June 2023
Rich Love
I had been chasing this problem for a year and finally found the culprit.
The symptom was that when you turn left, you hear a rumbling rattling noise.
It sounds like it is coming from under the left front of the car.
I thought this must have been related to the steering or suspension.
So I replaced the center link (with both left and right tie rods)
and examined the lower steering u-joint.
Nothing helped.
Who would ever think that the climate control blower could cause a noise when you turn left?
It would also make the noise if the car was on a slant with the right side of the car lower than the left side.
You can prove that it is the blower by lowering the blower speed to zero and then make your left turns. The rumbling sound goes away.
And you can shut the engine off and increase the blower speed to near maximum to hear the sound.
The other symptom is that when you turn the blower speed to maximum and make a left turn, the blower speed will drop. Turn right and it will increase.
It is no easy job to replace the blower.
You need to remove the dash.
The Bentley Manual has the procedure.
There is also a good procedure here:
http://www.bimmerboard.com/forums/posts/45351
Here is a recording I made of the sound:
https://www.carnationsoftware.com/BMW/Blower/Blower_noise.wav
Here are some helpful links I used
http://www.bimmerboard.com/forums/posts/45351
http://www.bimmerboard.com/forums/posts/77247
http://www.bimmerboard.com/forums/posts/31138
Using those helpful information pages in addition to the Bentley manual was all I needed.
See my time lapse videos below for removing the dash and blower.
Got the blower motor at FCP Euro for $175.00
BMW Blower Motor - Mahle Behr 64118391809
https://www.fcpeuro.com/products/bmw-hvac-blower-motor-740i-740il-750il-behr-64118391809b
However, that motor was a problem and had to be returned.
See below for more info:
==========
Removed the dash and blower motor.
Took me a couple of hours.
Here are two time lapse videos I made when I removed the dash and blower. You can download them and open them in your movie player (QuickTime Player for example) and use the arrow key to step though one frame at a time. But they are fun to watch at full speed.
https://www.carnationsoftware.com/BMW/Blower/Removing_the_dash_time_lapse.MOV
https://www.carnationsoftware.com/BMW/Blower/Removing _the_blower_time_lapse.MOV
Finished the job and problem solved.
No more strange noises from the blower motor.
Examining the old motor, I could see that the problem was worn out bearings.
There was a lot of sideways play in the motor shaft.
NOTE: The Bentley manual says to remove the glove box before removing the dash.
But that is not necessary.
All you need to do is disconnect the left and right suspension parts and let the glove box swivel to the floor. It will still be connected at the back.
That gives you room to remove three screws above the glove box to lower the upper cover.
(Then you have access to the nylon screws that hold the wood and leather trim pieces.)
After you remove those trim pieces, you can raise the glove box again to get it out of your way while working to remove the dash and blower.
The Mahle blower motor was a bad part for my 1995 740i
The problem with it was that it would work until you turned off the ignition key and then turned it back on. The motor would not come back on.
I am guessing it was overheating.
A good test for this is to leave it running for 10 minutes and turn if off and back on.
I tried a new resistor but that did not help.
I returned the blower motor for an exchange and the new blower had the same problem.
So I gave up and repaired the original BMW motor.
To prevent side to side movement of the motor shaft, I installed a compression ring.
See my photo here
https://www.carnationsoftware.com/BMW/Blower/Motor_with_compression_ring_Installed.png
I just happened to have the right size in my parts bin.
It is very small and pretty tricky to insert.
NOTE: The problem with the motor shaft side to side play is that it moves the commutator over and positions the brushes on a narrow section of the commutator.
That makes the motor loose power and slow down on left turns.
And it makes a rattling noise.
Problem solved with compression ring removing the play in the shaft.
Total cost for the repair is zero.
I returned the motor and resistor that did not work.
One last thing:
Here is a drawing that explains what happens to a worn blower motor that has too much play in the motor shaft.
https://www.carnationsoftware.com/BMW/Blower/BMW_Motor_Shaft_Excessive_Play.jpg
NOTE:
The Behr motor was a real time waster for me. After I installed it, I tested and it worked.
Put the dash back in and drove to the store and the motor quit working.
Evidently it overheats and stops working and will not work again until it cools down.
I thought it was just a bad motor so I returned it for a replacement and also ordered the resistor pack.
Exact same symptom. Overheats in about 10 minutes and stops working.
NOTE that the Behr motor had different color wiring. I asked FCP Euro about that and they said the part number was correct and it should work. It did not.
That is when I gave up and figured out how to just repair my original BMW motor with a spacer.
So, my advice is to either repair your original motor or Buy a genuine BMW motor.
