Footwell Blower Motor Lubrication

[dkirk]

With the advent of cooler weather, the heating system in my 1988 911 is now being pressed into service. Powering up the passenger side for the first time this year, I noticed the dreaded “squeal like a pig” dry bearing noise from the footwell blower motor. Having previous success with lubricating the driver’s side motor bearings, it was obviously time to service the passenger side motor.

I’ll skip the blower removal process (very easy) and get to the specifics. With blower on the bench, disassembly is quite simple and obvious, up to the point where the squirrel cage fan is removed from the motor shaft. The plastic fan is a light press fit on the motor shaft. The fan has to be removed from the shaft to allow the motor to be removed from its plastic housing, thereby allowing access to both bearings. Mark the rotational position of the motor relative to the housing so when motor is reinstalled, proper alignment is reestablished. Remove the two housing screws such that motor can drop free of housing.



With the assembly held loosely in the vice with a shop rag providing some cushioning, lightly tap the end of the motor shaft with a drift punch – the motor will slide downward and the shaft will be withdrawn from the fan. I found that a little preheating with a heat gun on low setting made this much easier. Once the fan is free from the shaft, the motor may be pulled from the housing with a little twisting.



When free, the motor was blown clean with compressed air and examined. Brushes and commutator visually appeared perfectly serviceable and armature windings looked good. There was no radial (side-to-side) play obvious in either bearing, indicating bearings were not worn to the extreme.



Both bearing housings at each end of the motor are identical. As is typical with small electric motors, porous copper bearings are surrounded by felt oil reservoirs. After 29 years, these will be essentially void of any lubricant. The oiling access slots (2 each per bearing) appear as shown.



The success of this motor servicing is totally dependent on what is used for a lubricant. Years ago, an owner of an electric motor shop recommended that I use a 75/25 mixture of Marvel Mystery Oil and STP for any and all motor plain bearing lubrication and I’ve followed this advice…and it always has worked for me.

I applied 2 drops in each slot for both bearings, plus a drop on the shaft/bearing interface. This seemed to moderately saturate the felts to the right degree – you don’t want to over-lubricate as this can be detrimental if oil gets on the brushes or commutator. Once lubricated, it was very noticeable how much easier the motor shaft rotated. I test ran the motor on the bench and it ran quietly with no audible distress.

Reassemble in reverse order remembering to align motor properly in the housing by referencing the previously established rotational assembly marks. Clean the motor shaft and fan bore with a degreaser (lacquer thinner) prior to reassembly. Support the motor shaft with a wood block when tapping the fan back onto the shaft. I used a deep well socket for a tapping arbor. The shaft should protrude out of the fan hub by about 1 mm.

Once reinstalled into the car, a test run verified quiet operation and surprisingly, much better airflow due to the motor now running at a higher speed.

To those naysayers who think re-lubricating these motors is a waste of time, I did this exact procedure 7 years ago to the drivers-side footwell motor and it has remained quiet and fully functional. The lubricant is the key to making this a long lasting fix. If there is radial play in the bearings, this fix will be only temporary and a new blower motor will be required.

[T77911S]

pull the brushes out and sand the motor contacts with fine sand paper.

[T77911S]

[HaroldMHedge]

Nice write up. It will help me put this weekend.

[DWeg1998]

This is on my list to do shortly. Here is the thread I had saved for reference and those that want more pictures of disassembly.

Footwell blowers squeaky, how to fix.

[86 911 Targa]

I have begged, pleaded, offered gold bars to our
host to list these on a stand alone basis without housings.

No joy yet...........

Gerry

[dan88911]

Thanks for posting this dkirk.

[dar636]

Thank you dkirk.

Is the main blower in the engine compartment lubed the same way? Mine just started to squeal...

[Daves911L]

Cool! The rt. side footwell blower in my wife's '88 has squealed a few times recently. Guess what I'll be doing this Saturday morning? Thanks.
DG

[T77911S]

BTW, I oiled mine last year, they are making noise again.

look at my first pic, this is what can cause these to catch fire. add in resistance to spin from the bearings and that just makes it worse.

[rubenmad]

Thank you for the write up!

[dkirk]

Thanks gentlemen – I appreciate the compliments.

T77911S – The burned commutator shown in your first two photos can be caused by over-lubricating the upper bearing. Oil runs down on to the brush-commutator and causes arching and burning. Having to re-oil the bearings every year is due to either using oil that is not viscous enough for the application, or your bearings are worn excessively such that a new motor is the only recourse.

I’ll be the first to admit that I’m no chemist or lubrication expert – I took the recommendation of an electric motor technician with much experience to use the 75% Marvel Mystery Oil to 25% STP mix for electric motor plain bearings (for those of you with an interest in both of these products, check out Wikipedia for the full chemical breakdown). I’ve personally used this from oiling bathroom fan motors to furnace and air compressor motors and it seems to work better than any other oils I’ve tried. The typical 3 & 1, Singer Sewing Machine Oil, Electric Motor Oil, etc., all seem too “light” for remaining in the felt bearing reservoirs over time. It appears that evaporation may be the cause of this. I’m sure that the highly viscous STP prevents evaporation and the penetrating action of the Marvel oil wicks through the sintered bearing material to maintain proper shaft/bearing lubrication over an extended time span. This is just conjecture on my part, but seems logically plausible as all of my electric motors have responded positively from this lubricant concoction.

DWeg1998 – Thank you for finding and posting that article. This contains great photos and details on blower disassembly.

Dar636 – The main blower in the engine compartment may be lubricated with this mix – I did mine several years ago, not because it was making noise, but just as good insurance. It has remained quiet and works well. Check for excessive radial clearance – if you can see movement of the shaft in the bearing radially (side-to-side), then time for a new motor. If yours just started to squeal, bearings should still be ok. Just be sure not to over-lube…3 to 4 drops in each bearing is ample.

[adias]

I agree that the Singer Sewing machine oil is too light for this, but what about motor oil?

[T77911S]

car had about 50k on it when I pulled the fans, that's how they were. I doubt the PO oiled them.

my opinion (as an electronics tech and short time auto electric tech).
the motors get hard to turn and what you get is burning from dust and the brushes and you get what I I have. then eventually a fire.
or, its just excessive carbon buildup that probably got hard from heat and then caused the scoring
BTW, the front condenser fan caught fire with the PO.

[Tremelune]

Great post.

Another source of squealing is the plastic squirrel cage making physical contact with the housing—though there would be a visible indication of wear in that case. The solution there is just to pry another millimeter of clearance.

Not a bad idea to fuse the wires at these blowers like the later cars...

[sugarwood]

Originally Posted by dkirk

I applied 2 drops in each slot for both bearings, plus a drop on the shaft/bearing interface. This seemed to moderately saturate the felts to the right degree – you .

Sorry for the stupid question, but can you be more clear on where exactly you place the oil? I have not had my footwell blowers out in a few years, but when I did, I had no idea what I was supposed to lube. There was no way to remove the shaft. I just directly applied oil onto the felt washer, but that seemed totally stupid. Which is exactly how I felt. I still have no clue how you're supposed to lube this motor, and my blowers still squeal like a pig.

[rokemester]

Very useful post. Good question on where and how much oil to apply? Subscribed. Has this topic been covered previously?

[hcoles]

Excellent post. Adding this to my to-do list.

[dkirk]

Thank you friends – hope it proves useful (see disclaimer at the end).

Adidas – I’m sure there are several lubricants that would be perfectly suitable for this application. An engine oil may work as well as the MMO/STP mix but I have not run experiments nor conducted any comparison tests to confirm. What I’m recommending is just something that has worked well for me over the years.

Tremelune – Good point on checking fan clearance to housing, especially after assembly. I forgot to include this in my original post.

Sugarwood – there is no such thing as a stupid question. If you look closely at the slots formed in the bearing housings at each end of the motor (2 slots/housing, 4 total), you’ll notice a felt-like material near the shaft end of the slot, as shown below:



This felt is intended to be the oil retention device (reservoir) for providing oil to the bearing. Put 2 drops of the recommended oil onto this felt, giving time between drops to allow the oil to soak in. Repeat this for the remaining 3 slots. Then put a drop of oil on each end of the motor shaft that protrudes from the bearings. Rotate motor shaft to distribute, then wipe off the excess. Very important – 2 drops per slot should be ample for many years of operation – don’t exceed this as over-lubrication can cause other problems.

The loose felt ring at the top of the motor housing does not need to be lubricated. This appears just to be an anti-rattle cushion between motor and cover.

Rokemester – hope this clears up your question on where and how much. The topic was covered in much greater detail in a previous post as contributed by DWeg1998:

Footwell blowers squeaky, how to fix.

Please note – I’m only recommending the MMO/STP brew as something that I’ve found works well on lubricating small electric motors. There may be something available that would be superior. Recommending oils is something that’s always controversial, as can be seen in the many “great oil debates” concerning engine lubricants. I have no test data to prove what I’m suggesting is valid – only life experience. And in my life, I’ve only been “right” (correct, that is) about 50% of the time, so take this into consideration before taking my advice.

[sugarwood]

Oh, I thought the felt washer was OUTSIDE of the shaft, plainly visible.
Everyone has been referring to a felt washer that is inside, and out of sight??
I was oiling this, and it made absolutely no sense to me.
You're the first person who ever explained this correctly.