Bump when gears shift at start-up

[rlm9622]

I have a 2006 M35 with about 80,000 miles. Over the last several weeks, I've noticed a bump when the gears change (1st to 2nd, and 2nd to 3rd) at the start of a trip. This happens until I get the car into 4th for an extended period (a minute or two). It's pretty clearly felt (and audible) at the rear of the car. It doesn't matter how quickly I accelerate. Any thoughts?

[DeanM45]

Maintenance history? Last time trans fluid and filter were changed?

[rlm9622]

Good question--I'll check when I get home, but maybe at 50,000?

[seymore4]

Also check to verify that it really is the transmission and not the axle clicking

[daveM45]

How cold is it?
MIne has always done it when temps get below 0. Seems to be common issue as its been reported here several times and the cold climate dealerships are familiar with it. My understanding is the transmission fluid thickens, pressure increases so you get these jarring shifts for a while. Just drive gently until fluids have a chance to warm up.

If you have the problem above freezing I'd be concerned someone used the wrong fluid or perhaps overfilled the fluid.

[atlM35]

I get a 2nd to 3rd bump when it's cold. Experienced it in all 3 Ms that I've owned.
Changing the transmission fluid and diff oil helped a little.

[M4T5]

Explain this so called "bump". Does anyone have a video or this or cared to have a dealer pin point this issue???

Jim

[rlm9622]

Thanks for the responses. Transmission fluid and filter were changed at 67,000 so that should not be the issue. Temperature is not a factor--this is happening at temps well above 32. To the poster who asked what the bump feels like---the best analogy I can think of is if your car were in neutral and someone rear-ended you going about 1/10 mph---it feels like a hitch at the rear of the car when the gears change that seems to jar the vehicle very slightly.

[atlM35]

Sorry, I should have been more specific.
I meant that I feel it when the engine/transmission are cold... not ambient temp.
The bump is a very harsh gear change, worse when using manual mode.

It's been discussed before:
transmission-rough-shifting-in-cold-wea ... 11300.html
I might try unplugging the battery and resetting everything.

[rlm9622]

Thanks alt. I think that post you linked describes my problem, although I've had the car since 2005 and this is the first winter I've experienced this. I guess maybe I should just let it run for a minute or two before driving.

[Su33]

I have had this exact symptom since I have had the car, regardless of weather temp. It's much worse when accelerating fast and up-shifting. I have to ease off the gas for a moment at the right time during the shift to avoid the bump. It's a 2008 M45x. I have a JX loaner right now and the shift is smooth as butter regardless of the amount of gas you give it. Is the bump normal?