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5sp Shifting Problems


rossiz

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update: bled the clutch and flushed out what looked to be 30+ year old fluid. it shifts through all gears now, but not well under load. i think i still don't have quite enough throw at the slave rod to throwout fork. i'm going to pick up the correct adjustable rod and wind out some of the slack.

 

if i shift gently it goes through all the gears smoothly, but it grinds horribly if i try to upshift or downshift under load.

 

the lever and bushings are from my 4sp - i had replaced all 3 bushings recently.

You may want to try this first before pulling the 5 speed:

 

I think your shifting problem is more likely a bad Master cylinder. Water contamination in old fluid will pit the inside of the bore. The seal lips get damaged from the pitting.  When this happens you will get a fluid bypass internally in the Master Cylinder. The Master Cylinder still works, but you will not get a full stroke of the Slave cylinder. You may not see any fluid leaking externally, but it's by-passing the seal lips Internally.

 

This causes the clutch to drag on shifts and thus the hard shifting. The tell tale is that it shifts hard in ALL gears. With bad Synchros it's usually only one or two gears that are hard shifting. Typically second gear is the worst, followed by first gear.

 

From experience at the Dealerships and racing these critters, it is common for the Master Cylinder to fail right after a new clutch is installed. The diaphragm springs in the old P/plate get weak with age and as soon as you put in a new P/Plate the old Clutch M/Cylinder seals couldn't quite handle the extra pressure. And you mentioned that you did install a Brand new clutch... correct?

 

This scenario also used to happen all the time with upgraded clutches on 510's. Replacing the stock P/Plate with a " Roadster " P/Plate ( higher pressure ) required a new Clutch M/Cylinder 90% of the time.

 

The Clutch Slave cylinder stands up better, because they were originally made of Cast Iron and the bores did not Pit as easily due to Water contamination.

 

If the Clutch M/Cylinder had black fluid in it I would definitely replace it.

 

Rock Auto has them at very reasonable prices, Beck/Arnley or Bendix are good products. $22.95 for the Beck/Arnley. That's Cheap!!:

 

https://www.rockauto.com/catalog/moreinfo.php?pk=485739&cc=1209260&jnid=435&jpid=1

 

BTW... Rock Auto has a very good selection of all Datsun parts, and some really good prices. I always check them out first.

 

Edit: And Nissan still carries the Factory Master Cylinder assy:

 

http://www.courtesyparts.com/clutch-master-cylinder-1970-1978-240z-260z-280z-p-569026.html?cPath=7724_7746&

Edited by Chickenman
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update: bled the clutch and flushed out what looked to be 30+ year old fluid. it shifts through all gears now, but not well under load. i think i still don't have quite enough throw at the slave rod to throwout fork. i'm going to pick up the correct adjustable rod and wind out some of the slack.

 

if i shift gently it goes through all the gears smoothly, but it grinds horribly if i try to upshift or downshift under load.

 

the lever and bushings are from my 4sp - i had replaced all 3 bushings recently.

 

 

Are you using this on your 1978 280Z? All 280Z's had a self adjusting Clutch Slave cylinder. And it should NEVER have any slack in it.

 

The later Slave cylinder, Slave rod and the Clutch fork are not the same as the earlier adjustable types. If you want to convert to the adjustable type, you have to have an early style  ( before Prod Date 07/72 ) Clutch slave Cylinder, Clutch rod with ball/nut and Clutch Fork. And you have to add an external " Pull Back " spring to the Clutch Fork. 

 

The later style self adjusting Slave cylinder had an internal expanding coil spring in it to take up any slack. The early style adjustable Slave cylinders had no internal spring if memory serves me correct. Length may have been slightly different as well... but my memory is less sure on that.

 

BTW... on self adjusting Slave cylinders, you do NOT install an external pull back spring on the Clutch fork. That will screw up the Clutch release travel. 

 

Clutch Master Cylinders are all the same and Nissan still supplies them, as well as does Aftermarket.

Edited by Chickenman
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Rossi,

If it goes into reverse without grinding then the clutch is disengaging properly. If not you can check the slave cylinder travel. It you have someone press the clutch pedal all the way in and you measure the travel at the end of the clutch fork. If everything is adjusted properly and you are getting around 15+mm you should be fully disengaging the clutch.

The slave cylinder should have around 10mm "free travel" to compensate for clutch wear. You can check that by pushing the spring back and measing the distance. If you heve something like 20mm, then you could have a mix up with the bearing collar and pressure plate finger height. Yes there are a lot of combinations out there in datsun world.

Another test. Hold the clutch pedal in half way down and check if the fork slowly moves back to released position. Don't do this test with the clutch pedal fully depressed. That is where the master cylinder is at its best. Pitting and corrosion tends to concentrate along the bottom and a little more at the front end (push rod) of its travel.

I think your problem is in the synchros and the PO tempering with it is also suspect. Synchros can be funny things. They look get but work like crap. A friend had a set that look worn, but they worked fine. He ordered new aftermarket synchros. We put them in and it was horrible.

PS: My question on the slave cylinder push rod. A lot of people think because "they" can't adjust it, its not adjustable. It is completly self adjusting. If everthing is working it will compensate for clutch wear and remove all the free play out of the system by the spring in the slave cylinder expanding when everything is at rest. The adjusting only falls down when people start changing the type of throw out bearing collar / pressure plate or incorrectly adjust the clutch pedal.

Note: If the pedal is adjusted to tight the mc primary seal wont pass over the reservoir port. This will effect the self adjusting action of the slave spring.

Chas

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thanks for illuminating me on the self-adjusting slave - makes perfect sense to me now. my first thought was that i wasn't getting full clutch disengagement, but the way it's acting tells me otherwise... second is the worst - misses the shift completely most of the time, accompanied by a slight grinding sound. first whines pretty bad. it slips into reverse ok - about as well as my 4sp, which occasionally had a little grind when dead cold, but otherwise fine.

 

i'm gonna see about replacing the master cylinder anyway, because it more than likely needs done and isn't a bank-breaker, but i don't have high hopes for the 5sp.

disappointing, but i'm getting used to this type of situation with this build...

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the way it's acting tells me otherwise... second is the worst - misses the shift completely most of the time, accompanied by a slight grinding sound.

By "miss" do you mean the lever moves to the proper position but the gear is not engaged?  That might be a broken or damaged shift fork.  Under light load it will push the coupler in to place but under higher load it deforms or twists.

 

If the problem is how fast the clutch releases, you'd expect it to scale with RPM and the speed that you move the lever.  On the clutch though, is it the factory design, or something like Centerforce,with the inertia weights.  I've read that the weights can hang at very high RPM.

 

Transmissions that don't shift right tend to make people angry, and it's a downward spiral from the first few grinds.  They start banging gears and pushing through the original problem, creating more problems.  You might have one of those.  I bought one for parts and for the front case, and there were so many broken parts inside it was hard to believe.  Ball bearings missing from races, broken synchros, broken shift forks.  But it still seemed to shift okay while sitting on the ground.

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I learned a trick from my BMW days, I put a new slave cylinder on about every other year. Get a big syringe from a Veterinarian and put a long tube on there. Stick it down the clutch reservoir and suck all the bubbles out. Probably won't fix your problem but I like to try anyways. LOL

Cliff

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By "miss" do you mean the lever moves to the proper position but the gear is not engaged?  That might be a broken or damaged shift fork.  Under light load it will push the coupler in to place but under higher load it deforms or twists..."

 

yup - exactly describes it.

 

the 5sp is on the ground now, going to pick up my new master/slave set along w/new slave connection hose from oreilly and maybe this afternoon i'll be on the road...

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swap complete - new MC/SC & hose, all works well. 

a miserable job on a hot, hot day but now i can drive my z...

We hit 98F here in Metro Vancouver BC. ( Coquitlam ) Abbotsford and Chilliwack hit 100F. A leetle warm for the PNW!!!

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