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Background
I am undertaking a 5-sped conversion on my 1992 GTS and I thought I would start a build thread to consolidate the the various stages of the project and get help and feedback from the fantastic and supportive 928 community.
Disclaimer
I realize some people would not choose to mess with the originality of a GTS given their limited production number. This is a fair point and something I have given substantial consideration. I have chosen to move forward with the conversion, I love this particular car with it's color combination, I want to drive it and have fun with it for a long time and that includes having a 5-speed. I'll retain the original parts if a future owner would like to revert it back to an automatic.
Project Update
I've been collecting parts for the conversion and working on some small projects since this past Spring and will post recaps of those soon. I am waiting on the dual clutch/flywheel assembly and then I should be ready to install everything. Right now I am getting started on some prep-work for the transmission before it goes into the car.
GTS 5-spd transmission @Mark Anderson of 928 International helped me source a 5-speed transmission and cross member. When I originally asked him he said he would look but told me to not hold my breath (I could practically hear him laughing in email). Within a week he had found a GTS transmission and were arranging shipping. I was shocked and impressed. Thank you Mark for your help, you are amazing! Here are some details on the tranny:
According to the Porsche Technical Specifications, the serial number: G28 / 57 30 02014 checks out as a 1992/1993 GTS PSD transmission. It looks like this was the 13th production transmission created. Whereas the engine my car was the 304th built So coincidently the tranny the same build year (1992).
Unfortunately the spray wand was modified, the threaded connection end was cut-off in favor of this hose clamp solution. This part is NLA and no luck from Mark Anderson. It would be nice to replace this if possible. So any of you have one, PM me.
I pulled the cover and inspected the gears, to me, everything looks to be in very good condition. I was able to shift through all the gears properly and both the centering spring and the reverse lock-outs are working really nicely. I took some photos of the gears and synchros for your viewing pleasure. Please feel free comment on the condition. It all looks perfect to me but I don't know diddly. So expert advice is welcome.
First off, the gear oil inside is PURPLE! what the heck brand is that? I think it may be Swepco, but not sure.
With the cover off, we can see the business of gears and synchros.
5th gear and synchro
5th gear and synchro
5th gear and synchro
4th gear and synchro (and 3rd gear too)
4th / 3rd gears
3rd gear and synchro
3rd gear and synchro
2nd / 1st gears
2nd and synchro / 1st gear
2nd gear and synchro (picture upside down)
1st gear and synchro
1st gear and synchro
Reverse Reverse Reverse
Last edited by Michael Benno; 12-12-2021 at 06:20 PM.
Well, I would say I have all the of the issues resolved. The clutch is working properly again (balanced and Flywheel machining), The stater properly engages (new intermediate plate). Revers lights are working thanks to some rewiring. And the excessive blowby has been fixed by removal of the crankcase vacuum pump and returning the breather system back to mostly stock.
The car is running great, driving awesome, and I cant wait for the break-in period of the clutch to pass so I can really open the revs up. The lower gear ratios on the GTS trans are so much better than that of the 87/88 5-speeds. Makes the car so much quicker. The car is more or less 100% dialed. The dual disk clutch was a huge pain in the *** and I don't think I would redo that decision. Those intermediate plates suck even when you understand them (which takes some time).
Anyway, thanks everyone for helping me along the way. It's good to have the car I want and now I get to enjoy it.
Question regarding installing a replacement gasket. Do I need to any other prep or sealant when using the paper gasket? There was no gasket when I removed the lid. It was sealed with some sort of boding agent (ie Hondabond).
Wow, talk about finding a unicorn. Nothing like a very clean GTS 5sp. Looks like it was well taken care of too.
Have you considered having Greg Brown take a look/go through it given he's probably the best out there and that you are planning on keeping the GTS long-term?
Either way, very cool project .
Will be following for sure.
P.S. I suspect the purple oil would be Royal Purple oil since most of their products are purple....but not sure
I don't know if you want or need help with anything but if you do, I will be in the area soon(ish) and am happy to lend a hand. What a great project. Cheers
Help is definitively appreciated since this will be more than a one person job, and I always like to work on projects with a friend. At this point I am not sure when the clutch parts will show up but it will likely in January when the conversion happens. Send me a personal message with your schedule. If anything I can have you over to check out the car and to grab some food/beverage.
Background
I am undertaking a 5-sped conversion on my 1992 GTS and I thought I would start a build thread to consolidate the the various stages of the project and get help and feedback from the fantastic and supportive 928 community.
Disclaimer
I realize some people would not choose to mess with the originality of a GTS given their limited production number. This is a fair point and something I have given substantial consideration. I have chosen to move forward with the conversion, I love this particular car with it's color combination, I want to drive it and have fun with it for a long time and that includes having a 5-speed. I'll retain the original parts if a future owner would like to revert it back to an automatic.
Project Update
I've been collecting parts for the conversion and working on some small projects since this past Spring and will post recaps of those soon. I am waiting on the dual clutch/flywheel assembly and then I should be ready to install everything. Right now I am getting started on some prep-work for the transmission before it goes into the car.
GTS 5-spd transmission @Mark Anderson of 928 International helped me source a 5-speed transmission and cross member. When I originally asked him he said he would look but told me to not hold my breath (I could practically hear him laughing in email). Within a week he had found a GTS transmission and were arranging shipping. I was shocked and impressed. Thank you Mark for your help, you are amazing! Here are some details on the tranny:
According to the Porsche Technical Specifications, the serial number: G28 / 57 30 02014 checks out as a 1992/1993 GTS PSD transmission. It looks like this was the 13th production transmission created. Whereas the engine my car was the 304th built So coincidently the tranny the same build year (1992).
Unfortunately the spray wand was modified, the threaded connection end was cut-off in favor of this hose clamp solution. This part is NLA and no luck from Mark Anderson. It would be nice to replace this if possible. So any of you have one, PM me.
I pulled the cover and inspected the gears, to me, everything looks to be in very good condition. I was able to shift through all the gears properly and both the centering spring and the reverse lock-outs are working really nicely. I took some photos of the gears and synchros for your viewing pleasure. Please feel free comment on the condition. It all looks perfect to me but I don't know diddly. So expert advice is welcome.
First off, the gear oil inside is PURPLE! what the heck brand is that? I think it may be Swepco, but not sure.
With the cover off, we can see the business of gears and synchros.
2nd and synchro / 1st gear
Very difficult to tell from pictures, but your 2nd gear synchro appears to have very little (if any) gap between the engaging teeth and the back of the synchro.
The new specification is to 1.1mm.
Worn out specification is .6 to .7mm.
You can reference this in Volume 3 of the 928 Workshop manual, page 36-212.
Note that when the synchros are "floating in space" (like in your pictures), this dimension is difficult to measure. However, if you gently push on the individual gear shift fork (in the direct of the gear/synchro you want to inspect(, the internal shift block will push the synchro towards the gear, allowing you to measure the gap. If you push too hard, the slider will simply slip over the synchro and engage the gear. Simply push the slider back to nuetral and push until the synchro is no longer "free" and is being forced on the gear.
Not sure what you are going to do about the PSD.....suffer with the slow reaction time or convert it to a real limited slip, but I've developed the technology to be able to accomplish this and still have the internal oil pump work....
Very difficult to tell from pictures, but your 2nd gear synchro appears to have very little (if any) gap between the engaging teeth and the back of the synchro.
The new specification is to 1.1mm.
Worn out specification is .6 to .7mm.
You can reference this in Volume 3 of the 928 Workshop manual, page 36-212.
Note that when the synchros are "floating in space" (like in your pictures), this dimension is difficult to measure. However, if you gently push on the individual gear shift fork (in the direct of the gear/synchro you want to inspect(, the internal shift block will push the synchro towards the gear, allowing you to measure the gap. If you push too hard, the slider will simply slip over the synchro and engage the gear. Simply push the slider back to neutral and push until the synchro is no longer "free" and is being forced on the gear.
Greg, thank you for the callout on the synchros and advice on how to measure the wear on the synchros. That was extremely helpful. I spent some time researching the WSM information regarding this measurement as well (WSM, Manual 2, page 35-204).
Following your instructions, I was able to press the selector arm against the synchro and was able to measure the gap on each synchro using a feeler gauge. Here are the measurements for Gap A
Reverse - 0.965mm
1st - 0.940mm
2nd - 0.828mm
3rd - 0.889mm
4th - 1.321mm
5th - 1.451mm
Second and third look to be the worst worn but not quite to the wear specification. I am not sure what kind of mileage to ware these have. So if you have a recommendation I am open to it.
Originally Posted by GregBBRD
Not sure what you are going to do about the PSD.....suffer with the slow reaction time or convert it to a real limited slip, but I've developed the technology to be able to accomplish this and still have the internal oil pump work....
I haven't given much thought to the PSD system other than to re-use the stock PSD pump to drive the differential lock. I didn't know that was even an option. Maybe it's my inexperience, but I am preferring the progressive nature of the PDS to the vs the instantaneous lock of the LSD on my 1988 S4. I was caught out a couple times with the LSD. The PSD feels more predictable. But I am open to learning about the possibilities of an improved system so please share.
Last edited by Michael Benno; 12-13-2021 at 02:09 AM.
What a cool project, I’m all for manual swapping otherwise desirable automatic 928s. How many old 911 “sportomatics” are still intact? I would estimate a low percentage, and very few people want them. There’s an argument to be made that valuation would not be hurt and maybe even helped by the swap. The PSD / LSD portion of the project is intriguing.
Greg, thank you for the callout on the synchros and advice on how to measure the wear on the synchros. That was extremely helpful. I spent some time researching the WSM information regarding this measurement as well (WSM, Manual 2, page 35-204).
Following your instructions, I was able to press the selector arm against the synchro and was able to measure the gap on each synchro using a feeler gauge. Here are the measurements for Gap A
Reverse - 0.965mm
1st - 0.940mm
2nd - 0.828mm
3rd - 0.889mm
4th - 1.321mm
5th - 1.451mm
Second and third look to be the worst worn but not quite to the wear specification. I am not sure what kind of mileage to ware these have. So if you have a recommendation I am open to it.
I haven't given much thought to the PSD system other than to re-use the stock PSD pump to drive the differential lock. I didn't know that was even an option. Maybe it's my inexperience, but I am preferring the progressive nature of the PDS to the vs the instantaneous lock of the LSD on my 1988 S4. I was caught out a couple times with the LSD. The PSD feels more predictable. But I am open to learning about the possibilities of an improved system so please share.
These style syncros are Moly coated and have the same issues as the Moly coated friction clutches in the pre-PSD limited slips.
Once the high spots of the Moly coat wear flat, this material will gall, damaging the steel that it is applying friction to.
In the past, this was solvable (in terms of the synchros) by simply purchasing the damaged gear set (expensive, but available.)
Currently, the first and second gear set is in "NLA" status (which is not encouraging...."NLA" means that Porsche is not planning on making more.)
Since your synchros are at the "end state of wear", I'd recommend taking the transmission apart and freshening what is worn...especially the synchros.
There are more modern (and cheaper) versions of these synchros available, which you might consider as an alternative, at that time.
A PSD discussion could take an seminar to discuss, especially when combined with various suspension set-ups, however I'll try and hit the high spots, in another post.
Uhg, I was really hoping I would not have to rebuild this transmission now. But it sounds like the wear is enough to warrant it before it goes in and considering the rarity of these it makes sense to project it. I don't have the skills or equipment to rebuild it. @GregBBRD is this something you would be willing to do for me? I could send it to you using the 'cooler method'
This is what I was alluding to above. Greg is probably the best person to go through the transmission and make sure that everything is perfect so you'll have no worries in the long-term.
P.S. Still amazed that Mark was able to find one of those 5sp GTS transmissions.
Originally Posted by Michael Benno
Uhg, I was really hoping I would not have to rebuild this transmission now. But it sounds like the wear is enough to warrant it before it goes in and considering the rarity of these it makes sense to project it. I don't have the skills or equipment to rebuild it. @GregBBRD is this something you would be willing to do for me? I could send it to you using the 'cooler method'
A PSD discussion could take an seminar to discuss, especially when combined with various suspension set-ups, however I'll try and hit the high spots, in another post.
This is a seminar I'd love to attend . I've got Louie's old GT transmission in my track car (currently running as open dif since it doesn't have any of the PSD pump/controller bits). Was planning on the "bolt" method to lock it to a specific slip percentage, but that has issues as presented in previous discussions. I think a separate thread is probably best on this....
This is what I was alluding to above. Greg is probably the best person to go through the transmission and make sure that everything is perfect so you'll have no worries in the long-term.
P.S. Still amazed that Mark was able to find one of those 5sp GTS transmissions.
That depends on your time frame.
To say that we are "overburdened with work", is a huge understatement.....
That depends on your time frame. To say that we are "overburdened with work", is a huge understatement.....
Thanks Greg. I will follow up with you directly to see if you can take this on over the next few months.I'd love to have the car up and running in the spring but understand if your backlog goes beyond that.
12-12-2021, 02:29 PM
GTS 5-spd manual transmission swap
. I've got Louie's old GT transmission in my track car (currently running as open dif since it doesn't have any of the PSD pump/controller bits). Was planning on the "bolt" method to lock it to a specific slip percentage, but that has issues as presented in previous discussions. I think a separate thread is probably best on this....