Could it be a slipping Clutch?

[txvepr]

So I just installed a 5 speed transmission in my 78 280Z. Used to have a 4 speed. Before installation, nothing was wrong with the clutch, and I did not think I needed to replace it at the time. It was strong and never slipped. I did not remove the clutch and it seemed to be in good condition as far as I could tell on the flywheel.

 

While test driving after the install, I notice that it seems like the clutch slips a bit at 3 & 4 gear shifts. The question would be is this a sure clutch going bad ? or could it be something along the lines of my clutch pedal/slave cylinder needs adjustment?

 

I find it odd that the clutch would go bad at this exact time, but I do not have experience in this area of installation.

 

Any ideas?

Thanks.

[EuroDat]

I take it you are driving hard to get this problem.

From your description, it sounds like it is an adjustment problem. I don't think it would be the clutch peddle because it wasn't slipping before and changing the transmision doesn't effect the peddles.

Did you keep your throw out bearing and clutch fork or are they from the 5 speed?

The throw out bearing collars can be different and if it doesn't match the pressure plate (the Zeds have three different pressure plate heights) it can keep the pressure plate from releasing completely.

Are you using an original 280Z slave cylinder or an adjustable one? If it's adjustable, check the free play at the clutch fork.

If it's the non adjustable type, you should be able to push the clutch fork into the slave cylinder about 5 to 15mm depending on clutch wear and tolerances. Apply constant pressure and it will push in slowly. You are pushing brake fluid through a small hole in the master cylinder.

I have some data on clutch fork distance measured from the front of the belĺ housing. That would give you an idea if your pressure plate and bearing collar match.

[siteunseen]

I take it you are driving hard to get this problem.

From your description, it sounds like it is an adjustment problem. I don't think it would be the clutch peddle because it wasn't slipping before and changing the transmision doesn't effect the peddles.

Did you keep your throw out bearing and clutch fork or are they from the 5 speed?

The throw out bearing collars can be different and if it doesn't match the pressure plate (the Zeds have three different pressure plate heights) it can keep the pressure plate from releasing completely.

Are you using an original 280Z slave cylinder or an adjustable one? If it's adjustable, check the free play at the clutch fork.

If it's the non adjustable type, you should be able to push the clutch fork into the slave cylinder about 5 to 15mm depending on clutch wear and tolerances. Apply constant pressure and it will push in slowly. You are pushing brake fluid through a small hole in the master cylinder.

I have some data on clutch fork distance measured from the front of the belĺ housing. That would give you an idea if your pressure plate and bearing collar match.

I apologize for hijacking your thread but Chas said something that rang my bell. 

 

I'm about to put the wide 5 speed into my 240.  I've got the taller collar but never put the clutch forks side by side.  I have one that's taller than the other, it has a large hole for the slave plunger and a smaller hole for a spring, I suppose.  The shorter one has no holes at all. 

 

Which one goes with the 5 speed?  My 280 doesn't have a spring so I'm guessing the shorter one, but I'd like to hear from the transmission guy, Chas.

 

Thanks!

[Jeff G 78]

Like others stated, I think you might have a throwout bearing collar mismatch.  You likely left the throwout bearing in the "new" trans before installing it, but it might be taller than the collar in the 4 speed trans.  Get under the car and see if there is play between the slave cylinder rod and the clutch fork.  If there is no play and you don't have an adjustable slave from a 240Z, you will need to pull the trans and swap the collar back to the one from the 4 speed trans.  Don't drive it the way it is if the collar is wrong.  You will ruin the clutch and burn the flywheel.  

[siteunseen]

The 5 speed stuff is on the left, 4 speed is the one on the right.  Notice the different height of the collar on the right side, 4 speed.  Hope this helps understand what Chas and Jeff are talking about.

 

It helped me, now I know which fork goes with the 5 speed. 

 

[EuroDat]

This might be side tracking the thread a litle bit.

Site, your clutch fork with the hole is a pre July 1972 clutch fork. It goes with the adjustable slave cylinder push rod and return spring.

Back in the early days manufacturers didn't won't the clutch release bearing running all the time. It remains stationary until the clutch pedal is depressed. Maybe because of the high speeds involved and low temperature grease. I have heard people say low quality bearings, but I think that is a fable.

The low temperature grease getting overheated and not lubricating the bearing seems more feasable. Remember this bearing is running three times as fast as the wheel bearing.

A lot of people refer to the collar by the transmission, but that can be misleading. Its better to go by the year. Datsun changed the pressure plate the same time they changed the 71A to the 71B transmission. After that its all over the place. You can get a 71B 4 speed with thre different collars, just depends if its in a 240Z, 280Z or a 2+2.

The to drawing below show how you can get confused by using the transmission to determine collar height. The second drawing show the same, but per model Zed.

[Jeff G 78]

Completely true Chas, but after 40 years, unless you are the original owner and know the history of the car, it's very possible that one or more of the components has been swapped.  I always check the collar height just to be sure and I've found them to be different than OE quite a few times.  

[Zed Head]

Ack.  So many parts and so many possibilities.  Best to remember that the throwout bearing collar height is designed to match the height of the levers it sits on in the pressure plate.  Collar and pressure plate are a matched set.  92 mm (+/- an mm) from the surface of the flywheel to the surface that the fork tines ride on is the key dimension.  If you have that number you will most likely be okay.  I will never install a transmission again without confirming that measurement.

 

Attached a picture, not perfect but I think it illustrates.

 

 

Edit - almost had the perfect post but had times instead of tines.  Carp.

Edited December 28, 2015 by Zed Head

[EuroDat]

I agree, not much original stuff out there anymore. The S30 series gives people the opportunity to swap around a lot.

The important thing to remember is the collar fits the pressure plate, not the transmission. You need to know which pressure plate your using and match the collar to it.

I'm wondering if the PO changed the collar and if so what combination he now has to induce this slipping problem. If the slave cylinder has no freeplay in the push rod. It's a good chance the problem is then in the collar.

[siteunseen]

Lots of good information here guys, thank you!  May have saved my arse. 

[siteunseen]

On 12/28/2015 at 11:10 AM, Zed Head said:

Ack.  So many parts and so many possibilities.  Best to remember that the throwout bearing collar height is designed to match the height of the levers it sits on in the pressure plate.  Collar and pressure plate are a matched set.  92 mm (+/- an mm) from the surface of the flywheel to the surface that the fork tines ride on is the key dimension.  If you have that number you will most likely be okay.  I will never install a transmission again without confirming that measurement.

 

Attached a picture, not perfect but I think it illustrates.

 

 

Edit - almost had the perfect post but had times instead of tines.  Carp.

Are you measuring off that ear on the collar?  Is that the tines the fork rest on you're talking about?  Thanks again for that helpful tip, I was going in blind. 

[Zed Head]

Yes, from the contact surface on the ear.  Others have determined the same 92mm number, EuroDat among them I believe.  There's a thread out there somewhere.