Just bought an '82 720 with a bad clutch cylinder, what do?

[theboraxkid]

First of all, Hello! I'm new here! Anyway, my Datsun 720 has a bad clutch slave cylinder and it needs to be replaced. Anything I should know before I dive in?

[datzenmike]

Sometime, (not always) owners don't always know what's wrong and have made a guess as to what's wrong and get off on the wrong foot. This leads to a new slave that doesn't fix the problem, then a new master and then ... well you see what I mean. The problem could be a badly adjusted clutch pedal push rod under the dash from an automatic to a standard swap or the previous owner told you it was bad. Often they just have air in them from running low and it simply has to be bled.

 

So just to be safe what is the problem and what does your 720 do... or not do? Has anything been replaced recently? Has it ever worked correctly?

 

 

 

Assuming it really is the slave you can replace it or rebuild it. If rebuilding it get the good $15 kit from Nissan OR for about the same amount or less a rebuilt on from an auto parts store. (you get what you pay for)

 

Loosen the flex hose first while it's still bolted down.

Unbolt it, unscrew the flex line and remove it. 

Allow the old hydraulic fluid to drain out, you're replacing with fresh new.

Catch and save the push rod to the clutch arm. (the kit should have a new one)

Screw in the flex hose

Bolt the new slave in.

Attach push rod and tighten the flex hose.

 

Have plenty of new hydraulic fluid ready.

Top up master reservoir. Check it often and keep it full.

Loosen the slave bleeder screw... often fluid will siphon down and self bleed, otherwise...

Have a helper depress and hold the clutch pedal down and hold.

a/ Close bleeder then, raise the pedal.

b/ Open bleeder then depress the pedal and hold.

 

Repeat a and b until all air is expelled and only clear new hydraulic fluid comes out.

At all times keep the reservoir FULL... important.

Tighten the bleeder and wipe up any spilled fluid as it will remove paint.

 

Clutch pedal should have several mm (about 1/16") of free play before resistance is felt when pushing it down with your thumb.

[wayno]

Welcome :)

[theboraxkid]

When I push my clutch pedal in, it just sinks to the floor and will only work if I pump the pedal furiously while shoving the shifter into gear. It shifts fine once I get moving, but it will not go into gear from a stop unless I tshove the pedal around. That seems like the slave cylinder, right?

[wayno]

Sounds like air in the lines, did the reservoir get really low at any point, if it did, you need to bleed the system.

[xsdg]

When I push my clutch pedal in, it just sinks to the floor and will only work if I pump the pedal furiously while shoving the shifter into gear. It shifts fine once I get moving, but it will not go into gear from a stop unless I tshove the pedal around. That seems like the slave cylinder, right?

 

What wayno said.  You'll know you have a bad slave cylinder if it's dripping fluid on the ground and the reservoir is running out.  If your reservoir level isn't decreasing, then the likelihood of it being a bad clutch slave is pretty low.  As wayno mentioned, what you're describing sounds like air in the lines.

[theboraxkid]

Oh alright, that's an easier fix. I'll check it out tomorrow and let you know the findings

[720inOlyWa]

What wayno said. I had this happen way back when we had a mustard 620 and it was because I didn’t pay enough attention to the fluid level. Slave cylinders do wear out and I replaced that one because I, like you, assumed it was bad. But when I post mortemed it, it was fine except for a torn boot. As I recall, that was 70 wasted dollars when I should have just bled the system thoroughly first.