GUIDE : KitchenAid 5KSM7591 and 5KSM7990 Gearbox Disassembly [IMAGE HEAVY]
GUIDE : KitchenAid Heavy Duty 5KSM7591 and 5KSM7990 Gearbox Disassembly
This is intended to be a helpful guide to disassembly, cleaning and re-greasing of the gearbox and planetary ring of the newer KitchenAid Heavy Duty Stand Mixers. It is specific to the following two models as they have a completely redesigned gearbox and motor.
MODEL : 5KSM7591 (all variants)
MODEL : 5KSM7990 (all variants)
The process for the US (120V) and EU (220-240V) models is exactly the same.
As is often the case when taking a machine to pieces for the first time, you only discover the most efficient method of doing to AFTER you have taken your pictures and put it back together and this is no exception. I started by removing one piece at a time and taking pictures as I did so. I effectively nibbled the machine to bits in a logical manner. Afterwards I realised that several groups of pieces would come off in one block and make the reassembly process simpler. I will try to outline these discoveries as they will appear different from some of the pictures taken.
For this guide I am assuming you have one the of the relevant KitchenAid models and have unplugged it from the wall completely. There are no visible large capacitors but always be aware that there may be residual charge associated with the motor power supply. Leaving the machine unplugged for half an hour should take care of this.
Medium crosshead screwdriver
Small flat-head screwdriver
Torx T15 screwdriver bit
Medium Circlip (C-clip) pliers
Food Safe (1H) grease (only a modest amount is required)
Rubber gloves (disposable nitrile gloves are perfect for this)
Very hot soapy water and an old toothbrush
DISASSEMBLY - TOP COVER
As is usual for most of the KitchenAid Stand Mixers of this size, the top lid comes off to reveal the motor and gearbox. The screws to access the top lid are concealed behind the silver flexible band that runs round the machine.
There is a single screw at the back which will release the band. Take it off carefully and set aside.
This will reveal the four crosshead screws that secure the lid. There are two on each side.
Once the lid is off you can see the new design of the machine. The electrical control board is flat underneath the motor. The gearbox is inline with the motor and extends forward to the accessory socket. The planetary ring resides underneath via a 90-degree gear as usual.
Take particular note of the two cables that attach to the motor. We will have to remove those later in order to release the entire motor and gearbox assembly in one piece. One is a power connector with two wires that is locked together with a small tab. The other is a magnetic sensor on a black cable that fits into a slot at the back of the motor. It too is secured by a plastic tab but is fairly delicate.
DISASSEMBLY - PLANETARY RING
The first part to remove is the enamelled planetary ring to which you would attach the whisk, beater or dough hook. It is held in place with a single punch pin.
Taking care not to slip and mark the paint, tap the pin out from one side. Once it protrudes enough to remove, the complete enamelled planetary ring will slide down and off.
Turning it over will reveal a circlip (c-clip) which needs to be removed.
The best tool for the job is a pair of circlip pliers. The type that gape open when squeezed is better than the cheaper "squeeze to close" sort. Insert the two prongs of the circlip pliers into the eye holes of the clip, spread them just enough to clear the slot the clip is located in and remove it. The gear that is held captive will come off revealing that it has a slot on the underside.
You can see how the slot on the underside goes over a floating pin that passes through the planetary shaft.
Slide this pin out by hand and take off the spacer washer underneath. The planetary shaft will now drop out. I was surprised that in my specific stand mixer there was very little grease on the planetary shaft and it did show signs of wear. You do not need to remove the tool retaining cap, spring and circlips. A simple brushing should clean them enough.
Here are the small components in the order they belong.
Looking underneath the head of the mixer will reveal the large planetary ring gear.
Because I was not familiar with the disassembly of the machine in its sections I removed the four crosshead screws to release the large planetary ring gear. While there is no disadvantage in doing this, it is also released with a pair of reinforcing plates when the motor and gearbox is removed.
With the large ring gear removed you can see the underside of two reinforcing plates that provide extra strength to the motor and gearbox above. If you leave the large planetary ring in place, it drops free with those two curved reinforcing plates once the motor and gearbox are released.
DISASSEMBLY - MOTOR AND GEARBOX REMOVAL
Since I was "nibbling" my machine into its individual pieces I had not worked out at this point that the motor and gearbox came out easily in one piece. I had first separated the motor from the gearbox, discovered that the two cables to the motor needed removing to allow it to be lifted away and then took the gearbox into its component parts last.
The easiest way to take this to pieces is to remove the motor and gearbox in one piece then separate it into its individual pieces afterwards.
First disconnect the motor power cable. A small flat screwdriver can be used to press in the locking clip to allow the two sides to slide apart.
Next the magnetic rotation sensor has to be removed. It is the slim flat black cable attaching to the rear of the motor near the fan. I found the easiest way to release it was to press in on the locking tab while pressing upwards gently from underneath. I was not sure how strong the cable itself was to pulling so I chose to press up from underneath until the locking clip was passed. TAKE CARE here as the tip of that sensor is somewhat delicate. Lift it clear of the motor and to one side.
Now that both of the motor connections have been removed it is now possible to undo the eight screws that hold the entire motor and gearbox in place. Take note of the eight screws (four on each side) where the gearbox meets the enamelled frame of the mixer.
These eight screws go through the frame and into the pair of curved reinforcing brackets above the large planetary gear. Undoing these eight screws will release the motor and gearbox (which will want to tip down as the last screw is undone) as well as allow the large planetary gear to fall down freely.
EITHER remove the large planetary gear first and then catch the two curved brackets as they are released OR place a towel below the large planetary gear to catch it as it drops. It is not heavy.
Note that the two curved brackets have a flat side (bottom) and a side with studs (top). Both brackets are identical.
Once the last of the eight screws are removed the entire motor and gearbox will be released. Lift it all away in once piece, taking care not to let it drop onto the electronics board underneath as you remove it.
From this point on you will see that I split the motor from the gearbox when I disassembled my machine while taking the photos. The process from this point is exactly the same whether you leave the gearbox behind or take it all off with the motor in one piece.
DISASSEMBLY - MOTOR SEPARATION
Lay the motor and gearbox on a flat surface and remove the two long Torx T15 screws that hold the two sections together.
Slide the motor backwards slowly. You will probably find that the set of small gears at the back of the gearbox will want to fall backwards and come out with the motor. It may be more convenient to encourage them to stay forwards within the gearbox using a small flat screwdriver as you slide the motor backwards. Do not worry if any do fall out as there is only one way to put them back together afterwards.
If you manage to get all the gears to stay with the gearbox then the motor will be released revealing a short hexagonal shaft. Wipe this side of the motor clean of old grease with a dry piece of paper and set it aside. Take care not to disturb a thin rubber o-ring that goes between the motor and the back of the gearbox. In my case it was retained by a groove on the motor face.
DISASSEMBLY - GEARBOX COMPONENTS
It is now time to reveal the inner workings of the gearbox and get it clean. First use your Torx T15 screwdriver to remove the two short screws on the top gearbox cover. There is a thin fiber gasket attached to the back of the lid which should be handled carefully as it needs to be reused.
This will reveal the front accessory gear, the 90-degree planetary gear below that and a circular gearbox with two sets of small floating gears. Notice how little grease is used compared to the older models of KitchenAid. There is no large grease "reservoir" needed.
Gently slide the circular gearbox backwards and off the front housing. There is another delicate o-ring here and it is not guaranteed which of the two pieces it will stick to. In my case it stayed with the forward housing.
Once this circular gearbox is away then the front accessory shaft and its bushing can be slid backwards then up and away.
This just leaves the 90-degree planetary gear left in the housing.
Flip it over and note the large circlip on the underside. This needs to be removed with circlip pliers and it will then release a thin spacer and the 90-degree planetary gear.
Here are the parts grouped together.
CLEANING - ALL PARTS
All the gears, clips, spacers and housings are now ready for cleaning. Do not worry about the order or location of any small parts from the gearbox as they are easy to identify and only fit together correctly one way. I will examine the gearbox shortly so in the meantime all small parts can be cleaned and dried.
First remove any large blobs of old grease with the flat screwdriver and discard. Do not try to reuse any of the old grease as it will be dried and degraded.
Now boil a kettle and find an easily washable but shallow container that can hold about 2cm of water with a little extra room for splashing. Pour in some freshly boiled water and a generous squeeze of washing up liquid. It is beneficial to wear disposable gloves at this point as extremely hot water with strong detergent is very harsh on the hands.
DO NOT attempt to clean the motor with water. A simple wipe of the hexagonal shaft with a clean dry cloth is all that it needs.
Use the old toothbrush to scrub and clean each small part and housing until it is grease free. Rinse each part in cold water, shake dry and set aside on a paper towel to dry completely. You may find you need something like a small toothpick or cocktail stick to get into the central hole of the gears or places where a pin went through. You may need to change the hot water a couple of times. The old grease will melt and become suspended in the water only if it is very hot. Water that is not hot enough will simply result in the grease smearing over the part and brush.
Once all parts are clean and dry, it is time to examine the gearbox to understand how it works.
EXAMINATION - GEARBOX
Placing all the cleaned gearbox parts together it is possible to work out how rotation from the motor is geared down and transferred to the forward accessory shaft and also down to the planetary ring.
Here are the parts that run from the motor to the accessory shaft.
From right to left there is a small gear that sits on that hexagonal shaft of the motor. This small gear sits in the middle of three larger gears that sit on the three prongs of the central armature. Three more gears go in front of the armature and sit on the prongs of the accessory shaft. The whole assembly is surrounded by a toothed ring that holds it all together and helps with rotation and alignment.
You will have noticed that there are two sets of three gears that differ in thickness. The thinner ones belong at the rear (motor) side and the fatter ones belong at the front. All these sets of three gears are symmetrical so there is no front or rear to any individual gear.
So let's look at how these gears transfer power from the motor to the accessory and planetary shafts.
Firstly the motor itself engages with the smallest gear (12T). This has to rotate at the same speed as the motor. Next come the three larger gears (29T). These all turn the same way and slow down the speed. There are three of them to support the central gear evenly and reduce wear. They sit on the central armature.
By placing the armature inside the toothed ring, you now force the armature to turn in the same direction as the three gears.
Turning it round so you can see the front, it is apparent that the central armature has a small gear (12T) fixed to it. As the armature slowly turns, this fixed gear has to turn too.
Now the three fat gears (29T) are fitted and their job is to slow the rotation down even further. There are three of them again so that wear is evenly distributed and the central armature is supported properly.
Because it is hard to get the three gears lined up exactly (it is possible to be one tooth out in the outer ring and the assembly will lock rather than turn), it is better to use the forward accessory shaft to locate the three gears and only then bring them into the outer ring as a group. That way their alignment will be guaranteed to be correct.
For now set these gears aside until it is time to grease them but remember how they go together.
REASSEMBLY - GEARBOX AND MOTOR
Once I had completed taking my photos I realised that it would have been much more convenient to grease and build the gearbox and motor on the bench before trying to fit any parts back on the machine. I will describe the optimal steps to perform the greasing and reassembly but the pictures may differ from the description.
The first step is to fit the 90-degree planetary gear back into the front gearbox housing. In my specific machine there was no grease in the bearing of the housing and 90-degree planetary gear but I think there should have been. Apply a small amount of grease to the bearing where the 90-degree planetary gear will pass through the housing. Also lightly grease the "top" of the bearing where the 90-degree planetary gear will rest. Have a look at it before greasing anything and think about where two surfaces would touch and move. Only a light amount of grease is necessary here.
Pack the teeth of the 90-degree planetary gear with grease and lightly grease the underside of the gear where it rests on the floor of the housing. Drop it into place in the housing and secure it from underneath with its spacer and circlip. Make sure the circlip is correctly located into its groove.
Apply a very small amount of grease to the front of the accessory shaft where it passes through its bushing as well as the face where the two parts meet.
Pack the teeth of the accessory shaft with grease and place it back onto the housing. It will engage with the 90-degree planetary shaft as well as the front of the housing. The flat sides of the accessory shaft bushing should be oriented straight up and down to seat properly.
I tried to grease and build up the entire gearbox ring on one piece but quickly realised that the correct next step was to place the three fat gears onto the prongs of the accessory shaft as this will guarantee their correct spacing. Pack the teeth with grease. Also grease the prongs of the accessory shaft. Be somewhat generous with the grease but not excessive.
Now grease the small gear (12T), its three thin companion gears (29T), the central armature and the entirety of the inside of the circular gearbox housing. Again be somewhat generous but not excessive. Too much grease here will cause additional resistance for the motor and will just end up with the excess being forced forwards where it will not serve any purpose.
When placing the outer toothed ring over the armature, note that there is a step in the casing of the outer ring. The step goes forward towards the front housing and its flat face goes backwards towards the motor.
Making sure that the outer ring is facing the correct way, bring it in to the three fat gears resting on the front accessory shaft. It may take a little care to line up correctly but the three fat gears need to be engaged correctly with the teeth on the inside of the outer ring. Once correct they should slide nicely backwards until the small fixed gear (12T) on the central armature needs to fit in between the three fat gears. Do not use force. It should engage easily but be aware that the armature may want to slide backwards out of the ring.
This is the part where assembling the gearbox while it is off the stand mixer is much more convenient than trying to assemble it while the housing is attached to the frame.
Once it is all together correctly it should look like this. Note the amount of grease that you should be aiming for. Plenty but not too much.
It would now be appropriate to replace the gearbox top cover and its two Torx T15 screws. I do not have a picture of this stage.
Reconnect the motor to the back of the gearbox housing. The hexagonal motor shaft needs to locate inside the small central gear (12T). Use the two long Torx T15 screws to join the two sections. They should be snug but not excessively tight.
REASSEMBLY - PLANETARY
It is now time to reattach the complete motor and gearbox to the mixer. This is slightly awkward as the motor has to be supported so that it does not drop onto the circuit board at the same time as the two curved reinforcing plates are attached from underneath.
Four of the eight crosshead screws are necessary to attach the motor to the frame and the other four are used to secure the curved reinforcing plates. Counting from the front, the SECOND and FOURTH pairs of screws hold the motor and gearbox to the frame while the FIRST and THIRD pairs secure the two reinforcing plates.
Attach the gearbox and motor to the frame by fitting the SECOND and FOURTH pairs of screws. Do not tighten fully as we will slacken and retighten all the screws once all four pairs are fitted properly.
Next, hold each reinforcing plate in its place from underneath the planetary ring and fit the FIRST and THIRD pairs of screws. Both plates are the same. Once all four pairs of screws are fitted, slacken them slightly, make sure the gearbox housing is sitting straight then tighten all screws down properly.
Carefully reconnect the power and magnetic sensor cables to the motor until they snap into place and are held firmly. Be careful with the magnetic sensor.
We should now be back at this stage (ignore the presence of the enamelled planetary ring in this picture)...
Next, lightly grease the teeth of the large planetary gear. Do not use too much grease as there is not much load on this part of the machine.
Using the four small screws, fix the large planetary gear to the frame. Once all four are in place, loosen slightly, check the fit of the large planetary gear then retighten all four screws.
Very lightly grease the sides of the 90-degree planetary gear shaft.
Very lightly grease the sides of the shaft that goes through the enamelled planetary ring. Lightly grease the teeth of the small gear on the enamelled planetary ring and secure it correctly on the floating pin. Remember it has a notch on the underside that locates onto the floating pin. Secure it with its circlip.
Slide the enamelled planetary ring up onto the bottom of the 90-degree planetary shaft and hold it in place. Turn it round until you can see through the hole where the punch pin will go. Take the punch pin and tap it into place until it is central in the shaft and does not stick out on either side. Again take care not to mark the enamel with the hammer.
REASSEMBLY - TOP COVER
Place the top cover back on the machine and secure it with the four crosshead screws.
Put the silver flexible band in its groove round the top cover and secure it with the single screw at the rear. The end of the band with the serial number printed on it should be on the top.
REASSEMBLY - TESTING
Make sure the speed selector lever is in the Off position and plug the machine into a socket.
Move the speed selector lever forward slightly to the slowest position and be prepared to switch it off if necessary. Allow the machine to run at the slowest setting for half a minute to spread the grease evenly around the load-bearing parts. Only then should you gradually increase the speed until the machine is at full speed.
It is then safe to turn it off and return the machine to service.
Of particular interest is how much less grease this new style of gearbox requires when compared to the older models with the worm gears. They required a large grease "reservoir" to be packed into the gearbox that would melt and flow into use as the old grease degraded and parts heated up.
I am under the impression that this new gearbox style is much more efficient and should last a lot longer. This machine has been in use for five years of domestic use exclusively on speed 2 for dough making without any maintenance.
After cleaning I inspected all components for wear under magnification. I only found slight polishing between the accessory shaft gear and 90-degree planetary gear. There was also slight wear between the bottom of the 90-degree planetary gear shaft and the planetary ring which I believe was due to no grease being applied at that location by the factory.
Once reassembled I found that the machine ran much quieter under light load and when mixing heavy dough the regular "click click" noise as the planetary ring turned was still present but significantly reduced.
I hope this guide proves useful and will endeavour to keep these pictures uploaded in the long term. On the offchance that my hosting provider changes, here is a link to the pictures as a 7ZIP which the Forum Moderators may wish to secure a copy of.
ARCHIVE : PICTURES AS 7ZIP
PERMISSIONS : I am happy for this guide to be re-posted anywhere whole or in part along with the relevant pictures PROVIDED it is for NON-COMMERCIAL purposes and that I am CREDITED as the original author.