Clutch Fork, Master/Slave

[arizonajones]

I know there are some other versions of this topic out there, so I'll try to be concise with my question:

 

Background info:

-In the last week, shifting became rough - had to shift really slow to make sure I didn't feel teeth bumping each other.

I was going to dive into it tomorrow (and should have waited to drive it until then...) because today I pressed down on the clutch pedal and the slave cylinder popped apart. Piston cup shoved 90% out of the cylinder and the pushrod sticking way out. Squirts fluid with each clutch pump.

 

-It looked to me like the rod had been installed backwards so the dust cover didn't sit into its little notch. (maybe notable?) And compared to pictures I've seen of this installed, it seemed like this pushrod stuck out really far.

 

-I pulled the cylinder off. The fork was putting tons of pressure on it. As soon as I got it off, there was no pressure from the fork and now that I have put it all back together, the fork is very loose and not engaging with the pushrod.

 

-It looks like the spring holding the fork in place is fouled up and loose.

 

Main questions:

1- Can I/How do I remove and re-install the fork securely without dropping the trans?

 

2- Does this sound like a bad master, slave, system-needing-bled, clutch adjustment, or something bigger?

 

Thanks!

[datzenmike]

The fork fits into a pivot ball on the case. This little thing...

 

Take a look in side past the dust boot. The fork has a large hair clip shaped spring on the back side that grips the ball and holds the fork in place.

[wayno]

That you have been driving it without issues, and then slowly you start having issues is interesting, especially the rod becoming to short part.

We actually need more info, have you heard any noise from the front of the transmission lately(squealing, ect.), did the noise go away when you pressed in the clutch, did the pedal get hard to push at any point, did you have to start pushing the pedal all the way to the floor, or has it always been at the top or middle?

Is the fork going into the transmission bent?

Does the back of the fork hit the  transmission case when all the way back, or has it let any marks on the back of the hole in the case?

[arizonajones]

That you have been driving it without issues, and then slowly you start having issues is interesting, especially the rod becoming to short part.

We actually need more info, have you heard any noise from the front of the transmission lately(squealing, ect.), did the noise go away when you pressed in the clutch, did the pedal get hard to push at any point, did you have to start pushing the pedal all the way to the floor, or has it always been at the top or middle?

Is the fork going into the transmission bent?

Does the back of the fork hit the  transmission case when all the way back, or has it let any marks on the back of the hole in the case?

"have you heard any noise from the front of the transmission lately(squealing, ect.)"

--No squeeling that I have noticed. When the clutch pedal is engaged the 'spinning bearing' sound is louder than when it is in gear. FWIW

 

"did the noise go away when you pressed in the clutch?"

--the opposite. But not a squeel, maybe you could call it a hum?

 

"did the pedal get hard to push at any point, did you have to start pushing the pedal all the way to the floor, or has it always been at the top or middle?"

--the pedal never got harder to push, but I think I did start pushing it harder into the floor, when it started to feel like it wasn't shifting cleanly. FYI, the rod on the master cylinder was threaded as far out as it could be.

 

"Is the fork going into the transmission bent?"

--the fork looks straight, as far as I can tell

 

Does the back of the fork hit the  transmission case when all the way back, or has it let any marks on the back of the hole in the case?

--Not that I can see.

 

MORE Updates:

I've spent the last 2 days under the thing and here's what else I see:

 

--the fork retaining spring (the one that goes around the throwout bearing and hooks over the top of the forks) popped off. It may have only been 1/2 way connected in the first place.

--the other retaining spring (that connects the fork to the ball pivot) has pretty loose tension

 

Additional questions:

--is the ball pivot adjustable? would that make any difference?

--is there any way to put this assembly back together without dropping the transmission? (if there is, I am unaware)

 

Last question:

--If there is anyone in the Portland, OR area who would be willing to help me finish this repair job on Sunday Sep 1st, let me know. I can pay you some for your time/feed you and/or we could barter or something (I do carpentry and MIG welding.)

[wayno]

The fact that there is noise when you press the clutch in is bad, sounds like there is something up with the throwout bearing, and you are going to likely have to drop the transmission.

The arm/fork that goes in the case is not going to just get loose unless something actually breaks inside the case, or the arm gets bent, both require you to drop the transmission to fix, I suppose the fork ball could break, but I have never heard of that before, except when the front bearing explodes and breaks the front bearing cover, I have also heard of it getting loose when the front cover shaft that the throwout bearing rides on breaks, there just are not that many things on the outside of the tranny that can break and have that arm/fork get loose.

I am actually quite surprised that you were able to see that spring inside the case that holds the TB/collar on the fork, but even if it fell off, it will not make that rod looser.

I also don't recall the rod being adjustable on the 720 trucks, that was an early thing that was on the 521, and maybe some of the 620 trucks.

Where in portland are you located, I live in vancouver just off of 205 right after crossing the 205 bridge.

[datzenmike]

521s and 510 had the adjustable slave rod but also it fit into a hole on the end of the arm. Looks like this...

 

[arizonajones]

The fact that there is noise when you press the clutch in is bad, sounds like there is something up with the throwout bearing, and you are going to likely have to drop the transmission.

The arm/fork that goes in the case is not going to just get loose unless something actually breaks inside the case, or the arm gets bent, both require you to drop the transmission to fix, I suppose the fork ball could break, but I have never heard of that before, except when the front bearing explodes and breaks the front bearing cover, I have also heard of it getting loose when the front cover shaft that the throwout bearing rides on breaks, there just are not that many things on the outside of the tranny that can break and have that arm/fork get loose.

I am actually quite surprised that you were able to see that spring inside the case that holds the TB/collar on the fork, but even if it fell off, it will not make that rod looser.

I also don't recall the rod being adjustable on the 720 trucks, that was an early thing that was on the 521, and maybe some of the 620 trucks.

Where in portland are you located, I live in vancouver just off of 205 right after crossing the 205 bridge.

I live in SW PDX, but my truck is parked in front of my wood/metal shop in NW Industrial PDX. I could probably tow it in my work van w/ a tow rope, though...

[arizonajones]

UPDATE:

Dropped the transmission this weekend (did it totally solo, with the help of my handy Hazard Fraught transmission jack.)

Replaced the clutch, TO bearing, & pilot bushing. The clutch was actually in pretty good working order (looked it anyway) but I figured I'd replace it since I was already down there! The throwout bearing was toast - total loose mess. The pilot bushing was really worn out, too (interior worn into an elliptical shape.)

I put the original TO bearing hub and forks back into the system, as they didn't seem to have any damage. I adjusted both of the springs to make sure everything was nice and tight.

 

Put it all back together, and everything seems peachy-keen but I can't get the hydraulics to work properly! I had help bleeding the system for close to an hour so I feel like there shouldn't be anymore air bubbles. What's happening is: is gets bled and pressurized, then you press the pedal and the slave pushrod goes forward and you let off the pedal and the pedal springs back but the pushrod stays in place. If you push on the pedal enough times, you can shoot the pushrod right out of the cylinder. So the question is: to re-bleed the system? or buy a new slave or master-cylinder?

 

Any thoughts?

[wayno]

OK, the push rod should bottom out in the slave, then when you push by hand against the clutch arm away from the slave, the rod should just barely be lose, it should have about a 1/16 inch play.

If you can bottom out the slave, push against the arm and remove the rod, something is not right.

I would actually have to see this in person to tell you what I thought was wrong, it sounds like the rod is to short, but it was working, so this bothers me.

The 720 rods were not adjustable, and did not have a hole for the rod to go threw the arm, so if yours will go threw the rod like Datzenmikes photo below, then things have been changed, that is why I asked if the arm was hitting the back of the case hole when the clutch is pushed.

How long did you drive this before you started having issues?

Is the push rod threaded like the photo above?

Could have an extension have fell of the push rod if it is threaded, or did the push rod look broken on either end?

[arizonajones]

The pushrod is not the threaded style and it just sits into the little dimple on the fork.

The 1/16" of play when bottomed out is after you've bled and pressurized the system right?

I'll double-check but I'd say there is more than 1/16" of play when bottomed out. It's hard to say currently, though, because the rod won't return on the upstroke of the clutch pedal. The rod just keeps moving forward.

This might be a dumb question, but should there be tension in the clutch fork/TO bearing already,or is it the size of the pushrod and pressurized system that slides the TO bearing into the right spot to give it tension?

 

This truck is new to me so I haven't driven it much. I'd say the first 2 out of 10 trips it was shifting good then it felt like the clutch wasn't working right. On the last trip the slave cylinder popped apart.

[wayno]

There is no pressurization, you bleed it under pressure because you push the clutch down and bleed it.

What I mean about bottoming out the rod is, when the clutch is not being pressed down, , you grab the rod and push it in the slave till it will not go in any farther.

With the rod bottomed in the slave, it should only have a 1/16th inch play between the slave and the fork, and when you press on the clutch, it should move the fork towards the back, and when you let off the clutch pedal, it should be pushed back into the slave and have a 1/16th inch play again, a 1/16th inch play means just loose, as you don't want pressure on the TO bearing when not pushing on the clutch pedal.

The pushrod is not the threaded style and it just sits into the little dimple on the fork.

The 1/16" of play when bottomed out is after you've bled and pressurized the system right?

I'll double-check but I'd say there is more than 1/16" of play when bottomed out. It's hard to say currently, though, because the rod won't return on the upstroke of the clutch pedal. The rod just keeps moving forward.

This might be a dumb question, but should there be tension in the clutch fork/TO bearing already,or is it the size of the pushrod and pressurized system that slides the TO bearing into the right spot to give it tension?

 

This truck is new to me so I haven't driven it much. I'd say the first 2 out of 10 trips it was shifting good then it felt like the clutch wasn't working right. On the last trip the slave cylinder popped apart.

[arizonajones]

Okay. I just bought a little bleeder kit with a pressure gauge. I am going to re-bleed it tomorrow and see what happens. If it's still a fail, I'll start by buying a new slave cylinder and give it a shot. I kind of wish the 720 had the threaded rod and bolt-on fork connection instead of the rod/dimple setup -- it seems more secure & adjustable... anyway...

[wayno]

Without seeing it myself I cannot tell you for sure, but all it might need is a longer rod.

[arizonajones]

Okay, so I bought a new slave, which fit nicely right off the bat. I think the spring and the seals were shot on the previous slave. But... I installed it and bled the system and now I still can't get the pedal to move the slave. I ran a ton of brake fluid through the system, so I don't feel like I have trapped air. I was looking at other threads and noticed someone say if you watch the master cylinder reservoir when you press the pedal and the fluid bubbles up, the cylinder is bad. Is that accurate? That's what I saw on mine, so if that's true, I guess I need a new master...

 

Is there anything else to consider? If the slave is new and the system is bled, are there any other places to look for clues?

[wayno]

Okay, so I bought a new slave, which fit nicely right off the bat. I think the spring and the seals were shot on the previous slave. But... I installed it and bled the system and now I still can't get the pedal to move the slave. I ran a ton of brake fluid through the system, so I don't feel like I have trapped air. I was looking at other threads and noticed someone say if you watch the master cylinder reservoir when you press the pedal and the fluid bubbles up, the cylinder is bad. Is that accurate? That's what I saw on mine, so if that's true, I guess I need a new master...

 

Is there anything else to consider? If the slave is new and the system is bled, are there any other places to look for clues?

 

There is no spring inside a slave cylinder, if you found one inside the slave you removed, then someone that had no clue what they were doing has taken liberties with your truck systems.

In my opinion, if the clutch master worked before, it should work now, I suppose if someone adjusted the clutch pedal rod in, trying to get more throw/movement out of the slave, they could have adjusted it to the point where the seal could be bottoming out in the clutch master, that would destroy the seals in the master, but if that has been done, when you put a new master in, and leave the adjustment the same, it will just destroy the seals in the new master also.

How are you bleeding the system?

What you do is have someone pump the clutch pedal 4 or 5 times and hold to floor, then you open the bleeder screw on the slave and let the air out, then close the screw, then they can let up on the pedal, repeat several times till it moves the slave rod its full motion and you are only getting fuild out of the bleed screw.

If the rod between the clutch arm and slave is not the proper length, it's likely never going to work, also if someone has changed the clutch collar holding the throwout bearing, or put on a different style/size clutch cover/flywheel, but used the same throwout bearing collar, it will not likely work that way either.

The very fact that the piston was forced out of the hole in the first place sets off a lot of alarms, sounds like the rod is not long enough, which sets off more alarms, the angle that the arm comes out of the transmission case is also important, see how the arm is close to the slave in datzenmikes photo below, if yours is not that close, then it likely is not going to work properly.

I can come over and take a look at it this weekend, not saying I will be able to fix it, but I can likely tell you if it will work or not with what you have presently.

[arizonajones]

There is no spring inside a slave cylinder, if you found one inside the slave you removed, then someone that had no clue what they were doing has taken liberties with your truck systems.

In my opinion, if the clutch master worked before, it should work now, I suppose if someone adjusted the clutch pedal rod in, trying to get more throw/movement out of the slave, they could have adjusted it to the point where the seal could be bottoming out in the clutch master, that would destroy the seals in the master, but if that has been done, when you put a new master in, and leave the adjustment the same, it will just destroy the seals in the new master also.

How are you bleeding the system?

What you do is have someone pump the clutch pedal 4 or 5 times and hold to floor, then you open the bleeder screw on the slave and let the air out, then close the screw, then they can let up on the pedal, repeat several times till it moves the slave rod its full motion and you are only getting fuild out of the bleed screw.

If the rod between the clutch arm and slave is not the proper length, it's likely never going to work, also if someone has changed the clutch collar holding the throwout bearing, or put on a different style/size clutch cover/flywheel, but used the same throwout bearing collar, it will not likely work that way either.

The very fact that the piston was forced out of the hole in the first place sets off a lot of alarms, sounds like the rod is not long enough, which sets off more alarms, the angle that the arm comes out of the transmission case is also important, see how the arm is close to the slave in datzenmikes photo below, if yours is not that close, then it likely is not going to work properly.

I can come over and take a look at it this weekend, not saying I will be able to fix it, but I can likely tell you if it will work or not with what you have presently.

 

So I re-bled it again today. I did it the exact way you described, Wayno. Bled out about 1/2 a bottle of Dot3 to make sure there was no air in there. I saw the slave piston move maybe a 1/4" to 1/2". When I was confident we had no more air in the system, the piston was just making its first solid contact with the arm (not pushing it at all, though.)

 

If I bottom out the rod into the cylinder of the slave by pressing it all the way in, there is a lot of space (unfortunately I didn't measure yet and the truck isn't at my house...) but I would guess 1.5" of a gap. 

 

So, if I'm able to bleed the system and get some movement out of the slave, maybe the master's fine(?) Maybe the next move is to go buy a grade8 bolt and cut it into a pushrod that is approximately 1.5" longer than the stock pushrod.

 

Wayno, I'll send you a PM.

[arizonajones]

Wayno, I can't thank you enough for helping me get back on the road the other day! Let me know if you ever need a hand.

 

Unfortunately, though, the old 720 is not being very cooperative. We discovered that the TO bearing collar must be from a different vehicle because it is too short. We made a new pushrod to compensate for the difference, which got it going again, but it still shifts really rough. I've bled the system a couple times just to be sure but... When releasing the clutch pedal into gear, it goes into gear really quick in that pedal stroke. When shifting between gears, you can feel teeth against each other. Downshifting and reverse are especially ugly. 

 

So, just before I go try and find the perfect T.O. bearing collar + new fork and open up the bell housing again, are there any red flags to consider? Does it still seem reasonable that the right collar and pushrod combo are the answer? Are there any other (larger) transmission problems that this might indicate? I'm hoping not, but just wanting to think about a worst case scenario and make the most efficient plan...

[wayno]

I would have had to drive it to make any decision on if it drove funny, but it had a flat, and I thought I needed to leave, but I arrived a half hour early to my appointment, does it grind into all gears?

The forks are all the same, and guys, the rod was about 1 1/2" longer than the stock one, I checked the play at the slave with the new rod, it was good, the arm did not hit the back of the case when clutch pedal was depressed, the clutch grabbed fairly close to the floor, and there was a lot of play in the pedal at the top, the adjustment rod was all the way into the clutch master, it could not be adjusted any more to bring the pedal up(take play out of the pedal).

The arm/fork was not anywhere close to looking like datzenmikes photo above, it was a lot farther away from the slave.

 

I am not actually sure how it works for sure, but as I said, the clutch master pedal rod that goes into the clutch master was adjusted all the way into the master, no more adjustment was left in that direction, if you were to adjust it back out of the master(pulling the rod out of the clutch master when pedal is not depressed), it might give you more travel in the bore of the clutch master, therefore moving the slave farther, you have a lot of play at the top of the pedal, do you understand what I am saying?

In my head I see backing that rod back out will possibly make it better, but maybe it will make it worse, I just don't know, I did think it was weird that the rod was adjusted that way.

I have a few collars over here, most of them are for 225mm clutch covers/discs, if you were to pull your tranny again, you could measure your collar, mine with the bearing installed is 2 1/16 inches, and I have extras of this size.

[arizonajones]

 

On the left is the collar that was in there. The one on the right is the one spec'd for this truck. Interesting right?!

 

Here's the catch, though. It's shifting slightly better, but not significantly. The clutch drag won't go away! It's at its worst in 1,2, 3, & R. Less-worse in 4 & 5. Double-clutching helps some...

 

At this point i'm thinking of getting a new hydraulic line and/or master. If it's not that, is there any reason to suspect multiple bad synchros?

[datzenmike]

In effect the synchro ring is a tiny clutch that drags against two different moving surfaces until they match speeds. Driving with the short collar has allowed the clutch to drag against the flywheel and PP surface. In turn the synchro rings have not only had to slow the inertia of the gears so they can mesh quietly, but also the whole motor!!!  4th and 5th are less used so likely not as worn.

 

R still grinds? Then the clutch is still rubbing

[wayno]

When you put it in gear and let out the pedal now, is it still grabbing an inch off the floor with the proper collar?

How much play is there between the slave rod and the fork now?

You go back to the original rod?

[arizonajones]

In effect the synchro ring is a tiny clutch that drags against two different moving surfaces until they match speeds. Driving with the short collar has allowed the clutch to drag against the flywheel and PP surface. In turn the synchro rings have not only had to slow the inertia of the gears so they can mesh quietly, but also the whole motor!!!  4th and 5th are less used so likely not as worn.

 

R still grinds? Then the clutch is still rubbing

 

So, just to make sure I understand totally, you're saying it's most likely synchros that have been trashed because of this collar?

 

When you put it in gear and let out the pedal now, is it still grabbing an inch off the floor with the proper collar?

How much play is there between the slave rod and the fork now?

You go back to the original rod?

-It's still grabbing pretty quick. I don't know the exact measurements yet.

-I went back to the original rod and there was a little more than a 1/4" of play with the slave bottomed out, so I made a new pushrod about 1/4" longer than stock. The new collar made everything fit waay better, but the pedal action still doesn't do that much.

 

I noticed some drops of Dot3 around the connection between the last hydraulic line connection before the slave. I tightened it, and bled the clutch a couple times with no noticeable results.

 

I need to measure pushrod travel one more time and double check, but if it's still good, my list is:

-Bad master?

-Cracked hydraulic line?

-Bad synchros?

 

Anything else you think I should consider?