SM465 / Clutch

[Designo614]

So, my new to me 1988 1 ton with a Holmes wrecker body on her, and shifting issues continue. Here's what it's doing, and here's what I've done so far:

At rest, you can put it in any gear, however once moving, when it's time to upshift the stick doesn't move, like it's locked in place. Not grinding, just won't move. Once at rest again, it'll go anywhere. It also whined a lot so I determined my first course of action should be to change out the gear oil. Did that with a gallon of Sta-Lube 85-90 GL-4 Gear Oil. Turns out, I presume because I have a PTO attached on one side, that a gallon isn't enough, took about another quart, but now it's full to the bottom of the side fill hole. Removed shifter in order to fill from top, then learned the lesson on how to align the forks to reinsert. Test drive, same results.

So I inspected the clutch master and slave assemblies; turns out the pushrod going into the master had broken and the sharp edge had gouged up the backside pretty badly; and the flex portion of the line between master and slave was badly cracked at the hairpin turn. No leaks detected, but decided based on condition I would fully replace the whole assembly; did that, got it bled, and it seems that I am getting the pedal pressure and the travel needed to work properly. Slave cylinder travel is about 1", does that sound about right? Anyway, test drive, same result.

So, now I'm thinking that despite the new master & slave cylinders, perhaps the shifter is refusing to shift because the clutch is still not fully disengaging somehow, so I'm thinking I need to inspect it.

So, youtube suggests the way to replace a clutch on these is to remove shifter handle up top, remove driveshaft, support the tranny with a jack, remove the crossmember then remove bolts and slide the tranny back on the jack. Can this be done safely by myself, or do I need someone else there at least to call the medics when I drop it on my chest? Can someone point me to a good video or write-up about that?

One other thing, I understand that these can be hard to shift when the PTO is engaged; my PTO drives a hydraulic pump to feed the wrecker boom and wheel lift, and it has a plunger type-cable driven button on the floor to engage and disengage, however my wrecker hydraulics work no matter which position it's in. Could this be the source of the problem, rather than the clutch?

And, what else am I missing here? Sorry for the long post-

 

[hoagster]

As far as getting it out it is a heavy sob! I took mine out with the transfer case still installed using a floor jack and a cheap Harbor Freight transmission jack. Did it by myself but I wouldn't recommend it. Even with both items the combined weight smashed the transmission jack.

I don't have an answer for why, but there are some on here that have rebuilt their SM465's.

 

[PrairieDrifter]

Your pto shouldn't be running while going down the road. So that could be an issue, also i think you should have a little more than an inch of travel on the slave cylinder.

As for a rebuild for 465's it's just bearings and synchros lol, then sometimes little things that need to be fixed. Maybe a reverse gear like mine, because people are impatient lol.

I would say synchros or clutch disengagement first, but since you say no grinding I wanna say it's the pto. That would be your easiest option right now as well.

 

[Redfish]

The PTO should disengage with the floor plunger. I would crawl under the truck and make sure that the external linkage is moving with the push/pull cable. If it is you have issues inside the PTO and/or the transfer case.

I just crawled under my '87 while my son actuated the clutch for me. The end of the arm is moving EXACTLY 1 inch. I took a pic of it but couldn't get the camera exactly straight with one hand and hold the tape with the other hand. You can take my word for it. From fully pressed to fully released is 1 inch on the nose.

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[Juggernaut]

The clutch wouldn't be the problem. I once drove my truck home from a day of four wheeling without a clutch when the clutch rod broke. It's just a matter of getting the RPM right and jamming it in gear. I would try removing the PTO and see if that corrects the problem. Hopefully you have a spare cover

 

[Designo614]

Thanks. I feel better about the slave cylinder travel now, i appreciate you verifying on yours. I verified that the plunger does move the PTO cable which moves a lever on the side of the PTO, but of course I don't know what's actually happening inside.

And I don't have a spare plate cover, however since it's a wrecker it's always going to have a PTO pump there. What I plan to do now is drain the gearbox again and pull the PTO off, and see if there's some mechanical damage in there. I assume that moving the lever rotates the main PTO gear in to mesh with one in the tranny itself, so I guess I'll be able to see if moving the lever actuates anything. Since my wrecker hydraulics work all the time, I guess it would have to be stuck meshed all the time, which would be why I can't shift-

 

[Turbo4whl]

You will find that there are two problems. Yes your PTO should disengage. That is one problem. Your clutch is also not disengaging, bigger problem.

Some facts: The input shaft of the trans always spins when the clutch is engaged. The gear on the input shaft is always driving the counter shaft. The PTO gear also is driven by the counter shaft. So if you can not disengage the clutch, you can not stop the counter shaft from spinning. Can't shift into gear.

@Juggernaut is right, you can drive the truck without disengaging the clutch. Jamming the shifter into first gear is rough on the trans, but you can. Then up shift relying on the synchronizers to match the next gear to line up and shift.

Did you install new clutch parts? Miss matched parts? If the clutch parts are old and one of the three levers on the pressure plate failed, the clutch will not disengage. An old disc can also fail if the lining starts to come apart, then the disc gets wider and will not release.

 

[Designo614]

Turbo4whl, thanks. I haven't installed any clutch parts other than the master and slave cylinders, and I don't know how old or worn any of the rest is. I actually have begun to think the clutch is probably OK, because I can shift into and start from a dead stop in granny, 1 or 2, it just won't upshift from any of them once moving. I figure if the clutch wasn't fully disengaging, the truck would be lurching before letting it out, but that doesn't happen. I will attempt to remove and inspect the PTO first; if it's not disengaging like it should then I'll know it needs to be repaired/replaced no matter what. At the least, I can move it to where it's disengaged, leave it there and re-assemble and test drive then without touching it.