is the is250 manual tranny that bad?
08-29-09, 09:52 PM
#33
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08-29-09, 10:22 PM
#35
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08-30-09, 09:17 AM
#38
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Detailed Analysis of the RA62
It's not hard to build a front drive gearbox that feels better than many rear drive boxes primarily because front drive doesn't see much torque. The more torque the gearbox handles, the stiffer the gearbox ends up being for a lot of solid reasons.
The gearbox in the manual IS250 is junk.
Here's why:
In the drawing below, note the location of the bearings, especially the input shaft's rear bearing. Because input and output shafts almost always run inline with each other in modern manuals, it is common for them to be concentric and have a shared bearing between them. It is NOT good design to expect the output shaft to provide all the support for the rear of the input shaft, no matter how stoutly the output shaft is supported. In this gearbox the output shaft is located and supported by a pair of tapered roller bearings (good), but the output gear is on one end of the shaft, not in the middle of the support bearings (ideal position), so the output shaft is going to deflect toward the top of the gearbox under all conditions. This means the input shaft is already being pushed upward by the output shaft. Since the input shaft is also deflecting in an upward direction (the natural loading any gearset experiences because gears are always doing their level best to push apart) the bearing between the input and output shaft is constantly running under an angular load - always a bad thing for roller bearings - and the rear input shaft bearing is a roller bearing - not ball, not tapered, just a standard roller bearing with the inner portion of the bearing constantly loaded and creating an angle between the input and output shaft centerlines. Very bad. If the output gear were moved between the tapered roller bearings on the output shaft, the rear of the input shaft would fit concentrically with one of the output shaft bearings and the misalignment would be significantly less with a whole lot more bearing to support this critical part of the gearbox. This is why I say the design has a hinge in the middle.
The countershaft on this gearbox has synchros on it. This means the forward portion of the shaft has to be machined to fit the synchro hubs and also means the shaft must be thinner every millimeter forward of fourth gear. Thinner means greater deflection under load. Unfortunately the same concept is used for the rear portion of the input shaft - note the only gears actually cut from the input shaft itself are first and second gears (and the corresponding reverse which is misplaced at the front end of the gearbox - first gear should be here because you want first as close as possible to bearings since it experiences the highest deflection force of any gearset.) Finally, look at the bearings for the input and countershaft bearings - how does this design tolerate end loading? End loading is fundamental to helical cut gears - the helix drives the shaft either fore or aft by it's fundamental nature, yet in this gearbox, there's nothing but a conventional roller ball bearing limiting end movement in the input and countershaft. Once could argue the input shaft limits end play with the taper rollers in the output shaft, but there's nothing in the roller bearings between the input and output shaft to transfer the load effectively, so we're left with the roller bearing at the front of the gearbox to control the thrust from the input shaft. Not a particularly good plan for long service life.
So we've got poor bearing support, poor gear location, and poor shaft design. All transmissions live and die by their bearings. This design does more to create issues for the bearings than it does to solve any. The Getrag 233 in the Supra is so completely different and so much better supported/located it isn't even funny. But that's why the Getrag is known to survive 1000 ft-lbs of torque. I wouldn't expect much out of this Aisin gearbox under anything more than stock power, and even with stock power, I wouldn't be expecting it to tolerate much abuse at all.
Here's the diagram:
The gearbox in the manual IS250 is junk.
Here's why:
In the drawing below, note the location of the bearings, especially the input shaft's rear bearing. Because input and output shafts almost always run inline with each other in modern manuals, it is common for them to be concentric and have a shared bearing between them. It is NOT good design to expect the output shaft to provide all the support for the rear of the input shaft, no matter how stoutly the output shaft is supported. In this gearbox the output shaft is located and supported by a pair of tapered roller bearings (good), but the output gear is on one end of the shaft, not in the middle of the support bearings (ideal position), so the output shaft is going to deflect toward the top of the gearbox under all conditions. This means the input shaft is already being pushed upward by the output shaft. Since the input shaft is also deflecting in an upward direction (the natural loading any gearset experiences because gears are always doing their level best to push apart) the bearing between the input and output shaft is constantly running under an angular load - always a bad thing for roller bearings - and the rear input shaft bearing is a roller bearing - not ball, not tapered, just a standard roller bearing with the inner portion of the bearing constantly loaded and creating an angle between the input and output shaft centerlines. Very bad. If the output gear were moved between the tapered roller bearings on the output shaft, the rear of the input shaft would fit concentrically with one of the output shaft bearings and the misalignment would be significantly less with a whole lot more bearing to support this critical part of the gearbox. This is why I say the design has a hinge in the middle.
The countershaft on this gearbox has synchros on it. This means the forward portion of the shaft has to be machined to fit the synchro hubs and also means the shaft must be thinner every millimeter forward of fourth gear. Thinner means greater deflection under load. Unfortunately the same concept is used for the rear portion of the input shaft - note the only gears actually cut from the input shaft itself are first and second gears (and the corresponding reverse which is misplaced at the front end of the gearbox - first gear should be here because you want first as close as possible to bearings since it experiences the highest deflection force of any gearset.) Finally, look at the bearings for the input and countershaft bearings - how does this design tolerate end loading? End loading is fundamental to helical cut gears - the helix drives the shaft either fore or aft by it's fundamental nature, yet in this gearbox, there's nothing but a conventional roller ball bearing limiting end movement in the input and countershaft. Once could argue the input shaft limits end play with the taper rollers in the output shaft, but there's nothing in the roller bearings between the input and output shaft to transfer the load effectively, so we're left with the roller bearing at the front of the gearbox to control the thrust from the input shaft. Not a particularly good plan for long service life.
So we've got poor bearing support, poor gear location, and poor shaft design. All transmissions live and die by their bearings. This design does more to create issues for the bearings than it does to solve any. The Getrag 233 in the Supra is so completely different and so much better supported/located it isn't even funny. But that's why the Getrag is known to survive 1000 ft-lbs of torque. I wouldn't expect much out of this Aisin gearbox under anything more than stock power, and even with stock power, I wouldn't be expecting it to tolerate much abuse at all.
Here's the diagram:
Last edited by lobuxracer; 08-30-09 at 10:05 AM.
08-30-09, 08:56 PM
#39
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[QUOTE=lobuxracer;4807913]It's not hard to build a front drive gearbox that feels better than many rear drive boxes primarily because front drive doesn't see much torque. The more torque the gearbox handles, the stiffer the gearbox ends up being for a lot of solid reasons.
The gearbox in the manual IS250 is junk.
With much respect...I think that's a bit harsh. The jury still out on this one. I dont think comparing this manual transmission to say a supra is fair. Comparisons should be made to relative cars ie. bmw 320, merc 300 , audi a4, ( where the IS holds its own ) Frankly, when comparing any of these manuals to say an rx8 theyll probably come out on the short end.
And YES, the IS's auto is better than manual, but some of us wouldnt drive autos if our lives depended on it.
The gearbox in the manual IS250 is junk.
With much respect...I think that's a bit harsh. The jury still out on this one. I dont think comparing this manual transmission to say a supra is fair. Comparisons should be made to relative cars ie. bmw 320, merc 300 , audi a4, ( where the IS holds its own ) Frankly, when comparing any of these manuals to say an rx8 theyll probably come out on the short end.
And YES, the IS's auto is better than manual, but some of us wouldnt drive autos if our lives depended on it.
08-30-09, 08:59 PM
#40
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[QUOTE=dmocchi;4809108]
Sorry, but BMW uses a Getrag gearbox in their cars. It's very much like the Supra's gearbox. So it really is apples to apples. The RA62 is a Tacoma gearbox and always will be. Like it or not, you've got a truck gearbox in the IS250 and you've got a Getrag 200 series in the BMW very similar to the Getrag 233 in the Supra.
It's not hard to build a front drive gearbox that feels better than many rear drive boxes primarily because front drive doesn't see much torque. The more torque the gearbox handles, the stiffer the gearbox ends up being for a lot of solid reasons.
The gearbox in the manual IS250 is junk.
With much respect...I think that's a bit harsh. The jury still out on this one. I dont think comparing this manual transmission to say a supra is fair. Comparisons should be made to relative cars ie. bmw 320, merc 300 , audi a4, ( where the IS holds its own ) Frankly, when comparing any of these manuals to say an rx8 theyll probably come out on the short end.
And YES, the IS's auto is better than manual, but some of us wouldnt drive autos if our lives depended on it.
The gearbox in the manual IS250 is junk.
With much respect...I think that's a bit harsh. The jury still out on this one. I dont think comparing this manual transmission to say a supra is fair. Comparisons should be made to relative cars ie. bmw 320, merc 300 , audi a4, ( where the IS holds its own ) Frankly, when comparing any of these manuals to say an rx8 theyll probably come out on the short end.
And YES, the IS's auto is better than manual, but some of us wouldnt drive autos if our lives depended on it.
08-30-09, 09:20 PM
#41
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[QUOTE=lobuxracer;4809119]
Sorry, but BMW uses a Getrag gearbox in their cars. It's very much like the Supra's gearbox. So it really is apples to apples. The RA62 is a Tacoma gearbox and always will be. Like it or not, you've got a truck gearbox in the IS250 and you've got a Getrag 200 series in the BMW very similar to the Getrag 233 in the Supra.
Understood. But a Supra is a high performance sports car. The Bmw uses a getrag but so do other manufacturers . This IMO is not a criterion.
A manual car should be compared to its direct competition. (ie when Im shopping for a manual family sedan Im not comparing a manual supra to a manual bmw). To expand thes4e analogies even further, even though a bmw 335 has a getrag so does a Corvette and so does the Supra but their all provide a distinct feel. I agree that the bmw does make 'good ' manuals but my ultimate point was a rebuttal to your "is manual suck" point. I just think that if your brazen enough to classify the IS's manual as 'sucking' then the a4 2.0t, merc, 300, camry2.4 and so forth, also all suck according to this logic because they are a 'lesser' manual to the Supra.
Sorry, but BMW uses a Getrag gearbox in their cars. It's very much like the Supra's gearbox. So it really is apples to apples. The RA62 is a Tacoma gearbox and always will be. Like it or not, you've got a truck gearbox in the IS250 and you've got a Getrag 200 series in the BMW very similar to the Getrag 233 in the Supra.
Understood. But a Supra is a high performance sports car. The Bmw uses a getrag but so do other manufacturers . This IMO is not a criterion.
A manual car should be compared to its direct competition. (ie when Im shopping for a manual family sedan Im not comparing a manual supra to a manual bmw). To expand thes4e analogies even further, even though a bmw 335 has a getrag so does a Corvette and so does the Supra but their all provide a distinct feel. I agree that the bmw does make 'good ' manuals but my ultimate point was a rebuttal to your "is manual suck" point. I just think that if your brazen enough to classify the IS's manual as 'sucking' then the a4 2.0t, merc, 300, camry2.4 and so forth, also all suck according to this logic because they are a 'lesser' manual to the Supra.
08-31-09, 10:23 AM
#42
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Understood. But a Supra is a high performance sports car. The Bmw uses a getrag but so do other manufacturers . This IMO is not a criterion.
A manual car should be compared to its direct competition. (ie when Im shopping for a manual family sedan Im not comparing a manual supra to a manual bmw). To expand thes4e analogies even further, even though a bmw 335 has a getrag so does a Corvette and so does the Supra but their all provide a distinct feel. I agree that the bmw does make 'good ' manuals but my ultimate point was a rebuttal to your "is manual suck" point. I just think that if your brazen enough to classify the IS's manual as 'sucking' then the a4 2.0t, merc, 300, camry2.4 and so forth, also all suck according to this logic because they are a 'lesser' manual to the Supra.
A manual car should be compared to its direct competition. (ie when Im shopping for a manual family sedan Im not comparing a manual supra to a manual bmw). To expand thes4e analogies even further, even though a bmw 335 has a getrag so does a Corvette and so does the Supra but their all provide a distinct feel. I agree that the bmw does make 'good ' manuals but my ultimate point was a rebuttal to your "is manual suck" point. I just think that if your brazen enough to classify the IS's manual as 'sucking' then the a4 2.0t, merc, 300, camry2.4 and so forth, also all suck according to this logic because they are a 'lesser' manual to the Supra.
08-31-09, 11:17 AM
#43
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i crank out 650KM/Tank
and i dont drive like a girl.LOL
im happy with my 250. if ther eis anything im not happy with.. is the cloth interior. its feels like poopie canvas shoe material...im getting the black leathers out of a crashed one so im good:P
and i dont drive like a girl.LOL
im happy with my 250. if ther eis anything im not happy with.. is the cloth interior. its feels like poopie canvas shoe material...im getting the black leathers out of a crashed one so im good:P
08-31-09, 04:51 PM
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Yeah, but those other gearboxes don't fundamentally suck. Their designs aren't conceptually flawed by poorly supported unnecessarily thin shafts and poor bearing location. Sure the Getrag in the Supra is unique - it's a 233, but the same series Getrag lives in the 3 Series, the 5 Series, etc. I'm not intimately familiar with Audi's gearboxes, but Getrag engineers know how to build a stout gearbox. The 233 in the Supra isn't a fluke for Getrag (although it is a fluke for Toyota). The Camry gearbox isn't even in the same ballpark because it's front drive and very compact. Toyota's FWD transaxles are decent designs, and don't have the issues seen in the RA62 - the shafts are stout, the bearings are well supported and sized for the loads the Camry will encounter - I've seen this gearbox on the Scion tC - it's not a bad design. The RA 62 isn't even in the same league. I've been inside a fair number of gearboxes. It's just a bad design period.
I dont know man. I respect your knowledge on these matters but I still cant empathize with the whole 'is 250 manual sucks'. I guess Im more of a pragmatic person, in that sitting in my driveway I have accessible few of its german manual competitors and cant really see how a getrag or any other manual on a four door sport luxury manual is 'considerably' better relegating the IS as 'sucking'. i drivem everyday and they all do have their own quirks. To me the only 'perfect' financially accessible manuals exist on some hondas and a few of the mazda products everything else is superflous. I guess that this topic may also be subjective of sorts.
Anyways thanks for the detailed info!
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