Thinking about installing an BMW M6 engine in my Z

[grannyknot]

I fixed the oil cooler line then started the engine so to get it hot enough to trigger the electric fan, just before the fan turned on a coolant line I hadn't tighten fully blew off so back to cleaning the floor again.  Now that is repaired  I was going to take the car out for a spin, I jump in and it won't go in to gear, it seems the Datsun clutch MC is just a bit shy of enough displacement for the BMW slave cylinder.  I'm pretty sure somewhere on the shelves is a 7/8" clutch MC from back in the days when I had a TR6 but that's tomorrow.

[RyanT67]

You're so close!  

What a build, Chris.  Wow, just wow!  ?

[grannyknot]

8 hours ago, RyanT67 said:

You're so close!  

What a build, Chris.  Wow, just wow!  ?

Hey man, how's it going, haven't seen you in a couple of yrs. I guess with this plague Zfest will be called off, are you still running my old engine or have you finished the new one you were building?

Well this clutch problem has me stumped, I removed the Nissan 3/4" and installed a new 7/8" clutch MC, bled almost a litre of fluid through the system from both ends so I know there is no air in the lines. The slave is used but I took it apart and it is working fine, but the clutch pedal goes to the floor with no more resistance that the return spring and it still won't go into gear when the engine is running.  I hate to even think it but I may have to drop the transmission

At least the variable valve timing oil pressure is right where it should be.

 

[EuroDat]

Hi Chris,

A couple of questions, might sound obvious, but you never know until you ask.

Before you drop the trany, get someone to push the peddle to the floor and check the movement at the slave cylinder and measure its travel. What do you see?

Is the clutch throwout bearing up against the pressure plate and the free play (if it's adjustable) on the slave cylinder rod adjusted correctly?

Is the clutch disc stuck to the flywheel? After sitting for a long time it could be stuck to the flywheel. You could try starting it in 5th gear to see if it breaks loose.

If that is all good, it could be a disc plate not moving freely on the input shaft splines. When you depress the clutch, the disc will move slightly away from the flywheel.

Or a spigot bearing grabbing the input shaft. Either way you will need to drop the tranny.

Chas

 

 

[EuroDat]

The normal 280Z slave cylinder travels about 15mm +/- 2mm. That is depending on the clutch pedal adjustment.

[Zed Head]

I'm learning a lot about Nissan clutches.  I had assumed that the cylinders would be the same diameter but apparently they're not. ( Edit - they just put it in a different spot, it's there.)  Says 35 mm...

As EuroDat implied, you can have a lot of wasted movement at the rod from the foot pedal to the master.  The pedal spring can hide that slop.

Edited April 13, 2020 by Zed Head

[grannyknot]

It occurred to me this morning that I had installed the Nissan adjustable push rod instead of the Tilton rod, so pulled that and exchanged them, filled and bled it all again and with a little contraption I made measured the max travel of the  bmw slave, 16mm, I set it to that and started the car and it still won't go into gear. Chas I took your advice and started the car 6th gear a couple of times but it didn't help.

So I removed a perfectly good slave cylinder and replaced it with a brand new slave, filled, bled and gave that a try, no luck. At least now I know every part in the hydraulic system is new and working the way it is suppose to.

There is a strange thing happening that I hope will sound familiar to someone, when the engine is running, the clutch pedal is depressed and I try to push it into gear, it actually makes the car roll forward VERY slowly and trying to get it into reverse it does the same thing, there is no noise.  Unless anyone has any other suggestions I guess I'll start removing the exhaust system and drive shaft and see if I can drop the trans out the bottom.

 

[Zed Head]

16 mm is only half the stroke that Nissan shows.  That bigger master might be worth a shot. 

Any way to rig up a mechanical way to push the fork?  I don't know what BMW uses to move their pressure plate, is it a typical clutch fork?  Moving the fork would tell you if it's a hydraulics problem or a mechanical problem.

[grannyknot]

2 hours ago, Zed Head said:

That bigger master might be worth a shot. 

The 7/8" MC is already installed. The fork is two sided with the pivot on one side and the slave push rod on the other. Pretty sure now the hydraulic system working.

 

[Captain Obvious]

2 hours ago, grannyknot said:

There is a strange thing happening that I hope will sound familiar to someone, when the engine is running, the clutch pedal is depressed and I try to push it into gear, it actually makes the car roll forward VERY slowly and trying to get it into reverse it does the same thing, there is no noise. 

From your description , I'm guessing it has a synchronized reverse gear? if it wasn't synchronized, it would grind bloody murder if you tried to put it into reverse without disengaging the clutch.

Assuming it is a synchronized reverse... What you're doing is using the synchros as a "clutch" (which is actually exactly what they are). You're pressing the two synchro cones together using the shift lever and there's enough friction between the two surfaces to move the car a little. Probably wouldn't happen with warm transmission oil, but with the cold thick oil, you're getting enough energy transferred to move the car. The harder you press against the linkage, the more the car should move.

In theory (only), if you were to force those two cones together hard enough, the car would speed up and eventually snick into gear once everything "synchronized" to the same speed. But in reality, you would bend something in the linkage first or burn up a synchro with the heat.

So what's the point? The point is that it sounds like the transmission guts are doing that they're supposed to do, and the problem is somewhere in front of the input shaft. Clutch problem (as if you didn't already know that).  

[grannyknot]

9 hours ago, Captain Obvious said:

So what's the point? The point is that it sounds like the transmission guts are doing that they're supposed to do, and the problem is somewhere in front of the input shaft. Clutch problem (as if you didn't already know that).  

That's actually reassuring, the 6spd transmission was of unknown condition when I bought it, I could spin it and row through the gears but that's it. Thanks

[Captain Obvious]

Well I hope I'm not providing too much reassurance. You're not out of the woods yet on transmission quality.

There's still plenty of things that could be wrong that you won't be able to tell until you actually drive it (like bearings whining or synchros not working right at speed), but so far, so good!  Just the fact that it's quiet while spinning at engine speed is a great second test after the initial hand spun bench test.

So what the heck is wrong with the clutch system???