Thread Number: 84838  /  Tag: Vintage Automatic Washers
Frigidaire Unimatic Oil Pump Seals - explained
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Post# 1093003   10/12/2020 at 20:58 (1,284 days old) by swestoyz (Cedar Falls, IA)        

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Hello fellow AWers -

It's hard to believe I restored the '58 Unimatic about this time a year ago. During that write-up I had mentioned that I had plans to detail out the differences between the two Unimatic oil pumps, but more importantly provide cross reference information for both styles so folks had easy access to the correct o-rings for future reoperation of their mechanisms. We have a friend in need so I thought it was a good time to finally get this down on paper.

What we know is Frigidaire did a complete overhaul of the Unimatic oil pump at some point in the mid 60's. What I don't know is exactly when the revised kit was introduced nor their official reasoning for the revision. The January 1964 reprint of the SER-723 1947-1960 parts catalog still calls out the original style pump, so my best guess is the revised pump was introduced shortly after, judging by the part numbers used on the revised pump it (656 and 752 series PNs). The first instance of this kit popping up that I'm aware of is the 1971 Frigidaire Full Line Parts Catalog.

As for the reason why the revision was created - I suspect Frigidaire found that over time the original spring portion of the cap would give out causing the cover that holds the spring within the cap, against the bottom part of the seal, to blow out. Once this happens the oil would become oil soaked and the mechanism would be inoperable. This is pure speculation on my part but based on a few mechanisms that I have seen with this issue. This also gave them an opportunity to improve the pumping mechanism as well (see below).

The original service kit part number for the cap and seals was 5417162, which included a new cap, o-rings, oil seals (the mechanical seal), pump finger, and gasket. (photo 1 below, taken from the 1957 washer parts manual)

The revised service kit part number was 6591693 and introduces a completely new cap, new mechanical seal, and two new part numbers for the o-rings. (photo 2 below, taken from the instruction sheet from the service kit)

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This post was last edited 10/12/2020 at 21:47

Post# 1093004 , Reply# 1   10/12/2020 at 21:01 (1,284 days old) by swestoyz (Cedar Falls, IA)        

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During the restoration a year ago I decided to pony up for a used Parker O-Ring scale/sizing tool, to help pin-point with accuracy the correct replacement for any o-ring that would be required to restore any transmission or application with an o-ring. With this tool I was able to then cross reference the original sizes over to a Parker part number, that is universally used within the MRO industry.

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Post# 1093006 , Reply# 2   10/12/2020 at 21:06 (1,284 days old) by swestoyz (Cedar Falls, IA)        
Two pumps, side by side

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With the sizing tool on hand, all four o-rings have been cross referenced over to the Parker number, which I've included below. Some distributors call these numbers "2 dash" numbers, dropping the "2-" and cross referencing then with the last three digits.

In the shot below I've placed the original pump on the left hand side, with the revised oil pump on the right hand side, with the Parker 2 dash part numbers for cross reference, as well as the Grainger (GWW) equivalent number that I used to buy replacement BUNA-N o-rings.

So this can hit the search engines, here's the listing that can be used for copying/pasting:

5417162 Kit (Original) ---

5433237 lower o-ring (large, thick - steel) 2-213 41uk89

5433233 upper o-ring (large, thin - bronze) 2-119 41uk17

6591693 Kit (Revised) ----

7529595 lower o-ring (small, thin - steel) 2-115 41uk13

7529598 upper o-ring (large, thick - bronze) 2-213 41uk89

From a service perspective, Frigidaire recommended that the oil pump o-rings be changed during ANY reoperation of the mechanism, as well as replacement of the gaskets. Often times the cork gasket itself is good enough to be reused unless you want to cut your own. If so I'd recommend a hole punch kit to get the correct side of the oil pressure line hole within the gasket.

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Post# 1093007 , Reply# 3   10/12/2020 at 21:21 (1,284 days old) by swestoyz (Cedar Falls, IA)        

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So, what did GM solve with this kit? Two things:

1. The mechanical seal change is vastly superior. The seal no longer has an integral spring within the cap (see above) but instead relies on a spring mounted on the motor rotor to supply the necessary force for the mechanical seal to function. This change brings the bronze seal down to the lowest oil point in the whole mechanism at the base of the cap and becomes stationary with the steel part of the mechanical seal now part of the rotating mass, sealing around the motor shaft. This also ensures the motor splines are exposed within the sump and have proper lubrication as well. The original style has the bronze part of the seal mounted within the base of the drive shaft, with the steel part of the seal stationary in the base.

2. The pumping mechanism is also vastly superior. Rather than relying on the finger pressure against the eccentric part of the drive shaft, the revised cap now uses a two piece pump mechanism with a separate spring and vane. The pressure difference I witnessed during the '58 rebuild was dramatic in comparison to the pressure I saw with the '56 rebuild.

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This post was last edited 10/12/2020 at 21:49
Post# 1093008 , Reply# 4   10/12/2020 at 21:22 (1,284 days old) by sfh074 ( )        
Awesome ......

a type "A" Frigidaire mechanic after my own heart! Great job!

Post# 1093009 , Reply# 5   10/12/2020 at 21:28 (1,284 days old) by swestoyz (Cedar Falls, IA)        

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What I don't have an answer for is why Frigidaire changed the part number for the 5433237 o-ring. It's the exact same size as the revised 7529598 and is used in the exact same spot on the oil pump cap. In fact both parts that interface with the o-ring are the exact same diameter, the original steel part vs the revised bronze part.

If I had to guess they wanted it to be uniform from a part numbering perspective, and/or they changed the rubber material. It doesn't have the appearance of a Buna-N o-ring, but neither did the originals. Rubber material gurus may have better insight.

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This post was last edited 10/12/2020 at 21:52
Post# 1093010 , Reply# 6   10/12/2020 at 21:33 (1,284 days old) by swestoyz (Cedar Falls, IA)        

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Oh, one more note about the changes to the mechanical seal. Both the bronze and the steel parts are different between the two kits and CANNOT be interchanged. The bronze part has a different machined relief for the thicker o-ring on the later pump and it will not seal properly if used on a later pump cap. Similarly the steel part is slightly wider on the revised it and has a larger relief machined into the backside for the o-ring, whereas the original does not have an opening for this necessary o-ring.

Original on the left in both photos, revised on the right.

I also wanted to include the full instruction sheet from the revised kit, as these instructions are not found in any Unimatic service manual that I've found so far.

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Post# 1093011 , Reply# 7   10/12/2020 at 21:40 (1,284 days old) by swestoyz (Cedar Falls, IA)        

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So, does this mean the original pump is junk, or a ticking time bomb?

For us, it's neither. The chances of the cap blowing out the spring on the original style cap is slim, so much that if it hasn't blown out at this point it more than likely will be fine.

The original oil pump also produces enough of a supply of oil to the upper spin bearing that the mechanism will provide years of trouble free service. It just means that if you are going to use your Unimatic make sure to let it run for several seconds on pulsation BEFORE letting it rip into spin if the machine has sat for any given period of time. The revised pump will provide enough oil immediately to satisfy the lubrication needs of the spin bearing from a cold start.

So, if you are reoperating a mechanism and do not have an oil pump kit for a mechanism with an original style oil pump, have no fear. Replace the o-rings and you'll be fine.

And, I'll end this with an obligatory Unimatic action shot! These were taken this past weekend, a year since the original restoration occurred.

Enjoy any future reoperations, and happy Unimatic-ing!


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Post# 1093013 , Reply# 8   10/12/2020 at 21:49 (1,284 days old) by combo52 (50 Year Repair Tech Beltsville,Md)        
Unimatic Oil Pumps

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Hi Ben, Do we know how long the Unimatic mechanism was in production after 1958 for commercial washers and dry-cleaners ?


I suspect that FD improved the oil pump when lots of these mechanisms were being used in commercial service, GM-FD really started stressing quality and longevity in the 1961 and on time period in their laundry appliances.


John L.

Post# 1093014 , Reply# 9   10/12/2020 at 21:58 (1,284 days old) by swestoyz (Cedar Falls, IA)        
Commercial Unimatics

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From the literature Robert's posted in AE as well as comments he's made over the years, I believe the Unimatic was phased out of commercial use around 1964. With enough of those machines installed in commercial settings between 1958-1964 I imagine the bean counters got fed up with the warranty claims they were paying out to force the engineers to address the issue.

I'd love to get my hands on the Service Tips/Tech Talk that would have discussed this change.

Both commercial service manuals he has posted on AE (1959 and 1961) show the original style pump, so I'm not sure if the last 1964 mechanisms would have had the revised pump, or not.


Post# 1093029 , Reply# 10   10/13/2020 at 07:00 (1,284 days old) by gansky1 (Omaha, The Home of the TV Dinner!)        
Well done!

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This is a wonderful resource for future restorations, Ben, thank you for the thread and time it takes to put these informative posts up.  I have a couple of mechanisms around here that need re-operation this winter so I'll get my o-rings ordered.  

Post# 1093034 , Reply# 11   10/13/2020 at 07:38 (1,284 days old) by Unimatic1140 (Minneapolis)        

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Hi Ben, I checked the Tech-Talks, it seems the new oil pump was introduced in 1962 and probably only used for the 1962-1964 line of Unimatic coin-ops. By '65 the Super-Duty (souped-up Multimatic) coin ops were introduced.

This is from the 1962 commercial washer tech-talk, I'll get it scanned sometime soon and get it into the library.

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Post# 1093041 , Reply# 12   10/13/2020 at 08:08 (1,284 days old) by swestoyz (Cedar Falls, IA)        
We have a winner! 1962

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Robert, thank you! For me anyway, this helps clear up the timing of the revised pump as well as the production use within the commercial line when the Unimatic was the source of motivation. I'll look forward to seeing this added to AE.


Post# 1093057 , Reply# 13   10/13/2020 at 11:13 (1,283 days old) by Jetcone (Schenectady-Home of Calrods,Monitor Tops,Toroid Transformers)        

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the redesign was made due to the pump finger springs' fatigue and snapping in half inside the oil pump. I have seen two units with snapped pump finger springs. I had read and I think Robert has found it in that piece of Doctrine that it was for the heavily used commercial machines but the two units I reworked were residential. Always nice to upgrade a home machine though. Eddies machine had such low use I am not rebuilding the pump at this time as I have one new kit left and will keep that for the Blackstone B-250 machine. 

What interest me is Ben's idea that the motor splines get lubricated. Must ponder that.

Post# 1093061 , Reply# 14   10/13/2020 at 11:37 (1,283 days old) by Jetcone (Schenectady-Home of Calrods,Monitor Tops,Toroid Transformers)        

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Good point about never spinning a dry mechanism, that oil is designed to flow down and out so after being stopped a day I would always agitate the unit before ever attempting a dry spin !!  I see Robert slapping in the spin dial and wafting away all the time- "oo look its doing 1140"! BAD BAD BAD !



Post# 1093066 , Reply# 15   10/13/2020 at 13:47 (1,283 days old) by Unimatic1140 (Minneapolis)        

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I see Robert slapping in the spin dial and wafting away all the time- "oo look its doing 1140"! BAD BAD BAD !

AM I hmmmmph! Never had that issue, and I use my WO-65 for extraction only all the time when I want fast drying if I've washed them in poor extraction machine (like Kenmore, Bendix, Horton, etc). I think it's more important to do that if the machine has sat for a very long time without use, the oil film doesn't evaporate off the bearing and would stay greasy for some time.

Post# 1093097 , Reply# 16   10/13/2020 at 18:55 (1,283 days old) by combo52 (50 Year Repair Tech Beltsville,Md)        
Starting A FD UM Directly Into Spin

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I agree with Robert, the only thing that is going to harm the top bearing in the mechanism is water leaking in from a bad seal above, besides by the time the tub reaches 1140 the oil pump is pumping oil into the bearing.


John L.

Post# 1093104 , Reply# 17   10/13/2020 at 19:59 (1,283 days old) by joelippard (Hickory)        

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Nice Reading, thanks for all the work Ben!

Post# 1093143 , Reply# 18   10/14/2020 at 08:37 (1,283 days old) by Jetcone (Schenectady-Home of Calrods,Monitor Tops,Toroid Transformers)        

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thats an interesting question John, we will test that theory when I get the mechanism all together again. My gut tells me oil does not reach the upper mechanism in spin because part of the pumping is due to the agitate shaft and trunnion pumping during wash. The oil pump is not powerful enough to cause flow to the upper mechanism it needs that oscillation but we can put this to the test in a few weeks !!! I will video the mechanism in spin and wash.

Post# 1093146 , Reply# 19   10/14/2020 at 09:02 (1,283 days old) by swestoyz (Cedar Falls, IA)        

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Both oil pumps would rely on the motor to be up to full speed at 1140 RPM to reach normal pumping capacity. With the finger style pump, full capacity is about as much force as the oil dribbling out of the top oiling hole that feeds the spin bearing, after it had ran for several seconds. Photo taken during a rebuild of a '56 mechanism with an original style oil pump back in '08 at Greg's.

During the rebuild of the '58 I attempted to take the same photo, but instead oil was literally shooting 5 to 6 feet away from the oiling hole and across the room, rather than this "dribble". With this in mind, even if the motor is only rotating at a fraction of 1140 RPM, the two piece spring/vane pump is definitely delivering oil up through to the bearing.

So yes, the oiling passages do indeed carry oil through the drive shaft, up through the reciprocating mechanism, through the pulsator shaft, and ultimately out the spin cage oiling holes.

YouTube link to the '56 rebuild with video of the finger style oil pump in action.



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Post# 1093153 , Reply# 20   10/14/2020 at 11:00 (1,282 days old) by sfh074 ( )        
If you are worried ....

about a dry top spin bearing, could you use a sealed bearing alternative?


I used this sealed top spin bearing in place of the original open style on my multimatic rebuilds. Have done 5 this way so far and they have worked out great. They are totally water resistant, permanently greased with synthetic bearing grease that is non-hydroscopic and never dry out.  No oil is needed above the bearing on anything in the uni just like the multimatic . The multimatic simply relied on splash lubrication to oil this original bearing ..... and it is much further up the housing than a uni design. I say this because I wonder WHY they went from a positive pressure oiling design on the uni ..... to a splash oil design on the multimatics. The stresses are the same, but maybe they figured the old design and all that oil was just not needed? 


Below is a picture of the sealed bearing I used in my multi rebuilds.

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Post# 1093157 , Reply# 21   10/14/2020 at 11:31 (1,282 days old) by swestoyz (Cedar Falls, IA)        
Sealed bearing alternative?

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Great minds think alike :)

This thought has crossed my mind before as well. The problem then becomes - what to do with all that pumped oil? It would pool on top of the rubber seal in the housing neck with nowhere to go/drain back down to the mechanism base.

The top hole on the spin cage shaft could technically be plugged, as there is a hole above the bearing and one just below the washer that provides lubrication to the rotating mechanism just below in the spin cage. While the intent is good it's probably not worth it. GM wisely submerged the rotating mechanism in oil within the Multimatic, relying then on splash lubrication to throw oil up through to the bottom bearing on the mechanism housing support, as well as the pulsator shaft.

John and Robert have a good point about the top bearing on a Unimatic, however I like to err on the side of caution to ensure that the bearing does have enough lubrication to avoid any unnecessary stress, even if it is only to relieve stress in my mind. :)


Post# 1093210 , Reply# 22   10/14/2020 at 22:26 (1,282 days old) by combo52 (50 Year Repair Tech Beltsville,Md)        
Fun Thread

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While it is certainly true that the UM oil pumps will not pump much oil till the motor has reached full 1140 RPM speed, it only takes 10 or 15 seconds to reach full spin speed, no bearing damage would occur in that time.


The UM mechanism with its own oil pump forces oil through out the inside to all bearings, the agitation operation does not help assist the oil flow, in fact less oil would flow to the top bearing while agitating because when it is agitating more oil will escape out of the moving bushings.


The pressure oil system was over built and considering washing machines have no where near the stresses an internal combustion engine in think the engineers decided the splash system was more than sufficient for long life in the later Multimatic mechanisms, in my experience the MMMs out lasted the UMMs and certainly had less problems.


Hi Bud those new sealed bearings are really good, however they still not take water & detergent for long, I suppose you could try leaving out the main water seal but I can assure you the machine won't run a year with those bearings exposed to water etc.


John L.

Post# 1093220 , Reply# 23   10/15/2020 at 06:39 (1,282 days old) by Gyrafoam (Wytheville, VA)        
Years ago------

I was delighted to find an old Flat-Top with a low production-run number.
No telling how many decades it sat idle gathering dust until I came along.
Cosmetically it was in great shape and appeared to be low-mileage.

While I did have the forethought to run some hot water down it's hose and into the pump for an hours soak, I did not think-out the possibilities of a lubrication issue. So in my zeal to find out if it worked I advanced the timer through the fill and into Pulsation. Since it Pulsated without the tub turning, the next step was into spin. At the same moment I heard the trip-switch engage the thought occured to me that there might not be a drop of oil in it. By then it had been ten seconds or so, but, I shut it down anyway. The instant I did the whole machine seized-up and turned itself a half-turn on the floor nearly knocking me down in the process. (A Unimatic with an empty tub can get up to a pretty good speed in about ten seconds!)

In disgust I set it aside. I knew whatever the problem was, it would be a shlep to repair. A few years later and I decided to tinker with it and started to tear it down. As soon as I got the tub out I saw that the Tub-Support Mechanism had been torn in two. It was brittle almost like glass. So once again, in disgust, I walked-away. It still rests down in Triage awaiting assistance.

Lubrication may or may not have been the problem, but, someone would have a hard time convincing me that allowing it to Pulsate for ten minutes or so with the oil moving around might not have made a big difference in the outcome of my little spin-test.

Post# 1093246 , Reply# 24   10/15/2020 at 10:34 (1,282 days old) by swestoyz (Cedar Falls, IA)        

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John, I agree with part of your thinking in that the likelihood of bearing damage occurring on a rebuilt/reoperated mechanism would be slim if activating spin when the machine has been idle for a bit of time. While I wouldn't considering it babying the machine, if I can at least help the bearing out by getting oil up to the bearing before spin I will continue this practice and will continue to suggest the same to others.

What I would like to be clear on is the oiling system does supply plenty of oil to the top bearing, regardless if it is in agitation/pulsation, or spin. The photos and video within response 19 provide enough evidence for me to feel comfortable with this as fact; both the still shot and video were taken with the machine pulsating with an original style pump.

This would also be taking into account your hypothesis of oil pushing past the rubbing surfaces of the rotating mechanism during agitation, and still the pump is pushing enough volume of oil through this entire oiling system (orange is pressure/blue is passive return to the mechanism base). Is it over built? Absolutely. Is it definitely built by a car company? Absolutely. Is the mechanism less reliable due to it having a pressurized oiling system? Possibly - if we consider the idea that it can/will leak past the mechanical seal/or fail due to a broken finger.

GM did the right thing by ultimately moving to the Pulsamatic/Multimatic mechanism, outside of the early clutch fiasco, but it does leave some wonder of why they didn't go ahead and have all commercial machines start with the Multimatic mechanism staring in 1959.


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