Overheating transmission

[WrightWay]

This truck has been quite dependable on my trips without a trailer yet when I haul a heavy trailer for too long the clutch seems to start grabbing in first gear and the transmission case gets very hot to touch. It happened again yesterday while hauling loaded hay wagons. Couple trips of 30 minutes at 30 mph 3rd gear mostly. Sometimes I can smell it before I notice other signs.
The clutch, flywheel, and pedal linkage were replaced 4-5 years ago.
When that work was done ‘tractor fluid’ was put in. Since then I have drained and flushed that out and replaced with ATF which is correct I believe.
I am unskilled but willing to work on mechanical stuff.
reading the posts on this site has been very helpful through the years keeping this truck running good.

 

[Big Bart]

I beleive the 5 speed with aluminum case called out ATF but I will let folks with sticks weigh in here. As I recall there are folks who have tried other things. I have a C6 auto so not an expert by any means on fluid or fluid alternatives.

Keep in mind your engine temp is 190-220 F. So your engine can transfer that heat to the tranny. So perhaps if you have a laser temp guage you take the actual temp and let us know what that is. If under 220, I would not be surprised towing heavy and slow.

In the short term some other thoughts.

1) Did you check the ATF level to insure it is correct? Low on ATF could be your issue. Too full could also cause it to work harder. (Generally there is a plug on the side so hard to over fill unless you use the stick shift port.)
2) Did you use the right ATF last change? (Maybe it calls specifically for ATF - 4 (Synthetic.) not ATF Dex/Merc.) BTW some tractor fluids are mainly ATF with some additives. (Red ones) As in some tractors the axle, tranny, brakes, and lifting system all share the same case.
3) Have you mixed ATF brands or types to top off? Could be a mismatch that is causing a problem.
4) Have you re-routed the exhaust (Or is it very close to the tranny) in a way it sits close to your tranny and perhaps as you EGT's go up your tranny fluid gets hotter.
5) Is the truck happy in 3rd gear and 30mph? My point is if you are bogging it down or you are running say at 3,000 rpms (When unloaded you run at 2,200rpms.), you could be causing the engine and tranny to work harder or faster and that would also create more heat than normal. Or the lack of wind at 30mph, 95 degrees outside, and the heat pouring down from the engine and exhaust, is causing the tranny to heat up.
6) Could be a bad bearing or two in the tranny. So look for metal or shavings when you drain. There is usually some metal but not big shavings or pieces. Also if you fluid has lots of shinny ground up metal througout. (Not just for a second when starting to or finishing draining. Could be time to open it up.

Others will chime in on the fluid and their toughts. If others have seen this they can share what they did to resolve.

Let us know what you come up with!

 

[Danielle]

My first issue when I got my truck was I didn't realize I had leak in radiator and my ect was garbage. But I didn't know it!

So I was running very hot, which was cooking my transmission fluid! I couldn't figure out why my trans temps went up so fast.

I eliminated the radiator cooler and installed a big ass transmission cooler, trans temps dropped.

Then dug into it more and found my radiator top tiny leak. I still keep it bypassed but that truck has an e4od so I try to keep it cool as possible

 

[gandalf]

...

I eliminated the radiator cooler and installed a big ass transmission cooler, trans temps dropped.

Then dug into it more and found my radiator top tiny leak. I still keep it bypassed but that truck has an e4od so I try to keep it cool as possible

I did much the same, though I did not have a radiator leak. I simply wanted the E4OD to run as cool as possible. After all, it's a well known fact that heat is what kills the E4OD. The big transmission cooler is a lot less expensive than a rebuilt transmission. I run the fluid from the transmission through the radiator cooler, then the auxiliary cooler, and back to the transmission. My E4OD has never run hot.

This may all be academic though. I believe the OP is running a ZF5, as listed in his sigblock. OP, please verify.

 

[Big Bart]

My first issue when I got my truck was I didn't realize I had leak in radiator and my ect was garbage. But I didn't know it!

So I was running very hot, which was cooking my transmission fluid! I couldn't figure out why my trans temps went up so fast.

I eliminated the radiator cooler and installed a big ass transmission cooler, trans temps dropped.

Then dug into it more and found my radiator top tiny leak. I still keep it bypassed but that truck has an e4od so I try to keep it cool as possible

Danielle,

Just a couple of things to consider and monitor. Others who did the radiator delete on their auto tranny said -

1) Found out on hot days in bumper to bumper traffic towing their temps got too high. (Trans cooler was not cooling as no air going through the fins.)
2) Also in very cold temps the ATF took much longer to warm up.

Neither may be a consideration for you, but just some food for thought. I have always run both and had good results.

 

[Big Bart]

Andy,

I looked into it, from what I see Mercon - V is what is called for. (Synthetic ATF.) Let's see what others say works best for their ZF5.

Here is a link from prior discussing this.

https://www.oilburners.net/threads/atf-or-mercon-v-in-your-zf5.71178/

 

[IDIBRONCO]

I can say that the clutch in my Blue Truck also gets a little bit odd when I'm pulling a load and the transmission is (relatively) hot. I guess the best way to describe it is that it gets jumpy. My solution is to rev the engine a little bit higher and slip the clutch slightly more. It may be mostly from the 3.55 gears. I don't recall the same clutch, pressure plate, and flywheel doing it very much in the bronco which had 4.10 gears. I'm getting ready to switch from dino ATF to synthetic and I want to do it before I go to Colorado at the end of the month. I'll have feedback after I do the switch.

 

[WrightWay]

Thanks all for your replies and information.

Brad
1) Yes a ZF5 and i will have time to check level and will drain it to check for metal tomorrow
2) fluid i used 18 mo ago was Castro trans max Merton V which I believe is synthetic. From the other thread maybe I should go with 1
3) there was no mixing of brands
4) no exhaust change, truck has always been kept stock
5) this truck is happy to pull, I don't bogg it down. it seemed quite happy in 3rd gear at 30 mph, seems to like higher rpms although the tach is not accurate at all.

From other postings, sounds like I need a tranny cooler. Any suggestions on a specific type?

IDIBRONCO- 'jumpy' is great description of way the clutch feels in first gear at these episodes and yes if you rev and play with clutch it takes off well and no issue in upper gears.

Thanks again for all the replies, I get working on it tomorrow and get back to you folks

 

[Gumpy]

I'm not familiar with the internals of a zf5 but I think most manual transmissions do not have a fluid pump in them. An auto transmission has a fluid pump in it that performs various functions but it will also pump fluid through an aux cooler. I think manual transmissions generally do not get hot enough to need any special cooling considerations.

 

[Big Bart]

Andy,

I think a drop and replace of the ATF will bode you well. Smell it to see if it smells burnt or if the coolor is off like it has been overheating. You will see grey matter throughout the ATF if it has issues. However as I mentioned before you may see some grey material when you open the drain plug or when the tranny is down to the last part draining. Pour out the pan after draining and look for metal in the bottom of the pan. If you find anyting concerning take a pic and post for the group to look and report back on.

No cooling lines on a ZF5 so no external cooler avaialable. Trans cooler comments were in regards to if you had an automatic tranny.

Perhaps pick up a laser infrared temp gauge. $20-40. Then you can kneel down, click, point, and see what your tranny temp is. I would guess it runs around 190-220F as it would absorb heat from the engine 200F, exhaust would also add heat, and the transmission itself would develop some heat. If 230-240F after a long hard pull, still would not concern me to much. Over 250 would want to know if that is normal for a ZF5.

Send a couple of pics and let us know what you find!

 

[IDIBRONCO]

fluid i used 18 mo ago was Castro trans max Merton V which I believe is synthetic.

I think you're right. I believe that all Merc V fluids are synthetic.

IDIBRONCO- 'jumpy' is great description of way the clutch feels in first gear at these episodes and yes if you rev and play with clutch it takes off well and no issue in upper gears.

It only does this while starting out from a dead stop and only after towing for an hour or so. I feel that it's due to the 3.55 gears so I live with it and consider it kind of normal. I forgot to mention that I have a Luk SMF conversion kit. It may be possible that it wouldn't work with a DMF or even another brand.

I think most manual transmissions do not have a fluid pump in them.

This is true except for the ZF6. They do have cooler lines and use a trans cooler so they must have a pump inside them. That's only from observation. I have never had a ZF6 open.

 

[WrightWay]

The tranny was full, drained out into a clean pan. Fluid was red and seemed normal viscosity compared to new stuff. It was slightly darker and had a barely detectable burnt smell. Left in the pan were 15-20 1mm or so grey metal flecks. Fluid was not cloudy. Refilled with Mercon V valvoline
Seems to be some question if it is blended or fully synthetic from other info??
The truck has only 5K miles on this fluid as it is stored in a barn during salt season here.
See if can send pics

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[Big Bart]

Andy,

I do not see anything note worthy in the pan. There are always small flakes from wear and tear as well as syncro's and other wear parts.

Let us know if the Mercon V ends up shifting better or worse than the Castrol. If towing I would recommend changing your tranny ATF every 30,000 miles.

Since your fluid was not a burnt color and did not smell burnt (Or in your case slightly) then your tranny is not getting too hot. If still concerned you could get a laser infrared temp gun and shot the tranny in a couple of places each time you think it is heating up. Would expect front of case to be warmer due to engine heat transfer, the bottom half to be warmer than the top half due to the ATF sitting in the bottom half.

 

[WrightWay]

Brad
Appreciate your input, sounds like there nothing else to do there. That tranny has a lot of miles on it (likely 440k) but truck was very well maintained in its first life. I have learned a great deal from this site to continue that.
I’ll see if I can round up a temp gun then check when pulling next time and get back to the group.

It’s 90 today again and fortunately my hay hauling duties are done for now. send some rain here if anyone has extra.

 

[Philip1]

If you do find the transmission is in fact overheating, there is a bolt on cooler that attaches to the pto covers called fast coolers that might help.

https://www.ebay.com/itm/313551569226
I do not personally have any experience with them yet but I do plan on installing them in the future onto my zf5