Petza914

Working on a dual plate clutch yesterday. When we took it out, found this rivet for the intermediate plate was broken apart and the assembly is a little loose where you can shake it and hear a rattle.



Since we didn't have a new intermediate plate to install, we had to put things back together with the one that has the rattle and the broken rivet.

The clutch worked before we took it apart with the worn friction discs, but I believe was slipping. Discs had no valleys between the trapezoid of friction material and were totally smooth.





However, after reassembly with full thickness friction discs, we moved the intermediate plate all the way back so it could self adjust forward and we adjusted the threaded rod at the pedal for no play then looser 1/4 turn and now the clutch won't fully disengage and with the car running can't shift into any gears.

Before we take things apart again is this likely a problem caused by the broken rivet on the intermediate plate where something is getting clocked under pressure and dragging or is there something else that would cause this. We don't want to take it apart again if we can't fix it until we have a new intermediate plate, but if it can be fixed with the current plate, may try that.

Thanks.

AirtekHVAC

I was there, and this is perplexing. Anyone have any ideas here?

drscottsmith

Ok - I'll add to this thread...first off though, a public thank you to Pete (Petza914, the OP) for helping so graciously with this project) and to Ron and Woody for giving up a Saturday to help as well. This is my car we are working on. After several hours of disassembly and struggling a bit with that pilot bearing, Ron needed to get back to Charlotte (3+ hour drive) and Woody as well, so Ron gave me a ride home (on the way). Pete stayed up until midnight (Out of his own good nature!) and got everything back together for testing.

I can't say enough about this board - and the great friends I have met and made since getting this car several years ago. So...where are we now?

Pete needed to get another car on the lift, so Woody and I went back yesterday with his car trailer (another huge thank you) and we brought the car back to Woody's house (he has a lift too). So it waits for me to get over there...

The rattling sound is still there - exactly the same as it was before disassembly, and the same sound is evident just by wiggling the Intermediate plate, so that is definitely an issue to address - in addition to what Pete is describing. Out will come the clutch pack again.

My thoughts are this. I am not sure the missing t-nut is causing the engagement/disengagement issues, but I am fairly convinced the outer ring on the IP should have no movement related to the inner part. It should be one solid assembly. I am concerned about the balance of the unit, so what would be the concern with drilling all 6 t-nuts out of the plate, and replacing them with a new t-nut with a hex head bolt or even a socket cap allen head bolt?

1. It does not appear that there would be any interference of the operation of the system with this set up protruding from the disc.
2. Use loctite on the t nuts
3. If the loctite DID happen to work loose, the t nuts could be retightened/replaced without removing the clutch pack - just rotating the engine.

The entire assembly seems to be in very good condition (except for the worn friction discs, trashed bearings (expeceted) and the sheared t-nut. No wear at all on the splines, and probably did not even need to replace the pressure plate itself.

As it sits right now, the car will move on its own. It will upshift (painfully) but downshifts are a no go. It will not go into any gear with the engine running. The clutch is dragging, but the car can be started in gear with the clutch in and it will move (in any gear). We have adjusted the pedal travel incrementally to try to adjust the amount of disc release to no avail. Pete rebled the system and we don't think that is the issue. The slave pushes the fork all the way back until it hits the bellhousing. The socket of the fork (with a new cup) is seated firmly on the ball.

Thoughts? - and thank you again all!

drscottsmith

Here is what I am thinking for repair...?

Petza914

Length of the barrel of the T-nut will need to be shorter than the total clamped width for this idea to work. Seems like those rivets were pretty long and probably is, but figured I should mention it. Scott, the broken rivet is in your box of parts we removed for a length reference.

For those catching up to try an help, here are photos that might show something useful.

Well, this one's not useful, but we did have a good time during our get-together. Woody, unfortunately, was the photographer, so not in the photo, but was in the ones we took at our pre-tech session breakfast at Cracker Barrel.


Me, Scott, & Ron getting started


Now, on with the task at hand


Broken T-Rivet




Old removed friction discs - flush hub side




Old removed friction discs - hub collar side




orientation of friction discs upon removal - collar side of hub toward pressure plate (new ones went back in the same way)




New Pilot Bearing Installed




New Clutch Assembly Reinstalled (see question on this photo at the end)




Pivot end looks to be fully seated



... and here's a video of the reinstalled clutch assembly with the play in the intermediate plate - https://photos.app.goo.gl/yXgzx3cyoLz538Bi7


Regarding the previously mentioned question - I remember reading something about there being two different versions of the torque arm - one with a flatter center section and one with a rounder center section. I don't recall what the proper one of these needed to be paired with to function correctly though - maybe the pressure plate (but maybe not). Can anyone tell from this picture if we've used a compatible pair of parts?

Also, see how far out the T-springs are in that same photo. Upon torqueing the clutch to flywheel bolts, the U-shaped spacers actually just fell out. On my previous clutch removal and reinstallations, I actually had to pry or knock them out, but the ones that came preinstalled in this pressure plate were very thin and the ones I normally use are much thicker, which could be the difference. With my thicker ones I can set the pressure plate essentially all the way down onto the intermediate plate pins when bolting things together. With these thinner ones, I could get the pressure plate located onto the pins, but it took tightening the 6 bolts to draw it fully down. I'm assuming this is because of the difference in thickness of the U-shims, but if not, does that provide any type of clue? If a photo of the two different sizes of shims would help, I can provide that too.

jcorenman

Pete, thanks for the additional info. I've been following and scratching my head, but clueless.

Yikes!! That's the starter-ring flopping back and forth??!! I've got a spare DD that I need to go look at, but I am struggling with what is flopping, and where the broken rivet came from. Do you have a picture of that?
What is the OD of that rivet? I don't think a M6 bolt and T-nut is going to be a suitable replacement for an 8mm rivet if that's what it is. Torque on an M6 is only 6 ft-lb or so, they are not very strong.

Can't tell from the pic. The only issue I am aware of is where the release-arm meets the flange on the release-bearing: If the release arm has a flat contact surface (which it appears to, here) then the bearing-flange needs to have rounded "nibs" at the point of contact. And vice-versa, if the arm has rounded nibs, then the release-bearing flange has flat nibs. One arrangement was earlier and the other later, I don't recall which but either works-- just not two flats or two rounded's.

That's likely just new discs-- the thicker the discs, the farther those "T" pieces stick out. The reason you need the U-spacers is to partially compress the pressure-plate, to allow the clutch assembly to be removed. With no spacers you can still unbolt the clutch assembly but you won't be able to get it out because the release-arm is trapped. If you got it in, then the spacer is thick enough. Just remember to tighten the clutch housing to flywheel incrementally, in a crisscross fashion. (Lots of engine-rotating, pull the spark plugs).

So why is the clutch dragging? It sounds like you have plenty of travel. Has the clutch master cylinder been replaced at some point? Currently-available masters have less travel than earlier ones, fine for the single-disc but not enough for the dual's. There is a thread here (Stan's I think, MrMerlin) on how to shorten the piston-rod for more travel. But if the release-arm is hitting the bellhousing then that's not the issue...

Petza914

Thanks Jim,

I don't have a picture of Scott's part with the broken rivet but can show you a picture from when I did my clutch and you can see where it goes. It's one of those 6 rivets that hold the intermediate plate to the starter ring, but since it's loose and rattling, all of them appear to have worked loose to some extent, even though only one is broken. The other 5 should still hold things securely, which they're not.

Does a new intermediate plate come with a new starter ring or do those have to be put together. If the latter, will the bolt and T-nut idea work or is that going to create interference on one side or the other as that needs to rotate, or is there enough clearance in the rotational path?

Chris Lockhart

Some good info in this thread on Dual Disc clutches:

https://rennlist.com/forums/928-foru...plate-ers.html

Pete, I was using the wrong term yesterday regarding the T-nuts. I guess what I'm talking about is the three "H" clips that the intermediate plate should be moved to the middle of the fore and aft travel. It's something like 2 or 2.5mm in the WSM.

Bigfoot928

1st of all don't start it again. It all has to come back out. The broken rivet & the loose starter ring tells us all that the intermediate plate is the problem. More than one rivet has failed and will probably fall out or pop out on removal. Was the rivet in the lower bell housing or did it come out when the clutch was removed?

Petza914

Chris, that is a great thread. Wish I had seen it yesterday while Scott's car was still on the lift.

Based on the info in it, I believe his intermediate plate is set too far toward the front and that it's the front friction disc that's dragging since we seem to have plenty of travel on the shift rod (so much that you can make it hit the back of the bell housing. We can fix that part by adjusting the threaded rod that's part of the pedal assembly. I don't think the front disc is fully releasing and didn't fully understand the intermediate plate adjustment until reading through the first 30 or so entries in that thread with Mark's pictures. Did he ever write the separate thread with all the pics and the procedure he said he was going to do - if so, does someone have that link.

Woody & Scott, I'd say remove that lower bell housing and move those H-adjusters back a little bit so the front disc has more room to spin freely in. (in theory, you should be able to move them too far back and they should self adjust forward, but I think to be safe, I wouldn't move them further back then maybe a 1.2-1.5mm gap. Then adjust the threaded rod so the play is gone, then looser about 1/4 turn and I bet things start working.

I never had to make that adjustment on my clutches since my disc material is so tough (like a sintered metal) that it barely wore in the 5 years I've been driving it. I then put in new friction discs and because the intermediate plate was positioned far enough back, didn't run into the dragging clutch issue since the new discs must not have been much thicker than the old discs.

Sorry I wasn't familiar with this aspect when we were working on it over the weekend. I still think you need to address the rattling starter ring with a new intermediate plate and if that comes pre-adjusted, then none of this will matter and when that gets installed, it will work anyway.

jcorenman

OK, that makes sense. Except that the other rivets are not loose because one broke, but rather they were all loose and the weakest one broke. It can't have broken if the others were all tight.

New intermediate plates come with a new starter ring attached and balanced. I agree with Sterling, do not risk running the car until the intermediate plate gets replaced. The starter-ring is large and heavy and spins at engine speed, that's a lot of momentum. If it is loose then it is also certainly unbalanced, and a big piece of unbalanced steel (with teeth) spinning at a couple thousand RPM can do a LOT of damage.

For the same reason I would not trust M6 bolts and T-nuts. One of the useful things about rivets is that they expand as they get set, so that the two holes being joined are centered on each other. That preserves the balance. Nuts and bolts have clearance on the holes, and an M6 is not as strong as the rivet was.

On the H-adjusters: I've used the fixed-gap method with success. I made a bent U-shaped "feeler gauge" from some welding rod and filed the tips to 0.7mm thick, and used that to check the gap on both ends of the "H"-- that worked out to be approximately centered for our (relatively new) intermediate plate. And it seems to stay in adjustment pretty well but I do have to get in and re-fiddle occasionally (every 10-20K miles).

drscottsmith

Ok great advice and thanks all. I think we are all in agreement that the clutch pack is going to have to come back out to address the intermediate plate.

The only reason I posted those pictures of the t-nut and bolt was just for the style of fastener...I would want to use a t-nut whose outside diameter fit snugly in the hole, and an appropriate bolt for that t-nut. It would probably be an M8 I'm thinking. I do understand a rivet would be stronger. Will assess more and post some more pics when I take it back out.

I wish I knew when or what caused the t-nut to shear off. It only fell out when we pulled the clutch pack out (and we originally thought that might be the rattling). I had the bottom bellhousing off once before and it did not come out.

drscottsmith

Ok - in doing some additional research, I came across this thread:

​​​​​​https://rennlist.com/forums/928-foru...ate-plate.html

Apparently the early 1978-79 intermediate plates had a bolt-on ring gear with hex-head bolts that fit into threaded holes in the ring gear itself. Obviously there was a reason that a change was made to the later riveted/pinned design for some reason, but it leads me to believe that a bolt on solution may not be quite so far fetched. I do not race or track the car.

Any other thoughts?

GregBBRD

Whoever put this together, last time, missed one of the most important details (that the WSM assumes people are smart enough to know)....the splines of the clutch discs and the clutch shaft must have high pressure grease on them. See all that red rust inside the splines, which has migrated out and is slung all over the clutch discs? That red rust is caused by metal wearing off of the clutch disc splines and the clutch shaft. Later in this thread, it is mentioned that the clutch shaft shaft is perfect.
It's not...not with all that rust!

Buy a tube of the correct factory lubricant (it's the only lube, I've found, that will cling and stay on the splines) Part #000 043 305 73. Use it on the splines, on the end of the shaft that goes into the pilot bearing, and under the washer (the special thick washer that pulls on the pressure plate) on the T/O bearing.

Remember, if the splines in the discs can not freely move on the clutch shaft (from lack of lubrication or from wear on the shaft), the clutch will never release consistently!

And don't drive the car if the clutch doesn't release, completely! That will absolutely kill the synchros in a very short period of time! These dual disc clutches, not releasing properly, is why the synchros are always bad in the early transmissions. These cars all worked great and there was no issue, until some idiot replaced the clutch, the first time. 500 miles later, the transmissions were grinding when shifting!!!!

When you are done, with the car in neutral and running, you should have someone under the car, watching the torque tube shaft, while someone depresses the clutch. The shaft MUST stop spinning in a couple of seconds after depressing the clutch.

Do not drive the car until this is true!

islaTurbine

Where do you plan to find a new intermediate plate?...