Diagnosing ZF6

[fl0w3n]

I'm pretty green when it comes to the ZF6, so I'm hoping to get some help from the experts here.

Having a few problems with mine and want to see if I can narrow it down.

When the trucks cold, the 2-3 shift and sometimes 3-4 is pretty crunchy. It's not really audible, but you can feel it goin in. Once the truck is warmed up, it feels fine 95% of the time. Clutch feels like it engages about halfway through the swing of the pedal.

When it's really hot, as in just blasting up a grade in 6th with 80* ambient, and then I roll up in traffic shortly after, it almost feels like there's less throw on the clutch pedal. And the clutch seems to grab after letting out just 10-25% (100% being fully engaged).

Also, not sure if it's more my motor still running rough or the trans, but in above mentioned traffic while hot, trying to put in 2nd or 3rd around 12-1600 rpm it sometimes get really rocky where the truck starts surging back and forth. It makes me look like a big Newb at manuals... which I am :roflmao: but I'd rather know if it's just the motor running rough, something up with the trans, or it's just me. It doesn't seem to do that when cold. It didn't happen every time either.

To be honest I haven't even started with some obvious things like checking fluid in the trans, or fully looking at clutch fluid - at a glance it looked full. I'll try to get to it this week. It's a weekend truck mainly.

 

[zf>allison]

I'd do new fluid In the slave and clutch master cylinder. 12 and 1600 rpm rockyness could be tuning, the zf trucks with sensitive throttle tuning can make you wanna burn the thing. Crunchyness when cold is normal especially if it has some miles probably just synchros worn. Or to slow or to fast of a shift.

 

[fl0w3n]

I'd do new fluid In the slave and clutch master cylinder. 12 and 1600 rpm rockyness could be tuning, the zf trucks with sensitive throttle tuning can make you wanna burn the thing. Crunchyness when cold is normal especially if it has some miles probably just synchros worn. Or to slow or to fast of a shift.

Sweet! Any recommendation for fluid type/brand?

Stock tuning, but sounds like this one might not be me and even better nothing much to worry about mechanically.

I thought I was shifting too fast maybe as well, but when cold I've deliberately slowed down and really casually go from 2-3 around 2k and take my time, still feels crunchy the first half dozen shifts. Definitely has some miles, and they weren't easy ones. If it's syncros, am I going to hurt anything else further by continuing to run for a while till I tear it apart?

Lastly, the truck is going to be geared towards street, off roading, and towing - only shooting for the 450-500hp range. Other than a dual disc clutch that people have recommended, is there any other things I should look at doing to this zf6?

 

[precision37]

Try changing the trans fluid. Mobil 1 synthetic ATF made a huge difference in my old '02. It eliminated the "crunchiness" you talk about as well as the "hard clutch pedal" after long trips at highway speeds.

 

[fl0w3n]

Thanks, I'll give that a shot

 

[zf>allison]

4 to 500 hp get a good rebuildable dual disc. Some of the more modest ones used to not have an inlay you can replace on the flywheel. I like valair for they're customer service.

 

[Ed04zf6]

The hard clutch pedal could be from over powering the clutch. I remember when I had my stock clutch if I beat on my truck especially in higher gears the pedal would get hard. And not engage really low. After pumping it a few times it would go back to normal. Since I put my dual disk in I haven’t had that issue. Short of splitting the trans it would be tough to diagnose the crunching. If it’s the original trans with 340k it could be worn synchros or maybe even worn shifter forks depending how it’s been driven.