2nd gear dogteeth ring welded to gear - 1978 915/61 transmission w/ 3.2L engine
02-24-2010, 10:00 AM
#1
Instructor
Thread Starter
2nd gear dogteeth ring welded to gear - 1978 915/61 transmission w/ 3.2L engine
Background:
We currently use the 911 for race and time trials.
3rd gear is gone away and we dropped the engine/trans and took the trans to our favorite Indie. The Indie tech has opened our 915 transmission and found several interesting upgrades -- Turbo syncros and welded 2nd gear dogteeth ring to 2nd gear.
We have known that 3,4,5 are short gears by the PO and have just worn out the syncros by tracking the 911 for 4 seasons.
Some research reveals that this is done to make the 2nd gear more durable during racing use.
Question:
Does anyone on the Rennlist forum have experience or knowledge about this practice??
TIA for your response.
We will be replacing the 2,3,4,5 syncros and machining off the old 2nd gear syncro and tack welding on I believe a 962 syncro to 2nd gear.
In addition:
Our 2nd gear is a "standard/stock" ratio gear, but the gear changes into 2nd during track use are really severe. We think this why the syncro weld was done by the PO. However, it is 3rd gear that has failed this time - maybe because the 2nd gear was welded (?)
It is my understanding from the tech:
The use of 930/turbo syncro sets saves the transmission when a normal 915 syncro ring/dogteeth fails and is launched into the inside of the transmission. The 930 ring has a grove to hold the ring in place under the dogteeth ring -- whereas the normal 915 synco ring is held in place only by the overlapping dogteeth -- and when the dogteeth are worn down enough the synco ring is launched into the transmission (there are some pics of this somewhere on these forums - I'll look them up and post a link later). I believe this saved our 915 this time when 3rd gear was worn down to nothing, but the ring was held in place (and Brian finished the race with 2,4,5).
We are currently talking (through our Indie tech) with a race transmission builder who also may have a longer lasting solution to the 915 syncro/dogteeth wear problem.
It seems that "rounded" teeth (maybe like a 962) may last longer than pointed teeth.
Does anyone have experience with this design solution??
TIA for all responses,
Roy/Brian
We currently use the 911 for race and time trials.
3rd gear is gone away and we dropped the engine/trans and took the trans to our favorite Indie. The Indie tech has opened our 915 transmission and found several interesting upgrades -- Turbo syncros and welded 2nd gear dogteeth ring to 2nd gear.
We have known that 3,4,5 are short gears by the PO and have just worn out the syncros by tracking the 911 for 4 seasons.
Some research reveals that this is done to make the 2nd gear more durable during racing use.
Question:
Does anyone on the Rennlist forum have experience or knowledge about this practice??
TIA for your response.
We will be replacing the 2,3,4,5 syncros and machining off the old 2nd gear syncro and tack welding on I believe a 962 syncro to 2nd gear.
In addition:
Our 2nd gear is a "standard/stock" ratio gear, but the gear changes into 2nd during track use are really severe. We think this why the syncro weld was done by the PO. However, it is 3rd gear that has failed this time - maybe because the 2nd gear was welded (?)
It is my understanding from the tech:
The use of 930/turbo syncro sets saves the transmission when a normal 915 syncro ring/dogteeth fails and is launched into the inside of the transmission. The 930 ring has a grove to hold the ring in place under the dogteeth ring -- whereas the normal 915 synco ring is held in place only by the overlapping dogteeth -- and when the dogteeth are worn down enough the synco ring is launched into the transmission (there are some pics of this somewhere on these forums - I'll look them up and post a link later). I believe this saved our 915 this time when 3rd gear was worn down to nothing, but the ring was held in place (and Brian finished the race with 2,4,5).
We are currently talking (through our Indie tech) with a race transmission builder who also may have a longer lasting solution to the 915 syncro/dogteeth wear problem.
It seems that "rounded" teeth (maybe like a 962) may last longer than pointed teeth.
Does anyone have experience with this design solution??
TIA for all responses,
Roy/Brian
02-25-2010, 12:09 PM
#2
Instructor
Thread Starter
The purpose of this thread is (1)to find others' experience with the same issue of welding syncro parts onto gears, and (2) learn about special designs for 915 syncro parts in the racing application.
I have learned that the 2nd gear shaft size is different between the 915 and 930 gearboxes -- where the 3-4 gear size is the same. This is the reason for the welding on the 2nd gear - to allow the application of the 930 syncro rings with the stock 915 2nd gear.
Also, I have learned that it is NOT recommended to be applying high heat to the gear in this welding process - this affects the heat treated strength of the gear teeth and may cause teeth to break off under high torque loads. (Thanks Matt! )
However, we have experienced a 5 year, 4 racing season endurance of the existing 2nd gear with welded dog teeth ring. The only reason we are repairing the 2nd gear is to replace the syncro parts and worn dog teeth ring.
We have sent the 2nd gear to a national known shop to have the work done on the 2nd gear - machine off old and fit new parts.
This thread is also posted at:
http://forums.pelicanparts.com/porsc...ml#post5203505
Thank you in advance for any experience stories you may have -- success or not
Roy
I have learned that the 2nd gear shaft size is different between the 915 and 930 gearboxes -- where the 3-4 gear size is the same. This is the reason for the welding on the 2nd gear - to allow the application of the 930 syncro rings with the stock 915 2nd gear.
Also, I have learned that it is NOT recommended to be applying high heat to the gear in this welding process - this affects the heat treated strength of the gear teeth and may cause teeth to break off under high torque loads. (Thanks Matt! )
However, we have experienced a 5 year, 4 racing season endurance of the existing 2nd gear with welded dog teeth ring. The only reason we are repairing the 2nd gear is to replace the syncro parts and worn dog teeth ring.
We have sent the 2nd gear to a national known shop to have the work done on the 2nd gear - machine off old and fit new parts.
This thread is also posted at:
http://forums.pelicanparts.com/porsc...ml#post5203505
Thank you in advance for any experience stories you may have -- success or not
Roy
