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Reverse grinds Clutch or Shift linkage?

panterrorpanterrorMy 74 GTS
OK guys, I just need to make sure I’m thinking straight here. All opinions welcome.

I started out with shift linkage that had slipped but I’m pretty sure I have that properly sorted. I been through the various alignment procedures outlined here and elsewhere several times. The shifter is centered in the gate and straight in line with the 2nd and 3rd slots in the gate when in neutral, and the selector shaft in neutral position. It will easily slip into all gears with the engine not running (even the non-synch’d reverse). Initially, before the car has been driven, it will shift into every gear smoothly with the engine running and runs through the gears real nice. However, after some driving, I can’t get it into reverse. It grinds as if the clutch isn’t disengaged. At the same time, it will still slip in and out of all the other (synchronized) gears very nicely while at rest or driving. If I shut the engine down, I can still easily slip it into reverse. If I start the car with the clutch disengaged and the ZF in reverse, there is not even a hint of clutch hanging up and there is normal travel of the clutch pedal before I feel the friction point of the clutch in reverse. If I let the car sit and cool off, all is well and proper until I get it heated up and then the symptom repeats.

Why not just start the car in reverse when it’s hot you ask? Well, I’d prefer not to have to shut down to grab reverse and also am not too crazy about having the crank loaded against the thrust bearing by (heavy) clutch force before I have oil pressure.

I have a dual disc clutch (see picture below) and I suspect it’s the culprit. It holds like a vice but I’m thinking that the floater plate and the two friction discs may be floating around a bit on the input shaft when the clutch is disengaged causing a little communication with the flywheel, floater, and pressure plate when I get everything good and hot. On the other hand, perhaps the floater plate grows when it gets hot and doesn’t float or hangs up a bit on it’s three guide bushings.

I have a long throw slave and I have ample stroke, a good 7/8”+ or so. I’ve removed the inspection cover and had a look with it running but still cold and it looks like the friction plates are fairly static, but it’s sort of hard to say. There’s lot’s of pressure plate stroke, that’s for certain. I see most of the clearance between the pressure plate and second disc, that’s why I sort of suspect the floater plate isn’t floating well when hot. -I need to do this with everything heated up when reverse want’s to grind.

I read in another post here about the possibility of the pilot bushing causing the similar problems. It seems plausible but I sort of doubt it in this case.

Am I missing something here? Any thoughts?

Kelly

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panterrorpanterrorMy 74 GTS
quote:
(Kelly you need to measure the clearance with a feeler gauge at full travel, hot.
Since you went to a dual disc, now you need .035" for each disc.


Yah-but IMO, that's a bit more nebulous with multiple disc clutches. I definitely need to have another look at it while hot, but there was so much stroke at the slave, and so much separation at the pressure plate while cold, I discounted the amount of stroke as being a problem. Visually, there could easily be 3-4 times that much clearance. Problem is nothing positively extracts the discs and floaters from the flywheel. They just have to float on the input shaft splines and although you can see the stack relax when the clutch is disengaged, the gap is just between the last disc and the pressure plate. I figure, if the floater plate hangs up a bit on the guides, or the discs on the input shaft splines, the gap measure is not very meaningful. I figure I need to have someone disengage the clucth while hot, and then shut the engine down while keeping the clutch disengaged so I can have a look at where the pieces in the clutch stack land.

quote:
Sorry, gotta' get outta here before they all come and kill me again)


Have you been misbehaving?
E edmguru (Guest)
you may have a situation where everything is good when cold but as they warm up and the metal expands, even a few tenths or thousandths, the floater is not as free to travel. That may go against common thought that a hole gets larger when heated, but it may not be growing as much as the shaft. But, hey, I'm just an old guy who mumbles alot.
hope you get it worked out.
Glenn
panterrorpanterrorMy 74 GTS
Yup Glenn,

I'm right there mumbling with you. Mostly under my breath and things I can't post in open forum Mad but I'll get'er sorted. Your comment is pretty much what I suspect at the moment.

The flywheel is aluminum. The floater isn't. Must be a hardened steel. The floater guide bushings are mounted on the aluminum flywheel near the outer circumference and the location of the centers will change as the flywheel grows. The floater doesn't have a lot of places to get rid of heat and is contacted on both sides by friction discs where as the flywheel and pressure plate only see contact on one side. The flywheel and floater will expand at different rates due to the dissimilar materials and different heating. It may come down to whether there is sufficient clearance in the guide bushings for the floater.

I hope I'm overthinking this a bit and it turns out to be something else, because I'm not too enthused at the prospects of having to pull the clutch and open oup the clearance on the floater plate bushing holes.

Kelly
Last edited by panterror
zr1panterazr1panteraForum Sponsor - SACC Restorations
Since you said that you can easily select all forward gears when hot, have you tried putting it in first then quickly selecting reverse.

When my clutch was hanging up this would work for me. I couldn't select reverse without going into first and then quickly selecting reverse. Or like you said. I would start it in reverse.

In my case, a long throw slave fixed the problem...
panterrorpanterrorMy 74 GTS
quote:
Since you said that you can easily select all forward gears when hot, have you tried putting it in first then quickly selecting reverse.


Yup. I've tried going to reverse from all gears. Same result when hot. Enough of a grind that I'm sufficiently discouraged from even thinking about jamming it into reverse.

quote:
When my clutch was hanging up this would work for me. I couldn't select reverse without going into first and then quickly selecting reverse.


That works well for me when it's cold or when the engine isn't running. I think engaging it in one of the synch'd gears bumps the cluster enough that you can get the non-synch'd reverse in mesh and then it slides right in.

quote:
Or like you said. I would start it in reverse.


It's my only option at the moment, but as I said, I'm not at ease with starting with the crank loaded against the thrust bearing. Maybe that's not a big deal? However, having to shut down to grab reverse is objectionable.

quote:
In my case, a long throw slave fixed the problem...


I have a long throw slave and ample stroke. I agree they're a good idea Though they tend to increase the required pedal force a bit, they're well worth it.

Thanks for the post.

Kelly
Last edited by panterror
panteradougpanteradougMember
I guess that I am somewhat safe if I qualify my answer as saying that it is my opinion that...

Yes I would think that the clearances would have to be measured when it is hot or when the unit is malfunctioning.
I may be spelling it wrong but the term is Dercel or Marcel or Duracell or Marcel Merso.
One of them gotta be right...too much crap in my head. I gotta put stuff back where it belongs. My mother was right. I hope it isn't going to be a written test. I need multiple choice.
That is the curvature of the spring-metal portion of the clutch disc at no load.
It is there to aid in releasing the disc from the face of the flywheel and reduce the chatter in a street clutch.
If the disc has none then it is a competition clutch and has different characteristics.
It sounds like your discs have none.

I would have to think that the non syncro gears, (limited to just the rear in the Pantera) would require more travel (clearance) to release.

My DN+5 loved to grind reverse. I learned to push it into 3rd gear before reverse and it had the tendancy of slowing down the spinning of the neutral shaft and alighning reverse (synchronizing it).

Try that in the Pantera first. Maybe it will save you a lot of needless grief?
Last edited by panteradoug
panterrorpanterrorMy 74 GTS
quote:
I may be spelling it wrong but the term is Dercel or Marcel or Duracell or Marcel Merso.
One of them gotta be right


Yup. It's Marcel

quote:
That is the curvature of the spring-metal portion of the clutch disc at no load. It is there to aid in releasing the disc from the face of the flywheel and reduce the chatter in a street clutch. If the disc has none then it is a competition clutch and has different characteristics. It sounds like your discs have none.


It does have Marcel. It's a version of the McLeod Street Twin. It actually has great hold and feel. It's not chattering at all, just hanging up slightly. I suspect the floater is hanging up just enough such that the Marcel can not completely overcome it? I drove it for a half hour the night before last and for the first time it was perfectly fine when I came home. No grind of any kind and I didn't change a thing other than it got driven a little easier than usual, so perhaps a little less heating. Being brand new, maybe it just needs a little breaking in, and I know how to do that. Big Grin

I'll keep you posted. I have to get a friend to come along so I can check it hot. Thanks for the input.

Kelly
Last edited by panterror
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