Transmission options for 87S
01-16-2016, 11:41 AM
#1
Transmission options for 87S
Hi all,
I knew my S's transmission wasn't treated very well by the PO and now it has developed a knock that changes with car speed. It is intermittent and I suspect the LSD is on its last legs.
I could try to find another one but what's unique about the S? I think it has one similar to a turbo?
I'm just trying to get a feel for the budget on this. Thanks
Chris
I knew my S's transmission wasn't treated very well by the PO and now it has developed a knock that changes with car speed. It is intermittent and I suspect the LSD is on its last legs.
I could try to find another one but what's unique about the S? I think it has one similar to a turbo?
I'm just trying to get a feel for the budget on this. Thanks
Chris
01-16-2016, 11:44 AM
#2
Rainman
Rennlist Member
Rennlist Member
S transmission can be thought of as 951 gears and case, with a 944NA type differential.
the difference between 951 and 944 gearing is pretty slight so you could put a regular 944 gearbox in there and probably be OK, but make sure its one thats been cared for.
i don't recommend a 951 box for your S because the S is pretty lacking in low-down power and the 951 box will amplify that.
the difference between 951 and 944 gearing is pretty slight so you could put a regular 944 gearbox in there and probably be OK, but make sure its one thats been cared for.
i don't recommend a 951 box for your S because the S is pretty lacking in low-down power and the 951 box will amplify that.
01-16-2016, 02:12 PM
#3
Rennlist Member
The S has somewhat unique gear ratios. It's geared slightly taller than an N/A, and slightly shorter than an S2, which is shorter than the Turbo. It has the short 5th gear as well.
An N/A box will work but it is somewhat weaker than the S transaxle, at least from what I've read.
My S transaxle is also on its way out, the pinion bearing has been howling for quite some time and it's been getting worse lately. I have been on the lookout for an S or S2 transaxle with LSD to replace it.
Here is a comparison of the different ratios available: 924/944 Transaxle Gear Calculator
An N/A box will work but it is somewhat weaker than the S transaxle, at least from what I've read.
My S transaxle is also on its way out, the pinion bearing has been howling for quite some time and it's been getting worse lately. I have been on the lookout for an S or S2 transaxle with LSD to replace it.
Here is a comparison of the different ratios available: 924/944 Transaxle Gear Calculator
01-16-2016, 06:12 PM
#4
Rennlist Member
There is some misinformation in some previous posts. The 944S shares the same basic transmission as the 944S2 and Turbo. Its only difference is the ratio of the ring and pinion, which is shorter in the S than that in the 944 Turbo and close to that of the 944S2. Its uses the same gears and their ratios are the same as those in the S2 and Turbo, except that the S2 got a unique, taller 5th gear that helped Porsche meet CAFE requirements.
The 944S and the 944 "normal" (eight-valve, normally aspirated) cars share the same ring and pinion ratio, and the gear ratios are darned close. However, mechanically the parts (r&p, gears) are different and do not interchange. While a 944 normal transmission will install in your car, I do not recommend doing so unless a) it's in top notch condition, b) you are willing to keep it that way. The 944 normal pinion gear is known for its failures which are due to the marginal width of the pinion gear tooth root, and using that in an S with more power is only more likely to end badly. I have racer clients who do this successfully and with the even skinnier 4.11 r&p, but they are racers who maintain their cars and are willing to tolerate winching the car back on the trailer from time to time.
The 944S/2/Turbo cars have thicker gears, and the pinion and input shafts as well as the case are all slightly longer to accommodate. The differentials interchange between them: they measure the same. However, there were three major versions of the LSD which was improved over the years. There are also a great many undocumented changes to the design of the open differential over the lifetime of the 924S/944 series. The tooth root width in these cars' pinion gears were widened to handle their greater power.
Your 944S transmission is very rebuildable, parts remain available. Consider that path rather than another used gearbox: to quote Stan Hanks, "You already own a used gearbox; why buy another?"
The 944S and the 944 "normal" (eight-valve, normally aspirated) cars share the same ring and pinion ratio, and the gear ratios are darned close. However, mechanically the parts (r&p, gears) are different and do not interchange. While a 944 normal transmission will install in your car, I do not recommend doing so unless a) it's in top notch condition, b) you are willing to keep it that way. The 944 normal pinion gear is known for its failures which are due to the marginal width of the pinion gear tooth root, and using that in an S with more power is only more likely to end badly. I have racer clients who do this successfully and with the even skinnier 4.11 r&p, but they are racers who maintain their cars and are willing to tolerate winching the car back on the trailer from time to time.
The 944S/2/Turbo cars have thicker gears, and the pinion and input shafts as well as the case are all slightly longer to accommodate. The differentials interchange between them: they measure the same. However, there were three major versions of the LSD which was improved over the years. There are also a great many undocumented changes to the design of the open differential over the lifetime of the 924S/944 series. The tooth root width in these cars' pinion gears were widened to handle their greater power.
Your 944S transmission is very rebuildable, parts remain available. Consider that path rather than another used gearbox: to quote Stan Hanks, "You already own a used gearbox; why buy another?"
01-19-2016, 09:52 PM
#6
Rennlist Member
There is some misinformation in some previous posts. The 944S shares the same basic transmission as the 944S2 and Turbo. Its only difference is the ratio of the ring and pinion, which is shorter in the S than that in the 944 Turbo and close to that of the 944S2. Its uses the same gears and their ratios are the same as those in the S2 and Turbo, except that the S2 got a unique, taller 5th gear that helped Porsche meet CAFE requirements.
The 944S and the 944 "normal" (eight-valve, normally aspirated) cars share the same ring and pinion ratio, and the gear ratios are darned close. However, mechanically the parts (r&p, gears) are different and do not interchange. While a 944 normal transmission will install in your car, I do not recommend doing so unless a) it's in top notch condition, b) you are willing to keep it that way. The 944 normal pinion gear is known for its failures which are due to the marginal width of the pinion gear tooth root, and using that in an S with more power is only more likely to end badly. I have racer clients who do this successfully and with the even skinnier 4.11 r&p, but they are racers who maintain their cars and are willing to tolerate winching the car back on the trailer from time to time.
The 944S/2/Turbo cars have thicker gears, and the pinion and input shafts as well as the case are all slightly longer to accommodate. The differentials interchange between them: they measure the same. However, there were three major versions of the LSD which was improved over the years. There are also a great many undocumented changes to the design of the open differential over the lifetime of the 924S/944 series. The tooth root width in these cars' pinion gears were widened to handle their greater power.
Your 944S transmission is very rebuildable, parts remain available. Consider that path rather than another used gearbox: to quote Stan Hanks, "You already own a used gearbox; why buy another?"
The 944S and the 944 "normal" (eight-valve, normally aspirated) cars share the same ring and pinion ratio, and the gear ratios are darned close. However, mechanically the parts (r&p, gears) are different and do not interchange. While a 944 normal transmission will install in your car, I do not recommend doing so unless a) it's in top notch condition, b) you are willing to keep it that way. The 944 normal pinion gear is known for its failures which are due to the marginal width of the pinion gear tooth root, and using that in an S with more power is only more likely to end badly. I have racer clients who do this successfully and with the even skinnier 4.11 r&p, but they are racers who maintain their cars and are willing to tolerate winching the car back on the trailer from time to time.
The 944S/2/Turbo cars have thicker gears, and the pinion and input shafts as well as the case are all slightly longer to accommodate. The differentials interchange between them: they measure the same. However, there were three major versions of the LSD which was improved over the years. There are also a great many undocumented changes to the design of the open differential over the lifetime of the 924S/944 series. The tooth root width in these cars' pinion gears were widened to handle their greater power.
Your 944S transmission is very rebuildable, parts remain available. Consider that path rather than another used gearbox: to quote Stan Hanks, "You already own a used gearbox; why buy another?"
I don't necessarily mind paying an expert for specialty work like this but so far I have done every single job on my 944 myself and I'd like to keep that streak going if I can.
01-20-2016, 07:36 AM
#7
Rennlist Member
Steve,
You can usually skip use of the VW385 tool to establish pinion depth in a simple rebuild, unless your car is a 968 or 944S2 where the factory made mistakes, or you have any reason to believe the depth may be incorrect.
The rebuild is not out of the question for a DIYer. However, it's a challenge and I would recommend against skipping any of the steps. For example, getting the preload correct on the pinion shaft bearings and the diff carrier bearings, and getting the ring-to-pinion backlash correct are all really important.
Some special tools are essential or really really helpful, others less so. Of course you'll need a hydraulic press. There was a walk-through posted by someone from Australia some time ago -- take a pass through it, see what you think. Good luck!
You can usually skip use of the VW385 tool to establish pinion depth in a simple rebuild, unless your car is a 968 or 944S2 where the factory made mistakes, or you have any reason to believe the depth may be incorrect.
The rebuild is not out of the question for a DIYer. However, it's a challenge and I would recommend against skipping any of the steps. For example, getting the preload correct on the pinion shaft bearings and the diff carrier bearings, and getting the ring-to-pinion backlash correct are all really important.
Some special tools are essential or really really helpful, others less so. Of course you'll need a hydraulic press. There was a walk-through posted by someone from Australia some time ago -- take a pass through it, see what you think. Good luck!
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01-20-2016, 08:47 AM
#8
Rennlist Member
Steve,
You can usually skip use of the VW385 tool to establish pinion depth in a simple rebuild, unless your car is a 968 or 944S2 where the factory made mistakes, or you have any reason to believe the depth may be incorrect.
The rebuild is not out of the question for a DIYer. However, it's a challenge and I would recommend against skipping any of the steps. For example, getting the preload correct on the pinion shaft bearings and the diff carrier bearings, and getting the ring-to-pinion backlash correct are all really important.
Some special tools are essential or really really helpful, others less so. Of course you'll need a hydraulic press. There was a walk-through posted by someone from Australia some time ago -- take a pass through it, see what you think. Good luck!
You can usually skip use of the VW385 tool to establish pinion depth in a simple rebuild, unless your car is a 968 or 944S2 where the factory made mistakes, or you have any reason to believe the depth may be incorrect.
The rebuild is not out of the question for a DIYer. However, it's a challenge and I would recommend against skipping any of the steps. For example, getting the preload correct on the pinion shaft bearings and the diff carrier bearings, and getting the ring-to-pinion backlash correct are all really important.
Some special tools are essential or really really helpful, others less so. Of course you'll need a hydraulic press. There was a walk-through posted by someone from Australia some time ago -- take a pass through it, see what you think. Good luck!
I do have a press and I think I could fashion some way to take most of the necessary measurements.
I think I'll give it a shot if I can find a cheap trans to toss in for the meantime.
Thanks!
01-20-2016, 10:48 AM
#9
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that's bias and I disagree with that statement, if you have a broken 951, S2 or 968 transmission replacing the unit vs rebuilt, it will always be less expensive to swap it for a used unit, prices for open differential 951 transmissions start around $ 450.00 that's how much Kevin is going to charge you by just touching your transaxle. lol, no way rebuilt is cheaper.
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Last edited by lart951; 01-20-2016 at 12:42 PM.
01-20-2016, 02:55 PM
#10
Rennlist Member
Hi all,
I knew my S's transmission wasn't treated very well by the PO and now it has developed a knock that changes with car speed. It is intermittent and I suspect the LSD is on its last legs.
I could try to find another one but what's unique about the S? I think it has one similar to a turbo?
I'm just trying to get a feel for the budget on this. Thanks
Chris
I knew my S's transmission wasn't treated very well by the PO and now it has developed a knock that changes with car speed. It is intermittent and I suspect the LSD is on its last legs.
I could try to find another one but what's unique about the S? I think it has one similar to a turbo?
I'm just trying to get a feel for the budget on this. Thanks
Chris
01-20-2016, 07:34 PM
#13
Rennlist Member
that's bias and I disagree with that statement, if you have a broken 951, S2 or 968 transmission replacing the unit vs rebuilt, it will always be less expensive to swap it for a used unit, prices for open differential 951 transmissions start around $ 450.00 that's how much Kevin is going to charge you by just touching your transaxle. lol, no way rebuilt is cheaper.
01-21-2016, 08:01 AM
#14
Rennlist Member
Yes, that seems to be the case. I have also seen this for 944S2 transmissions, although I don't know others that have.My bias is toward people who want to keep their car for the long term, that's true. If you are just interested in getting another year or two use out of your car, then by all means a used transmission can be a good option. However, a used transmission is almost always a pig-in-a-poke. While rebuilding is more expensive in the short term, if you do the math on cost-to-rebuild / anticipated-longevity, a rebuild is always less expensive.
01-21-2016, 08:23 AM
#15
Yes, that seems to be the case. I have also seen this for 944S2 transmissions, although I don't know others that have.
My bias is toward people who want to keep their car for the long term, that's true. If you are just interested in getting another year or two use out of your car, then by all means a used transmission can be a good option. However, a used transmission is almost always a pig-in-a-poke. While rebuilding is more expensive in the short term, if you do the math on cost-to-rebuild / anticipated-longevity, a rebuild is always less expensive.
My bias is toward people who want to keep their car for the long term, that's true. If you are just interested in getting another year or two use out of your car, then by all means a used transmission can be a good option. However, a used transmission is almost always a pig-in-a-poke. While rebuilding is more expensive in the short term, if you do the math on cost-to-rebuild / anticipated-longevity, a rebuild is always less expensive.
