Heavy duty torque tube bearings, Gretch needs advice.
07-18-2008, 10:40 AM
#31
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I don't want to rain on anyone's parade, but I saw the shaft at SITM and the bearings look great.
However, the spines are cut and not rolled and are susceptible to stress fractures at the root of the thread. This is the reason that no auto manufacturer has cut splines for a very long time.
I work in the auto industry and currently at a couple of my plants they are making all the shafts for the Ford/GM 6 speed automatic transmission, so have a lot of contact with failure modes on these shafts.
A larger shaft (and flex plate for auto / clutch disk center for manual) may mitigate that problem.
However, the spines are cut and not rolled and are susceptible to stress fractures at the root of the thread. This is the reason that no auto manufacturer has cut splines for a very long time.
I work in the auto industry and currently at a couple of my plants they are making all the shafts for the Ford/GM 6 speed automatic transmission, so have a lot of contact with failure modes on these shafts.
A larger shaft (and flex plate for auto / clutch disk center for manual) may mitigate that problem.
07-19-2008, 06:23 AM
#32
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Hi Rod,
Understood about rolled versus cut threads. However your statements are an over generalization and do not take into account the material being used for our new drive shafts and their application.
When you say "these shafts" are you referring to 928 drive shafts or transmission shafts? The 928 drive shaft should not be considered to be the same as a transmission shaft and has different operating parameters as you well know being in your business.
Your last statement is also a bit curious. Larger shafts are not always the answer and the 928 does use both a flexplate design and a clutch for their their different models.
We have sourced the new drive shafts from a well established manufacturer that has been making similiar products for many years and have a solid and respected reputation in the industry. The material specified for our application was discussed with their engineers and we are extremely confident our drive shafts will last and are an upgrade to what Porsche used for theirs. If we weren't we would not be offering them for sale.
I will always welcome a discussion about our products. I only ask that before a doubt is cast upon ours or anyone else's products more information would be obtained on that product. I wish you would have brought up your concern to me while we were both at SITM so we could have had a conversation about this subject face to face.
Regards,
Constantine
Understood about rolled versus cut threads. However your statements are an over generalization and do not take into account the material being used for our new drive shafts and their application.
When you say "these shafts" are you referring to 928 drive shafts or transmission shafts? The 928 drive shaft should not be considered to be the same as a transmission shaft and has different operating parameters as you well know being in your business.
Your last statement is also a bit curious. Larger shafts are not always the answer and the 928 does use both a flexplate design and a clutch for their their different models.
We have sourced the new drive shafts from a well established manufacturer that has been making similiar products for many years and have a solid and respected reputation in the industry. The material specified for our application was discussed with their engineers and we are extremely confident our drive shafts will last and are an upgrade to what Porsche used for theirs. If we weren't we would not be offering them for sale.
I will always welcome a discussion about our products. I only ask that before a doubt is cast upon ours or anyone else's products more information would be obtained on that product. I wish you would have brought up your concern to me while we were both at SITM so we could have had a conversation about this subject face to face.
Regards,
Constantine
I don't want to rain on anyone's parade, but I saw the shaft at SITM and the bearings look great.
However, the spines are cut and not rolled and are susceptible to stress fractures at the root of the thread. This is the reason that no auto manufacturer has cut splines for a very long time.
I work in the auto industry and currently at a couple of my plants they are making all the shafts for the Ford/GM 6 speed automatic transmission, so have a lot of contact with failure modes on these shafts.
A larger shaft (and flex plate for auto / clutch disk center for manual) may mitigate that problem.
However, the spines are cut and not rolled and are susceptible to stress fractures at the root of the thread. This is the reason that no auto manufacturer has cut splines for a very long time.
I work in the auto industry and currently at a couple of my plants they are making all the shafts for the Ford/GM 6 speed automatic transmission, so have a lot of contact with failure modes on these shafts.
A larger shaft (and flex plate for auto / clutch disk center for manual) may mitigate that problem.
07-19-2008, 09:35 AM
#33
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Hi Rod,
Understood about rolled versus cut threads. However your statements are an over generalization and do not take into account the material being used for our new drive shafts and their application.
When you say "these shafts" are you referring to 928 drive shafts or transmission shafts? The 928 drive shaft should not be considered to be the same as a transmission shaft and has different operating parameters as you well know being in your business.
Your last statement is also a bit curious. Larger shafts are not always the answer and the 928 does use both a flexplate design and a clutch for their their different models.
We have sourced the new drive shafts from a well established manufacturer that has been making similiar products for many years and have a solid and respected reputation in the industry. The material specified for our application was discussed with their engineers and we are extremely confident our drive shafts will last and are an upgrade to what Porsche used for theirs. If we weren't we would not be offering them for sale.
I will always welcome a discussion about our products. I only ask that before a doubt is cast upon ours or anyone else's products more information would be obtained on that product. I wish you would have brought up your concern to me while we were both at SITM so we could have had a conversation about this subject face to face.
Regards,
Constantine
Understood about rolled versus cut threads. However your statements are an over generalization and do not take into account the material being used for our new drive shafts and their application.
When you say "these shafts" are you referring to 928 drive shafts or transmission shafts? The 928 drive shaft should not be considered to be the same as a transmission shaft and has different operating parameters as you well know being in your business.
Your last statement is also a bit curious. Larger shafts are not always the answer and the 928 does use both a flexplate design and a clutch for their their different models.
We have sourced the new drive shafts from a well established manufacturer that has been making similiar products for many years and have a solid and respected reputation in the industry. The material specified for our application was discussed with their engineers and we are extremely confident our drive shafts will last and are an upgrade to what Porsche used for theirs. If we weren't we would not be offering them for sale.
I will always welcome a discussion about our products. I only ask that before a doubt is cast upon ours or anyone else's products more information would be obtained on that product. I wish you would have brought up your concern to me while we were both at SITM so we could have had a conversation about this subject face to face.
Regards,
Constantine
Have you done fatigue testing vs. the factory shaft? This shaft sees some of the most abusive conditions a shaft ever will. 6000rpm then both acceleration and deceleration shocks of high magnitude frequently (every shift and lift of the throttle).
The fact is that splines have been around for a long time and if the spline is large enough then stress fractures are not a problem. From the failures I have seen here even with rolled splines they generate stress fractures at the root.
It is a known fact that rolled splines are stronger and less likely to generate these types of failures. If you have not done fatigue testing on these vs. the factory ones I will stand by my original statement that they cannot be less likely to have this failure no matter what material they are made from.
Removing the necked down portion is a good engineering practice but the root diameter of the splines is the largest that you need as that is the maximum strength point on that connection.
I would love to spend some time talking with you as these types of conversations are my favorite. I hope we can keep it civil (I intend to) but also want to educate the general public because the more they know the better off we all are.
Cheers,
07-19-2008, 10:12 AM
#34
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Rod,
I don't really understand your point about our new shaft vs. the OE shaft.
The OE 28mm shaft has been well documented to have shearing problems at the neck down area of the drive shaft. I guess Porsche's fatigue testing procedure for this shaft was not as good as it could have been? This is the problem our new drive shafts will address.
As far as the splines of the new drive shafts being able to handle the stresses found in our drive lines, we will stand behind them and our original statements about them.
Kind regards,
Constantine
I don't really understand your point about our new shaft vs. the OE shaft.
The OE 28mm shaft has been well documented to have shearing problems at the neck down area of the drive shaft. I guess Porsche's fatigue testing procedure for this shaft was not as good as it could have been? This is the problem our new drive shafts will address.
As far as the splines of the new drive shafts being able to handle the stresses found in our drive lines, we will stand behind them and our original statements about them.
Kind regards,
Constantine
07-19-2008, 01:28 PM
#35
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Fair enough.
So how many 928 torque tubes have experienced failure at the splines.
Anyone have any old torque tubes lying around and willing to peek at the splines with magifying glass. Magnaflux or some other crack detection device to test the old splines would even be better.
So how many 928 torque tubes have experienced failure at the splines.
Anyone have any old torque tubes lying around and willing to peek at the splines with magifying glass. Magnaflux or some other crack detection device to test the old splines would even be better.
07-19-2008, 02:02 PM
#36
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Fair enough.
So how many 928 torque tubes have experienced failure at the splines.
Anyone have any old torque tubes lying around and willing to peek at the splines with magifying glass. Magnaflux or some other crack detection device to test the old splines would even be better.
So how many 928 torque tubes have experienced failure at the splines.
Anyone have any old torque tubes lying around and willing to peek at the splines with magifying glass. Magnaflux or some other crack detection device to test the old splines would even be better.
07-19-2008, 02:21 PM
#37
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The 928 and 924/944/968 line that use the same style drive shaft have all experienced failure of the splines. From what we have seen some are caused by not using proper tightening techniques (not using a good torque wrench) of the pinch bolts. Other times damage is caused during poor TT installation techniques (banging on the drive shaft, using vice grips on the spline area, misalignment of the transmission during install, etc.) and others by just plain old fatigue of the metal.
How many 928s have had spline failure due to metal fatigue really won't be found out for use in a exacting study of our drive shafts. Tried it and chased my tail for a long time.
Porsche really did a very good job with our drive shafts, except for the 928 automatic 28mm shafts, and their use for so many years and many currently surviving boosted/racing applications is a testament of that.
YMMV,
Constantine
How many 928s have had spline failure due to metal fatigue really won't be found out for use in a exacting study of our drive shafts. Tried it and chased my tail for a long time.
Porsche really did a very good job with our drive shafts, except for the 928 automatic 28mm shafts, and their use for so many years and many currently surviving boosted/racing applications is a testament of that.
YMMV,
Constantine
07-19-2008, 06:55 PM
#38
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Just curious - all the failures I have seen have been at the transition from splined to smooth. (Both 25 and 28mm shafts) In some cases however this was accompanied by permanent twisting of the shaft and "delamination" of the splines from the central core of the shaft, between the transition point and the clamp. The best description of the appearance of the splines in this area is that they resembled the outer layer of wire rope.
An off the wall data point - I used to run old Land Rovers - these were notorious for breaking half shafts in the rear axle. Failures were always at the differential end of the shaft and always failure was at the transistion from splined to non splined. Failure mode was always the classic cone shaped torsional shear failure. IIRC the failure didn't happen at the wheel end because the splines were longer.
07-22-2008, 04:43 PM
#39
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07-22-2008, 04:50 PM
#40
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No love for the OB......
Oh well, I'm dumping the transmissions in my 78 / 81 for newer style with the matching tirque tube anyway
Nice work Constantine, we spent a lot of time admiring the pinch bolt solution you sent for Shane when it arrived in town.
Oh well, I'm dumping the transmissions in my 78 / 81 for newer style with the matching tirque tube anyway
Nice work Constantine, we spent a lot of time admiring the pinch bolt solution you sent for Shane when it arrived in town.
07-22-2008, 07:36 PM
#41
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Hi Stan,
Well Porsche rebuilt TTs went for $1500-$1800 and I'm not sure if that included new drive shafts or not. I don't know if they are even available anymore from Porsche, I've heard both yes and no.
The $495.00 rebuilt units come with re-used parts and pieces to include the drive shafts but with new bearings installed.
Our new drive shafts are just that, brand new. I guess we'll see what the price points are once the manufacturer gives me a multiple unit order qoute.
Cheers,
Constantine
Well Porsche rebuilt TTs went for $1500-$1800 and I'm not sure if that included new drive shafts or not. I don't know if they are even available anymore from Porsche, I've heard both yes and no.
The $495.00 rebuilt units come with re-used parts and pieces to include the drive shafts but with new bearings installed.
Our new drive shafts are just that, brand new. I guess we'll see what the price points are once the manufacturer gives me a multiple unit order qoute.
Cheers,
Constantine
07-22-2008, 07:41 PM
#42
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No,no, I love the OB models!
I just don't know how many people would want new drive shafts for them. If people want them we will stock them.
And thank you for the nice comment on the 928 Super Clamp. How did y'all like the sticker? That is a newer addition to the installation package which we believed was needed.
Let me know about the OB drive shaft need.
Cheers,
Constantine
I just don't know how many people would want new drive shafts for them. If people want them we will stock them.
And thank you for the nice comment on the 928 Super Clamp. How did y'all like the sticker? That is a newer addition to the installation package which we believed was needed.
Let me know about the OB drive shaft need.
Cheers,
Constantine
07-22-2008, 07:52 PM
#43
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Hi Stan,
Well Porsche rebuilt TTs went for $1500-$1800 and I'm not sure if that included new drive shafts or not. I don't know if they are even available anymore from Porsche, I've heard both yes and no.
The $495.00 rebuilt units come with re-used parts and pieces to include the drive shafts but with new bearings installed.
Our new drive shafts are just that, brand new. I guess we'll see what the price points are once the manufacturer gives me a multiple unit order qoute.
Cheers,
Constantine
Well Porsche rebuilt TTs went for $1500-$1800 and I'm not sure if that included new drive shafts or not. I don't know if they are even available anymore from Porsche, I've heard both yes and no.
The $495.00 rebuilt units come with re-used parts and pieces to include the drive shafts but with new bearings installed.
Our new drive shafts are just that, brand new. I guess we'll see what the price points are once the manufacturer gives me a multiple unit order qoute.
Cheers,
Constantine
