porsche 996 - early models
Discussion
johnsuper said:
can somebody tell me if the early models with 3.4L, are prone to have gearbox reliability issues ? thanks
Don't early model 3.4's have reliability issues in a lot of areas or have i dreamt this, still that aside still reasonable value for money if you are one of the lucky ones, i towed with getting her in doors one and getting rid of her RX8, but was told by a well known specialist to leave well alone, so i did.Hi there
The 3.4L cars around 1998-2000 do have a tendancy to go through pinion shaft bearings....but in a couple of years it could be 2000-2003 cars as they get older.
If you are thinking of buying one just get a good inspection done on the vehicle prior to purchase....if you can get the 111 point check over and warranty then even better.
Mike
Sportsandclassic ltd
The 3.4L cars around 1998-2000 do have a tendancy to go through pinion shaft bearings....but in a couple of years it could be 2000-2003 cars as they get older.
If you are thinking of buying one just get a good inspection done on the vehicle prior to purchase....if you can get the 111 point check over and warranty then even better.
Mike
Sportsandclassic ltd
Tiptronics seem very reliable except for the occasional wiring loom replacement needed in the sump.
Manuals have 2 main faults.
(1) The pinion bearing is not really up to the job in some cars but OK in others (depending on manufacturing tolerances, assembly quality and use). It usually wears the surface by "compaction" a process where the loads press hard surface metal into the softer substrate and fatigue the layer until a small piece of hard metal falls away leaving a small hole that then gets worse. This is usually accompanied with a typical diff whine. A Taper roller bearing would support the loads better (but then didn't work too well in the 968) or a combination of ball and roller bearing - but then they cost more.
Strangely the surface that usually wears the most is not that resisting the lateral load from the pinion gear but the forward load from the angle of the helical internal gear teeth.
(2) In the past - most gearboxes allowed the internal selector to move forwards and backwards with the movement of the gear lever and it stopped when the selector was unable to go any further into engagement.
Now the pinion shaft is always shimmed along its length to get the right position for the pinion gear to run at its best with the crown wheel - so every gearbox has the pinion shaft in a slightly different position along its length and this moves the position of the selectors relative to the casing and therefore moves the position that the gear lever selector moves in and out of gear.
Previously this did not affect the gear selection because the lever simply moved as far as it can until the selector was fully engaged, but in this gearbox a selector system has been employed that has a dead stop in it to prevent the lever moving any further than the exact movement that would be perfect if the shaft happened to have been fitted central.
Because the shafts are all fitted in different positions (due to the pinion nose penetration positioning) it results in either 1st or 2nd selector not being able to travel quite as far as a full engagement would prefer.
The over centre springs and pawls pull the last bit into gear but over time and with wear - some gearboxes happen to be in a position where one gear (usually 2nd) fails to engage and damages the engagement teeth and start a process towards poor engagemnt all the time.
Wear in the pinion bearing can of course exacerbate this.
Just changing the 2nd gear parts can cure this but we also check the lateral positioning (not easy as the stop is fitted to the casing and so has to be done by measurement) and will correct any badly out positioning to improve selector movement.
Grinding some off the stop seems like a logical solution but then it also is the stop for 3rd 4th 5th & 6th and as they don't have pinion adjustment - they are set up OK and don't need it.
Baz
Manuals have 2 main faults.
(1) The pinion bearing is not really up to the job in some cars but OK in others (depending on manufacturing tolerances, assembly quality and use). It usually wears the surface by "compaction" a process where the loads press hard surface metal into the softer substrate and fatigue the layer until a small piece of hard metal falls away leaving a small hole that then gets worse. This is usually accompanied with a typical diff whine. A Taper roller bearing would support the loads better (but then didn't work too well in the 968) or a combination of ball and roller bearing - but then they cost more.
Strangely the surface that usually wears the most is not that resisting the lateral load from the pinion gear but the forward load from the angle of the helical internal gear teeth.
(2) In the past - most gearboxes allowed the internal selector to move forwards and backwards with the movement of the gear lever and it stopped when the selector was unable to go any further into engagement.
Now the pinion shaft is always shimmed along its length to get the right position for the pinion gear to run at its best with the crown wheel - so every gearbox has the pinion shaft in a slightly different position along its length and this moves the position of the selectors relative to the casing and therefore moves the position that the gear lever selector moves in and out of gear.
Previously this did not affect the gear selection because the lever simply moved as far as it can until the selector was fully engaged, but in this gearbox a selector system has been employed that has a dead stop in it to prevent the lever moving any further than the exact movement that would be perfect if the shaft happened to have been fitted central.
Because the shafts are all fitted in different positions (due to the pinion nose penetration positioning) it results in either 1st or 2nd selector not being able to travel quite as far as a full engagement would prefer.
The over centre springs and pawls pull the last bit into gear but over time and with wear - some gearboxes happen to be in a position where one gear (usually 2nd) fails to engage and damages the engagement teeth and start a process towards poor engagemnt all the time.
Wear in the pinion bearing can of course exacerbate this.
Just changing the 2nd gear parts can cure this but we also check the lateral positioning (not easy as the stop is fitted to the casing and so has to be done by measurement) and will correct any badly out positioning to improve selector movement.
Grinding some off the stop seems like a logical solution but then it also is the stop for 3rd 4th 5th & 6th and as they don't have pinion adjustment - they are set up OK and don't need it.
Baz
hartech said:
Tiptronics seem very reliable except for the occasional wiring loom replacement needed in the sump.
Manuals have 2 main faults.
(1) The pinion bearing is not really up to the job in some cars but OK in others (depending on manufacturing tolerances, assembly quality and use). It usually wears the surface by "compaction" a process where the loads press hard surface metal into the softer substrate and fatigue the layer until a small piece of hard metal falls away leaving a small hole that then gets worse. This is usually accompanied with a typical diff whine. A Taper roller bearing would support the loads better (but then didn't work too well in the 968) or a combination of ball and roller bearing - but then they cost more.
Strangely the surface that usually wears the most is not that resisting the lateral load from the pinion gear but the forward load from the angle of the helical internal gear teeth.
(2) In the past - most gearboxes allowed the internal selector to move forwards and backwards with the movement of the gear lever and it stopped when the selector was unable to go any further into engagement.
Now the pinion shaft is always shimmed along its length to get the right position for the pinion gear to run at its best with the crown wheel - so every gearbox has the pinion shaft in a slightly different position along its length and this moves the position of the selectors relative to the casing and therefore moves the position that the gear lever selector moves in and out of gear.
Previously this did not affect the gear selection because the lever simply moved as far as it can until the selector was fully engaged, but in this gearbox a selector system has been employed that has a dead stop in it to prevent the lever moving any further than the exact movement that would be perfect if the shaft happened to have been fitted central.
Because the shafts are all fitted in different positions (due to the pinion nose penetration positioning) it results in either 1st or 2nd selector not being able to travel quite as far as a full engagement would prefer.
The over centre springs and pawls pull the last bit into gear but over time and with wear - some gearboxes happen to be in a position where one gear (usually 2nd) fails to engage and damages the engagement teeth and start a process towards poor engagemnt all the time.
Wear in the pinion bearing can of course exacerbate this.
Just changing the 2nd gear parts can cure this but we also check the lateral positioning (not easy as the stop is fitted to the casing and so has to be done by measurement) and will correct any badly out positioning to improve selector movement.
Grinding some off the stop seems like a logical solution but then it also is the stop for 3rd 4th 5th & 6th and as they don't have pinion adjustment - they are set up OK and don't need it.
Baz
Can you provide an executive summary Manuals have 2 main faults.
(1) The pinion bearing is not really up to the job in some cars but OK in others (depending on manufacturing tolerances, assembly quality and use). It usually wears the surface by "compaction" a process where the loads press hard surface metal into the softer substrate and fatigue the layer until a small piece of hard metal falls away leaving a small hole that then gets worse. This is usually accompanied with a typical diff whine. A Taper roller bearing would support the loads better (but then didn't work too well in the 968) or a combination of ball and roller bearing - but then they cost more.
Strangely the surface that usually wears the most is not that resisting the lateral load from the pinion gear but the forward load from the angle of the helical internal gear teeth.
(2) In the past - most gearboxes allowed the internal selector to move forwards and backwards with the movement of the gear lever and it stopped when the selector was unable to go any further into engagement.
Now the pinion shaft is always shimmed along its length to get the right position for the pinion gear to run at its best with the crown wheel - so every gearbox has the pinion shaft in a slightly different position along its length and this moves the position of the selectors relative to the casing and therefore moves the position that the gear lever selector moves in and out of gear.
Previously this did not affect the gear selection because the lever simply moved as far as it can until the selector was fully engaged, but in this gearbox a selector system has been employed that has a dead stop in it to prevent the lever moving any further than the exact movement that would be perfect if the shaft happened to have been fitted central.
Because the shafts are all fitted in different positions (due to the pinion nose penetration positioning) it results in either 1st or 2nd selector not being able to travel quite as far as a full engagement would prefer.
The over centre springs and pawls pull the last bit into gear but over time and with wear - some gearboxes happen to be in a position where one gear (usually 2nd) fails to engage and damages the engagement teeth and start a process towards poor engagemnt all the time.
Wear in the pinion bearing can of course exacerbate this.
Just changing the 2nd gear parts can cure this but we also check the lateral positioning (not easy as the stop is fitted to the casing and so has to be done by measurement) and will correct any badly out positioning to improve selector movement.
Grinding some off the stop seems like a logical solution but then it also is the stop for 3rd 4th 5th & 6th and as they don't have pinion adjustment - they are set up OK and don't need it.
Baz
Short version.
(1) A cheaper way to provide a main thrust bearing on the input shaft (applied in the 996) sometimes results in premature failure.
(2)A design change in the stop system on the selector shaft positioning when engaging 1st and 2nd gear - in some gearboxes (depending it seems on how the nose penetration was originally set), results in 2nd gear not fully engaging when moving the gear lever and eventually wearing out the engagement dogs as other parts gradually wear.
Both can be replaced.
n.b. Very few "hone mechanics" would be able to repair a gearbox and so my previous full version was to inform other specialists (who may then be able to offer better help) why there is a problem and what to look for.
Baz
(1) A cheaper way to provide a main thrust bearing on the input shaft (applied in the 996) sometimes results in premature failure.
(2)A design change in the stop system on the selector shaft positioning when engaging 1st and 2nd gear - in some gearboxes (depending it seems on how the nose penetration was originally set), results in 2nd gear not fully engaging when moving the gear lever and eventually wearing out the engagement dogs as other parts gradually wear.
Both can be replaced.
n.b. Very few "hone mechanics" would be able to repair a gearbox and so my previous full version was to inform other specialists (who may then be able to offer better help) why there is a problem and what to look for.
Baz
I prefer the first version Baz ... But then , I am on a day off!!Gassing Station | Porsche General | Top of Page | What's New | My Stuff