ZF6 transmission cooler pump

[rascal]

Ok, I have done some research but can't find anything.

I have a ZF6 and recently added the DieselSite transmission filter. I ordered the pressure gauge with it but I never get a reading. I have disconnected the lines with the truck running but I do not get any flow.

However, my fittings were leaking (did not have enough teflon tape) and the lines had fluid in it. The general consesus is that the pump runs when the engine is running but it seems to only run with the truck in gear. I have done everything short of putting the rear on jack stands and putting it in gear.

Is anybody here familiar with these pumps and how they operate?

Thanks,

[jimmyp]

ZF6 is a manual transmission..... doesnt have a pump, and i cant imagine it needing a cooler

Jim

[rascal]

Jimmyp, do some research on the ZF6.

[jimmyp]

I stand corrected...... learn something new every day.

Jim

[Matthews]

The pump should run anytime the clutch is out. The pump runs off of the cluster shaft in the transmission. The cluster shaft spins anytime the input shaft spins. There is no need to jack up the back end. If you are certain you are not getting flow then there is probably something wrong with the pump or an obstruction on the suction line to the pump. I would be surprised if you ever saw any significant pressure on the line unless you had blockage in your cooler. Is this gauge meant for an automatic transmission?

[rascal]

Originally Posted by Matthews

The pump should run anytime the clutch is out. The pump runs off of the cluster shaft in the transmission. The cluster shaft spins anytime the input shaft spins. There is no need to jack up the back end. If you are certain you are not getting flow then there is probably something wrong with the pump or an obstruction on the suction line to the pump. I would be surprised if you ever saw any significant pressure on the line unless you had blockage in your cooler. Is this gauge meant for an automatic transmission?

Ok, that is what Bob@DieselSite told me too. However, it appears that fluid is being run through the system since I am getting leaks. However, when the truck is idiling it does not appear to be moving fluid throught the system.

Another question, could the pump not working properly really hurt the trans? I know many manuals do not have any type of fluid cooling system. The tranny shifts fine while driving it. Also, as I am sure you know, the ZF6 has an aluminum case so heat should not really be an issue.

Do you know if the pump runs at a single speed or does it pump faster when the rpms are up? Just wondering why it appears I am getting flow while driving but none while idling.

Yes, the pressure gauge is mainly for the autos but I am glad I put it on.

[Matthews]

Whether or not you hurt the transmission without the pump would depend on what you are doing with the truck. From the sounds of it, there are people who end up with pretty high temps when hauling large loads and that would presumably with a good cooler pump so I would say there is a risk if you work it hard for a long time. While the zf6 has an aluminum case, it is a very densly packed transmission and there are no external fins to increase surface area.

The transmission fittings could still leak without moving fluid because they are below the level of the fluid in the transmission. I would not take the leak as a sure sign fluid is pumping.

The pump is a positive displacement style pump so the amount of fluid it pushes is directly related to pump speed which is directly related to engine speed. It will pump more fluid at higher rpm.

Why are you glad you put the pressure gauge on especially if its not showing any pressure? What is the range on the gauge? I would guess the most you would ever see on your system if you put it directly at the outlet of the pump would be 1psi or something. If you have a gauge that goes to 100psi or more then you would never expect to see it move. The cooling system on the zf6 is not meant I operate under pressure, it is simply a circulation pump. On an automatic, the system works under pressure. I don't think your gauge is serving any purpose.

[rascal]

Originally Posted by Matthews

Whether or not you hurt the transmission without the pump would depend on what you are doing with the truck. From the sounds of it, there are people who end up with pretty high temps when hauling large loads and that would presumably with a good cooler pump so I would say there is a risk if you work it hard for a long time. While the zf6 has an aluminum case, it is a very densly packed transmission and there are no external fins to increase surface area.

The transmission fittings could still leak without moving fluid because they are below the level of the fluid in the transmission. I would not take the leak as a sure sign fluid is pumping.

The pump is a positive displacement style pump so the amount of fluid it pushes is directly related to pump speed which is directly related to engine speed. It will pump more fluid at higher rpm.

Why are you glad you put the pressure gauge on especially if its not showing any pressure? What is the range on the gauge? I would guess the most you would ever see on your system if you put it directly at the outlet of the pump would be 1psi or something. If you have a gauge that goes to 100psi or more then you would never expect to see it move. The cooling system on the zf6 is not meant I operate under pressure, it is simply a circulation pump. On an automatic, the system works under pressure. I don't think your gauge is serving any purpose.

Ok, I just meant I was glad because it alerted me to a potential issue. Is the pump only accessible by gutting the tranny?

Are you a transmission mechanic? You are the most knowledgeable person I have run into so far.

Thanks for your help

[Matthews]

I am not a transmission mechanic. I am a guy who has done a lot of automotive work in my lifetime but it has all been personal or for friends and family. I tend to get into a lot of my own projects. I know what I do about the zf6 because I just did a zf6 conversion on my own truck and after I got it together found out that my donor transmission had some shifting issues with second gear. The problems was bad enough that I wanted it fixed but I didn't want to pay a couple grand to fix it. So I tore into it myself. I had to disassemble almost all of it to change out second gear on the main shaft as well as the slip ring and 1st and 2nd synchro wear parts. It costed me about $275 in parts and a fair amount of time but it also allowed me the opportunity to find that the last guy to get into it didn't shim it properly and I fixed that while I was in there.

I haven't driven it much since I got it back together but my dad did some hauling with it the other day and said it felt good. So, the knowledge I have about it is mostly firsthand knowledge and some knowledge I found researching for the project. Let me know if there is anything else you like to know.

Something to think about is that the gm version of the transmission doesn't have a cooler (from what I have read) but is very similarly built.

[rascal]

Originally Posted by Matthews

I am not a transmission mechanic. I am a guy who has done a lot of automotive work in my lifetime but it has all been personal or for friends and family. I tend to get into a lot of my own projects. I know what I do about the zf6 because I just did a zf6 conversion on my own truck and after I got it together found out that my donor transmission had some shifting issues with second gear. The problems was bad enough that I wanted it fixed but I didn't want to pay a couple grand to fix it. So I tore into it myself. I had to disassemble almost all of it to change out second gear on the main shaft as well as the slip ring and 1st and 2nd synchro wear parts. It costed me about $275 in parts and a fair amount of time but it also allowed me the opportunity to find that the last guy to get into it didn't shim it properly and I fixed that while I was in there.

I haven't driven it much since I got it back together but my dad did some hauling with it the other day and said it felt good. So, the knowledge I have about it is mostly firsthand knowledge and some knowledge I found researching for the project. Let me know if there is anything else you like to know.

Something to think about is that the gm version of the transmission doesn't have a cooler (from what I have read) but is very similarly built.

That's awesome. I do a lot of my own work but I don't really know how to repair this transmission. I could probably take it out but as far as tearing into...well...I am sure I could take it apart but I am not sure I would know how to put it back together properly.

As for your GM ZF6 comment I have thought about that and that is why I asked if it was hurting the tranny if the cooler pump is indeed not working.

Have you ever disconnected the cooler return line with the truck running? I would be curious to know if fluid would be just gushing out.

I have just changed the tranny fluid and put in Royal Purple Syncromax fluid. That is how I could tell new tranny fluid was in the cooler and lines.

Again, thank you for your help. If you get bored please disconnect one of your lines and let me know what you see. However, I won't hold my breath that you get that bored.

Thanks