Yep.

So if you have or when you have to rebuild your transmission you will go with the same tranny again? That must mean you think what your X came with is good enough and reliable enough?

It's lasted 128k miles. 126k of them supercharged.

Yes.

OT on On topic...

I have done numerous bolt drains a one pan drop

I did a full drop/and flush through the lines.
I was getting the 2-1 and I'm not going to say the full flush did something different, but the 2-1 has been gone since !

Jbelknap, good to know you got that many miles supercharged. One reason I am asking is that I have all the Dinan engine and transmission mods except supercharger plus I have 150 shot of nos. It is not something I use all the time but---

Anyone know why a later transmission like a 4.8 six speed won't work? What do you think of that transmission. Anyone know if 1st gear in a 4.8 is a lower gear ratio or did BMW stay with the same gear ratios through 5th and have 6th gear be a better mileage gear?

I can attest to the first gear being low in the 6hp26... it's done by 30mph!

I had my doubts about it before I changed the filter / fluid, but it has been solid as a rock for the last 6 months. No complaints here!

Well... that's not completely true. The $4.50 / gal for premium and only getting 23mpg is something we could touch base on, but it's not worth it :bustingup

No problems at 233K
 

Not running any performance equipment other than a K&N filter, but I have at least 20,000 miles of towing a big Yamaha Waverunner on mine. With 233,000 miles so far, I've never had a transmission performance issue and have never changed fluid. I am of the school of thought that unless you are regularly running fluids at extreme temperatures or in very dirty environments, you can cause more problems by introducing new fluid that has fresh "cleaning" agents into your transmission, especially with today's synthetic based, long-life fluids. A Mazda MPV I had went over 200,000 miles with the same fluid as well.

The X5 is equipped to tow 5000-6500 pounds from the factory with the simple addition of the receiver hitch and wiring harness. That's a pretty good indication of the reserve capacity of the engine cooling system and transmission's capabilities. Now if I were regularly towing in 3500 pound and up range, I would probably install an additional transmission cooler just to be sure.

If I ever do need to replace the transmission, I wouldn't hesitate to do it with a properly rebuilt unit of the same model again. Now about the improperly designed splines of the front driveshaft - that's a whole different situation!

150 good lord. That will shock the trans a bit harder than a centrifugal s/c, lol. Perhaps IPT could help.

The 6HP26 won't easily work due to a different communication protocol. The 5HP30 would be a closer swap:

http://www.xoutpost.com/bmw-sav-foru...-thoughts.html

Still, if it ain't broke.....

I don't have a high mileage X5 automatic as a reference point, but just a thought here. Transmission failures on X5s have shown the characteristics of reliability issues rather than durability issues. When odd components like temperature sensors, wiring harnesses, actuators, solenoids, computer controls, etc, fail, they tend to do so at very random times. The transmission is often deemed to have 'failed' even though most of it hasn't. The very existence of a wide spread of failure points is indicative of a reliability issue. When a transmission has durability issues, ie it wears out, the failures will usually be related to lubrication, heat and/or load, there will be a correlation with those factors and the miles at failure, and the failures will tend to be grouped or clustered more closely, (ie a common mileage limit)
since they have a common cause.

I think there is a confusion between reliabilty failures and durabilty failures on X5 transmissions. It explains why some people can drive 300,000 miles on original fluids, while others have failures in the 30k to 50 k mile range. It explains why failed transmissions are often not burnt, but rather pretty good inside, with normal fluid and good clutch plate life remaining. It also explains why the parts to fix an X5 transmission aren't really expensive (as not many are usually needed). Admittedly, labour is expensive.

For all of the above reasons, many of us won't change the fluid in our BMW automatics, and personally, I would never try to upgrade a BMW transmission with another automatic. It wouldn't be worth it, because hp and temperature haven't been shown to be the problem. No comment on whether your nitrous shot pushes it over the limit, I don't know. But the box used in the same model year diesel would be a reasonable option to investigate.

I agree 100% with JCL on reliability vs durability. I did have "silly" issues when the transmission harness connector was infiltrated by high water and dirt. The engine computer flashed out every possible error code it could think of and put the transmission into failsafe mode a couple of times. Once the pins in the connector were clean, everything worked fine. It turned out I had a "dry" wiring harness - one that didn't have any sealing grease in the connectors.