yes absolutely with no qualms at all.”

Graham, Juggernutz has already fitted SR gboxes to fjs. Requires a modified bell housing. Ask him.

FJ CA SR and RB20 all use the same size gears. At this level the strength is the same. But bearing sizes makes all the difference and this is where SR boxes poopoo on FJ ones. Theyre like RB20 ones. People like RB20 ones cause theyre easy to fit, slot, cut dowel and youre away or weld and redrill if you have a mate like Juggernutz

Resizing my FJ bellhousing cost $100 . If they're charging you more your getting ripped off big time . I am a Fitter/Machinist by trade and how time consuming do you think clamping the bellhousing down in a vertical mill or centre lathe would be ? Set it up on centre and run the boring bar through soft aluminium a few times .

RB71 boxes use the same sized centre plate bearings as the FJT box , same with the upper front or first motion shaft bearing as well . Some people feel that the Iron centre or sandwich plate is better than the aluminium one . We used the iron one .

Every FJT or RB71 box I've ever seen fail dramatically tore the teeth off 2nd and or third gear pairs . Constant long term high torque loads will cause wear to the std FJT lower front bearing . They give lots of warning when worn out . People who killed their FJ box because the bearings collapsed did so because they drove on and on and on long after the bearings starting making "danger Will Robinson" noises .

As I said to each their own , if you want factory strength and reliability this is the way to do it .

Does RB71 box = RB20 box

i dont understand the bit too which every one is refering too that has to be machined..

i guess when i get the box ill kno

Disco,

if youre saying RB20 boxes are the same as fj boxes (if gears and bearings are the same) why is it that they are stronger than and last longer?

You are right with the FJ box warning you its on way out....mine has done so for a long time now. No easy fix but to change it to CA18DET box, just because i have one the garage and have already spent too much on this car.

Graham, RB71 = RB20 box. I have seen a few high powered srs run rb20 boxes efficiently and since these are meant to be same as SR boxes which are also strong (i dont know, just going from the skylines thread) I dont see why disco says they have the same small bearings. I dont know, never tested it or seen them so Im taking everything into consideration. One things for sure, RB25DET box s1 and youre fine. 1.5k later youre not.

just out of curiosity, can someone post pics of either the plate that has to be drilled for the larger RB20 bearing, or how they slotted/welded and drilled/re-dowelled the transmission. im real interested in this swap later down the line and would like to know how much is really involved. i have a bit of fabrication skills but don't know if i'd want to weld/redrill a bellhousing, boring the trans for the larger bearing sounds alot safer. also, can someone post some pics of the trans mount for an RB20 or 25 box, just curious how different it is from an original FJ20 box.


on a side note, since the FJ20 shares the same bellhousing bolt pattern as a datsun L28 (just cocked a little) there is a kit for putting a 300zx tt (fairlady twin turbo) trans onto a L28, and im curious to know if this kit can be adapted to put that 300zx tt trans to a fj20 motor because those transmissions can hold up to 800 ft/lb torque. the kit is sold by mazworx.com, check it out and tell me what you guys think.......

The 71 series gearboxes go back a long way , the 71 means mm between the shaft centres (mainshaft and countershaft or lay shaft if you like) . There has been many changes to them over the years mainly to the wider gear set/iron centre plate/aluminium and brass selector forks/larger diametre selector rails (shafts) and three variations of selection mechanism . The earliest mechanism was the "monkey motion" one from very early 240Z's and possibly the Datsun Fairlady/Sports 2000 . The second or B type mechanism can be found in cars like Bluebirds/280ZX/720/S12 and all R30 series Skylines . The very early boxes did not haxe the sliding tailshaft joint at the back , instead they had a drive flange like the front of a differential does and this style was what the Nissan option boxes were based on . Originally these had Servo Syncronisers which were not as strong or durable as the Warner Syncromesh (brass baulk ring type) . They had more parts in the syncro hub and were poisonously expensive to service . The inner part of these hubs were not as strong as the warner type and could be broken by ham fisted driving or high torque loads .

I'll start with the K or 240K box as most remember them as the easiest to get five speed box of the 70's . Narrow gears , small warner syncros , small selector shafts , steel forks , servo syncro on OD or 5th , and I think wide ratio or 3.6 1st gear . Wide ratios were a problem for rally , the small selector rails had small roll pins to fix the forks to these rails and the roll pins could shear under hard use . Servo syncro on 5th broke at times as well . Nissan knew so as time went by they started to beef things up ie warner 5th syncromesh , small roll pins inside the std roll pins , larger 1-2 selector rail , a times wider gear pairs but not on all ratios , first off larger warner syncro hub on 1-2 then 1-2 and 3-4 . With turbo engines torque loads rose so boxes like the DR30 FJT got the all wide gear set with 3.3 1st 1.9 2nd etc . With the RB series engines the gearbox got the C type change mechanism which some say has a better "feel" than the "B" type , leaked a bit less oil anyway . These normally have the big rails and both large syncro hubs where the 3-4 hub on the FJT was the original smaller warner type hub .
Don't forget that 71 series boxes also lived behind L series sixes and occasionally you find these with the larger front lower lay shaft bearing . High torque loads from turbo engines and heavier cars makes the front gear pair try to spread themselves appart so the last strength mod was the larger diametre bearing on the front of the lay gear shaft .

There comes a time when you can't widen gears and get a strength increase (plus no space left inside the gearbox casings) . So Nissan had to spend some money and get the larger box again found the GTR R32/3 R33GTS25T/Z32/VLT .

So if you want the nth degree from a 71 series box fit the RB box to RB20's or do the front bearing mod to FJ20 boxes . Its less agro and WILL bolt into any vehicle that had a 71 series box with no speedo/mount/shift mods needed . Plenty of people buy import boxes like the RB71 type only to find noisy bearings or worn out syncros . When you think about it buying a 2nd hand box is a risk because you've no idea what condition its in till you drive it . If you went to considerable cost and effort to fit the RB20 box and its RS all the mods to get it in were for **** . Had you merely got a good experienced mechanic to rebuild your original FJ box and do the front bearing mod you KNOW what you have . You can tell him yeah 1 2 3 syncros shot and noisy front bearing or whatever . He can service the worn parts , fit the larger front bearing and you can bolt the thing back in with NO external mods just like a standard one . I know about these things because I went to some expense to get the internals from an RB20DET box fitted inside FJ20T gearbox casings , a lot of efforted wasted to realistically gain only a larger 3-4 syncro hub which the FJT box didn't have or need . Some of the fiddlies included redrilling the FJ 3-4 selector rail to suit the RB20 type larger 3-4 shift fork , welding two speedo drive worm gears together because they are in a slightly different position on the rear of the RB mainshaft . I think some kind of mod was needed to the 5th/rev selector mechanism because it was different to the FJ's . The speedo pilot drive never fitted as well as I would have liked but it did work . After all this crap the baulk (syncro) rings were buggered on 1-2 and 3-4 . Too much effort to R/R the box so I lived with it .

What AJ suggested was rebuild the FJ box completly std or at most with the front bearing mod . Would have cost about 1/3 of what it did .

Do as you will .



Z18T Bluebird was probably the last of the narrow gear

BUt if you think about it

generally your fj20 box will be more worn out then the RB boxes as they are a bit newer..

say you rebuild the fj20 box as you say, (i have no idea how much this would cost you lets say $400.00)

well thats a grand total of $400.00 spent

on the other hand say if you found a decent RB20 gearbox which would be in perhaps generally better condition..

purchase of the gearbox $500.00

say the rebuild would cost $300.00

plus money from selling the FJ20 box -$250

thats a grand total of $550..

only $150 bux more for a much stronger, newer box

works in my books

Newer yes but where do you get the much stronger box idea from ? Same shafts , same gears , and except for one - same bearings .

Plenty of R32 GTST's get the arse flogged off them and don't for one minute think they didn't cop a hiding back home in Japan AND in a heavier Skyline . Its only the fact that RB20DET's make SFA torque at low revs that allows this gearbox to survive at all in a 2wd R32 . Note the R32 GTS4 uses basically a GTR style transmission . All the RB71 box did was provide adequate strength with less weight and cost in a 2WD R32 than the larger 2.5/2.6/3L turbo box would have .

If the RB20 box floats your boat do it . When it strips gears like FJ boxes do given enough abuse don't say you were not told .

I have used FJ20 ET, RB20 DET and RB25DET gearboxes in my cars.

The FJ20 ET box broke 3rd gear and the synchros were always buggered from the moment I bought the car. Moved to the RB20 DET gearbox with a much nicer shift, stronger bearings and I also reckon the gears were a smidge wider than the FJ20 ET, from my measurements anyway, but definitely bigger bearings, nicer synchros and shift forks. The output shaft was the weak link in my application (Drag racing) and that broke in the high 10 sec zone. The output shaft of RB20 DET gearbox is identical to all the earlier boxes, so that was the weak link in my experience.

Down to the RB25DET box, much stronger gears, bearings and synchros, much bigger output shaft and hence no problems since, running into low 9 second zone for many passes. The input shaft is the only thing they havent changed from the earlier boxes, but it appears to hang in there OK. BTW I simply filled the holes with tapered alloy dowel (no welding keeps the alloy hard, no loss of heat treat) and redrilled to suit FJ engine plate in all my RB gearboxes, and can say this is fine if done accurately, never had a problem and my application is as extreme as anyones. Can't imagine why someone would go to all the trouble and expense to swap /machine bellhousings when this is such a simple conversion.

BTW, the RB25 DET boxes come up for sale reasonably regularly in places like e-bay (one there now in fact I see), and prices vary enormously from $1200 to over $1800. Best value for money must be the RB20 DET box though, as how many of you are running into the 10's ? In my experience its abuse that kills gearboxes, not necessarily excess torque produced by the engine...

From an engineering point of view its because the bellhousing is not located by the through bolts . They are there to clamp the bellhousing to the back face of the block . The dowels are there to line the gearbox up on centre with the crankshaft , if not they wouldn't be there .

Hi I just read your bit on Fj20 boxes. I need a new box for my bluebird. I gather you recomend staying with the fj box instead of messing around with the Rb20 conversion. You mentioned upgrading the bearing and having the box serviced? Would you mind giving me some more info on this please? ie where to get the parts, (i'm in Melb), and what I should expect to pay for the service.
Cheers, Doug.

Forget the FJ box mate, i broke 3rd gear on mine, was holding onto a fair bit of power though for a while. Ive gone to the RB20 box in my bluebird now and its one of the best $450 ive spent. ive posted a article on fitting a few weeks ago, search it out and you'll get the idea!

Gareth

I drive a DR30 Skyline and want to know is there any mod I have to do to put a RB25 Transmission in my car other than changing the bellhousing?

Thanks!

anyone can answer the question thats on the top!!
dont' have to be just Ben D!!

anybody got any hints?

Thanks

I guess nobody knows...

All the info is there dude. No offence.

oh!! ok, let me reread it...sorry guys!!