Ring & Pinon???
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Joined: Feb 2003
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From: saratoga, ca
Keep trying, my mechanic - Jim Page @ Page Auto in Green Bay, has an S4 transmission with the 2.75 R&P from a 78 in his S4.
Kibort - to answer the question why......because he wanted to use 5th gear (1-1 ratio) as much as possible on the race track since it's the strongest gear set in the box.
Kibort - to answer the question why......because he wanted to use 5th gear (1-1 ratio) as much as possible on the race track since it's the strongest gear set in the box.
when i lost my geaer box 2 times in 15 years of racing, first was on the dyno , it was 5th gear input. 2nd time it was the actual 5th gear teeth. so, i dont think the strengh is any issue, but i could be wrong.
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From: Mount Mort, Ipswich , Australia
SO the that wear on the ring and pinion ? which is a bit more problematic if I understand this correctly , than I would expect that these would wear at the same rate ?
THe ring gear should interchangeable from the g10 and beyond , as long as the unit is shimmed correctly .
THe ring gear should interchangeable from the g10 and beyond , as long as the unit is shimmed correctly .
Three Wheelin'
Joined: Sep 2003
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From: SF Bay Area
There is no way I can see putting a early pinion shaft in a newer transmission. I would do it if it was possible.
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From: Up Nort
Jim has been working on Porsche's for over 35 years and would never, willingly, put any money into a pre-85 transmission because of the synchros (my 79 is his old track car).
He wanted newer synchros with the 78/79 R&P. Jim and Todd figured out how to do it (ok, mostly Todd). I'm sure there are quite a few custom pieces created in Todd's garage to make it happen, but he's known for doing stuff like that.
Todd has developed quite a reputation for being told stuff he's already accomplished is impossible
Three Wheelin'
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From: SF Bay Area
Forgive me if I am still skeptical. I have heard of people bending valves when breaking a 16 valve timing belt. In fact it was almost at the proportions of an Urban Myth. But no one ever provided hard evidence.
Looking at the two pinion shafts side by side I just see no way short of making a new pinion shaft. I will look again, but when I looked at it the synco on the reverse gear as was a big difference. The nut holding the first gear in place was very different from the newer gear stack. I have many years of automotive experience, have owner transmission rebuilting shops for British and VW transmission and have worked as a machinst. I will look again as I would like to do this to an 85 2.20 tramsmission.
Looking at the two pinion shafts side by side I just see no way short of making a new pinion shaft. I will look again, but when I looked at it the synco on the reverse gear as was a big difference. The nut holding the first gear in place was very different from the newer gear stack. I have many years of automotive experience, have owner transmission rebuilting shops for British and VW transmission and have worked as a machinst. I will look again as I would like to do this to an 85 2.20 tramsmission.
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From: SW FL
Dan,forgive me but my 16 valve 928 85 euro would bend valves,how do i know? when changing belts as preventive if you turn the engine with belt in the wrong place (by hand) the engine goes clang and stops,ouch,if that had been running.
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From: saratoga, ca
Three Wheelin'
Joined: Sep 2003
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From: SF Bay Area
Mark,
There is a difference in the manual for installing the belt between 16 and 32 valves. The 16 valve engines have no 45 degree mark and no timing belt light circuit.
I have an 83 S Euro and two 84 US engines and you can spin them all day long and not hit a valve. Porsche engineers are neither stupid nor do they waste words. If the factory had made a 16 valve interference they would have documented it.
Now I will allow that modifications like putting a 5.0 bottom end on a 16 valve upper can cause issues, but that is not the issue here. I am also sure many mechanics have charged 16 valve owners for valve jobs when breaking a belt - but fraud and urban myths often go together.
Like the six speed 928 you went chasing into Mexico I would still like to see documentation on how to put a 78 pinion shaft into an S4 box.
There is a difference in the manual for installing the belt between 16 and 32 valves. The 16 valve engines have no 45 degree mark and no timing belt light circuit.
I have an 83 S Euro and two 84 US engines and you can spin them all day long and not hit a valve. Porsche engineers are neither stupid nor do they waste words. If the factory had made a 16 valve interference they would have documented it.
Now I will allow that modifications like putting a 5.0 bottom end on a 16 valve upper can cause issues, but that is not the issue here. I am also sure many mechanics have charged 16 valve owners for valve jobs when breaking a belt - but fraud and urban myths often go together.
Like the six speed 928 you went chasing into Mexico I would still like to see documentation on how to put a 78 pinion shaft into an S4 box.
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Joined: Mar 2005
Posts: 1,387
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From: London, UK
Mark,
There is a difference in the manual for installing the belt between 16 and 32 valves. The 16 valve engines have no 45 degree mark and no timing belt light circuit.
I have an 83 S Euro and two 84 US engines and you can spin them all day long and not hit a valve. Porsche engineers are neither stupid nor do they waste words. If the factory had made a 16 valve interference they would have documented it.
Now I will allow that modifications like putting a 5.0 bottom end on a 16 valve upper can cause issues, but that is not the issue here. I am also sure many mechanics have charged 16 valve owners for valve jobs when breaking a belt - but fraud and urban myths often go together.
Like the six speed 928 you went chasing into Mexico I would still like to see documentation on how to put a 78 pinion shaft into an S4 box.
There is a difference in the manual for installing the belt between 16 and 32 valves. The 16 valve engines have no 45 degree mark and no timing belt light circuit.
I have an 83 S Euro and two 84 US engines and you can spin them all day long and not hit a valve. Porsche engineers are neither stupid nor do they waste words. If the factory had made a 16 valve interference they would have documented it.
Now I will allow that modifications like putting a 5.0 bottom end on a 16 valve upper can cause issues, but that is not the issue here. I am also sure many mechanics have charged 16 valve owners for valve jobs when breaking a belt - but fraud and urban myths often go together.
Like the six speed 928 you went chasing into Mexico I would still like to see documentation on how to put a 78 pinion shaft into an S4 box.
I have a EURO S2 - 10.4:1 compression and it is most definitely an interference engine. I know from experience - 4 bent valves out of 16 speak for themselves. Ask any of the many Euro S2 owners who have suffered a broken timing belt and it is certainly an interference design....
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From: Up Nort
As Jim put it in an e-mail to me recently. He had a 78/79 transmission apart with the S4 box on the bench. Todd came over, inspected everything, looked at the two pinion shafts and said: "No problem" and came back later with a modified pinion shaft from a 78/79 to bolt into an S4+ box.
They didn't take any pictures, there wasn't an internet to show off custom work like this back then, and Jim isn't about to tear out his transmisison just to prove the work was done.
More from Jim:
There were a few reasons I wanted to change to the early gear ratio in the late box.
# 1 I don’t like the durability of the early style Porsche syncros.
# 2 I wanted the early gear ratios & could not afford a GTS trans. Remember this was back when they were still making 928’s.
At Road America I would never use fifth gear. It was pretty much a stock car. If you are not using top gear at that track I doubt that there are any other tracks that I would go to that it would be used.
Using top gear is desirable because the design of the 928 gear box is such that you when you are in fifth gear the power flow is straight through the top shaft of the trans. You could literally take the lay shaft out. When you are in any other gear the power flow goes through “fifth” gear & what ever gear you are in. Funny thing is that when you are in fifth gear it is the only time that fifth gear is not being “used.” I felt that this was unnecessarily using up power & creating heat.
# 1 I don’t like the durability of the early style Porsche syncros.
# 2 I wanted the early gear ratios & could not afford a GTS trans. Remember this was back when they were still making 928’s.
At Road America I would never use fifth gear. It was pretty much a stock car. If you are not using top gear at that track I doubt that there are any other tracks that I would go to that it would be used.
Using top gear is desirable because the design of the 928 gear box is such that you when you are in fifth gear the power flow is straight through the top shaft of the trans. You could literally take the lay shaft out. When you are in any other gear the power flow goes through “fifth” gear & what ever gear you are in. Funny thing is that when you are in fifth gear it is the only time that fifth gear is not being “used.” I felt that this was unnecessarily using up power & creating heat.
Addict
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From: Helsinki, Finland
I have a EURO S2 - 10.4:1 compression and it is most definitely an interference engine. I know from experience - 4 bent valves out of 16 speak for themselves. Ask any of the many Euro S2 owners who have suffered a broken timing belt and it is certainly an interference design....
As for the gearbox problem you have. Find ROW '85-86 G28/10 box. I know, easier said than done but they are out there. They have same 11:30 and 2.73:1 ring & pinion ration as GT box and parts should be bolt on. Only difference is slighly different teeth design which mostly means little more friction and possibly less noise than original G28/55 gear pair. Also 2.64:1 from ROW S4 G28/12 will work directly and you wouldn't loose that much by using it. So any '85-91 ROW box will do.
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From: London, UK
Most '84 MY S/S2 engines use older 10.0:1 K-Jetronic engine pistons. They are safer than true 10.4:1 CR engines used from late '84 MY forward.
As for the gearbox problem you have. Find ROW '85-86 G28/10 box. I know, easier said than done but they are out there. They have same 11:30 and 2.73:1 ring & pinion ration as GT box and parts should be bolt on. Only difference is slighly different teeth design which mostly means little more friction and possibly less noise than original G28/55 gear pair. Also 2.64:1 from ROW S4 G28/12 will work directly and you wouldn't loose that much by using it. So any '85-91 ROW box will do.
As for the gearbox problem you have. Find ROW '85-86 G28/10 box. I know, easier said than done but they are out there. They have same 11:30 and 2.73:1 ring & pinion ration as GT box and parts should be bolt on. Only difference is slighly different teeth design which mostly means little more friction and possibly less noise than original G28/55 gear pair. Also 2.64:1 from ROW S4 G28/12 will work directly and you wouldn't loose that much by using it. So any '85-91 ROW box will do.
Though ring & pinion was only good part in them.