I think I've decided that I'm going to try to flush my transmission when it finally warms up around here, but was hoping somebody could provide confirmation on the flow direction of the tranny fluid.

Am I correct in my understanding that the lower transmission pipe going into the radiator is the supply line (i.e. fluid going from transmission to radiator) and the upper hose coming out of the radiator is the return line (i.e. fluid going from radiator to transmission)? Thanks in advance.

 

There are a number of files in the link below related to our ZF 6HP26 tranny.

As to flushing, maybe you should consider removing/replacing the pan/filter combo, a whole lot bigger project but perhaps worth considering.

DISCO3.CO.UK Photo Gallery - ZF 6HP26 Automatic Transmission in LR3

 

Thanks. I actually ended up doing this yesterday and can confirm that the upper hose is, in fact, the return hose.

If anybody ends up doing this themselves in the future, note that you need a 1/2" inner diameter hose (I cut it into 2 pieces) and a 1/2" ID barb connector. I disconnected the upper transmission line to the radiator and then connected a short hose to the transmission hose with the barb. I fished this up to the top of the engine bay and put a funnel in the top. I then used the other part of the hose that I cut to attach to the radiator (it fit snug enough that I didn't need to use a clamp) and fed it down through the engine bay to a milk jug on the ground.

I thought that I would turn the engine on and try to feed oil in at the same time as it was pumped out by just pouring it into the funnel. I quickly realized that this was not going to work. I would say that the entire 1 gallon jug filled with fluid in 45 seconds or so... but it probably took me 45 seconds to pour in 100ml of new fluid (if that gives you any idea). The hose was just too small and gravity wasn't strong enough to push the fluid into the tranny.

So... I ended up recruiting my wife to hold the gallon jug and I would turn the engine on, pump out 1/2 gallon of tranny fluid, then spend forever pouring 2 liters of fluid back in. Repeat. Repeat. Repeat. Repeat.

In the end (after about 10 liters of fluid), I started to get the golden colored stuff coming back out, so I made sure I overfilled a little bit, then buttoned her back up and went through the fluid leveling process.

I would say that this process was significantly easier than I thought it might be, BUT it also took me a loooooong time (maybe 3 hours) due to the slow rate at which the transmission accepts the new fluid via gravity feed. Considering the temperatures here right now, it was still preferable to trying to crawl under the car and pump fluid in via the fill hole.

Oh, and as far as the transmission filter... I just replaced the tranny filter on my L322 RR and it was in good shape at 100k miles despite not being a well taken care of car in it's previous life. Therefore, I figure the LR3 filter is probably fine and I don't want to go through the hassle and headache of trying to replace that thing. My plan is to change the tranny fluid every 75k miles or so and do the filter (or pay somebody to do the filter) at every other oil change (so every 150k miles).

In the end, the fluid did make a big difference. The shifting is soooo much smoother now and the car feels fantastic. I would say that the shifting is still not quite as smooth as the L322, but it is greatly improved over what it was and the oil change was definitely worthwhile. I'm very happy about the results!!

 

I think this is a brilliant way to go. I understand your process, but can you please explain what you did for the final "Leveling process"?
Filler plug removal, check for a drip, add or let drain, etc......?
Thanks.

 

Sure... I'll give you the long winded answer.

One thing to note though. I read somewhere else online that people have had much success feeding fluid in like I did by using some sort of pressurized device - either a garden sprayer, a manual pump, a gas canister that's been pressurized, etc. I would highly recommend adding some sort of pressure (even if it's just a little bit) to feed the fluid in. It literally takes forever to let gravity do it. :P

I leveled the fluid according to the manual, and while this is not technically challenging, it is definitely more difficult than on the L322. The problem lies in where the stupid fill plug is located on the LR3 tranny. It just happens to be directly above the exhaust and right next to the catalytic converter. Whatever genius did that deserves to have his arms branded with a hot poker!

Anyway... steps are listed below:

1. When you are flushing the tranny, make sure you overfill by a little bit (I aimed for 200cc or so, but probably put much more in by accident).
2. Crawl under the car and find your transmission fill plug. It is located on the passenger side at the rear of the transmission.
3. Get a (8mm I believe) allen socket and loosen the fill plug, but do not remove it yet.
4. Go start your engine.
5. Slowly shift through your gears, pausing 2 seconds or so in each gear. I did this a few times to make sure the oil was getting into every nook and cranny of the transmission.
6. Crawl back under the car and remove your fill plug. Be careful because the exhaust heats up quickly. Oil will immediately begin to flow out of the fill hole. That's okay and expected. You did overfill the tranny (but just by a little bit I hope).
7. Monitor the transmission temperature. I did this via a BT IID tool. Just watched my ipad until the transmission temperature finally crawled up to 30 degrees C which took FOREVER in the cold temps we've had around here. I suppose you could try an infrared thermometer on a metal part of the tranny pan too, keeping in mind that there is probably a temperature lag with that method (pan will likely be cooler than the fluid). You have a fairly wide margin as you want the transmission temperature to be between 30 and 50 degrees Celsius.
8. As the fluid heats up, it expands, so you will continue to get a small drip/dribble from the fluid fill hole. Once you are within the temp range, simply replace the transmission fill plug and turn off the engine.

Two notes here - first, by the time you get the transmission fluid up to temp, the exhaust will be freaking hot. In order to avoid burning myself, I put on my mechanix gloves and wrapped a rag tightly around my forearm. I then cinched/velcroed the wrist part of my gloves around the rag to hold it in place. This worked great. I also went very slowly because I knew I had a lot of time. I would recommend just getting the plug in the fill hole a few turns, then shutting the engine off and coming back when the exhaust has cooled down in order to tighten it. - second, if you turn the engine off at any time during this process, lots of fluid will immediately spill out of the hole. Having the engine on keeps the fluid in motion and prevents it from settling in the pan. I guess what I'm saying is that you need to put the fill plug back in before shutting off the engine or you will lose a bunch of fluid.

All in all, this is actually much simpler than I'm making it sound. Just wanted to try to give as much detail as possible.

Hope this helps!

 

Thank you!!!!
Very straight forward and clear.
Cheers,

 

Thank you, I'll be doing this in a week or two and I have found very little info on flushing. I have read a lot of people say their filter looked fine. I'm at 80k and I feel flushing is the way to go to get more fluid exchanged. I think you have the right idea about doing the filter on the next change.

Would a fluid pump work to put fluid back in?

I've done flushes before where each line is in a bucket. One for old fluid coming out and one with new fluid getting sucked in. It makes it easy to see put in exactly what comes out. But I think I read that our systems don't have a strong enough vacuum (or maybe it's vented?) so this process doesn't work. Can you confirm?

 

A fluid pump should work just fine. I used a hand pump to fill my L322 transmission with fluid directly into the fill plug on the transmission. Still a bit slow (you won't be able to fill the fluid as it comes out - you'll have to do the same start/stop method that I did), but it should be much faster than doing it via gravity.



I believe the transmission is vented, yes. And I can confirm that there is no vacuum to draw in fluid. I tried this initially by filling the funnel, hoping that it would get "sucked down" into the tranny. No such luck. :P

 

Maybe blocking the transmission breather tube will allow fluid to be drawn in during your flush? The tube is between the engine and the firewall. The transfer case breather tube is also there. They are both black thin tubes, similar to the front diff breather tube, except neither of them have the cap like the diff breather. The tubes simply curve downwards to prevent water ingress.