1979 928 Clutch issues. Need advice - Rennlist Discussion Forums



1979 928 Clutch issues. Need advice

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Old 03-19-2017, 11:55 AM   #1
ShawTurnage1988
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Default 1979 928 Clutch issues. Need advice

Recently I acquired a 1979 928 5 speed. The car runs, but I have a leak from the rear main seal that has to be replaced. The car will also not shift into gear while running. It grinds trying to put in reverse and will not connect with 1-5. However when the car is not running it will connect with gears 1st, 4th, and 5th. Is this from air being between the master and slave cylinder or a clutch issue where I need to replace the clutch. New to these cars, so any advice would be great. Thanks

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Old 03-19-2017, 01:15 PM   #2
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These clutches can be fussy and have a fairly unique design. You should read the manual sections and search this website for information on clutch bleeding and clutch adjustment.
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Old 03-19-2017, 01:36 PM   #3
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Thank you GLen, I have already started doing research on this site.
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Old 03-19-2017, 01:45 PM   #4
James Bailey
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Since you bought it this way do you know if the prior owner " tried" to fix it ?? Especially if a replacement clutch master cylinder was fitted. Because the replacement does not have a long enough stroke !! And must be modified internally.
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Old 03-19-2017, 02:05 PM   #5
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First off, I apologize if this seems obvious, but stop driving the car. Let's assume the synchros are OK in the transmission, even a little use with a clutch in this condition will make short work of the very soft synchros in the early boxes.

Second, IMO these clutch systems are not all that complicated. Sure a bit daunting at first, break down each component they are rather simple.

Third and probably the worst news, the 78/79 cars, if still equipped with the original clutch, could be a very costly endeavor. Some of the key pieces are not compatible with what you can buy new. All of the parts were superseded to the latest version from the 85/86 cars. Yes good used parts do float up from time to time....

First step, you will need a helper, figure out if the hydraulics are working. With a helper working the clutch you can see the slave shaft move via an inspection hole in the bottom of the bell-housing. In the WSM there is a range you should be able to measure. I'm trying to find it, but at the moment not finding the correct page.
When I took delivery of my 78 a couple years ago with a bum clutch, this is the first thing I did. I put a simple line on the shaft with a marker, had someone push the pedal to the floor and the mark didn't move much at all. Bingo...hydraulic issue.
If I were you, this is the first thing I would do, see if the shaft moves at all. If it does we need to find in the WSM the allowable distance.

Assuming you have little to no movement, the problem could be one or multiple things:
1. "Blue" hose which feeds fluid to the master could be kinked
2. Maser and / or slave failing
3. Pedal is adjusted wrong, not allowing for fluid to fill the master or not pushing in all the way
4. Someone installed one of the "new" styles with a nipple on the piston which doesn't allow for full travel (couple threads on this).
5. A leak somewhere else

More on #4 as Mr. Bailey mentioned, this is why I opted to have the clutch master in my 78 rebuilt by White Post Restorations. I didn't want to screw around with modifying a new one and IMO the rebuilt units are superior to new since they are bored out with a copper sleeve installed. No more corrosion.

More on #1 - routing & length of this hose is crucial. Easier on the 78/80 cars since the brake master is smaller, still just as important. There must not be any "dips" or low spots in this hose. Air bubbles need to go up, seems obvious but this gets messed up all the time.

If you have zero history on this car and plan to make things perfect, I would just dive in and replace the master, slave, blue hose and hydraulic line between the two. That's what I did with my 78.


Once that is all figured out, it may still not work (same with my 78). Now onto the clutch mechanics, any single component could be locked up & causing this issue.
1. Something with the fork, either worn beyond tolerances or the plastic cup in the upper bell-housing has failed
2. Release bearings is toast - yes it can keep the clutch from disengaging
3. Someone assembled the clutch shaft dry or with the incorrect lube. Surprisingly this is rather common, must use the correct MOLY lube.
4. Clutch shaft is damaged, one small burr will keep things from moving properly
5. Intermediate disc is stuck - this is the single #1 costly part of the clutch and the 78/79 unit is unique. If this part is the culprit, plan on buying a complete clutch pack which is a few thousand dollars, unless you can find a good used one. If you find two good used ones, let me know since I think I need one.

Many combinations of the above have been found in many cars, it's rarely one thing. This happens due to the cost of a complete clutch pack, so shops would piece together parts as they failed leaving mediocre parts still installed.

How I installed a clutch master:
http://rennlist.com/forums/928-forum...he-fender.html

About 13 years ago my 81 had a pesky randomly releasing clutch, long story short it ended up being the release baring. This post sums up what the problem was (I've now experienced this twice) and also shows the inspection hole we made in a spare bellhousing so we can see the clutch operate which greatly helped diagnose things:
http://rennlist.com/forums/928-forum...ml#post3145762

I also use the inspection hole to adjust the intermediate disc. There are dozens (if not more) discussions on the "proper" way to do this. The WSM details how to bench adjust it prior to installation, few follow this and I've found that no matter which side of this discussion you are on, using an inspection hole and "centering" the intermediate plate between the discs will work every time since that is where it should be when the clutch is disengaged. Frankly, had Porsche provided such an inspection / adjustment holes, mechanics over the past 30 years wouldn't of had such a difficult time working on these things.
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Old 03-19-2017, 02:25 PM   #6
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^ thank you for that post. Very helpful. Need to troubleshoot the clutch on my '79 which is grinding going into reverse and first. Was hoping it might just need bleeding but noticed the blue hose fabric outer weave is frayed mid-way.
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Old 03-19-2017, 02:31 PM   #7
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Quote:
Originally Posted by kiwiokie View Post
^ thank you for that post. Very helpful. Need to troubleshoot the clutch on my '79 which is grinding going into reverse and first. Was hoping it might just need bleeding but noticed the blue hose fabric outer weave is frayed mid-way.
Remember, it's only "not grinding" into 2nd and other gears due to the synchros covering up the issue. The clutch has no idea what gear you are grabbing so it's grinding in all of them ( you just cannot hear it....yet). Driving the car "as is" you are prematurely wearing down what is left of the synchros.

Your scenario is the exact reason why so many 928's are for sale with comments listed like: "Grinds in 2nd, known issue with these cars". These clutches get a little wonky, some experts says that grinding is normal...... and people keep driving their cars.

This is why I parked my 78, other projects in the way and I don't want to risk damaging the transmission. I sorted out the hydraulics, discovered that was only half the problem and parked it. I'm fortunate that I have a fully functioning 79, that clutch will be moved to the 78 and I'm converting my 79 to a single disc. It's a track car and after much self debating, I've decided having a single disc in a track car is one less thing I'll have to potentially deal with on a track weekend.
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Old 03-19-2017, 03:02 PM   #8
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Quote:
Originally Posted by Hacker-Pschorr View Post
First off, I apologize if this seems obvious, but stop driving the car. Let's assume the synchros are OK in the transmission, even a little use with a clutch in this condition will make short work of the very soft synchros in the early boxes.

Second, IMO these clutch systems are not all that complicated. Sure a bit daunting at first, break down each component they are rather simple.

Third and probably the worst news, the 78/79 cars, if still equipped with the original clutch, could be a very costly endeavor. Some of the key pieces are not compatible with what you can buy new. All of the parts were superseded to the latest version from the 85/86 cars. Yes good used parts do float up from time to time....

First step, you will need a helper, figure out if the hydraulics are working. With a helper working the clutch you can see the slave shaft move via an inspection hole in the bottom of the bell-housing. In the WSM there is a range you should be able to measure. I'm trying to find it, but at the moment not finding the correct page.
When I took delivery of my 78 a couple years ago with a bum clutch, this is the first thing I did. I put a simple line on the shaft with a marker, had someone push the pedal to the floor and the mark didn't move much at all. Bingo...hydraulic issue.
If I were you, this is the first thing I would do, see if the shaft moves at all. If it does we need to find in the WSM the allowable distance.

Assuming you have little to no movement, the problem could be one or multiple things:
1. "Blue" hose which feeds fluid to the master could be kinked
2. Maser and / or slave failing
3. Pedal is adjusted wrong, not allowing for fluid to fill the master or not pushing in all the way
4. Someone installed one of the "new" styles with a nipple on the piston which doesn't allow for full travel (couple threads on this).
5. A leak somewhere else

More on #4 as Mr. Bailey mentioned, this is why I opted to have the clutch master in my 78 rebuilt by White Post Restorations. I didn't want to screw around with modifying a new one and IMO the rebuilt units are superior to new since they are bored out with a copper sleeve installed. No more corrosion.

More on #1 - routing & length of this hose is crucial. Easier on the 78/80 cars since the brake master is smaller, still just as important. There must not be any "dips" or low spots in this hose. Air bubbles need to go up, seems obvious but this gets messed up all the time.

If you have zero history on this car and plan to make things perfect, I would just dive in and replace the master, slave, blue hose and hydraulic line between the two. That's what I did with my 78.


Once that is all figured out, it may still not work (same with my 78). Now onto the clutch mechanics, any single component could be locked up & causing this issue.
1. Something with the fork, either worn beyond tolerances or the plastic cup in the upper bell-housing has failed
2. Release bearings is toast - yes it can keep the clutch from disengaging
3. Someone assembled the clutch shaft dry or with the incorrect lube. Surprisingly this is rather common, must use the correct MOLY lube.
4. Clutch shaft is damaged, one small burr will keep things from moving properly
5. Intermediate disc is stuck - this is the single #1 costly part of the clutch and the 78/79 unit is unique. If this part is the culprit, plan on buying a complete clutch pack which is a few thousand dollars, unless you can find a good used one. If you find two good used ones, let me know since I think I need one.

Many combinations of the above have been found in many cars, it's rarely one thing. This happens due to the cost of a complete clutch pack, so shops would piece together parts as they failed leaving mediocre parts still installed.

How I installed a clutch master:
http://rennlist.com/forums/928-forum...he-fender.html

About 13 years ago my 81 had a pesky randomly releasing clutch, long story short it ended up being the release baring. This post sums up what the problem was (I've now experienced this twice) and also shows the inspection hole we made in a spare bellhousing so we can see the clutch operate which greatly helped diagnose things:
http://rennlist.com/forums/928-forum...ml#post3145762

I also use the inspection hole to adjust the intermediate disc. There are dozens (if not more) discussions on the "proper" way to do this. The WSM details how to bench adjust it prior to installation, few follow this and I've found that no matter which side of this discussion you are on, using an inspection hole and "centering" the intermediate plate between the discs will work every time since that is where it should be when the clutch is disengaged. Frankly, had Porsche provided such an inspection / adjustment holes, mechanics over the past 30 years wouldn't of had such a difficult time working on these things.


Thank you Hacker, I do not have any history on the car currently. Picked it up two days ago in Arizona. I haven't driven the car just tried to put it into gear after starting it, when I realized it wouldn't go, immediately stopped, lifted the car and checked the bell-housing hole. There is movement from the slave shaft and it is a "new" shaft, so it appears someone "worked" on it. However after taking off the bell-housing, starter, and slave I found large quantities of dirt built up inside. The clutch and flywheel seem to have a decent amount of rust.
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Old 03-19-2017, 07:55 PM   #9
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going to follow this thread closely. Proud owner of a 79 5 speed that came to me with the instructions, " it'll need a clutch. I just had both discs relined, and will be investigating the clutch system soon. I know I need a new slave cylinder and line.

James
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Old 03-19-2017, 07:57 PM   #10
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Quote:
Originally Posted by ShawTurnage1988 View Post
Thank you Hacker, I do not have any history on the car currently. Picked it up two days ago in Arizona. I haven't driven the car just tried to put it into gear after starting it, when I realized it wouldn't go, immediately stopped, lifted the car and checked the bell-housing hole. There is movement from the slave shaft and it is a "new" shaft, so it appears someone "worked" on it. However after taking off the bell-housing, starter, and slave I found large quantities of dirt built up inside. The clutch and flywheel seem to have a decent amount of rust.
Stop screwing around and pull the whole clutch.

It's an amazingly simple process.
You are going to have to do it, from your description.

You need to get it out and apart on a bench to see what is and isn't new or old, good or bad, all that.

WSM covers it very well.

Many times, whoever works on it only puts 4 bolts back into the bell housing (leaves out the 2 that hide under the exhaust) so that dropping the BH is easier.
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Old 03-19-2017, 08:08 PM   #11
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three things: I bought the correct clutch master cylinder from Pelican and it did NOT need any mods.
-worked fine as is.
-forget the workshop manual's adjustment advice and do what works
-it IS possible to replace without cutting holes in your car (some blind work however)
-the blue hose thingy is over-stressed. I re-used the old one. after all it has zero pressure on it.
and can be changed later with little effort.
-
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Old 03-19-2017, 08:21 PM   #12
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Originally Posted by Hymodyne View Post
going to follow this thread closely. Proud owner of a 79 5 speed that came to me with the instructions, " it'll need a clutch. I just had both discs relined, and will be investigating the clutch system soon. I know I need a new slave cylinder and line.

James
James, where did you send your clutch discs to be relined? Cheers, John
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Old 03-19-2017, 08:25 PM   #13
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No worries, just pulled the intake plenum so it ain't going nowhere! Just trying to figure out my scope of work. Have two other project cars going on so was hoping this car would be a relatively quick mechanical fix but nothing is ever so simple! Cheers, John

Quote:
Originally Posted by Hacker-Pschorr View Post
Remember, it's only "not grinding" into 2nd and other gears due to the synchros covering up the issue. The clutch has no idea what gear you are grabbing so it's grinding in all of them ( you just cannot hear it....yet). Driving the car "as is" you are prematurely wearing down what is left of the synchros.

Your scenario is the exact reason why so many 928's are for sale with comments listed like: "Grinds in 2nd, known issue with these cars". These clutches get a little wonky, some experts says that grinding is normal...... and people keep driving their cars.

This is why I parked my 78, other projects in the way and I don't want to risk damaging the transmission. I sorted out the hydraulics, discovered that was only half the problem and parked it. I'm fortunate that I have a fully functioning 79, that clutch will be moved to the 78 and I'm converting my 79 to a single disc. It's a track car and after much self debating, I've decided having a single disc in a track car is one less thing I'll have to potentially deal with on a track weekend.
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Old 03-19-2017, 09:45 PM   #14
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three things: I bought the correct clutch master cylinder from Pelican and it did NOT need any mods.
-worked fine as is.
It's a crap shoot, that is what makes it frustrating. That's why it's recommended to take apart and compare new to old just to be safe.

Quote:
Originally Posted by upstate bob View Post
-the blue hose thingy is over-stressed. I re-used the old one. after all it has zero pressure on it.
Changing the hose is cheap insurance, some have experienced the hose coming loose, draining the resivior.

I always put a clamp on both ends now, as seen in the thread I linked to above:
http://rennlist.com/forums/928-forum...he-fender.html

Changing just the hose in-situ is much easier in the 78-80 cars with the smaller brake booster.
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Old 03-19-2017, 10:21 PM   #15
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James, where did you send your clutch discs to be relined? Cheers, John
Tampa Clutch Supply. $70.00 per disc.
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