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Good video showing how synchros work. When he shows the new and old synchro, I understand the bad one spins freely but when I look at them in the video I don't see a difference. Is the issue with the bad one that the inner cone shape has worn?
What you say about the thermal coefficient of expansion makes sense but even when C is a large number you are still talking about a very small difference. I am not sure that's your problem but I like the way you think.
Good video showing how synchros work. When he shows the new and old synchro, I understand the bad one spins freely but when I look at them in the video I don't see a difference. Is the issue with the bad one that the inner cone shape has worn?
What you say about the thermal coefficient of expansion makes sense but even when C is a large number you are still talking about a very small difference. I am not sure that's your problem but I like the way you think.
Yes the issue with the bad synchronizer is that the inner cone has worn down so much that it no longer creates a friction or interference fit with the cone on the steel gear so it just constantly spins as the shift selector sleeve goes to engage the synchro. If the inside cone of the synchronizer was not worn out, when you push the synchronizer down on the cone part of the gear it will eventually get snug and create a friction fit and not spin. Adding heat - increasing the inner diameter of the synchronizer cone - will exacerbate this issue. Given that my transmission doesn't even want to hint at popping out of gear when cold, but pops out once it's warmed up, I suspect this is the issue. Especially if there is a delta temp from cold (0C) to hot of 120C. Most of these transmissions are assembled and held together by press fits / interference fits which are assembled by heating and cooling parts during assembly.
I'm not a transmission expert but I think the math adds up. I wanted to know what part is responsible for keeping the car in gear.... so if the synchronizer is bad, then it won't hold the gear...
Ya if you look at the other link I posted above you can see my bill and that the 1/2 and 3/4 syncros were replaced. I recall 1st or 2nd gear, I can't remember which, was popping out because I tried the detent first. EDIT: I am pretty sure it was second gear that was popping out: https://www.gboxweb.com/detent.html
Do I have my math right? Using your 120 degree C the difference would be 1.64mm?
= 18.5 e^-6 *120 -13 e^-6 *120 = 1.6359764366
Seems too high
EDIT: I see the problem, lol it's treating the "e" as Euler's constant LOLOLOL.
Easier to just think in microns (µ=10^-6). Here is my math revisited:
18.5*120 -13*120 = 660 µm = .66mm
But upon thinking about this more, I think that's still wrong, that would be for something 1 meter long. In this case the brass synchronizer and steel gear are much shorter than 1 meter, so the value is going to be much smaller than .66mm. https://study.com/skill/learn/how-to...%20in%20Kelvin.
Maybe you are right if it's already near the threshold? Mine would pop-out cold or hot.
Ya if you look at the other link I posted above you can see my bill and that the 1/2 and 3/4 syncros were replaced. I recall 1st or 2nd gear, I can't remember which, was popping out because I tried the detent first. EDIT: I am pretty sure it was second gear that was popping out: https://www.gboxweb.com/detent.html
Do I have my math right? Using your 120 degree C the difference would be 1.64mm?
= 18.5 e^-6 *120 -13 e^-6 *120 = 1.6359764366
Seems too high
EDIT: I see the problem, lol it's treating the "e" as Euler's constant LOLOLOL.
Easier to just think in microns (µ=10^-6). Here is my math revisited:
18.5*120 -13*120 = 660 µm
Maybe you are right if it's already near the threshold? Mine would pop-out cold or hot.
We will never be able to calculate dimension A effects with thermal expansion without knowing the angle of the cone on the gear. If this angle is very steep a change in the diameter of the synchro would have huge impacts. If the angle of the cone was very shallow, you could have a massive diameter increase on the synchronizer but it still wouldn't slide that far down the cone of the gear.
But assuming the brass ring ID is 3" or 76.2mm, this means diameter increase = (18.5e^-6mm/mm)*(76.2mm)*(120C) = .169mm or 0.006" or ~ six human hairs.
Assuming steel ring ID is 3" or 76.2mm, this means diameter increase = (13e^-6mm/mm)*(76.2mm)*(120C) = 0.119mm or 0.0046" or ~4.5 human hairs.
Delta diameter between steel and brass rings would be 0.0014in or 0.05mm. This doesn't seem like a lot, but if the angle of the cone was extreme, let's say 90* (unrealistic), the synchronizer could slide down until it hits a bump stop, the helical gear clutch teeth.
Installation (new) dimension for A is 0.8mm and wear is 0.5mm or a delta drop of 0.3mm as the synchro slides down the cone of the gear. By taking inverse tangent of 0.3/0.0025 (0.0025mm for radius from 0.05mm diameter), the cone would have to be an angle of 89* to produce the kind of drop in "A" dimension from 120C increase in temp. It may be that my wear dimension A is .1mm cold, which is still enough to make a press fit, but once it warms up all it has to do is slide down 0.1mm for it to now freely spin. tan^-1(0.1mm/0.0025mm), but this still results in a steep angle of 88*, unrealistic for that cone. Still need to pop it open and check...
But I like what you listed above. Thank you for that. I might be driving cross country to see Stan at GBOX with transmission in tow...
That is a great point about the effects on the angle of the cone, why didn't I think of that. I also agree with your math, this is the same as what I finally landed on above. I am hoping you can fix this yourself since you have already done a huge deep dive here but if you can't or it just isn't worth your time to keep dropping the gearbox you always have the GBox option in your back pocket. If you don't feel like road trippin' you could always send it to Stan, I would guess it's about $1,000 freight roundtrip. In my invoice in that other thread I paid $192 shipping + $80 insurance but I am almost sure that was just one way. Prices have gone up with inflation so instead of $600 round trip insured it's probably closer to $1,000 now. Not the end of the world by any stretch of the imagination unless you feel like driving out there but it's a distance from Baltimore......
I know some transmissions hold gear via bumps/detentes/angles on the side of their dog teeth. Kinda like but not snaps. When these bumps wear, there is nothing holding the assembly together except for the force of the shifter fork. Again, so many variables here... But, can you see the knubs?
Peace
Bruce in Philly (now Atlanta)
Something like this...
Got to 2:10 and 4:08 where they show a back cut to lock the parts in place, at 4:08, they denote symptom of worn taper is popping out of gear:
That is a great point about the effects on the angle of the cone, why didn't I think of that. I also agree with your math, this is the same as what I finally landed on above. I am hoping you can fix this yourself since you have already done a huge deep dive here but if you can't or it just isn't worth your time to keep dropping the gearbox you always have the GBox option in your back pocket. If you don't feel like road trippin' you could always send it to Stan, I would guess it's about $1,000 freight roundtrip. In my invoice in that other thread I paid $192 shipping + $80 insurance but I am almost sure that was just one way. Prices have gone up with inflation so instead of $600 round trip insured it's probably closer to $1,000 now. Not the end of the world by any stretch of the imagination unless you feel like driving out there but it's a distance from Baltimore......
I'd say anything under $500 shipped round trip shipped is "free" in my book. If I can't figure this out on my own during the next trans drop I'll send it to Stan. Already wasted $1k on that other shop. I think this whole situation would be easier to digest if the shop that did my clutch and flywheel and then broke my shifter cables for $5k, never happened.
Nice to know I'll never have to pay a Porsche shop to do a clutch again. I think what worried me on that job was the quasi-lack of information or confidence that I could have done it myself.
~ time 6:00 he's talking about what DasCayman is looking at ... "it's a cone clutch" and ~ time 7:25 he shows the new vs the old ring locking onto the gear. Possibly your threads are worn?
The more I look at these things the more I realize they're very sophisticated and it's tough if you're not familiar and looking at it day in and day out. This would not be a good job for me to be doing in my garage late at night when I am tired, that's usually when I make my stupidest mistakes.
I think my issue, or our issue if you have the jam, is exactly a "blocking" issue... the points of those teeth are rounded off. So when the rings are pushed together, they don't slide into alignment but just butt heads; see in that video I posted and in your video at around 5:15, he talks about "blocking" when they are "point to point". Your vid shows it could be a few things causing the block like the "key slot" is worn wider... I say it is blocking for two reasons: 1) I have an active imagination, and 2) I was at the shop a local Porsche guy who rebuilds old 911 manual transmissions... his shop was a flippin' mess of a mad scientist... transmissions, parts all over the f'n place. Anywho he was showing me all the common wear parts of these very small and relatively simpler machines, and he showed me a ring with the pointy teeth rounded off. My problem? I have no clue... but I always suspected block out. As a sort of proof, to get the transmission to seat, I (everyone has their dance), I put the clutch back in/out, shift into 2nd and then back into 1st... rarely I go to third. This gets everything spinning and the lottery is back in my favor.
Peace
Bruce in Philly (now Atlanta)
Last edited by Bruce In Philly; 01-03-2024 at 05:26 PM.
I'd say anything under $500 shipped round trip shipped is "free" in my book. If I can't figure this out on my own during the next trans drop I'll send it to Stan. Already wasted $1k on that other shop. I think this whole situation would be easier to digest if the shop that did my clutch and flywheel and then broke my shifter cables for $5k, never happened.
Nice to know I'll never have to pay a Porsche shop to do a clutch again. I think what worried me on that job was the quasi-lack of information or confidence that I could have done it myself.
Hey man, I apologize for getting slightly off topic but is that lightweight flywheel you installed dual mass? Single mass flywheels have no harmonic dampening, Jake Raby used to have a page about this on his website, the entire assembly needs to be balanced.
This was the link on Jake's site but he has since removed it with his site re-design. However, I still have his notes below in italics. http://www.flat6innovations.com/broken-crank
I feel that this failure was attributed to by a couple of things-1- The engine was "upgraded" to a lightened flywheel. This new flywheel was installed onto the existing stock engine without being balanced to that assembly. This created an imbalance in the rotating mass AND it did away with the factory dual mass flywheel.2- The dual mass flywheel was removed to allow the single mass lightened unit to be installed. This eliminated ALL MEANS OF HARMONIC DAMPENING!! The crankshaft was forced to absorb ALL harmonics from the engine and transaxle when the dual mass unit was removed..So adding the light weight flywheel was a double negative, not only did it create imbalance, it also eliminated the harmonic dampening of the dual mass arrangement. Due to this I feel that adding a lightweight flywheel to any existing engine is not a wise decision, and that they should only be added when the entire rotating mass can be balanced and indexed to accommodate the lightweight unit. This means engine disassembly, so I'd only add one of these when doing one of our performance upgrades so the entire assembly can be precisely balanced.
I know some transmissions hold gear via bumps/detentes/angles on the side of their dog teeth. Kinda like but not snaps. When these bumps wear, there is nothing holding the assembly together except for the force of the shifter fork. Again, so many variables here... But, can you see the knubs?
Peace
Bruce in Philly (now Atlanta)
Something like this...
Got to 2:10 and 4:08 where they show a back cut to lock the parts in place, at 4:08, they denote symptom of worn taper is popping out of gear:
~ time 6:00 he's talking about what DasCayman is looking at ... "it's a cone clutch" and ~ time 7:25 he shows the new vs the old ring locking onto the gear. Possibly your threads are worn?
The more I look at these things the more I realize they're very sophisticated and it's tough if you're not familiar and looking at it day in and day out. This would not be a good job for me to be doing in my garage late at night when I am tired, that's usually when I make my stupidest mistakes.
Another great video and explanation of how these work. I did a lot of YouTube University on these transmissions but couldn't find these. Thank you! Checking the lead time on the 6th gear synchro, guide sleeve and shift sleeve. I can't imagine needing a new gear since it's steel, my worry would be the clutch teeth being worn out. But I believe that's why they use softer / sacrificial metals for the syncros and sleeves.
I don't mind doing the work myself. I was also able to get a hold of the pull 6000 page workshop manual. I also have access to machine shops for all their precision equipment from my day job as a mechanical engineer.
Hey man, I apologize for getting slightly off topic but is that lightweight flywheel you installed dual mass? Single mass flywheels have no harmonic dampening, Jake Raby used to have a page about this on his website, the entire assembly needs to be balanced.
This was the link on Jake's site but he has since removed it with his site re-design. However, I still have his notes below in italics. http://www.flat6innovations.com/broken-crank
I feel that this failure was attributed to by a couple of things-1- The engine was "upgraded" to a lightened flywheel. This new flywheel was installed onto the existing stock engine without being balanced to that assembly. This created an imbalance in the rotating mass AND it did away with the factory dual mass flywheel.2- The dual mass flywheel was removed to allow the single mass lightened unit to be installed. This eliminated ALL MEANS OF HARMONIC DAMPENING!! The crankshaft was forced to absorb ALL harmonics from the engine and transaxle when the dual mass unit was removed..So adding the light weight flywheel was a double negative, not only did it create imbalance, it also eliminated the harmonic dampening of the dual mass arrangement. Due to this I feel that adding a lightweight flywheel to any existing engine is not a wise decision, and that they should only be added when the entire rotating mass can be balanced and indexed to accommodate the lightweight unit. This means engine disassembly, so I'd only add one of these when doing one of our performance upgrades so the entire assembly can be precisely balanced.
Thank you for the feedback. This AASCO / RSS flywheel was installed by myself on my 987.2 Spyder. I plan to add the harmonic damped pully from RSS this winter. I have only put maybe 200-300 miles on the car with the new flywheel. It's also only driven on the weekends / no track work. I'm not sure of the conditions that Jake Raby's engine failed / how long it was installed for, etc. When I spoke to BBI and Sharkwerks about adding the flywheel they didn't mention anything about getting a harmonic damper, but I will be leaning on the side of caution and instal the harmonic damper this winter when they come back in stock.
Here is also a great source of information on harmonic dampers from HP Academy that I'll review this week. They mention that Porsche is one of the only companies that doesn't put a harmonic damper on the stock engines or flywheels. Name of the game seems to be avoiding resonant frequencies, which occur at certain RPM ranges and staying there. That frequency could be 2k RPM and just cruising down the highway could resonate your engine to failure, or it could be at redline at 7-8k RPM and being there constantly, like the track, will prolong this time and cause the failure.
01-03-2024, 08:46 AM
