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I have no idea. I know what goes with what and hardly ever check what Porsche says.
This does "mess" up many a clutch replacement, however.
The easy way to remember the confusion about T/O arm and T/O bearing (for all years) is simple:
Never flat with flat. Never curved with curved. The only thing that works is curved with flat!
If you stop and think about how the arm moves and how the arm pulls on the T/O bearing, it's crystal clear.
You need a curved surface on a flat surface, so the "contact patch" is at the top of the curve, allowing the flat part to "pivot" on that curve.
I completely get and agree with your point. When both new parts arrived I did scratch my head a bit because I remembered you and @Mrmerlin making this comment before about never using flat to flat or curved to curved.
I have no clue what's up with Porsche's system. I'll have to make a phone call tomorrow to see what's up as it appears they may not even know....
@Mark Anderson
Can you weigh in on this as well? I just checked 928Intl and it shows the -09 (flat) release arm as being applicable to early cars and your rebuilt throw out bearing shown in the pics is also flat.
There’s gotta be an explanation to this. Surely not everyone and their brother are installing components that are gonna soon implode....
When I tell you guys that there are more tricks to these clutches than a New Orleans ***** has....you think I'm just trying to be funny. I'm not...these things are a real _itch to get right.
Look up Technical Bulletin 9401, in Book "K", page 51. Note that the change in the T/O arm only applies to '87-'95 cars. No mention of the '78-'86 cars, because it doesn't apply....
I did go look up the "09" arm in the price list. It appears that all of the arms superceed to the '09 arm, which explains why I redo so many clutch jobs that don't release properly/chatter. Porsche either lost track of what pieces fit together....or ran out of all the correct arms.
You guys are welcome to use whatever pieces you choose....it's the old "you can lead them to water" thing.
This makes two interesting discoveries on parts anomalies this week.
Maybe others already knew, but I found out that the -03 pressure plate for the early diameter-centered flywheel, and the -26 pressure for the subsequent pin-centered flywheel, BOTH supersede to the most recent -27 pressure plate which is also for the first generation of pin-centered flywheel.
Currently supplies of the -03 and -26 are still available, but they will both be replaced with the -27 when stocks run out. But just as we’ve been discussing here as it relates to the superseding of the release arm, it makes me wonder if these three pressure plates truly are 100% compatible?
We pressed the new bearing into the old housing, and I am reusing my release fork. It looks like the fork part number is 928 116 832 06 (pic attached).
Using part numbers and the info in the last few posts, here's what I deduce and someone can confirm:
Throwout Bearings
-24 early version flat bearing
-25 later version curved bearing
Arms
-06 early curved arm
-09 later flat arm
So, according to Greg, the two combinations that will work correctly are:
a -24 flat bearing with an -06 curved arm
a -25 curved bearing with an -09 flat arm
This means that if the part numbers in the system supercede to the newer versions of both parts and someone buys both parts, they end up with the latter pairing of a -25 curved bearing with an -09 flat arm which works together, but they can't reuse an older bearing with a new arm or a newer bearing with an old arm.
Scott, from your number, it looks like you have an older -06 curved arm paired with a newer -25 curved bearing and those two won't work together. I don't know whether it's easier or cheaper to replace the arm or the bearing, but looks like one or the other is going to need to be changed.
Is it the bearing housing/sleeve that is the issue or the bearing itself? It does not look like the fork touches the actual bearing, and I am wondering since we pressed in a new bearing into the original housing are we ok? I don't have a pic that shows the part number of the sleeve/housing.
The concern is that the new -09 arm and the new -25 bearing are both flat, which is apparently a problem. This is what I've got prepped for assembly and that I'm going to have to undo.
Scott's setup above should be ok because he has the early curved -06 arm and the newer flat bearing housing.
All of the '78-''86 throwout bearings, from day 1 to the most current bearings are flat.
All of the T/O arms in those cars were curved.
There has never been any change to a "flat arm" for the '78-'86 cars.
The '06 fork is correct. The '09 arm is only for '87-'95 cars only.
Quit fighting it.....just do it correctly.
My old -06 arm is back on the assembly now. Crisis averted thanks to this thread and Greg.
I’m working on communicating this concern with PCNA too. I’d hate for others to be led down the primrose path to failure...
Yeah, we can all pretend that they care....or have anyone left (even in Germany) with the technical expertise to know what works together in a pre-1987 928.
In the end, logic trumps anything anyone thinks, says, or prints in PET.
Flat on flat, with an arm that pulls in an arc, starts pulling on the T/O bearing crooked. Somewhere in the middle of the travel, the two flats are parallel...and that works, fine....only at that particular position! At the end of the travel, the bearing is crooked in the opposite direction it was, when it started moving.
This results in clutch chatter, followed by rapid wear of the snap ring that holds the thrust washer onto the T/O bearing, followed by rapid wear of the fingers on the pressure plate.
The T/O bearing needs to be pulled back square to the pressure plate!
Not that important? Look at the subtle change Porsche made in 1993....they "reversed" the two surfaces of the arm and the T/O bearing (changed the arm from curved to flat and the T/O bearing from flat to curved) to make the clutches have less chatter!
01-22-2020, 09:28 PM
