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OS Giken 5 speed close ratio gears

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Old 01-13-18, 04:47 PM
  #51
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Originally Posted by billyboy View Post
One of the cars that ran a PAR here, the mechanic ended up cutting a hole in the body to speed up "rectification" work on the shift mechanism that happened at virtually every session during each meeting. Ended up biting the bullet in frustration "putting" a Hollinger in the stock case eventually....where the case there just accommodated the input quill, which is about all it's good for. Reality is, stock cased gearsets are pretty much a joke if you're doing anything half-serious - track day warrior might just be ok, OS will eventually **** the bed too......but for other reasons.
I’m sorry, but respectfully disagree. A Hollinger is a whole other animal as any real racing trans. However there are some nice builts using both of these transmissions without issue. Sometimes the factory casings are weak and yeah that’s a different story. The 1sr generation Aisin craptastic vs much stronger top-loader 2nd generation RX8 6-spd boxes are one example. Any trans is going to wear out and break even. Sometimes it comes down to the driver and how hard they are on it too. I tend to break more than most because I’m not afraid to shift fast and hard ...



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Last edited by TeamRX8; 01-13-18 at 04:50 PM.
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Old 01-13-18, 06:54 PM
  #52
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Well, transmissions fail for different reasons and its a balance to some degree (alternate gearbox designs withstanding).

Torque-
The Type R box (TII, FD 5 speed) shears 3rd gear as the main shaft and counter shaft flex away from each other.
One could machine a new 3 speed +1 gearset (custom ratios) that took 3rd gear out and replaced it with a cuff to hold the two shafts together while increasing the input shaft diameter and it would be a pretty damn strong gearbox in the stock case as far as torque handling.

Frictional forces-
The Type R gearbox fails early under high rpm use at the track (like behind a NA P-port) because it has a pretty robust high mass gear set. To counter these weaknesses you need component processing techniques like WPC, exact clearancing and/or alternate mesh machining (straight cut), and more advanced lubrication system.

Shifting-
Some boxes like the smoothcase Type M and the smoothcase S1 RX-8 gearbox have weak shift forks that like to break if you shift with too little mechanical empathy. Put heavier heavy duty shift forks in and you punish the synchos with too much mass behind the shift action and the synchros wear fast leading to poor high rpm shifting.
Another shifting issue is all Mazda boxes (in native chassis) after FD Type R have the power plant frame flexing to deal with. Under load the transmission rotates clockwise and as you lift throttle and pull the gear selector out of 2nd gear removing engine torque from the power plant fame the gearbox rotates back counter clockwise and where you though 3rd gear "gate" would be is 5th gear and *crunch* you force the shifter into 5th with too much speed differential damaging the 5th gear synchro. Miata and RX-8 don't usually have torque so this is less of a problem than with the FD.

It was the comment above comparing S1 RX-8 trans to the S2 trans that made me think of this because the S1 RX-8 trans has been proven to be strong behind the relative high torque of a turbo 3 rotor, you just have to be careful shifting. However, breaking while shifting is definitely still a weak point in the transmission when comparing various transmissions strengths.
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Old 01-13-18, 08:02 PM
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I believe ( but could be wrong) the Giken set uses stronger shafts and a shallower angle on the gear cut - so its getting towards a straight cut rather than helical. This would make it stronger than OEM to an extent wouldn't it?
I mainly chose it for the ratios than strength though.
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Old 01-13-18, 09:35 PM
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Originally Posted by BLUE TII View Post
Well, transmissions fail for different reasons and its a balance to some degree (alternate gearbox designs withstanding).

Torque-
The Type R box (TII, FD 5 speed) shears 3rd gear as the main shaft and counter shaft flex away from each other.
One could machine a new 3 speed +1 gearset (custom ratios) that took 3rd gear out and replaced it with a cuff to hold the two shafts together while increasing the input shaft diameter and it would be a pretty damn strong gearbox in the stock case as far as torque handling.

Frictional forces-
The Type R gearbox fails early under high rpm use at the track (like behind a NA P-port) because it has a pretty robust high mass gear set. To counter these weaknesses you need component processing techniques like WPC, exact clearancing and/or alternate mesh machining (straight cut), and more advanced lubrication system.

Shifting-
Some boxes like the smoothcase Type M and the smoothcase S1 RX-8 gearbox have weak shift forks that like to break if you shift with too little mechanical empathy. Put heavier heavy duty shift forks in and you punish the synchos with too much mass behind the shift action and the synchros wear fast leading to poor high rpm shifting.
Another shifting issue is all Mazda boxes (in native chassis) after FD Type R have the power plant frame flexing to deal with. Under load the transmission rotates clockwise and as you lift throttle and pull the gear selector out of 2nd gear removing engine torque from the power plant fame the gearbox rotates back counter clockwise and where you though 3rd gear "gate" would be is 5th gear and *crunch* you force the shifter into 5th with too much speed differential damaging the 5th gear synchro. Miata and RX-8 don't usually have torque so this is less of a problem than with the FD.

It was the comment above comparing S1 RX-8 trans to the S2 trans that made me think of this because the S1 RX-8 trans has been proven to be strong behind the relative high torque of a turbo 3 rotor, you just have to be careful shifting. However, breaking while shifting is definitely still a weak point in the transmission when comparing various transmissions strengths.
Well I sheared 2nd gear off the counter-shaft on five S1 RX8 boxes with Renesis NA 6-port engines (both OE factory & 272 bhp/190 ft-lb Daryl Drummond Stock Racing class build), which that gear is so small that it's integrally cast with the lay shaft and then machined, and the road race guys had nothing but problems with them. So for you to say it lives well behind a 3-rotor sounds to me like weak-wristed shifting and just taking it easy because I guarantee you I can blow one up on a 3-rotor on the very first try of doing a 1-2 drag shift (using clutch etc., not speed shifting). The center gearset casing is also integral 1-pc assembly with the bell housing too and it doesn't have any removable sides, not one. It's weak, flimsy, and moves all around under load. Rebuilding them takes a whole host of special tools and is just a PITA all around. Unil the S2 came out Mazda Motorsport sold and recommended the import RX8 5-spd trans, which is the FD3 center casing/gearset with RX8 specific bell & tailshaft housings, if your classing allowed it. Sorry, going to call BS on that ...

The S2 RX8 box is way better strength wise and everyone says so/knows it, except Mazda really hosed ratios in their usual fashion; 1st is way too low & the 2nd-3rd gear ratio gap is too big for North American models. I don't know what their problem is with getting the right ratios in place? For road racing though with the 5.125 Motorsport rear gear you get a nice spread from 3rd - 5th/60 - 130 mph.

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Last edited by TeamRX8; 01-13-18 at 09:54 PM.
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Old 01-14-18, 11:20 AM
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Originally Posted by BLUE TII View Post
Frictional forces-
The Type R gearbox fails early under high rpm use at the track (like behind a NA P-port) because it has a pretty robust high mass gear set.
Diyman dynoed his PP engine in the chassis, and on an engine dyno and the T2 junk takes 83hp to spin to 9k....

plus the ratios are terrible for a high revving car. the R box is much better suited to a low revving engine with torque, like the T2

the 5th gear thing is just a problem with that transmission design, our B2600 pickup had a broken 5th gear too
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Old 01-15-18, 03:25 AM
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Originally Posted by WANKfactor View Post
I believe ( but could be wrong) the Giken set uses stronger shafts and a shallower angle on the gear cut - so its getting towards a straight cut rather than helical. This would make it stronger than OEM to an extent wouldn't it?
I mainly chose it for the ratios than strength though.
Don't know about a different helix angle. It will still kill 3rd, like a stock box, if the dead one here is any indication, so wouldn't place too much faith in it being a huge improvement!

New race series over here for S1 Rx8s requires stock gearboxes, hopefully not rushing shifts or vainly hoping any syncro gearbag will cope with 8k+ abuse will let them live.

RX8 Cup Australia ? One-Make RX8 Rotary Racing

Oh yeah, there's a bloke arranging a group buy on s5/6/7/8 gearsets from Albins at the moment on fdrx7.

Last edited by billyboy; 01-15-18 at 03:27 AM.
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Old 01-15-18, 07:21 AM
  #57
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Yeah, shift easy, the right oil helps; my recommedation is Ford Motorcraft XT-M5-QS is you can get it down there. Best 90W manual trans oil on the market IMO, and it works the best in either RX8 box..

We also have an aftermarket company here in the US that sold an adjustable shift-blocking device that bolts-on at the top of the shifter called a Syncho-Saver. It has adjustable limiters that stop the shifter from pushing past the gear engagement point. This helps a lot on an S1 box because it's easy to push or pull past the engagement point if a lot of force is used for shifting, and then all kind of bad things start to happen. Kind of surprised they don't allow gearset changes though. Par has a nice gearset for both the S1 and S2 gearboxes that will greatly improve life. It's not a,performance enhancer, it just makes the box stronger and last longer between rebuilds. I guarantee you'll end up spending more buying replacement or rebuilding stock gearboxes than what the Par gearset cost.
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