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Riceburner

FJ20t gear ratios

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Most of the fast cars run a 4.1 or 4.3 top speed is 144 mph  .the track is all about corner speed and you need the short diff to get off the tight stuff

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Xnke, we have a commercial machine shop here that does a .889 fifth gear, but it is at standard width, and they only do small batch runs, when they can fit them in.

If you were to produce some wider, and closer to 1.0 fourth fifth gear pairs, at a better tooth count than the horrid 0.752 or the not so bad 0.832, i am sure there would be a few down this way interested in purchading!

 

The Sylvia/180sx/200sx model that was a JDM car that many were private imported to Australa, had the C type boxes with a 0.832 fifth.

The larger six cylinder engined, both in line and V config motors, ie rb, vg/vq using the C type box, had the 0.752 fifth, ( great for economy!)

 

I'd be interested in obtaining a qty of fifth gear sets, rather than sending individual sets over time.

I have been converting a number of both B and C types to close ratio sets, and have found that the C types are quite superior to the B box, including the fjturbo box ( DR30 model)

Jason

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5th gear is a 18mm gear and does not have oil holes in it and does live at the hp and torque we make , thats why we all use it , the stock L box has a 16mm 5th with oil holes and when the gear fails it cracks from the oil holes out the gear falls in 3 bits, the fjt box does not have the oil holes

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AH, so now I understand. I thought you were breaking the 18mm gears!

 

So what makes the FJ box so desirable over any of the other standard, probably more common FS5W71C/E/G transmissions?

 

Is it just the gear ratios plus the undrilled 18mm 5th?

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The only advantage I see is it bolts in where the old B box is with no cross member changes but you get a box with a better 5th gear design and wider gearset. Once you have the FJ box installing the Kameari gearset gives you a good strong close ratio box with a good 5th. Having said that we have seen 5th gear still fly to bits in the 71C boxes = changing gear while over a bump/car unloaded = too much loading on the gear = bye bye 5th.

 

 

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I see. Being as 5th is trapped between the steel centerplate and the tailshaft/countershaft rear bearings, I see no reason for it to fail once we have the actual gear strength up high enough to prevent the gear splitting.

 

There is a local shop that can cut me a helical gearset (stronger, quieter) and I will be calling them up to see what they'd have to have to do the job.

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I'm going to tear down my RB20det box this weekend and asses the condition, if it's repairable I might look into a CR set. Kameari seem the least expensive.

 

Can anyone make sense of the link? http://www.rhdjapan.com/kameari-super-close-gear-set-s13-s14-r31-r32-58307

 

It looks like the super close Kameari gear set has a fifth of .759  ??? That's crap! I can see a few

Other sets listed, the top Silvia Q seems to have the best ratios, but is that compatible with the RB20det box? Then how do you specify which set you want?

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That's because it's the stock 5th gear for the box. Kameari gear set is 1st 2nd 3rd and counter shaft (4th 1:1)

 

 

This makes it more clear:

http://kameariusa.com/L6_Gearset.php

 

 

FJ20ET boxes are easier to fit and have the 5th ratio you are after.

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I see. Being as 5th is trapped between the steel centerplate and the tailshaft/countershaft rear bearings, I see no reason for it to fail once we have the actual gear strength up high enough to prevent the gear splitting.

 

There is a local shop that can cut me a helical gearset (stronger, quieter) and I will be calling them up to see what they'd have to have to do the job.

Yes as that was the fix. A custom 5th (it is noisy) in the ratio required - I think 0.88, that and making sure the rear nut can't back off which is the common issue causing 5th to slide up and down a bit and smash its self to bits too. One common fix is replace the penned nut for 2 thinner nuts that tighten down on each other.

 

It looks like the super close Kameari gear set has a fifth of .759  ??? That's crap!

As pointed out - only a 1-3 gear set 4th and 5th are not changed so you are stuck with what the box has and most 71C boxes that is a crap 0.759 - unless you get the 0.83 5th from a NA RB20 box IIRC - or just go custom 5th that is stronger and the ratio you want/need.

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Ah didn't realize it was only 1,2,3. First gear is pretty much useless on track and no issue on road, the other RB20det ratios don't look bad except fifth. If the RB box looks ok I might just look at getting a fifth second hand or from Albins.

 

RB20det ratio's Transmission 5 speed manual     

Gear Ratios

1 3.321

2 1.902

3 1.308

4 1.000

5 0.759

Reverse 3.636

 

Kameari L6 CR  L6

(FS5W71B)

1 2.624

2 1.814

3 1.360

4 1.000

5 0.813~0.933

 

Interesting that Kameari usa are over $500 more than RHD Japan!

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Although the ratios dont look that different, throw them into gear calc and see the speeds you will be doing in each gear. You also need to see the change in RPM after each gear shift.

 

 

If you dont want to spend a lot of money wouldn't an FJ20ET box be the easiest options since it has the strong gears, the 5th gear ratio you want and bolts in?

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I have an RB20det box in the shed. I also have a modified bellhousing i got for $20. It looks like $600 would get me a known good condition FJ box which would probably need bearings, maybe more. I believe the RB20det boxes are meant to have double syncros on second and third which the FJ doesn't, it's also a newer box so hopefully not as many miles on those syncros.

 

I think with either box ill end up at about the same cost. I'll have a better idea of which box i go for after the weekend.

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The figures quated above for Kameari ratios will alter, depending in input drive/driven ratios.

First can be either 2.6 or 2.4.

The boxes i do are the 2.4 first gear.

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So far so good with the RB box, except the centre counter shaft bearing has cried enough, ball bearings falling out everywhere. Gears & other stuff looks ok.

 

I can't get the main shaft & bearing out of the sand which plate, any ideas? Do you need a hydraulic press?

 

Also where do you get a rebuild kit for these boxes?

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Bearing came out, I just needed an extra set of hands on the pullers and muchos grunt to get the fifth gear syncro hub moving on the shaft.

 

All pulled down. I'll need to get the Lseries bellhousing plunge cut 2mm, bearings, syncros, fifth gear, seals, main/counter shaft nuts. Possibly a CR set.

 

A few things (see pics), I noticed some funny colors on the syncro hubs.... Could it be oxidising from the failed bearing? Also the reverse counter gear has some decent chips on the edge is it still usable?

 

PPG/Pfitzner offer gearsets but they state on the website no warranty unless the sandwhich plate is modified to stop oil starvation on sr20 which is the same as rb20, is this a worthwhile mod (see pic)? I have it out so it's easy to do.

post-1489-144023719731_thumb.jpg

post-1489-144023719739_thumb.jpg

post-1489-144023719747_thumb.jpg

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I have RB20DET gearbox bearing part numbers if anyone needs them in the future they are,

 

Counter shaft front: NSK 25TM15U1 (sealed bearing)

Counter shaft centre: NSK HR6305

Counter shaft rear: Nachi NUPK204

 

Main shaft front: NTN TMB306CNXC3 (sealed bearing)

Main shaft centre: NTN 6306CC3 japan RS

Main shaft rear: NSK TM205U40A (sealed bearing)

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There should be a loose internal circlip that sits on top of the upper white plastic ring.

Also under the rectangular shift plate cover, a detent ball and spring, held in by a bolt, head is larger than others, it is a wpecific length.

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OK thought I would open this discussion some more. So I picked up an fj20 box that I will pull apart soon and use this as the build for a strong track 71b box using new gear set.

 

I used to own (and one Datsun I should not have sold...cool and very different) a Datsun 160jsss 710 that had a factory fitted dogleg 63a 5SP.

 

The layout is like this

R..2..4

|--|--|

1..3..5

 

I liked this dogleg layout and think it is great for a track car as 2345 are mostly used gears aka in the H pattern. This box was an overdrive box not a 1:1 5th.

 

I might even see if I can pickup one of these 63a doglegs to see if the selector setup can be replicated in a 71b box as they have a very similar tail/selector design.

 

Does anyone know if that is even possible?

 

Cheers Mike

 

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It's a great shift pattern, I had the same shift pattern in my first car, a Datsun 1600. Was great for ripping through the gears.

 

I have contacted pfitzner about the sandwich plate oil mod as they are virtually the same as SR20 boxes, no reply yet.

 

I'll post the RB rebuild in my build thread.

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OK so I studied the parts catalogs that shows the selector setup. This is what I have worked out.

 

The 3 selector rods are for each bunch of 2 gears. In a standard 5spd pattern this is how they are laid out.

 

Top rod = 1 & 2 selector

Middle rod = 3 & 4 selector

Bottom rod = 5 & reverse both of  these are in the tail if the box

 

The dog leg is like this

Top rod = reverse & 1 both in the tail of the box and in the reverse order to the standard box.

Middle rod = 2 & 3

Bottom rod = 4 & 5

 

That is comparing the 63a dogleg selector controls to the 71b selector controls.

 

So it could be possible but complete new internals will be required. Ie new top selector rod and leaver, new reverse gear and new first in the rear and reverse order to stock. The same in the front ie new selector rods and forks and all new gears in the ratios required keeping the 1:1 as 5th gear.

 

So a lot of work :(

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A local racer here has a holinger 71b dogleg 1:1 5th dog engagement box (I think all new internals) might have to see inside that box one day and see if it can be replicated.

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That would be super cool! Awaiting picks!

I got some pics,,, somewhere,, of the Nismo Option 1;1 box in the 120Y

Yes its a FJ jobbie, with the proper dogleg shift.

It runs dog engagement instead of synchro rings.

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We know what you are like with getting pics up on the forum though haha.  ;D

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