ZF6 cooling needed

[Clutch_less]

I recently started pulling a 6,000 lb boat/trailer combo and my ZF6 is getting a lot hotter than in the past. Hot enough, I believe, to cause clutch disengagement issues after a long day of hauling the boat. My 02 3500 CC is converted to a class C motor home and when fully loaded the gross vehicle weight is around 12,000 lb. So now with the boat/trailer in tow its no wonder the transmission is heating up. When cool the ZF6 shifts fine.

I want to add some external cooling to the transmission fluid to help with the heat build up issues. I have seen the Fast Coolers PTO cover add-on sumps that achieve up to 2 additional quarts of fluid to the tranny. I have also seen the TDS PTO covers which have threaded ports, supposedly to allow fluid to be pumped from the transmission through a transmission cooling radiator. And years ago some one on this board even offered a complete kit for a circulating external cooler for the ZF6. But I can't find that person now, so I'm hoping folks on this forum can help point me in the right direction with this cooling need I have. Thanks

 

[Chevy1925]

id be more enclined to say what you have is just a dual mass fly wheel issue. they are not known for longevity or strength.

have you looked at switching to a single disk, single mass fly wheel?

 

[Clutch_less]

The last 2 clutches were installed with new slave cylinders and single mass flywheels. The clutch friction disc has always been single. Next month I plan to pull the transmission and inspect the clutch parts for signs of what's going on. At that time I also plan to put in a new master cylinder and off course change the tranny fluid. So this would be a good time to install auxillary cooling if there is anything out there that would work.

 

[Chevy1925]

hmmm interesting. i find it hard to believe the trans its self getting hot would cause it as the heat has to travel a long ways to a part that would take a heck of a long time to heat up due to its thickness/density to then cause a slip.

now if the slave is heating up, not shimmed correctly or somehow holding a little tension on the pressure plate, i can see this issue coming up.

whos clutch and flywheel are you using?

 

[gmac32]

Powerstroke zf6's all have external coolers on them. You should just be able to use some AN fittings and a good setrab cooler

 

[Clutch_less]

I was told by the drive line shop in BC that installed the last clutch that it is a South Bend single organic disk. New single mass flywheel and slave were installed too.

I agree that it seems hard to me for the transmission would heat up enough to cause the disengagement problem. (There is no slipping as I'd expect to see increase in engine RPMs on a hills---but there are none--even in 6th gear before I downshift to keep engine running at least at 1800 rpms.)

But a technical service rep at South Bend Clutch recently told me that with the loads I'm pulling the transmission will heat up enough to heat up the hydraulic system and produce poor clutch disengagement. The excessive heat causes the hydraulic fluid to loose viscosity and ability to fully expand the slave cylinder. Over time he said the hot fluid will evaporate from the master cylinder reservoir (I have found a drop in fluid level there and very hot to the touch reservoir. There are no signs of slave cylinder or master cylinder leaks.)


The SBC rep recommended changing the slave and master cylinder and fluid to at least DOT4. He also recommended trying to add external cooling, and if I can figure out how the Powerstrokes do it I will try that that. I was hoping someone here has experience with that.


Could you explain more about proper shimming of the slave cylinder? I don't recall the mechanic shimming anything.

 

[clrussell]

I’ve dealt with this issue. Ended up putting a dual disc in and it’s been fine


Also gm Zf6 does not have ports for cooling like the fords

 

[gmduramax]

You can start with a better fluid for the master. Castrol SRF or motul 660.

 

[Clutch_less]

I’ve dealt with this issue. Ended up putting a dual disc in and it’s been fine


Also gm Zf6 does not have ports for cooling like the fords

CL--I'm glad to hear that a dual disc solved your disengagement problem. Do you think that it was a heat build up issue caused by a single disc slipping on you? As I've noted above, I don't believe my single disc clutch is slipping, but a dual like yours should answer any question of slippage.



I've not driven a dual and don't know how it would perform backing the trailer. That is the only time I have to slip the clutch for the slow backup speeds I need to control the trailer. I wish the ZF6 transfer case had a 2W low range speed (not just 4W low) so creeping in reverse was possible.



Also, the Fords having ports is what I expected. Do you know where on the tranny case those Ford ports are located? I wonder if I could install some ports in the PTO covers of my GM ZF6---one one one side for exiting fluid and the other side for return fluid from a cooler.

 

[Clutch_less]

Motul 660 sounds like the way to go on the hydraulic fluid. Good for racing and can take the heat!

 

[Bdsankey]

CL--I'm glad to hear that a dual disc solved your disengagement problem. Do you think that it was a heat build up issue caused by a single disc slipping on you? As I've noted above, I don't believe my single disc clutch is slipping, but a dual like yours should answer any question of slippage.



I've not driven a dual and don't know how it would perform backing the trailer. That is the only time I have to slip the clutch for the slow backup speeds I need to control the trailer. I wish the ZF6 transfer case had a 2W low range speed (not just 4W low) so creeping in reverse was possible.



Also, the Fords having ports is what I expected. Do you know where on the tranny case those Ford ports are located? I wonder if I could install some ports in the PTO covers of my GM ZF6---one one one side for exiting fluid and the other side for return fluid from a cooler.

You could wire it up on a switch to NOT allow the front diff actuator to engage. I don't know how angry the truck would get if it were a push button 4x4 but on a manual tcase it would be pretty easy.

 

[clrussell]

CL--I'm glad to hear that a dual disc solved your disengagement problem. Do you think that it was a heat build up issue caused by a single disc slipping on you? As I've noted above, I don't believe my single disc clutch is slipping, but a dual like yours should answer any question of slippage.



I've not driven a dual and don't know how it would perform backing the trailer. That is the only time I have to slip the clutch for the slow backup speeds I need to control the trailer. I wish the ZF6 transfer case had a 2W low range speed (not just 4W low) so creeping in reverse was possible.



Also, the Fords having ports is what I expected. Do you know where on the tranny case those Ford ports are located? I wonder if I could install some ports in the PTO covers of my GM ZF6---one one one side for exiting fluid and the other side for return fluid from a cooler.

You will have to use 4low to back up like you do now. It’s a side effect of a clutch that will actually hold up sadly.

As for fittings they are in the passenger front area, the gm doesn’t even have the slightest provisions for them.

If you’re going to try and cool fluid through a cooler via pto covers you’ll need a pump to move the fluid as the fluid just sits in the bottom of the trans persay. There is no pump system on the pto covers

 

[gmac32]

I think you could replace the bottom drain plug and put a 90 degree AN fitting in it place and put a pump inline, then up to a cooler in the front and return the fluid in the pot cover

 

[Clutch_less]

I like these suggestions. CL and BD suggest using a circulating pump to move fluid from the tranny to a cooler up front. I'd wire it to a switch so I could cut it off in freezing weather until the tranny heats up. I'll need a temperature gauge for the tranny.


I probably don't understand BD's suggestion to "wire up" the transfer case to not allow the front differential actuator not to engage. My transfer case is fully manual with no opportunity to electrically control the front differential engagement. But I may be missing something here.

 

[melms23]

I found lowering the idle did wonders for being able to back trailers up nicely in 2wd in my rclb. A little heavier truck like yours would probably be a little smoother backing up with the dual disc clutch.

 

[2004LB7]

I probably don't understand BD's suggestion to "wire up" the transfer case to not allow the front differential actuator not to engage. My transfer case is fully manual with no opportunity to electrically control the front differential engagement. But I may be missing something here.

Are you sure its mechanical all the way to the actuator and not just the lever in the cab? It was my understanding that the lever just activated a switch that indicated to the BCM what to do and the 4lo actuator was still electrical. Of course the older ones where fully mechanical abd I'm not sure what year was the transition

If you haven't already, pop under your front end and see if it is wires or linkage to the actuator

 

[Clutch_less]

I found lowering the idle did wonders for being able to back trailers up nicely in 2wd in my rclb. A little heavier truck like yours would probably be a little smoother backing up with the dual disc clutch.

Melms--that's a great suggestion.:thumb: I'll ask the diesel technology guys who do the wrenching on my truck to lower idle for me when they do the clutch work for me next month. How much can the idle be lowered without causing problems when not backing?

I'm getting mixed messages about the dual disc clutch. I've been told that if the clutch modification is not done correctly the trailer backing can become more difficult because the clutch can become "on or off" due to the quicker and more powerful engagement the dual discs provide. If the discs are not ceramic then I'm guessing the "on off" may not be as pronounced. Thanks

 

[Clutch_less]

Are you sure its mechanical all the way to the actuator and not just the lever in the cab? It was my understanding that the lever just activated a switch that indicated to the BCM what to do and the 4lo actuator was still electrical. Of course the older ones where fully mechanical abd I'm not sure what year was the transition

If you haven't already, pop under your front end and see if it is wires or linkage to the actuator

I've not paid much attention to the part of the truck. But I'll do as you suggest and look for any wiring. My diesel technology drive line guys will know for sure. BTW, my truck is early 02 4WD.

 

[Bdsankey]

I like these suggestions. CL and BD suggest using a circulating pump to move fluid from the tranny to a cooler up front. I'd wire it to a switch so I could cut it off in freezing weather until the tranny heats up. I'll need a temperature gauge for the tranny.


I probably don't understand BD's suggestion to "wire up" the transfer case to not allow the front differential actuator not to engage. My transfer case is fully manual with no opportunity to electrically control the front differential engagement. But I may be missing something here.

You could interrupt the wire going to the front diff actuator via a switch. You would need to find out what the proper "resistance" value is and simulate that via your switch. I am not super familiar with the way the BCM knows the front diff is activated but all that happens is the actuator extends and locks in the passenger side stub shaft.

I.E interrupt the circuit when you flip the switch but tell the BCM that all is well and the front diff is engaged.

 

[Chevy1925]

plug and play

https://dieselperformance.com/shop/...1-2014-2500-3500-4wd-2001-2013-1500-4wd-19239