Really confused about my '78 620 clutch :(

[Erik765]

Hello all!

 

I just picked up a '78 620 as a project. The clutch had no resistance to it and did not work at all and I can press the brake pedal to the floor and rotate the front tires with my hands when it's jacked up (different topic)!

 

Other than that, it starts right away and runs really well. I just need to get it fixed so the wife will stop wondering what the heck I was thinking!

 

Anyway, I went down and grabbed a master and slave (control) cylinder and replaced them both, had the wife help me bleed and (here's the super-confusing part) there's no air in the lines (even pushed back the slave and had her watch the master reservoir), but the clutch still doesn't work. There's basically no resistance at all (unless they're just really light and I've never had a Datsun before).

 

I found a good manual (looks like the official repair manual) and have browsed for an answer to no avail. (See attachment for reference).

 

 

The part I'm not quite sure about, and my main question is- the pin in the slave (control) cylinder is pushed as far out as it should normally go, but the withdrawal lever that the pin pushes doesn't push the pin back into the slave cylinder when the pedal is released... Is this normal? (I hope so, so I don't have a clutch to replace too). I can manually push the control lever on the side of the transmission back but, even w/o the clutch pedal depressed, when I let go it just goes back by itself.

 

So, basically, I'm at a fully new hydraulic system (minus the lines) and still don't have a working system. The level in the reservoir is still at the same since bleeding (no leaks that I can tell). Is it possible the clutch cover isn't pulling off the clutch disc? Is it supposed to? I'm really lost here ;(

 

Thanks in advance for the help and for looking it over!!

[Zeusimo]

I Hear Crickets... :lol:

Where's Datzenmike?

[oldskoolvws]

Sounds to me like a bad pressure plate. The pressure plate returns the arm back to push back the pin into the slave. There's a slim chance that it could also be any one of the components in between the slave and the pressure plate, but either way, a trans drop is in order.

[datzenmike]

Clutch

To speed up the bleeding process a new master can be bench bled on the vehicle. Get a short length of suitable brake line and attach one end to the master output. Bend the other end up over and into the reservoir. Begin pumping the peddle. Fluid will be circulated without waste and the trapped air bubbles separated out. This could take 20 to 30 pumps to fully expel all the foamy air bubbles. Connect up the line to the slave and...

Pump several times and hold the clutch peddle down. Open the slave bleeder screw and let out any pressurized fluid and air bubbles. Close bleeder. Keep reservoir full at all times. Continue bleeding until 4 or 5 attempts in a row produce fluid only without air bubbles. Depress peddle and the slave push rod should move indicating the clutch is working.

[Erik765]

Thanks much for your replies. I'll definitely start with the extended bleeding. I'm thinking there may have to be air still due to the fact that the slave push rod pretty much just stays out the whole time regardless of if you push the pedal down (like it's expecting something to push it back once you let the pedal up).

 

Will try a little later and keep y'all posted!

 

 

[HRH]

The other option should bleeding fail is the clutch master seals have deteriorated/rolled, and when you push the plunger, it recycles in on itself, not providing any pressure. I'd lean toward bleeding though.

[datzenmike]

When you replaced the master, there was a push rod connecting the peddle to it, right. Being as you just bought it there could be missing parts. ?

 

Also some 'new' parts are bad in the box.

[Erik765]

Yes, there was the push rod that connected to the pedal. I did have a little trouble getting it connected and had to move it quite a bit without and brake fluid it the cylinder. Could I have ruined it you suppose?

 

Also, one thing I'd like to know for sure is why the push rod on the slave is always extended all the way out regardless of what you do with the clutch pedal (like it's expecting or needing to be pushed back in by something). Does the clutch cover plate push it back when you start the engine? If it's always all the way out, where is all the brake fluid going when I press the clutch pedal? (confused on that one).

 

I'm on my way to Napa to pick up some bleeder valves and will definitely re-bleed and start with the master like datzenmike suggested.

 

God I hope I don't have to drop the tranny. I can do quite a bit on my own, but in no way have the means of doing that one solo in my little garage ;(

 

I'll let you know how it goes after the re-bleed.

 

Thanks again for all the input.

 

 

[Erik765]

OK, so I got a short brake line and bent it around to flow back into the reservoir and bled that out. Didn't seem to be any bubbles in there, etc. and it pushed the liquid just as I expected it to. Hooked the main line back up, bled the whole system again and the push rod on the slave (control) cylinder still stays out as far as it goes (as far as the withdrawal lever allows it to) when the clutch pedal is let up again.

 

What I've tried so far to narrow this down a bit is pushing the withdrawal lever back into the slave cylinder manually while I have my wife push the clutch pedal. When she does, the hydraulics all seem to work as intended and the push rod comes out and goes as far as it can.

 

I've pushed the push rod back into the slave leaving the withdrawal lever alone and then moved the withdrawal lever back and forth as far as it will go either way. It certainly has no resistance to push either way on its own without the rod up against it.

 

The part that still baffles me is if you push the clutch pedal down, and then let it back up and the slave cylinder rod stays all the way out (which would draw more dot 3 into the system from the reservoir), then if you push the clutch pedal back down again and nothing is moving (rod is still all the way out) where in the world is that dot 3 going? If I'm thinking correctly, I should not be able to push the pedal down if the rods all the way out pushed up against the withdrawal lever. Unless I didn't pay attention in physics class, that one is baffling me to no end.

 

So, all in all, I think Oldskoolvws may be right on this one. Sounds like a clutch, or its withdrawal lever (not the hydraulics). Anyone disagree? If so, please do! Looks like I'm gonna have to pay the shop now and have it towed there (unless you guys can save me here with something I'm missing maybe) :(

 

Whatya think DatzenMike? Anyone?

 

Thanks again in advance.

 

 

 

 

btw, noticed a few guys from Spokane here. Must be a good datsun group in the area. Glad to join it, just hope I can get mine going now!

 

 

 

[datzenmike]

 

The part that still baffles me is if you push the clutch pedal down, and then let it back up and the slave cylinder rod stays all the way out (which would draw more dot 3 into the system from the reservoir), then if you push the clutch pedal back down again and nothing is moving (rod is still all the way out) where in the world is that dot 3 going? If I'm thinking correctly, I should not be able to push the pedal down if the rods all the way out pushed up against the withdrawal lever. Unless I didn't pay attention in physics class, that one is baffling me to no end.

 

Thanks again in advance.

 

btw, noticed a few guys from Spokane here. Must be a good datsun group in the area. Glad to join it, just hope I can get mine going now!

 

 

 

First, is there a 1/16" play in the clutch peddle? Just push down lightly with your thumb on it and it should move slightly against the peddle return spring before any resistance is felt from the spring in the master. The push rod up under the dash can be adjusted.

 

Do you have any history on this vehicle. Was it running before you got it?

 

 

Yes as you describe it, that's impossible.

 

So the fluid may move if there is no load or resistance... like bleeding, but when trying to move the pressure plate, it backs up and leaks back into the reservoir. If it were working the push rod would move or there would be a hydraulic lock and the peddle would not move. I hesitate to suggest a new master but this may be the only other thing to try. Be sure to bench bleed on the car before bleeding the slave. Up to you but if the master is bad a mechanic will charge more to change it for you.

[Zeusimo]

A Quick Way To Check If Master Is Bad Is To Take Lid Off And Push Clutch Pedal In And Out

The Fluid In The Resivour Should Not Move At All If You Get Gushing, Squirting Ect... It Is Bad

 

When I Replaced My Hydraulics I Had To Take My New Master Apart, Put It Back Together And Try Again And It Worked :lol:

[Erik765]

OK. I tried what you said Zeusimo, with the cap off and me pushing the pedal down, there is no noise at all and the fluid in the reservoir doesn't move in the least.

 

There is a little play in the pedal, yes.

 

One thing I have failed to mention, which trumps all else here is that no matter where the withdrawal lever is (if I move it manually, etc.) the truck will not go into gear while it's running. It's not like the rod from the slave pushing the lever all the time means it simply goes into gear. It won't go into gear unless the truck is off, no matter where the lever is.

 

I was told when I bought it that the clutch was iffy and simply needed a slave cylinder (guessing because 'slave' sounds less-expensive to replace than a 'master'...) I thought, oh, that's easy. I can have it goin in no time... yeah... no. Guessing the guy who brought it to me started it in gear (which is currently the only way to move in the truck, then shifted w/o the clutch. It's about a 20 minute drive (in a running car) with about 30 stop lights up and down big hills from where he brought it, to my place. No wonder he was like an hour later than he said he'd be...

 

Problem is, I was working and hardly had any time on a break when he got to my place. I took him for his word, did the deal and off he went (to catch the bus home).

 

So, in other words, I think the hydraulics are in working order, I could even pull off both cylinders and put a line between them to test the operation, but don't really see the need at this point since I'm 99% sure they are not the problem here.

 

I only paid $500 for the rig and the motor runs great, starts immediately, etc. I replaced the cap, wires, plugs, oil and filters and will tune the carb a little as needed, but I still feel pretty bummed (at myself mostly) at this point, lol.

 

 

 

 

Anyone got a rough idea how much I would end up having to pay someone to replace the clutch?

 

Ugh... my little project truck isn't so much fun at the moment any more but I know these things are super cool once up and running so I don't wanna just junk it.

 

Thanks again in advance.

 

 

[banzai510(hainz)]

HRH lives in Spokane he can help you.

 

this is not hard.

Bleed the sytem and make sure the clutch lever(fork) is fully FWD.

 

look under there if the push rod on slave is not pushing the clutch fork. its the master or the slave.

Now that being both NEW I wouldnt think they be bad.

Now push in the clutch while your on TOP and see if the resivior has tiny air bubbles comming out. If yes then Master could be bad.

 

But try this first. Stick your finger in there and plug the hole. and have soembody pump the pedal a few times. it you fill it shoot fluid then that part is alright. This fixed my proplem. Wasnt pushing fluid( but we caught this during the bleeding process.

 

 

PS Man up these are simple rigs

[Erik765]

:) Thanks for the encouragement. I'll try that stuff again.

 

One question before I do- by forward, do you mean the push rod extending the fork all the way out? Or having it pushed back in (as if the pedal was not pressed down)? I'll bleed accordingly.

 

You don't think the truck not going into gear while it's running no matter where I push the fork manually is an issue though?

 

 

[banzai510(hainz)]

clutch fork FWD means its fwd towards the motor. when the slave pushes it to the back. then it should go back fwd when pedal is relased.

 

Now if you push the clutch ,the fork should go toward the back and engage the clutch and go in to gear.

 

Maybe its not pushing in far enough.maybe the fork is not even moving. Have you seen it move?

 

Put on Jacks look under there and have soembody push the pedal and look.

 

Being he started it in 1st gear drove it and shifted it in gear which one can do ,I have done it also theres a trick to it but can be done. I would assume its a adjustment issue , or master or slave push rod length?

 

If the clutch isnt pushed in enough the trans will not go into gear.This is normal

 

maybe a bent clutch fork or bent but I have never seen this myself

 

HRH maybe can help you

[Gearshredder]

Sounds like you have more than one problem but I would put money on the Master cylinder. The master cylinder would continue to build pressure as another mentioned earlier. You would build it until your pedal would get hard as a rock (moving the lever towards the clutch) even if the slave cylinder was still extended. I don't think you have to remove the transmission right at this moment. When you said where is the dot3 is going, you are correct, its going nowhere because pressure is not being made and the pedal is effortless.

[Erik765]

Thanks again Banzai510 and thanks Gearshredder, that's the confirmation I've been looking for all along (well, one of them). What I'm gonna do tonight is pull off both the slave and master and bench bleed the master to try to narrow down which may be the issue and then throw a line between them and test. If I remember right, when I had a short line for testing on the master, it seemed to push the fluid really well and the pedal would stop while I was manually blocking the end of the line so, could be the slave too I guess. I'll find out tonight.

 

HRH did offer to help me so I may very well hit him up this weekend when he's free if I can't get it myself before then.

 

My other question that I'm still not sure on is why the lever just moves freely when I manually bring the pin off of it (and when I left the pin go, the lever doesn't push the pin back into the slave). Is it supposed to? In other words, when the truck is running, I can't manually simulate the clutch pedal being pressed by moving the lever (unless I'm just not pushing hard enough). It won't go into gear, period.

 

Thanks again guys! Really appreciate it!

[banzai510(hainz)]

My other question that I'm still not sure on is why the lever just moves freely when I manually bring the pin off of it (and when I left the pin go, the lever doesn't push the pin back into the slave). Is it supposed to? In other words, when the truck is running, I can't manually simulate the clutch pedal being pressed by moving the lever (unless I'm just not pushing hard enough). It won't go into gear, period.

 

 

Im getting more confused.!!!!

sounds like your saying the clutch fork moves freely like the forkarm is busted

HRH has to see this. I assume the slave and master work. But if clutch arm moved freely I assume the slave cyl rod would bush out all the way and brake the seal

[Erik765]

Im getting more confused.!!!!

 

See what I mean?!!

 

Maybe if I'm good, I can even take a video of the lever from under the truck and post it later. (after I troubleshoot the hydraulics a bit more).

 

What you're saying about the slave is probably true and exactly what is happening.

 

 

[HRH]

Clutch is now working, bad master cylinder and a shitload of bleeding. Working on some other issues with the truck now.

[Erik765]

Thanks again a ton for your help today!!!