The transmission has a leak on the right side around the middle bolt on the pan is where it drips. Does this only when the transmission is hot.
If the car sits in the garage for a few days, there is no spotting on the floor.
It does not appear to be the seal for the solenoid valves(which I replaced when doing the pan, filter, tube seals etcetera) or the fill plug as best I can tell. Those areas seem dry.
I believe It was doing this before I did any work on this car but i never noticed it because the car was just sitting.
The pan has been replaced twice now and torqued correctly in the proper sequence but nothing changes. Seals on both new pans look good.
The bottom of the transmission that seals on the pan has been cleaned and checked for dirt and imperfections.
Any ideas?
THanks

 

My only idea is a straightforward bandaid: use a very thin line of Hylomar under the o-ring cavity. Am assuming you have an O-ring type seal. Thats what my Mercedes sourced 722.6 transmission has on the pan. Not sure if yours is similar.

Z

 

The electrical plug is the most likely source if it does not drip when standing as both the main pan seal and the fill plug are below the fluid level and I would expect those to drip continuously. You need to get under the car and spray everything with brake cleaner so there is no oil visible anywhere and then get the fluid hot and pinpoint exactly where the fluid emanates from as it might well be running down the side of the pan and along the seam before dripping.

Richard

 

The transmission fill plug is a single use part and often does not survive service events. You will note that the seal built into that plug is not very proud of the hard part.
Use a mirror to see if your leak is actually coming from above the oil pan.

 

I think that it's the drain plug that is a single use part on the 6HP plastic pan. The fill plug is metal and is above the pan.

Richard

 

The only likely leak points I can think of that would cause fluid drops on the right side are the fill plug and the electrical connector sealing sleeve. There is a tube on the top that runs from the front of the gearbox to the bellhousing, which I assume is a vent, but if fluid was leaking from that you would see it coming down the side of the transmission housing.

On the left side are the cooler lines - could fluid be leaking there, then finding its way around the pan to the middle right screw, which might be the lowest point?

Cheers,

Don

 

Thanks for all of the suggestions.
If I run it but don't get it warmed up, I see no drips. Only when it gets heated up.
Anyway, I have ordered another seal set for the electrical connector. Also a new fill plug
I never head that the fill plug is not reusable. Is that truly the case?
I have often wondered if the drain plug is never meant to be reused. Is that what you guys are meaning?
I have reused both in the past without issue but never liked reusing the drain plug.
I will continue to clean and investigate this issue.

 

The fill plugs with the green "rubber" seal are intended to be single-use items. One can re-use them in a pinch, but the probability of leaks increases.

 

OK. I must be wrong but I've refilled many ZF gearboxes over the years and I've only ever see single use drain plugs, not single use fill/level plugs, and only on the plastic pans. All the fill plugs I've ever seen on the 5HP, 6HP and 8HP have been metal ones in the side of the gearbox above the pan.

Richard

 

The plug is metal but the integral plastic seal is the concern. Many people re-use them without leaks, but service recommendations are to replace both the drain and fill plugs. YMMV

 

The filler cap is a standard part, available at any hydraulic parts supplier. Yes, it's best not to reuse it, even though it's usually included in the kits. As our colleagues have mentioned, the electrical connector can also cause problems; it's best to replace the entire assembly (not just the gaskets).

 

That's certainly not my experience as I've never replaced the metal fill plug and I've done many of these and they have never leaked. I don't even recall changing a rubber O-ring on the fill plug.

It's also pretty much the norm for manufacturers to state that a new oil drain plug should be used when changing the engine oil. However, over 60 years, I have changed hundreds of engine oils and I have never used a new drain plug but have only ever, if necessary, changed the crush washer. I've never had a leak.

It would be interesting to know how many people on here who have serviced ZF gearboxes have actually changed the metal fill/level plug? Either way, I very much doubt that the fill plug is the source of the OP's leak unless it has not been tightened correctly,

Richard

 

Well, I guess we can always learn something new. I have done many of these over the years and never replaced the fill plug with the green seal.
That being said, they are not expensive and i have ordered several for future use.

Now, has anyone ever reused the plastic drain plug or just gotten another pan?
They sell the drain plugs on a few sites so some one must have tried it, right?

 

I'm not sure why anyone would re-use the plastic drain plug?

It's definitely not supposed to be re-used but a new one comes fitted in the new pan which contains the new filter so, under normal circumstances, why would there be any need to re-use it unless you were not going to change the filter?

Richard

 

@RichardS I generally agree with that but I have seen instances where someone did the filter/pan replacement and one of two things occurred
They did not change the 4 tubes seals and/or the electrical connection seal and had to go back in or they tried a different fluid to try to fix an issue and did not like the results. For example, trying Mercon SP and wanting to back to LifeGauard.
Other than that, I see no reason either.
Thanks

 

The latest genuine ZF service kits includes a new pan/filter, new upgraded pan screws, and a new fill plug, so I now replace the fill plug as a matter of course. Before the ZF kits were available on the aftermarket, I reused the fill plugs. I don't recall having problems with a leaking fill plug, but it makes sense to at the very least replace the O-ring on the fill plug.

One thing to think about is that as the fluid heats up, it expands, so the fluid level in the pan rises. This is the reason the fluid level must be set at a specific temperature (40°C) and may be a clue as to why your leak only occurs when hot.

I have never re-used a pan drain plug because I have never re-used a pan. I've always replaced the pan/filter. However, when replacing the fluid by multiple drain-and-fill procedures, I will reinstall the drain plug in between drains. I do not like the way the plugs go in with that notchy-ratcheting feel, and I have tried to torque one to the spec that is embossed on the pan (8 Nm?), and the plug felt like it was not tight at the torque spec.

Cheers,

Don

 

@Don B I have never like the way the drain plug felt either but have never had one leak.
I plan to keep fill plugs in stock now.
Your explanation about fluid heating and rising makes sense.
Thanks

 

Interestingly, my fill plug (2004) did not have an O-ring, rather it had a flat soft plastic "gasket" bonded into a shallow circumferential recess in the underside of the plug. Reusing it did result in a small oil puddle underneath the car. The wet area on the transmission case was apparent with flashlight and mirror. Replacing the plug remedied that.

 

The green O-ring does sit in a shallow groove in the underside of the plug and, over time, it will harden and set into a flat profile. Did you try removing it as I suspect that it was simply an age-hardened O-ring.

Richard

 

As I mentioned, these plugs can be found at distributors of hydraulic automation systems (also online) and are inexpensive compared to the risk of using non-new ones and overtightening the plug. Even just to check the oil level (with the engine running and the crankcase at the correct temperature) after an oil change, it's advisable to replace it with new oil.