clutch / gear grinding / ugly sounds

[andrew]

My '70 SIIA 88" was working just fine...yesterday.

This morning it was shifting only with some effort into 3rd and then once or twice did not want to go into 3rd at all. Then, it on occasion from a stop would not want to go to 1st (or 2nd) -- the gears were spinning quite fast it seemed and there was no way to get it synced up and into gear without grinding off all the teeth (or so it would seem, I of course did not force it). I actually had to shut the truck off, shift into gear when it was stopped, and then start the truck up again to get away from a dead stop. I drove home this way (3rd seemed to work for the most part), though at one stop sign things worked fine, but then back to grinding again. So, it would seem that the clutch is not disengaging the clutch plate/pressure plate from the flywheel, for whatever reason (seems to me...). I suppose the problem could be with the throwout bearing, slave/master cylinders, or something else. Thankfully (or sadly), I'm not a clutch expert by any stretch, yet...but I'm thinking I will need to be soon.

By the way, double-clutching did not help.

Did my clutch or the components mentioned above just go bad? Does that happen so suddenly? The sudden and intermittent nature of the problem confuses me (but it's not intermittent now...just does not want to get into gear without grinding like hell). Where should I start, with the logic of looking into the simplest/cheapest/most likely culprits first? Other thoughts and ways to diagnose/fix?

Thanks for any help...much appreciated.

[lumpydog]

Sounds like your clutch is no longer disengaging... hydraulics? Mechanical linkage? ]

Take a look from underneath while someone pushes the clutch - check the slave cylinder rod and linkage. Is the slave actuating the linkage?

[andrew]

Yes, the slave cylinder is actuating the linkage ("late type" clutch mechanism by the way). I'm not sure what's normal but the arm/linkage moves down only a small amount (maybe 1") when the pedal is pressed and in turn rotates the shaft/rod (ok, the "operating lever", I looked it up) that presumably connects to the clutch plate. This shaft/rod/lever rotates maybe 30 degrees or so when the pedal is depressed.

Also, the slave cylinder has some play in it (that is, I can move the rod in and out of the slave cylinder a good bit before there is purchase or resistance). Again, not sure what's normal here.

[lumpydog]

An inch(ish) of travel is right. Your last paragraph is not right tough- it sounds like there is no load on the slave rod at rest - you can push the rod into the cylinder with some force but, it should not move freely after the clutch is actuated - rather, the rod should sit firmly in place. A few thoughts:

1) The tube that extends into the bell housing, through a rubber grommet, has two clevis pins going through it. Those pins can fall out or break. This would make it look like the linkage was working but there would be no transfer of that movement to the throwout linkage.

2) The pressure plate diaphragm may be damagaged - less likely.

What I'm getting at is that the slave's pushrod should not have play like that, so it has me thinking that the linkage is not allowing the clutch diapragm spring to push/return the slave's pushrod into the cylinder leaving it under slight load. Which would mean the linkage connection is lost at some point. Or the spring diaphragm has failed. You could pull the floor/tuneless cover and observe diapragm engagement through the bell housing's top inspection port...

[andrew]

Thanks for the ideas. Some additional info and a question:

The play in the slave rod is when the pedal is not being pushed. I don't think I tried it when the pedal was depressed so don't know if it has play in it then too.

Which side of the tube has the clevis pins in it that I need to check? The side that is exposed from beneath the truck connecting to the slave or the inaccessible side in the bell housing?

[lumpydog]

Thanks for the ideas. Some additional info and a question:

The play in the slave rod is when the pedal is not being pushed. I don't think I tried it when the pedal was depressed so don't know if it has play in it then too.

Which side of the tube has the clevis pins in it that I need to check? The side that is exposed from beneath the truck connecting to the slave or the inaccessible side in the bell housing?

There should be no free movement in the Slave push rod at rest. It should be firmly in place between the piston and the arm.

The pins are in red, in the image below and are accessible externally - without cracking open the bell housing. The pins can appear to be fine externally but in fact be sheared...

https://goo.gl/photos/pkcP732KbhA7VPnH9

[andrew]

Thanks for the continued help.

The clevis pins don't seem to be broken but I did not yet pull them to verify. Because the slave cylinder seems to have been leaking, and given your comments about the loose play in it, my next step will be to replace it, along with the clevis pins just in case since I'll have the floor/tunnel removed anyway which should make the process easier. Any tips on slave replacement are welcome but it seems straightforward.

I can't get to this for a bit but I'll report back for the benefit of people in the future who might read this thread.

Of course if anyone has any ideas or other thoughts in the meantime please let me know.

Thanks again.

[lumpydog]

The slave leaking is new info... It's certainly possible that this is a hydraulic issue (as mentioned). Swapping the slave is a breeze with the tunnel cover removed. I've done it with the tunnel cover in place and that's a little harder.

If you replace the clevis pins - make sure they are "hardened" so they don't wear/sheer easily.

[andrew]

The slave leaking is new info... It's certainly possible that this is a hydraulic issue (as mentioned).

It was news to me too, when I finally got the firmly-stuck-in-place clutch master cylinder cap off to look (after taking the hood off to get to it better), which I had not done in many years. The reservoir was very low. I did notice fluid on the slave when I was under there before, but there's no shortage of fluid under there from any number of sources on any given day...

And, I did order the hardened clevis pins, thanks.

[lumpydog]

It was news to me too, when I finally got the firmly-stuck-in-place clutch master cylinder cap off to look (after taking the hood off to get to it better), which I had not done in many years. The reservoir was very low. I did notice fluid on the slave when I was under there before, but there's no shortage of fluid under there from any number of sources on any given day...

And, I did order the hardened clevis pins, thanks.

Nice work Andrew - let us know what you find!