I'm going for it: GTS ring & pinion replacement with an S4 unit
01-05-2009, 06:06 PM
#1
Rennlist Member
Thread Starter
I'm going for it: GTS ring & pinion replacement with an S4 unit
I’m going for it 
my GTS Ring & Pinion will be replaced with an S4 unit from Mark. This is a direct translation from my posts on PFF-Online Germany. This topic will be updated while I’m working on the issue. Here is the link to the first attempt to solve the problem: https://rennlist.com/forums/928-foru...light=backlash
First the car was jacked up and put on my lift bars. The mufflers where removed, the cats remained on the car.
After that I removed the rear axle, sounds complicated but can be done in about 2 hours without help.
- Remove parking brake cable from the brake handle
- Unbolt brake callipers and swing them out of the way
- Disconnect the connectors for RDK, ABS, brake wear and push the rubber plugs to the outside where the spare wheel is located
- Unbolt the shock absorbers inside the trunk
- Remove the sway bar bolts
- Unbolt the tranny mounts and write down the position and amount of shims
- Unbolt the PSD slave cylinder
- Unbolt the toe exzenter bolts and mark their position with paint and remove
Important!!! Before you unbolt the rear axle from the body of the car, secure the tranny with a chain connected to the sway bar!!!
- Unbolt the remaining 6 axle bolts and remove the rear axle
I removed the transmission and opened the differential housing. Everything looks absolutely normal no visible wear. The magnetic drain plug was free of metal shavings.
Daily report 1. January
Before the differential bearings can be removed the lower PSD adjustment bolt has to be measured and the value has to be written down. In my case 25.6 mm, the bolt has to be adjusted to the same value at the end for trouble free PSD operation.
After the differential bearing holders are removed, it is easy to remove the complete differential unit. The clutch fork sits loosely on the pressure plate, everything looks like a miniature clutch assembly. The later cars don’t have the huge aluminium speed sensor wheel , this allows for an easier ring removal without pulling the differential bearing as described in the WSM.
After this I removed the differential housing, no problem. The first problem started when I tried to remove the pinion central nut. A 3/4” breaker bar did not help, finally the nut was split with a Dremel and will be replaced.
The pinion with the bearing assembly was removed. I couldn’t use the puller as described in the WSM. But a solution was finally found.
After cleaning....
Housing will be done later...
Done and ready for measurement....
To find the correct position of the ring and pinion, the inscribed value on the R&P must be adjusted. My new R&P comes out of a salvaged S4 and needs 74.88 mm. The bearing holders were bolted into position again and the seals removed (will be replaced). The diameter of the outer bearing race is 68.1mm. This means that the centre is exactly at 34.05 mm, the first step to adjust the new position.
Continued with good and bad news...
My home made special tool to is ready and will be used to find the correct centre position again. It is an altered version of the tool that Erkka used. It’s a simple aluminium tube with M8 threats at both ends. It is a little bit tricky to find the correct position but with a little patience it can be done. The old R&P was adjusted to 75 mm, this was achieved with a 0.5 mm shim. The shim will be replaced with a 0.4 mm shim and this will bring the distance down to 74.9 mm (factory spec.). Final adjustment findings will be posted later....
Next task: Pressing out the bearing of the pinion bearing assembly. Everything went fine until disaster struck... The AT side bearing was removed with no problems.
The smaller bearing remains on the pinion and has to be removed separately.
Put the inner race in the appropriate puller and....
...the bearing slipped out of the puller and destroyed the bearing cage. The complete unit is made by SKF and the bearing is type is: SKF 32210-45B-Q-CL7C
The bearing does not show up in any SKF bearing list.
I contacted SKF Germany directly in Schweinfurt and they have the bearing available. It is not sold to private customers, but they were so nice and gave me the address of my local supplier in Munich. The bearing will cost €90, this is still better than €914 for the complete assembly. The bearing can be picked up next Saturday.
I used the available time to check the correct height of the bearing assembly according to the WSM.
Result: 34.65 mm without shim
Shim thickness 0.6 mm
Total value: 34.05 mm as describes in the WSM
Last attempt of the day was the removal of the ring bolts...
Removal of the safety lock plates was easy. BUT!!! The bolts are 20 mm, I have many tools but NO 20 mm socket! Even in ALL metric Germany this socket was not readily available and had to be ordered. I can pick it up on Wednesday.
To be continued....
my GTS Ring & Pinion will be replaced with an S4 unit from Mark. This is a direct translation from my posts on PFF-Online Germany. This topic will be updated while I’m working on the issue. Here is the link to the first attempt to solve the problem: https://rennlist.com/forums/928-foru...light=backlash First the car was jacked up and put on my lift bars. The mufflers where removed, the cats remained on the car.
After that I removed the rear axle, sounds complicated but can be done in about 2 hours without help.
- Remove parking brake cable from the brake handle
- Unbolt brake callipers and swing them out of the way
- Disconnect the connectors for RDK, ABS, brake wear and push the rubber plugs to the outside where the spare wheel is located
- Unbolt the shock absorbers inside the trunk
- Remove the sway bar bolts
- Unbolt the tranny mounts and write down the position and amount of shims
- Unbolt the PSD slave cylinder
- Unbolt the toe exzenter bolts and mark their position with paint and remove
Important!!! Before you unbolt the rear axle from the body of the car, secure the tranny with a chain connected to the sway bar!!!
- Unbolt the remaining 6 axle bolts and remove the rear axle
I removed the transmission and opened the differential housing. Everything looks absolutely normal no visible wear. The magnetic drain plug was free of metal shavings.
Daily report 1. January
Before the differential bearings can be removed the lower PSD adjustment bolt has to be measured and the value has to be written down. In my case 25.6 mm, the bolt has to be adjusted to the same value at the end for trouble free PSD operation.
After the differential bearing holders are removed, it is easy to remove the complete differential unit. The clutch fork sits loosely on the pressure plate, everything looks like a miniature clutch assembly. The later cars don’t have the huge aluminium speed sensor wheel , this allows for an easier ring removal without pulling the differential bearing as described in the WSM.
After this I removed the differential housing, no problem. The first problem started when I tried to remove the pinion central nut. A 3/4” breaker bar did not help, finally the nut was split with a Dremel and will be replaced.
The pinion with the bearing assembly was removed. I couldn’t use the puller as described in the WSM. But a solution was finally found.
After cleaning....
Housing will be done later...
Done and ready for measurement....
To find the correct position of the ring and pinion, the inscribed value on the R&P must be adjusted. My new R&P comes out of a salvaged S4 and needs 74.88 mm. The bearing holders were bolted into position again and the seals removed (will be replaced). The diameter of the outer bearing race is 68.1mm. This means that the centre is exactly at 34.05 mm, the first step to adjust the new position.
Continued with good and bad news...
My home made special tool to is ready and will be used to find the correct centre position again. It is an altered version of the tool that Erkka used. It’s a simple aluminium tube with M8 threats at both ends. It is a little bit tricky to find the correct position but with a little patience it can be done. The old R&P was adjusted to 75 mm, this was achieved with a 0.5 mm shim. The shim will be replaced with a 0.4 mm shim and this will bring the distance down to 74.9 mm (factory spec.). Final adjustment findings will be posted later....
Next task: Pressing out the bearing of the pinion bearing assembly. Everything went fine until disaster struck... The AT side bearing was removed with no problems.
The smaller bearing remains on the pinion and has to be removed separately.
Put the inner race in the appropriate puller and....
...the bearing slipped out of the puller and destroyed the bearing cage. The complete unit is made by SKF and the bearing is type is: SKF 32210-45B-Q-CL7C
The bearing does not show up in any SKF bearing list.
I contacted SKF Germany directly in Schweinfurt and they have the bearing available. It is not sold to private customers, but they were so nice and gave me the address of my local supplier in Munich. The bearing will cost €90, this is still better than €914 for the complete assembly. The bearing can be picked up next Saturday.
I used the available time to check the correct height of the bearing assembly according to the WSM.
Result: 34.65 mm without shim
Shim thickness 0.6 mm
Total value: 34.05 mm as describes in the WSM
Last attempt of the day was the removal of the ring bolts...
Removal of the safety lock plates was easy. BUT!!! The bolts are 20 mm, I have many tools but NO 20 mm socket! Even in ALL metric Germany this socket was not readily available and had to be ordered. I can pick it up on Wednesday.
To be continued....
01-05-2009, 08:22 PM
#4
Nordschleife Master
Shocki, awesome post and mentions of other threads got me adding more "keepers" to my subscription folder for when I fit the LSD I have on the shelf for my currently open-diff car.
What final drive ratio ring/pinion are you using?
Same ratio as your GTS to keep other ratios the same? (i.e. parts from a 90-91 S4?)
What final drive ratio ring/pinion are you using?
Same ratio as your GTS to keep other ratios the same? (i.e. parts from a 90-91 S4?)
01-06-2009, 12:09 AM
#5
Race Car
Kewl! Your GTS will have the gearing it should have got from the factory originally! What is that PSD adjustment bolt for? Is it for making the PSD engage range closer to 100%?
Dan
'91 928GT S/C
475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ft
01-06-2009, 03:01 AM
#6
Rennlist
Basic Site Sponsor
Basic Site Sponsor
BTW:
Porsche never provides backlash numbers for used ring and pinions, only new. Always increase the factory backlash by at least 20% for used pieces....more if there is significant wear. If you set up the backlash to "new" specifications, it will be too tight and can fail. This is a common problem when people rebuild gearboxes and decide to set up the ring and pinion to "new" specs. Pinion depth doesn't change, as both bearings wear at the same rate, in theory, so you can use the factory numbers for this.
There is another way to measure the pinion depth, in a transmission that has not failed. You can simply measure the distance (with a dial depth gauge) from where the rear cover bolts on to the actual face of the pinion...when the whole thing is assembled. Then when it is disassembled, measure the distance from where the bearing closest to the pinion head sits, to the actual face of the pinion. Do this for both pinions and compare...it is usally extremely close. Now simply subtact the two different desired pinion depths (scribed into the pinion) and add or remove shims as required. You can almost always get the pinion with-in a few 100th's of a mm, doing this.
When you remove the ring gear, from the differential, old friction disc material can "seep" between the cover and the main body of the differential. Be sure to disassemble and clean these surfaces, or the replacement ring gear can have a bunch of "run out", when you tighten it down. You might also want to look at the friction discs inside the limited slip and check them for wear, while it is apart.
Nice pictures and write up!
Porsche never provides backlash numbers for used ring and pinions, only new. Always increase the factory backlash by at least 20% for used pieces....more if there is significant wear. If you set up the backlash to "new" specifications, it will be too tight and can fail. This is a common problem when people rebuild gearboxes and decide to set up the ring and pinion to "new" specs. Pinion depth doesn't change, as both bearings wear at the same rate, in theory, so you can use the factory numbers for this.
There is another way to measure the pinion depth, in a transmission that has not failed. You can simply measure the distance (with a dial depth gauge) from where the rear cover bolts on to the actual face of the pinion...when the whole thing is assembled. Then when it is disassembled, measure the distance from where the bearing closest to the pinion head sits, to the actual face of the pinion. Do this for both pinions and compare...it is usally extremely close. Now simply subtact the two different desired pinion depths (scribed into the pinion) and add or remove shims as required. You can almost always get the pinion with-in a few 100th's of a mm, doing this.
When you remove the ring gear, from the differential, old friction disc material can "seep" between the cover and the main body of the differential. Be sure to disassemble and clean these surfaces, or the replacement ring gear can have a bunch of "run out", when you tighten it down. You might also want to look at the friction discs inside the limited slip and check them for wear, while it is apart.
Nice pictures and write up!
__________________
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
01-06-2009, 03:05 AM
#7
Rennlist Member
Thread Starter
The final gear ratio is an US S4 2.2 (instead of a 2.53 for all S4's ROW). I DIDN'T want to go to a GTS R&P, because some cars have this noise problem at speeds between 30-40MPH. Porsche changed the machining process for GTS R&P's. S4 units are machined and finally hardened (Oerlikon Spiroflex). GTS R&P's are hardened and finally machined (Gleason). This allows for smaller tolerances in backlash and makes the final drive nearly tolerance free.
My theory on the GTS noise issue: The Gleason machining process removes part of the hardened surface of the R&P. As soon as some wear is introduced the R&P besomes noisy. What is very interesting is the fact that there is no visible or feelable wear on the gears.
Greg,
this is the 1st time that I hear of a backlash increase of 20% for used parts, where did you get the information from? The WSM mentions that the inscribed value should never be exceeded.
Pinion depth adjustment: I thought about your idea too. To but it is nearly impossible to remove the pinion bearing of the GTS pinion, I don't want to go through the process again. I will measure it with the aluminim shaft.
Dan,
the lower PSD adjustment bolt sets the zero position for the clutch fork. The fork itself is held in position on the throw out bearing by only two machined grooves. If you tighten the bolt further the throw out bearing will be under permanent load and wear out the bearing. If you loosen the bolt to much, the fork could wobble around and ultimately fall of the bearing outer race.
Question from me : Do you guys think that the 2.2 final gear ratio is more suited for the GTS?
My theory on the GTS noise issue: The Gleason machining process removes part of the hardened surface of the R&P. As soon as some wear is introduced the R&P besomes noisy. What is very interesting is the fact that there is no visible or feelable wear on the gears.
Greg,
this is the 1st time that I hear of a backlash increase of 20% for used parts, where did you get the information from? The WSM mentions that the inscribed value should never be exceeded.
Pinion depth adjustment: I thought about your idea too. To but it is nearly impossible to remove the pinion bearing of the GTS pinion, I don't want to go through the process again. I will measure it with the aluminim shaft.
Dan,
the lower PSD adjustment bolt sets the zero position for the clutch fork. The fork itself is held in position on the throw out bearing by only two machined grooves. If you tighten the bolt further the throw out bearing will be under permanent load and wear out the bearing. If you loosen the bolt to much, the fork could wobble around and ultimately fall of the bearing outer race.
Question from me
: Do you guys think that the 2.2 final gear ratio is more suited for the GTS?
Last edited by Schocki; 01-06-2009 at 05:25 AM.
Trending Topics
01-06-2009, 09:38 AM
#9
Rennlist Member
Shocki,
GREAT PROGRESS. Can't wait to see the remainder of the work, and to hear how you like the results. My 2.2 Ring and Pinion are on order, being held until you complete your work. Great Stuff.
Gary Knox
West Chester, PA
GREAT PROGRESS. Can't wait to see the remainder of the work, and to hear how you like the results. My 2.2 Ring and Pinion are on order, being held until you complete your work. Great Stuff.
Gary Knox
West Chester, PA
01-06-2009, 10:08 AM
#10
Rennlist Member
Thread Starter
Hi guys,
today is a holiday in Bavaria, cool Since I'm waiting for my 20mm socket and the bearing I took the time to measure the total length of both pinions and the pre-load of the bearing assembly.
Total length of BOTH pinions is 98.9mm no difference there.
Pre-load: I measured the bearing inner races and the spacer ring between the bearings.
Small Bearing (differential side) = 23.0mm
Spacer = 7.8mm
Big bearing (tranny side) = 19.0mm
Total length = 49.8mm
Intermediate ring (sits on the end of the pinion shaft) = 20.4mm
Total lenght of the complete assembly = 70.4mm
Finall I measured the pinion shaft length with the intermediate ring positioned on the pinion = 70.1mm
This means that the pre-load is 0.3mm on the complete bearing assembly. E.g. the differential bearings that connect to the CV-Joints are also set to a 0.3mm pre-load when new. The special pinion bearings are CL7C specification and shouldn't wear over time. Looks like the pinion bearing assembly uses the same pre load...
Below a picture of the intermediate ring at the end of the pinion shaft.
today is a holiday in Bavaria, cool
Since I'm waiting for my 20mm socket and the bearing I took the time to measure the total length of both pinions and the pre-load of the bearing assembly.Total length of BOTH pinions is 98.9mm no difference there.
Pre-load: I measured the bearing inner races and the spacer ring between the bearings.
Small Bearing (differential side) = 23.0mm
Spacer = 7.8mm
Big bearing (tranny side) = 19.0mm
Total length = 49.8mm
Intermediate ring (sits on the end of the pinion shaft) = 20.4mm
Total lenght of the complete assembly = 70.4mm
Finall I measured the pinion shaft length with the intermediate ring positioned on the pinion = 70.1mm
This means that the pre-load is 0.3mm on the complete bearing assembly. E.g. the differential bearings that connect to the CV-Joints are also set to a 0.3mm pre-load when new. The special pinion bearings are CL7C specification and shouldn't wear over time. Looks like the pinion bearing assembly uses the same pre load...
Below a picture of the intermediate ring at the end of the pinion shaft.
Last edited by Schocki; 01-06-2009 at 10:31 AM.
01-06-2009, 11:16 PM
#13
Drifting
Schocki,
Wonder why Mark (928International) didn't include the pinion bearing carrier with the pinion? That would be the way to buy a used ring/pinion set don't you think?
On the Greg's recommendation of new +20% for used…..
What Greg is suggesting sounds reasonable, but I personally don't think it will make any significant difference.
Remember, you can't dial in the backlash, but instead, must find a suitable stack of shims to set the backlash, because the shims are only available in prescribed thicknesses.
There is also something else to consider, and Greg already mentioned this, and that is run-out of the ring gear. You should see some run-out when you measure the backlash per the WSM in four different places along the perimeter of the ring gear.
If you take a look at my Excel Spreadsheet, you'll see how I plotted four different shim packs and measured a corresponding backlash. The WSM gives a backlash range of 0.13mm - 0.18 mm. On my pinion/ring set, the inscribed backlash is 0.18mm.
Any pinion/ring gear wear would translate to additional backlash, so if Greg is saying add 20%, then he must be assuming that that is to account for that much wear on the faces of both teath. If the backlash prescribed is 0.18mm, then he is expecting 0.036mm of tooth wear and a new backlash setting of 0.22mm.
On the pinion placement, like Greg said, you can measure directly, but without fitting up the differential to the transmission. See how I used a spreadsheet to determine the proper pinion placement shims.
On the pinion nut, how do you think you will torque the new nut without a way to counter hold the tranny?
And notice the recommended shim in the PET for the intermediate spacer. I reassembled mine with one from Porsche.
Finally, why not rebuild your automatic while you have it out? It's really fun to take apart and put back together with no left over parts! You could also change the gearing with a new planetary gearset.
I've been wanting to tear into mine again, that is to figure out how to modify it so it starts in first gear, but only when the solenoid valve is energized (like most V8 Mercedes). Then I could install the electronics I posted here... https://rennlist.com/forums/928-foru...or-gts-s4.html
Wonder why Mark (928International) didn't include the pinion bearing carrier with the pinion? That would be the way to buy a used ring/pinion set don't you think?
On the Greg's recommendation of new +20% for used…..
What Greg is suggesting sounds reasonable, but I personally don't think it will make any significant difference.
Remember, you can't dial in the backlash, but instead, must find a suitable stack of shims to set the backlash, because the shims are only available in prescribed thicknesses.
There is also something else to consider, and Greg already mentioned this, and that is run-out of the ring gear. You should see some run-out when you measure the backlash per the WSM in four different places along the perimeter of the ring gear.
If you take a look at my Excel Spreadsheet, you'll see how I plotted four different shim packs and measured a corresponding backlash. The WSM gives a backlash range of 0.13mm - 0.18 mm. On my pinion/ring set, the inscribed backlash is 0.18mm.
Any pinion/ring gear wear would translate to additional backlash, so if Greg is saying add 20%, then he must be assuming that that is to account for that much wear on the faces of both teath. If the backlash prescribed is 0.18mm, then he is expecting 0.036mm of tooth wear and a new backlash setting of 0.22mm.
On the pinion placement, like Greg said, you can measure directly, but without fitting up the differential to the transmission. See how I used a spreadsheet to determine the proper pinion placement shims.
On the pinion nut, how do you think you will torque the new nut without a way to counter hold the tranny?
And notice the recommended shim in the PET for the intermediate spacer. I reassembled mine with one from Porsche.
Finally, why not rebuild your automatic while you have it out? It's really fun to take apart and put back together with no left over parts! You could also change the gearing with a new planetary gearset.
I've been wanting to tear into mine again, that is to figure out how to modify it so it starts in first gear, but only when the solenoid valve is energized (like most V8 Mercedes). Then I could install the electronics I posted here... https://rennlist.com/forums/928-foru...or-gts-s4.html
Last edited by borland; 01-06-2009 at 11:34 PM.
01-06-2009, 11:31 PM
#14
Rennlist
Basic Site Sponsor
Basic Site Sponsor
[QUOTE=Schocki;6151827]
Greg,
this is the 1st time that I hear of a backlash increase of 20% for used parts, where did you get the information from? The WSM mentions that the inscribed value should never be exceeded.
Pinion depth adjustment: I thought about your idea too. To but it is nearly impossible to remove the pinion bearing of the GTS pinion, I don't want to go through the process again. I will measure it with the aluminim shaft.
[QUOTE]
35 years of rebuilding Porsche gearboxes, measuring backlash and doing failure analysis.
I have the Porsche factory tooling to measure pinion depth, so I use this method only to get "close " with the shims. I'm not sure I understand why you would remove the pinion bearings a second time...
Greg,
this is the 1st time that I hear of a backlash increase of 20% for used parts, where did you get the information from? The WSM mentions that the inscribed value should never be exceeded.
Pinion depth adjustment: I thought about your idea too. To but it is nearly impossible to remove the pinion bearing of the GTS pinion, I don't want to go through the process again. I will measure it with the aluminim shaft.
[QUOTE]
35 years of rebuilding Porsche gearboxes, measuring backlash and doing failure analysis.
I have the Porsche factory tooling to measure pinion depth, so I use this method only to get "close " with the shims. I'm not sure I understand why you would remove the pinion bearings a second time...