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First off, yes there are countless threads on this topic. And yes I’ve read them all, or at least as many as I could find over the past few months. And yes I’ve read my WSM a number of times as well.
Despite all of that, I’ve stumbled upon an issue that I don’t recollect seeing previously discussed, though I’m sure some here have also come upon it. I’ve got the clutch assembly exposed again on my ‘78 to do some double checking of the H-tabs on the Intermediate Plate. I was able to get them to move a bit more towards the rear so that the top of the hole on the H-tab (the side of the hole facing the rear of the car) is just barely showing. But when I’ve got the clutched disengaged, the rear disc (Disc II) is only about 1mm or less off of the Intermediate Plate, whereas the front disc (Disc I) is about 1/16” to about 1/8” off of the IP.
It was my understanding that when the H-tabs gaps were adjusted to be equidistant, that the clutch disc gaps would also be the same. Is this not accurate?
Also, with the clutch fully disengaged I can spin the short shaft and the clutch discs, but the rear disc (Disc II) makes the slightest sound of friction. It’s like it is still just barely kissing the IP. But I can’t get the H-tabs moved towards the rear of the car anymore. When I attempt to do so, and then release the clutch, the Pressure Plate pushes them back to the same position every time (with the top of the hole in the H-tab just barely exposed towards the rear of the car).
you need to run the new parts for about 2K miles then check it ,
right now all the parts are at max thickness after they get used then discs will begin to get thinner thus the drag should go away.
you need to run the new parts for about 2K miles then check it ,
right now all the parts are at max thickness after they get used then discs will begin to get thinner thus the drag should go away.
Understood. I’m just a bit spooked about zinging my shiny new synchros and gears in the mean time. She’s been generally shifting well but I had some first gear judder a few days ago and also some difficulty getting into reverse two days ago.
You will ruin the synchros and the sliders. Stop driving the car.
The "H" stops are designed to both limit the amount that the intermediate plate can lift, while also having the capability to be moved (forward) as the front clutch disc wears.
This works fantastic, when the intermediate plates are new and the rivet mechanism is tight enough to hold the "H" stops in position as the clutch releases. (The "H" stops must not move when the clutch is released....the rivet mechanism must be tight enough to be able to keep this from occurring.) With a brand new intermediate plate, with the correct clutch discs, one could slam the "H" stops all the way to the rear, and be done.
Internet Myth would lead you to believe that the "H stops do not wear, with use....they do. And this is your problem. What is happening, in your case, is that the intermediate plate is moving too far to the rear (lifting too far off of the front disc), because you have your worn "H" stops pushed all the way to the rear. This allows the intermediate plate to travel too far to the rear (too much front disc clearance) and decreases the available clearance of the rear disc (rear disc drags.)
This is simple to fix, with a good intermediate plate. Virtually impossible to repair with a intermediate plate that will not hold the "H" stops in the position where you adjust them to, without making changes to the intermediate plate.
Simply move the "H" stops forward, until the amount the intermediate plate lifts off the front disc is the same as the rear disc. Generally, you will want .8mm-1.0mm of air gap between the rear of inner surface of the "H" stop and the intermediate plate. (Make sure the "H" stops are square to the intermediate plate and not crooked.) If the "H" stops move rearward when you release the clutch, the rivet mechanism is worn out. In this case, you (1) need another intermediate plate with tighter rivet mechanisms. You need to (2) weld the "H stops into position (which works great, until the front disc wears and the "H" stops are unable to move to compensate for the disc wear.....and you've permanently ruined all the pieces) Or, you need (3) to remove the rivet, drill and tap the intermediate plate for a button head screw, re-assemble, set the air gap to the correct dimension, and tighten down the button head. (This method allows one to go back in once the front disc wears and re-adjust the "H stops.)
Try adjusting first. If the "H" stops can stay in position, all you need to do is adjust all 3 to the "sweet spot" (all three exactly the same) to allow both discs to spin freely.
You will ruin the synchros and the sliders. Stop driving the car.
The "H" stops are designed to both limit the amount that the intermediate plate can lift, while also having the capability to be moved (forward) as the front clutch disc wears.
This works fantastic, when the intermediate plates are new and the rivet mechanism is tight enough to hold the "H" stops in position as the clutch releases. (The "H" stops must not move when the clutch is released....the rivet mechanism must be tight enough to be able to keep this from occurring.) With a brand new intermediate plate, with the correct clutch discs, one could slam the "H" stops all the way to the rear, and be done.
Internet Myth would lead you to believe that the "H stops do not wear, with use....they do. And this is your problem. What is happening, in your case, is that the intermediate plate is moving too far to the rear (lifting too far off of the front disc), because you have your worn "H" stops pushed all the way to the rear. This allows the intermediate plate to travel too far to the rear (too much front disc clearance) and decreases the available clearance of the rear disc (rear disc drags.)
This is simple to fix, with a good intermediate plate. Virtually impossible to repair with a intermediate plate that will not hold the "H" stops in the position where you adjust them to, without making changes to the intermediate plate.
Simply move the "H" stops forward, until the amount the intermediate plate lifts off the front disc is the same as the rear disc. Generally, you will want .8mm-1.0mm of air gap between the rear of inner surface of the "H" stop and the intermediate plate. (Make sure the "H" stops are square to the intermediate plate and not crooked.) If the "H" stops move rearward when you release the clutch, the rivet mechanism is worn out. In this case, you (1) need another intermediate plate with tighter rivet mechanisms. You need to (2) weld the "H stops into position (which works great, until the front disc wears and the "H" stops are unable to move to compensate for the disc wear.....and you've permanently ruined all the pieces) Or, you need (3) to remove the rivet, drill and tap the intermediate plate for a button head screw, re-assemble, set the air gap to the correct dimension, and tighten down the button head. (This method allows one to go back in once the front disc wears and re-adjust the "H stops.)
Try adjusting first. If the "H" stops can stay in position, all you need to do is adjust all 3 to the "sweet spot" (all three exactly the same) to allow both discs to spin freely.
Understand?
Got it. My H-tabs are holding and do not move rearward when the clutch arm is released, so that’s good news. I suspect Stan’s reference about disc thickness is also playing into this a bit. Both clutch discs are brand new (superseded versions) so I’ll work to get the gapping just right.
A concern of mine is how to hold the release arm back in order to allow me to work. I hate using a lever against the casing of the pressure plate as I don’t want to crack it. And using ratchet straps on the release arm and rear crossmember seems a bit dangerous. Hacker’s solution with an extra bell housing with a hole in it would be ideal since it would allow the slave to remain installed and usable, but I don’t have access to something like that at the moment.
Got it. My H-tabs are holding and do not move rearward when the clutch arm is released, so that’s good news. I suspect Stan’s reference about disc thickness is also playing into this a bit. Both clutch discs are brand new (superseded versions) so I’ll work to get the gapping just right.
A concern of mine is how to hold the release arm back in order to allow me to work. I hate using a lever against the casing of the pressure plate as I don’t want to crack it. And using ratchet straps on the release arm and rear crossmember seems a bit dangerous. Hacker’s solution with an extra bell housing with a hole in it would be ideal since it would allow the slave to remain installed and usable, but I don’t have access to something like that at the moment.
Pry bar (with built in angle on the end) against the T/O arm and the edge of the pressure plate. You can set easily see the amount the intermediate plate and the clutch cover lift, with the lower cover off. I leave the torque tube shaft coupler off, so I can reach up and spin the input shaft with my other hand.
If you'd like and the UPS store stays open I could ship you my extra bellhousing with the hole cut it to borrow. Might not take too long to get from Columbia to Atlanta.
Take Matt up on his offer or pick up a spare cover and cut a hole in it. Frankly this was a boneheaded mistake by Porsche, these lower covers should have come with an inspection / adjustment door.
With such an opening it's easy to see what the clutch is doing as someone works the pedal. On a lift with the engine running, go through the paces and make sure it's releasing properly. Not sure I'd do that on jack stands though.
If you'd like and the UPS store stays open I could ship you my extra bellhousing with the hole cut it to borrow. Might not take too long to get from Columbia to Atlanta.
Got your PM. Will probably make a run to UPS at lunchtime.
Mine isn't as pretty as hacker's, but it worked for me. It's from an 86.5. I can't remember if it was the original one from my auto car that I cut or if it was the one from the manual car I got my swap parts from.
Some quick poking around makes it seem like it should work for your 78. I'm far from the expert here though.
Didn't have a picture of it on the car, but here's a quick video clip of it.
OCD and I were able to exchange texts today and compare the covers. It looks like a later 86.5 cover won’t fit as my 78 has posts / dowels protruding from the upper bell housing that helps to align the cover. The later covers don’t have this.
Cover from my ‘78 with the extra hole for the dowel.
Take Matt up on his offer or pick up a spare cover and cut a hole in it. Frankly this was a boneheaded mistake by Porsche, these lower covers should have come with an inspection / adjustment door.
With such an opening it's easy to see what the clutch is doing as someone works the pedal. On a lift with the engine running, go through the paces and make sure it's releasing properly. Not sure I'd do that on jack stands though.
03-30-2020, 05:18 PM
Double Clutch Adjustment - disc gaps
