Weight difference between Mag. and Alu. 915 boxes?
06-27-2003, 02:26 PM
#16
Rennlist Member
Steve,
Thank you for the very interesting notes. I have a question about the use of synthetic in the 915. Is the synthetic harmful for the synchros, or does it just make them a bit balky?
I don't have much of a shifting problem with the Mobil 1, but one of my two 915 equipped cars definitely shifts better than the other. (Both are low miles, one a 70,000 mile factory trans, the other a rebuild with around 30,000 miles). I recall many years ago, Alfa used a Porsche style synchro (this was in my 101 Giulietta Spider), and they would go bad quickly if an 'EP' additive oil (which is the most commonly available) was used in the transmission. After reading your notes, I wonder whether the Mobil 1 could be reducing synchro life in my 915s.
Thanks,
Tom
Thank you for the very interesting notes. I have a question about the use of synthetic in the 915. Is the synthetic harmful for the synchros, or does it just make them a bit balky?
I don't have much of a shifting problem with the Mobil 1, but one of my two 915 equipped cars definitely shifts better than the other. (Both are low miles, one a 70,000 mile factory trans, the other a rebuild with around 30,000 miles). I recall many years ago, Alfa used a Porsche style synchro (this was in my 101 Giulietta Spider), and they would go bad quickly if an 'EP' additive oil (which is the most commonly available) was used in the transmission. After reading your notes, I wonder whether the Mobil 1 could be reducing synchro life in my 915s.
Thanks,
Tom
06-28-2003, 07:35 PM
#17
RL Technical Advisor
Hi Tom:
The true answer to your question about synthetics in 915's is kinda tricky,...
Porsche specifies a GL-5 rated lubricant mainly for ring and pinion protection. The "perfect" 915 would have a sealed differential case so you could use a GL-5 synthetic in there and dino oil (like Swepco) in the transmission case. Brother, that would be just deluxe!
We are rather fortunate in having really good dino GL-5's like Swepco that protect that vulnerable R&P while permitting enough friction for the Porsche baulk-ring syncromesh to work. The GL-5 rated synthetics, while doing a proper job with the R&P, do TOO good of a job inside the transmission and allow excessive syncro teeth wear since these brake-band type syncros do not do a good enough job of slowing the gearsets down.
Sooooo,.........the answer to your question is,.......Synthetic gear lubes make a 901-915-930 tranny feel notchy and the syncros, operating sleeves, and dog teeth on the gearsets suffer faster wear. It simply won't last as long before needing overhaul.
My best advice to anyone with one of these trannys is to use Swepco and leave the synthetics to the G-50 folks.
I do hope this helps,
The true answer to your question about synthetics in 915's is kinda tricky,...
Porsche specifies a GL-5 rated lubricant mainly for ring and pinion protection. The "perfect" 915 would have a sealed differential case so you could use a GL-5 synthetic in there and dino oil (like Swepco) in the transmission case. Brother, that would be just deluxe!
We are rather fortunate in having really good dino GL-5's like Swepco that protect that vulnerable R&P while permitting enough friction for the Porsche baulk-ring syncromesh to work. The GL-5 rated synthetics, while doing a proper job with the R&P, do TOO good of a job inside the transmission and allow excessive syncro teeth wear since these brake-band type syncros do not do a good enough job of slowing the gearsets down.
Sooooo,.........the answer to your question is,.......Synthetic gear lubes make a 901-915-930 tranny feel notchy and the syncros, operating sleeves, and dog teeth on the gearsets suffer faster wear. It simply won't last as long before needing overhaul.
My best advice to anyone with one of these trannys is to use Swepco and leave the synthetics to the G-50 folks.
I do hope this helps,
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