Duramax Diesels Forum Truck of the Week
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Old 12-03-2018, 01:58 PM
Clutch_less Clutch_less is offline
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Default ZF6 cooling needed

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
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Old 12-03-2018, 02:03 PM
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Chevy1925 Chevy1925 is offline
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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?
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Old 12-03-2018, 02:47 PM
Clutch_less Clutch_less is offline
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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.
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Old 12-03-2018, 03:00 PM
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Chevy1925 Chevy1925 is offline
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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?
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Mike L is my role model. I want to be like him when I grow up.
James

02 LB7, LLY, LBZ, LMM, LML, L5P 2500HD CC/LB dmax/alli "The Limo"

BIG THANKS TO: Mike L, Steve, Trent, Guy, Dan, Ruben, Josh H, Scott, Brian and everyone else who has put a hand in to help me.

best time to date: 12.39

motor died/bent rods = 3/11/11
back from the dead 7:04pm 4/9/2012

Limo is back in the garage, now driving a built chevy tracker
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Old 12-03-2018, 05:09 PM
gmac32 gmac32 is offline
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Powerstroke zf6's all have external coolers on them. You should just be able to use some AN fittings and a good setrab cooler
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Old 12-04-2018, 07:08 AM
Clutch_less Clutch_less is offline
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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.
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Old 12-04-2018, 08:46 AM
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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
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Old 12-04-2018, 10:23 AM
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You can start with a better fluid for the master. Castrol SRF or motul 660.
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Old 12-04-2018, 01:10 PM
Clutch_less Clutch_less is offline
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Quote:
Originally Posted by clrussell View Post
Iíve dealt with this issue. Ended up putting a dual disc in and itís 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.
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Old 12-04-2018, 01:15 PM
Clutch_less Clutch_less is offline
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Motul 660 sounds like the way to go on the hydraulic fluid. Good for racing and can take the heat!
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Old 12-04-2018, 01:19 PM
Bdsankey Bdsankey is offline
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Quote:
Originally Posted by Clutch_less View Post
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.
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Old 12-04-2018, 02:22 PM
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Quote:
Originally Posted by Clutch_less View Post
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. Itís a side effect of a clutch that will actually hold up sadly.

As for fittings they are in the passenger front area, the gm doesnít even have the slightest provisions for them.

If youíre going to try and cool fluid through a cooler via pto covers youíll 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
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Old 12-04-2018, 05:20 PM
gmac32 gmac32 is offline
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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
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Old 12-04-2018, 07:15 PM
Clutch_less Clutch_less is offline
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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.
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Old 12-04-2018, 07:57 PM
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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.
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