Attn: Heavy pressure-plate users...
03-14-2011, 09:48 AM
#31
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forged is only stronger than billet in the engineering world in the magical world of rennlist billet is the ultimate .. like charly arms LOL....
some good points made about setting up the pedal correctly.. also when you build a clutch correctly you can set it it up with same fork load and increased clamp load by moving the fulcrum out on the drive plate .. you do give up a little plate travel ..
i guess the other options to consider are
some good points made about setting up the pedal correctly.. also when you build a clutch correctly you can set it it up with same fork load and increased clamp load by moving the fulcrum out on the drive plate .. you do give up a little plate travel ..
i guess the other options to consider are
03-15-2011, 03:47 PM
#33
Rennlist Member
Curious, where'd you get the 45ksi statistic? Seems low to me.
A newly-forged piece should be stronger than a new billet piece, or certainly a cold-rolled piece. Fact.
Also, cold-rolling makes a part more brittle, not less.
That said, these forks are old and get exposed to the elements for a couple decades. While the porosity of a forged piece is typically pretty low (compared to billet/cast), there is still a huge potential for corrosion, namely pitting and stress-induced.
To be honest, the only way to guarantee the fork isn't going to break is by either buying a less harsh PP, manufacture the fork prongs larger, or manufacture the fork out of titanium. Yes, you can certainly attempt to heat treat (I.e., martempering would be the most extreme you could realistically go, but even that may make it too brittle) but chances are that a brand new forged fork ain't gonna get much better than it already is without the aforementioned provisions.
Just my two cents. Now, if someone could CNC a beefier one out of billet andf THEN heat treat, then we'd have something.
Collin
A newly-forged piece should be stronger than a new billet piece, or certainly a cold-rolled piece. Fact.
Also, cold-rolling makes a part more brittle, not less.
That said, these forks are old and get exposed to the elements for a couple decades. While the porosity of a forged piece is typically pretty low (compared to billet/cast), there is still a huge potential for corrosion, namely pitting and stress-induced.
To be honest, the only way to guarantee the fork isn't going to break is by either buying a less harsh PP, manufacture the fork prongs larger, or manufacture the fork out of titanium. Yes, you can certainly attempt to heat treat (I.e., martempering would be the most extreme you could realistically go, but even that may make it too brittle) but chances are that a brand new forged fork ain't gonna get much better than it already is without the aforementioned provisions.
Just my two cents. Now, if someone could CNC a beefier one out of billet andf THEN heat treat, then we'd have something.
Collin
I'm wondering how big of a problem this really is...
Maybe there are a few "bad" years of forks from Porsche? A change in suppliers or something? There has to be quite a few people with heavy PPs, and either only a few have had problems, or no one talks about it. Its strange that Josh has broken 2 of them, in the exact same spot. One of them was even heat treated. Then Cole has broken one, only on the other side of the fork, but same location on the fork itself.
I'm thinking about making a few new ones out of some good cold roll plate. The stock unit is Forged (Not cast like I originally thought), but either way, the tensile strength is 45k psi. The difference is hardness. A good cold roll will have the same tensile strength, but will also be more ductile=Less brittle.
I don't have access to a CNC, so the plate version won't be as pretty... but it would be just as strong, and cheaper to produce...Unless one of you has access to a CNC. Then the billet unit would be the way to go.
Maybe there are a few "bad" years of forks from Porsche? A change in suppliers or something? There has to be quite a few people with heavy PPs, and either only a few have had problems, or no one talks about it. Its strange that Josh has broken 2 of them, in the exact same spot. One of them was even heat treated. Then Cole has broken one, only on the other side of the fork, but same location on the fork itself.
I'm thinking about making a few new ones out of some good cold roll plate. The stock unit is Forged (Not cast like I originally thought), but either way, the tensile strength is 45k psi. The difference is hardness. A good cold roll will have the same tensile strength, but will also be more ductile=Less brittle.
I don't have access to a CNC, so the plate version won't be as pretty... but it would be just as strong, and cheaper to produce...Unless one of you has access to a CNC. Then the billet unit would be the way to go.
03-15-2011, 04:10 PM
#34
Rennlist Member
Not to belabor the materials science rhetoric, but just one more quick note:
Hardness is typically not the best way to measure our fork's ability to be strong enough while simultaneously remaining ductile enough to not break under the applied cyclic stress. Hardness can be deceiving, particularly when heat treating, as it only has the ability to measure what is on the surface.
Hardness better lends itself to measuring determining the wear resistance of a part. Yes, the prongs of the fork are a wear surface, but i'd argue the bigger concern is ensuring the prongs don't end up breaking.
Using other processing methods intentionally designed to increase a part's tensile strength will result in an increased hardness anyway.
Hardness is typically not the best way to measure our fork's ability to be strong enough while simultaneously remaining ductile enough to not break under the applied cyclic stress. Hardness can be deceiving, particularly when heat treating, as it only has the ability to measure what is on the surface.
Hardness better lends itself to measuring determining the wear resistance of a part. Yes, the prongs of the fork are a wear surface, but i'd argue the bigger concern is ensuring the prongs don't end up breaking.
Using other processing methods intentionally designed to increase a part's tensile strength will result in an increased hardness anyway.
12-03-2011, 04:13 AM
#35
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My clutch has failed, won't disengage. Finally got it out and I also have a broken fork leg just like yours.
How's your welded repair and strengthening mod holding up? I want to do the same if it's still good.
12-03-2011, 09:15 AM
#37
My welded fork is also fine. Car was daily driven on a 40 mile stop and go rush hour commute for the last 6 months too. Lots of clutch work.
I also have an extra fork if someone needs one.
I also have an extra fork if someone needs one.
12-03-2011, 09:54 AM
#38
Rennlist Member
You're using an S/Bend setup too huh Dan? Hmmm....????
Ahh, wrong Dan R...
Ahh, wrong Dan R...
Last edited by 333pg333; 12-03-2011 at 06:48 PM.
12-03-2011, 10:37 AM
#39
Rennlist Member
Make sure you heat treat after welding, not before. Really sorry to hear about the fork. KEP 1 or 2?
12-03-2011, 11:15 AM
#40
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The breaking of clutch forks has been getting worse with the use of heavier pressure plates.
https://rennlist.com/forums/944-turb...ht=clutch+fork
https://rennlist.com/forums/944-turb...tch-forks.html
https://rennlist.com/forums/944-turb...ain-fixed.html
Since the OEM 944T fork is not available anymore, you need to buy a refurbished one for around $200 or fix your current fork. I don't see anyone wanting to develop a new fork for a very small market and the cost would be prohibitive compared to reinforcing one.
https://rennlist.com/forums/944-turb...ht=clutch+fork
https://rennlist.com/forums/944-turb...tch-forks.html
https://rennlist.com/forums/944-turb...ain-fixed.html
Since the OEM 944T fork is not available anymore, you need to buy a refurbished one for around $200 or fix your current fork. I don't see anyone wanting to develop a new fork for a very small market and the cost would be prohibitive compared to reinforcing one.
12-03-2011, 02:52 PM
#41
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With my up coming 2.8 swap I am shopping for higher load clutch-PP and considered the kep PP but I think now I will stay away just to be safe.
12-03-2011, 06:17 PM
#42
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Thanks for the replies.
Just the standard clutch and p/p. About 135k's on the fork so not happy. Especially as I had my engine out 5k's ago and I checked everything. The clutch and p/p were near new (replaced at 100k's). Getting the box and clutch out has been a bitch of a job.
I like the idea of welding and gusseting the fork. There's enough room to make the gusset wider than the arm without fouling anything.
Patrick I see you're in Sydney. Near Bruce? PM sent.
Just the standard clutch and p/p. About 135k's on the fork so not happy. Especially as I had my engine out 5k's ago and I checked everything. The clutch and p/p were near new (replaced at 100k's). Getting the box and clutch out has been a bitch of a job.
I like the idea of welding and gusseting the fork. There's enough room to make the gusset wider than the arm without fouling anything.
Patrick I see you're in Sydney. Near Bruce? PM sent.
12-03-2011, 07:51 PM
#44
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Lol, not a shot at you mate - just expressing that I _really_ don't want to swap forks again...
12-03-2011, 08:11 PM
#45
Nordschleife Master
Not that it isn't the weld of all welds, but I really think the issue was the uneven feet. With the beefed up PP, and only 1 foot taking 90% of the weight, its going to break. Grinding the feet even was the best cure.