1978 Datsun 620 going through slave cylinders faster than gasoline!

[HoffmanNJ]

So I decided to do a full clutch makeover so I replaced the master cylinder, the clutch, pressure plate, throw out bearing, and slave cylinder. The reason why I had to do the slave is because after reassembly of the tranny and I got everything put back together and my buddy and I were bleeding the clutch and suddenly the slave piston comes out of the cylinder. So I thought no biggy, and went to buy a new one. Did that, got home threw it on bled it and it was fine. The next day I was driving to work, roughly 10 miles from home with 1,001 stops on the way not a big deal until blammo the new slave went out. So I figured faulty part, O'Reilly's replaced it with no questions asked, put the new one on there and again it was fine until I went to test drive it then AGAIN it happened. So I replaced it again O'Reilly's no questions asked, was driving to pack wood from north seattle and it didn't have any problems until Morton. Then the same exact thing happene to that one. Unfortunately there is no O'Reilly's in Morton so I had to push the piston back in and drive to pack wood at 11 at night with no use of my clutch, I know terrible for my tranny and gears, but I was 110 miles from home and only 25 minutes from pack wood. Finished the trip drove back into Morton with my parents the next day and picked up 2 new napa ones. Put one on and started to bleed it then it happened while bleeding. Now I have it parked, after driving it back from packwood on no clutch, replaced the clutch fork last night, and I was waiting until today to do the drive train donut, and once I figure out the problem I will put the new napa one on. Please help me again. Sorry for being a pest but this is my only mode of transportation!!!!

[Boaty]

Hoffman,

 

Make sure your master cylinder is adjusted correctly. At the master cylinder rod, where it bolts up to the pedal itself, you have to have this adjusted correctly or the master cylinder will keep pressure without releasing it. When the rod moves *all* the way back, it releases all the pressure in the system and returns to 'normal'. If the rod is adjusted incorrectly, it is likely keeping just a small amount of pressure in the system, but moving far enough back to gain a bit more fluid each time.

 

On adjustment, you want it to have about 1/16"-1/8" of slack. This assures that the rod is coming back far enough. Some people are under the impression that adjustment at the master cylinder moves pedal position, and this is only partly true. There are two adjustments - pedal stopper/position, and rod disengagement.

 

If you go under, back off the lock nut on the rod adjuster, so that there is now slop between pedal and rod clevis. Doesn't take much, just enough so that the rod DOES come out all the way, and the pedal itself isn't preventing it from moving back farther.

 

In the case of my brother's truck, the rod was actually longer than it needed to be, and this required his clutch pedal to be much higher than his brake pedal. He simply cut off a portion of the rod so that the pedal could rest even with the brake pedal, so it doesn't look funky - but still had enough adjustment to maintain that 1/16" of slop. That would be my best guess for you - is that the master isn't returning properly and the pedal is out of adjustment.

 

Now another alternative, is that if you replaced the throwout bearing - the bearing was incorrect, or you used the incorrect throwout bearing collar. If you used a shorter collar, I can see the same thing happening - the slave has to push the fork 'back' (out) too far to engage the clutch, and thus when you hit the clutch the piston falls out. Unlikely if you re-used the same collar as you were using before, without problems. Another problem, could be an incorrect slave cylinder rod length. If the new slave rod is too short, it could cause the same issue. Compare it with your old slave rod and see if it's the same length, or shorter. Use the longer rod if you have two lengths.

[datsunaholic]

If you keep pushing the piston out you have a serious case of wrong parts. The piston should NEVER come out, the arm shouldn't be able to travel that far. I've never blown a slave piston out.

 

So unless it's just a case of having the master's pushrod adjusted too tight (should have a little slop), the next thing is maybe you have the wrong master and it's a bigger bore, so that it pushes too much fluid.

 

Other than that, wroung throwout collar or pressure plate that needs too much throw. Or too short of a pushrod.

[HoffmanNJ]

Yesterday my girlfriend and I were bleeding it in a 7-11 parking lot and the fork didn't move at all, I am hoping that if I throw my old throw out on it will fix it due to the new TO being tight on the shaft. I will see if this fixes it also I will throw the old master back on and see if it works. The new one worked before I swapped the clutch and only little adjustments have been made since. Maybe a full turn or so.

[Boaty]

It is possible you have an incorrect throwout bearing. Always compare the new one to the old one before you install it, so you can warranty it out or find a suitable replacement.

[datzenmike]

Have someone measure the slave push rod movement. It should move 1.18" .... more would indicate something wrong.

[metalmonkey47]

A local buddy has the same exact issue with his 620. After replacing one that he got from some unknown parts store, the piston keeps popping out.

 

 

I just take a bolt that was the right diameter and a tad bit longer then the push rod, cut the head off, and round it a bit. That is, assuming that the slave is the problem.

[thisismatt]

I think you just need to keep swapping them out. Five replacements with the same problem is far too small a sample size to conclude that you're doing anything wrong. Just go pick up a new one. Try a different brand this time.

[HoffmanNJ]

It was In fact the throw out bearing that came with the kit was wrong so we dug deeper and found out the right one. Also came to find out that the driveshaft donut I had purchased is the wrong one somehow. Damn you amazon.

So tomorrow I'm going to pick and pull for the front half of the driveline with donut so I don't buy one from O'Reilly's for $87 and instead $20 for the whole thing. Oooooh I'm so excited.

[banzai510(hainz)]

Who makes the clutch kit???

 

I got my 521 set from importrp.com.

 

your 620 should have the ez to find Daiken kit.