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Agno

Clutch Bleeding Problem

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Hi All,

 

When I took the box out of my car a few weeks back I changed the throwout/clutch release bearing and installed a new pilot bushing into the back of the crank. The car went back together easily enough but now it seems no matter what I do I cannot bleed the clutch hydraulics properly.

 

I have bled the system and I'll have a great feeling pedal but the pedal goes soft and spongy after five or six uses of the clutch until I cannot get the car in gear at all. I have found pushing back on the slave cylinder (pushing the pushrod back into the slave) a few times brings the pedal back but then the same problems happen again after a few uses of the clutch.

 

I have tried pressure bleeding, gravity bleeding, reverse bleeding, bench bleeding the master and also changed the slave cylinder for a new one (same pushrod). For the record the clutch, flywheel, bearing carrier and clutch fork are all the same units as they were all in good condition upon removal.

 

Any suggestions? Thanks in advance.

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Hi

 

Check the seals in the master cylinder, is there any moisture in behind the pushrod ?

 

Cheers

Edited by PB260Z

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Hi there, it sounds like it could be the Master Cylinder, you say you had a good pedal and then after a few pumps it starts to go spongey again, which means that you are drawing air from somewhere and you said you have done the slave already. while you had the box out for a couple of weeks was there still fluid in the hydraulic system?( i usually just pinch the line) Because with an old MC the seals can start to dry out and strink, so by the time you fill it back up with fluid its no good anymore!

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Update:

 

I rebuilt the master cylinder and gave everything a good bleed and the car felt great. After taking it out on its maiden voyage however the sh1tty swaging on my ebay spec braided clutch hose failed and I was stuck on the side of the road in the middle of Melbourne.

 

After a tow truck home and a new (locally made and much better quality) braided hose was fitted I went to bleed the system one more time... and the slave cylinder over extended and the piston popped out! To fix this I made a new pushrod out of a cut down and rounded M8 high tensile bolt.

 

Now everything works but it never ceases to amaze me how problematic older cars can be when you disturb the system or try and change parts... All I did was change the clutch release bearing for an OEM bearing sourced from Nissan locally and I don't really understand why that would necessitate a new, longer slave cylinder pushrod. Oh well!

Edited by Agno

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No, it was the same height and center bore as the original but slightly wider. In all my searching I couldn't find any information about release bearings being different heights between various iterations of FS5W71 gearboxes. I'm happy to be proven wrong though because this is doing my head in!

 

In car:

gsb335.jpg

 

What replaced it:

releasebearing_1.jpg

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I'll preface this with saying I'm no expert on 6 cylinder clutches, but on the 4's there are two style of pressure plate and each has their own corresponding release bearing. One type of pressure plate has a big "hole" in the spring fingers, with a matching bigger diameter release bearing. Other is small hole, small bearing. Using mis-matched bearings may cause issues, ?? I've not done it, and not sure of the exact consequences of doing it. Just a thought !

 

Big hole on right, small on left. You can see the bright wear mark where the release bearing touches the inner ends of the "fingers". Small one would look the same if it wasn't so rusty and greasy. Now imagine the large diameter bearing on the small hole plate - the bearing will contact the "fingers" further in than Nissan designed it.

 

 

both.jpg

Edited by 1600dave

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