Question for auto transmission gurus.
 

My '01 4.4i 135,000 mi X5 shudders during light load acceleration.
It will not shudder much at all under hard acceleration.

I though it could be a worn torque converter or trans fluid having over 100,000mi.
After much debate and reading all the horror stories of changing auto trans fluid, I decided I would change the fluid.
(dropping the pan and replacing the fluid/filter, not a power flush)
Figuring the viscosity was too low in the old fluid and causing some slipping.

However, one day I put the trans in manual to gear down for a big hill and it didn’t shudder at all.
I’ve been driving it for a while now in manual and it drives fine.

Does anyone know what would be different in manual mode vs. auto what would prevent the shuddering?

Older trans fluid will generally have a higher viscosity.

If it is shuddering in an automatic mode and not in manual mode that suggests a problem in the valve body or electronic controls.

Manual mode will usually force a lockup of the torque converter, sounds like the judder is from the TC slipping in auto mode.

Shuddering during acceleration does indicate TC issue. You may also hear an a whining or grinding sound. I would get it checked out ASAP as a bad torque convertor can damage the transmission. BMW dealers only replace transmissions. I suggest taking it to a recommended transmission shop that is familiar with BMW transmissions.

Wouldn't I get a TC slippage warning?
Or does it need to slip really bad to throw that code?

Might also be worth getting the MAFs checked out, they can cause gearbox funnies.

What, if any, codes are you getting?

If the MAF could cause transmission issues they would be consistent regardless of transmission mode. MAF symptoms are rough idle, loss of power, engine 'roars' and often fuel/air mixture error codes.

While it's shuddering you need to look at the rev counter needle closely. If the torque converter lock-up clutch is causing the issue the engine revs will fluctuate in sympathy with the noise but it's only usually by 100-200rpm so you need to watch carefully.

Phil

usually... but I've seen a few gearbox funnies on A8's (similar gearboxes) that have been traced to MAF issues. The MAF is 'good enough' for the engine, but the tranny doesnt' like it.

The primary function of the MAF is as one component contributing to the air/fuel mixture via electrical current. When the MAF is malfunctioning the signal to the transmission can result in above normal pressure in the transmission so it is a possible MAF is the cause though that seldom is the case.

I have always seen symptoms associated with a bad MAF such as rough idle, poor acceleration, roaring engine, mileage decrease and sometime black smoke from the exhaust.

Since it is easy and inexpensive to clean a MAF, might be worth a try, be sure to use MAF cleaner only. FYI- the result of cleaning MAF isn't always successful, sometimes the cleaning is ineffective or worse. If the MAF has somewhere around 60,000 mile on it you may want to just replace it.

That said, if you are not able to check for error codes in the OBC I would get it done ASAP, yes ASAP. Personally, I would do so before trying any possible fix. If this is a transmission issue it is very likely you will increase the damage to your transmission every time you drive it as is, and that means more $$$ to get it repaired. I would take it to indy tech that is very familiar with BMW transmissions.