External transmission filter
 

I've been lurking and reading all of the post's about changing tranny fluid or not. Seems like the main reason to avoid changing the fluid is that the new fluid has more detergent and dislodges particles that have nowhere to go.

I was wondering if an external transmission filter might be the answer.
Has anyone put one of these on their X5?

B&M 80277 - B&M Remote Transmission Filters - Overview - SummitRacing.com

I've never used one, but I have used additional remote engine filters in some applications.

You would need to determine whether you have a pressurized gallery on the transmission with external access, and an unpressurized one for the return flow.

The damage that can happen to valve bodies is with very small particles. They could cause that damage before ever getting to a filter.

I have added these to other cars and you just use the lines that go to the trans cooler that is mounted on (or in) the radiator. I'm new to BMW's, so not sure if that set up works.

That would work fine. The only question would be what the pressure drop is across the filter, and whether it restricts flow to the cooler.

This guy says not to do it on ZF transmissions. He is talking about Land Rovers, but I would guess that they are the same for the x5...


External Filters

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From: Gomes, David
Sent: Friday, September 29, 2000 11:44 AM
Subject: ZF says NO to external filter for LR auto trans
Okay, I've done a little research in response to Cliff's desire to fit an external transmission fluid filter.

First of all, let me say a HUGE thank you to Bill Ritchie for the (very timely) link to AUTOMATIC TRANSMISSION PARTS and OVERHAUL KITS the fellow I spoke to there (Jurgen) is, in my opinion, a true professional, very helpful, and dedicated to good customer service. This guy has been running all around for me for the last day and a half, and I didn't plan to spend a cent with him.

When I first asked Jurgen if I could fit an external filter to the ZF transmission's cooler line, his response was (in your best German accent), "it never hurts". I then told him I'd heard from some pretty reliable sources that the fluid flow in the cooler lines would reverse on torque converter lock up and effectively, back-flush the filter. He said he wasn't sure, and that this was the first time someone had asked him, but that he would check with ZF's US office in Chicago.

With a couple more rounds of phone calls, and Jurgen chasing down engineers at ZF, it came down to this.

The ZF transmissions in our Defenders and Discos have a mechanical valve body. There is an electronic valve body model, but it would be recognizable from in the cab by a "sport/economy" switch near the shift lever. ours is all mechanical (YEA!!!) and controlled by cables and levers. According to the engineers at ZF, in the mechanical version (like ours) the fluid flow in the cooler lines DOES reverse when the torque converter locks up, so unless some extra system of check valves and bypass lines were fitted along with the filter, the filter would be pointless because it would self-backflush every time the torque converter locked and unlocked. Or worse yet, if a canister type filter with anti-drainback valve were inadvertently fitted, it would try to stop all flow when the converter locked up and fluid reversed.

On top of that, Jurgen said he was advised by the ZF engineers that one should NEVER fit an external filter to this model of transmission. Upon torque converter lock up, the pressures in the cooler lines go to 60-70 psi and ZF knows of at least one case where an external filter ruptured, spilling fluid onto the exhaust and setting fire to the vehicle. So they say DON'T DO IT.

I know, I know, I too could design a system that would be safe and effective. But for the added cost and complexity, it's just not worth it, in my opinion. I'll stick to changing the fluid and the internal filter.

And here's Jurgen's words on that. He says it's his own personal opinion and practice (NOT from ZF, or anyone else) that the transmission fluid should be drained (what you can get from the pan) every 10,000 miles and the internal filter replaced every 30,000 miles for optimum performance and long life. Transmission fluid, even the good stuff, is cheap enough that I can afford to do this. And with the price of replacement transmissions and parts, I think it's cheap insurance. ZF is nice enough to provide an easy access drain plug, so I say, make use of it every 10,000 miles, or every 3rd engine oil change for most of us.

Jurgen also says he has repair manuals available for the ZF transmission. He says the only drawback of this manual is that it doesn't provide information on the valve body, one of the more complex parts of the trans. But if one is interested in overhauling the ZF trans with new clutches, seals, steels, bands, etc, this manual would help. I have him checking for me now on the price of the manual, and his price on filter kits. I'll follow up this post when I have more information. JIE also supplies various levels of rebuild kits for the ZF transmissions, with all OEM parts. Transtar is another source of rebuild kits, but they are not OEM ZF parts.

-Dave G.

Interesting information on the reverse flow with torque converter lockup. I do agree that an external filter adds an additional failure mode due to leaking.

The information is more than 10 years old, however. Times have changed, we have new transmissions that are fully electronic, and we have new fluids. I don't know if the electronic version they are referencing is the same as an early X5 or not. And ZF-specified fluid is not cheap, as they suggest.