AT slow shift when cold

[curtdfw]

My '96 318ti with 140k doesn't want to shift when cold, running up to 3k+ for up to 10 seconds before doing so for the first 5 or so minutes of operation. However, if I warm up the car for 5-10 minutes, all is well, shifting is fine.

I've had the car only for about 8 months, and it hasn't got any worse, which is mildly encouraging. Ambient air temperature doesn't seem to affect it either - summer in TX and now winter in UT hasn't changed the behavior. Since I don't know much history of the car (and the PO lied about several things) I'm wondering if a trans fluid and filter change might have an effect. I can't be certain that it's ever been done but, as it isn't a $19.95 job, I"m hoping for a likelihood that it could be a useful thing to do. Suggestions appreciated.

Tks,

Curt

[Manolito]

A noticeable lag between shifts when cold is normal for this transmission, but not 10 seconds! One second with a noticeable rev up and then a hard engagement when cold is normal. This goes away as the transmission warms up.

Regular transmission fluid and filter changes (every 40-50k miles) make the normal lag far less noticeable, but your ten second lag scares me a little.

To properly fill the transmission fluid, you need to be able to raise the car level, and to plug in and read the transmission temperature. Any good European specialty shop can do this but a quicky lube place probably can't. Some folks do their own at home, but this is one of the few jobs that I pay a shop to do. My wife's 330 is due, and I am dreading it because the synthetic fluid used in the e46 transmissions is like liquid gold.

[curtdfw]

Thanks for the reply. I wasn't especially clear - it isn't a lag between shifts, the shift cycle itself doesn't start for up to 10 seconds when cold. It'll run up to maybe 3500 rpm if I accelerate that far, which I generally don't. Once the shift cycle begins, it's a bit slow when cold, as you note, but acceptable.

I'm not inclined to home shop a trans fluid change either, so I suppose I'll pony up for a shop.

[Casmige]

Hi!!,

Just my 2 Loonies worth:-

Automatic Transmissions work off of Fluid Pressure.

The Fluid Pressure actions the hydraulic clutch packs, Shift Servo's (Which determine shift points based upon pressure pre-sets), & Lubricates the transmission.

When an Automatic Transmission shifts SLOW, it usually means that the Pump is unable to get enough of the transmission fluid to pump through the system to effect the Various "Actions" as required....so it's essentially suffering from fluid starvation until the transmission fluid is sufficiently heated up (So that it loses some of its viscous properties or "Thickness" when cold) to get around the insufficiency or bottle-neck in the process.

The bottle-neck is usually a clogged filter element.

Unlike an engine oil-filter system which has a built in By-Pass that allows the oil to "Go Around" the filter element when the filter is clogged & presents too much of a "bottle-Neck" for the oil to filter through (Said by-pass being the better of 2 evils:- Engine oil starvation versus filtered oil), the transmission does NOT have a "By-Pass" Option...excepting for the "natural" one whereas the thinning fluid is able to find the path of least resistance without bottle-necking at a clogged filter media which feeds the hungry pump & finally/fully provides enough fluid to subsequently cause the automatic aspect of the transmission (Which depends utterly upon hydraulic fluid "Action") to "Work".

1). Fluid & filter change after banging a quart of Trans-X flush through the system should be the cheaper of the 2 possible fixes.

WHAT???!!, what else could it be???.

2). the aged fluid that has prolly never been changed CAN cause sludge build up on the shift solenoids causing them to stick & not function properly until & unless they are heated up (Which expands the tight tolerances a bit) allowing them to operate somewhat properly.

#1 is easier to accomplish (Dropping the pan, getting fluid everywhere, changing the filter & fluid) than scenario #2 (Requiring much more invasive dis-assembly with regards to the Valve Body & internals).

WOWZA~~ sorry...that's more than a couple loonies worth...

hope it helps though.

[curtdfw]

Thanks for the detail - will get the fluid changed and pass along the result.

[InSanel]

Just out of curiosity, try taking your knob and shift through all the gears and then go back to drive and test it out. For some strange reason my car does the same thing for the first 2 minutes unless I do this and then it shifts just fine.

[curtdfw]

Got the fluid changed yesterday - an improvement, but still a little stiff when cold. Will try manually running through the gears and see how it goes.

[bostogrun]

This has been talked about so much on these forums.

These cars BMW 3 series supposedly have "lifetime tranny fluid" which is really plain old Dexron 3 because these are General Motors trannies anyhow. The lifetime fill means " life of the warranty or 100k most auto trans will last 100k without a change of fluid just like most engines will last 40-50k without an oil change. If you want to get another 100k out of the tranny beyond the first 100k you have to change the fluid, even though BMW says you dont here's why:

Tranny fluid is a hydraulic fluid, a lubricant and a coolant unlike motor oil that is mostly a lubricant and to a lesser degree a coolant. Tranny fluid unlike motor oil is in a sealed system so it doesnt get contaminated with carbon from combustion like motor oil. Tranny fluid does however get contaminated with microscopic debris similar to saw dust which is the result of the paper clutches wearing out and contanimating the fluid. Plus small metal shavings form metal parts wearing out also gets suspended in the fluid making it slighty abrasive thus speeding up the wear of the internal parts.
The fluid also wears out from molecular shear as a result of years of being smashed against metal gears millions of times. The fluid actaully looses it's ability to push mechanical devises.

Inside your tranny fluid body there are many worm like passges that are connected by a variety of very precise valves that can get gummed up by dirty fluid and make them not function correctly.

After too long, dirty fluid will clog the filter, so the tranny cant suck enough fluid to operate correctly causing lags in shifts.

Some people say dont change the fluid if the tranny is old and never had the fluid changed
before because they believe that the old tranny is used to and needs the "grippiness" of the contamianted fluid to compensate for worn out internal parts but thats not true. The problem is when you flush old fluid that stirs up all the debris in the pan and can clog thos passage ways and valves.

[aayesh11]

The easiest and best solution is to drop the pan, replace the filter and gasket. You will need to only refill it about 5-7 quarts with GM DEX VI. The new fluid will mix with the old fluid in the tranny creating a good balance. The mixture won't harm the transmission because the detergents in fluid are diluted. When draining, it's best to just let it sit for a few hours with the pan off and allow as much fluid as possible to drain out. Removing the solenoids allows additional fluid to drain out. Refill and you should see that this issue is greatly improved. It won't be perfect but a lot better. The only way to get it perfect is to replace all of the solenoids and maybe the vavle body. Plan on replacing the fluid every 30,000 miles after you have exceeded 100,000 miles for best results. I went to the dealer to get this service done at 156,000 miles and they advised me against doing it because they said that flushing it could harm the transmission with my high mileage. At 170,000 miles, the pan gasket started leaking and I had no choice but to drop the pan and replace the gasket. while I was at it, I replaced my filter. I had suffered from the issue of slow shift in cold weather for years at that point. I noticed after dropping the pan and replacing the filter and fluid the issue was resolved. I now have 221,000 miles and continue to do this service every 2 years.