Thread Number: 5392
What's a coaxial transmission?
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Post# 115240   3/14/2006 at 17:04 (4,175 days old) by roto204 (Tucson, AZ)        

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Okay, the lovely PennCrest made me need to know--what's a co-axial transmission with respect to the Hotpoint solid-tub-spiralator-fountain-filter machines? What's the difference between that and the later positive-brake design?

They sound fascinating!


Post# 115245 , Reply# 1   3/14/2006 at 17:21 (4,175 days old) by westytoploader ()        
Positive Brake Explanation

Hi Nate,

I would love to find out more about the Co-Axial, but here's how the Positive Brake tranny works.

According to my 1977 Hotpoint Repair-Master, the Positive Brake transmission is just that; it has a brake that is supposed to stop the rotating tub in less than 10 seconds. Looking at the diagram, it is composed of a pressure plate, brake spring, hub & roller, drive cone, cam plate, and brake pad assembly consisting of upper and lower friction pads.

Brake operation is as follows: "When the power to the motor is discontinued, torque to the transmission pulley ceases, thus releasing the torque at the hub and drive cone assembly. The brake spring force causes the hub and roller assembly to ride down the cam ramp and forces the drive cone and plate assembly to move upward; the pressure plate contacts the lower friction pads of the brake pad assembly, forcing the brake pad assembly upward and the top friction pads contact the underside of the transmission casting, stopping spin rotation."

Judging by the manual, the upper brake pads are softer than the lower brake pads so the machine will brake quietly. The brake exerts 100 lbs. of force on the transmission case during agitation...I'm not sure if that's enough to prevent a sympathetic index or not.

Now the Co-Axial on the other hand doesn't have a brake. Greg or Robert I'm sure will be able to provide more information on that...I know when I ran Greg's 1963 "Fabric Command" at the Convention with a full load, the turnover was great and there wasn't much indexing, the tub sort of "free-wheeled" back & forth during agitation (action similar to the Fisher & Paykel). Is a drive spring among the components in this transmission?

Also, both the Co-Axial and Positive Brake machines had reversing motors for spin, unlike the previous Beam-style design which relied on a solenoid.


Post# 115246 , Reply# 2   3/14/2006 at 17:26 (4,175 days old) by westytoploader ()        

One thing I LOVE about those Hotpoint machines is that the cabinet is the outer other words, if you put your hand on the cabinet, you can feel the water spinning off like in the early Frigidaires!

That's probably the reason they're so rare, IMHO; if the cabinet rusted through then nothing could be done about it short of plumber's epoxy and silicone!

Post# 115324 , Reply# 3   3/15/2006 at 03:28 (4,175 days old) by spinout ()        
Hotpoint co-axial tranny

I want to add a comment/clarification on this POD: The "positive brake transmission" as described above is also a co-axial transmission and is a derivative of the earlier co-axial design. It is "co-axial" in the sense that agitation is caused by rotation of an inner shaft and spin by rotation of an outer shaft that also encompasses the gearcase. This is a type of system that is also used by several other manufacturers in varying forms, usually with reversing motors. Examples would include Norge, Maytag, GE, etc..

I recently relined the clutch shoes on the subject (Hotpoint) machine, so I'll attach some photos depicting the assembly.

Here is the bottom of the early (without brake) co-axial tranny with the clutch assembly removed. The centrifugal clutch shoes drive the inside of the gearcase for "spin."

Post# 115325 , Reply# 4   3/15/2006 at 03:37 (4,175 days old) by spinout ()        
The clutch assembly

Note that the clutch shoes ride on the drive pulley. This is a strong, no non-sense clutch. And with substantial weight on each of these shoes (they are made from some sort of lead alloy) it wastes no time in bringing the tub up to speed.

Post# 115326 , Reply# 5   3/15/2006 at 03:41 (4,175 days old) by spinout ()        
Clutch installed in transmission

Here is the clutch assembly installed into the transmission. Note the large hub on the bottom of the pulley; that hub receives the agitate clutch spring.

Post# 115327 , Reply# 6   3/15/2006 at 03:44 (4,175 days old) by spinout ()        
And finally...

Here it is with the agitate clutch spring and hub in place. Spin it in one direction to agitate, the other way for spin. Elegant, isn't it?

Post# 115424 , Reply# 7   3/15/2006 at 15:27 (4,174 days old) by roto204 (Tucson, AZ)        

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Thanks, Joseph and Austin! That's fascinating!


Post# 115452 , Reply# 8   3/15/2006 at 20:22 (4,174 days old) by jetcone (Schenectady-Calrods,Monitor Tops,Toroid Transformers)        
Thanks Joseph

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I love tranny repair shots, those are nice and clear too!
It looks like the tranny is Cast Iron? How old is this machine??


Post# 115474 , Reply# 9   3/15/2006 at 22:41 (4,174 days old) by spinout ()        
This is the same machine that is pictured in thread #5365...

It was manufactured in June of 1967 and the tranny is cast iron, both top AND bottom. Additionally, the sector gear pivot shaft and compound gear are held in double shear, making it very rigid.

Hotpoint revised it around 1971 to incorporate a brake as is aptly described above by Westytoploader. Basically, the drive skirt was eliminated from the casting and a brake/clutch assembly was fitted in its place.

I would love to have a brake on this machine, as I hate waiting for it to coast 1-1/2 minutes to a stop. In fact, I have considered devising/adding a brake to it. (IF ANYONE OUT THERE HAS A POSITIVE BRAKE TRANNY OR PORTIONS THEREOF -- I'M INTERESTED, SO PLEASE LET ME KNOW.)

I did fabricate a mechanism to lock the tub during agitate, so the indexing problem is solved--but it is not a brake. At the time I did not know about the existence of the positive brake tranny.

My own experiments showed a substantial improvement in turnover just by reaching in and holding the tub (very scientific). So, yea, I think a 100# of braking force is plenty to hold the tub. It also adds quite a bit of reaction moment or "kick" to the works as the agitator reverses its stroke. Incidently, I can still "unlatch" the tub and let it index during agitate, which results in a more gentle cycle--or a more nostalgic look.

Post# 115586 , Reply# 10   3/16/2006 at 13:17 (4,174 days old) by westytoploader ()        

Great pictures Joseph...thanks for sharing!! I've been curious about the mechanicals of the Hotpoint spin clutch...from what I saw at the Convention it doesn't waste any time getting the tub up to speed!

How does your tub-locking "anti-index" mechanism work? I tried both the Hotpoint Spiralator and long-neck agitator on the 1963 "Fabric Command" at the Convention, and it seemed to index more with the Spiralator, which makes sense considering the curved vanes. With the long-neck, it had incredible turnover and there was hardly any indexing; the tub just "free-wheeled" back & forth, similar to a Fisher & Paykel machine.


Post# 115601 , Reply# 11   3/16/2006 at 14:37 (4,174 days old) by spinout ()        

My machine will index about 30 deg. CCW on the forward stroke of the spiralator. (The stroke that pulls clothes down and into the tub.) There is very little indexing on the back stroke because of the stock brake spring on top of the tranny intended to prevent reverse rotation of the tub.

My impression is that Hotpoint designed the Helix (i.e., spiral) of the agitator in the wrong direction. (???) Had it been opposite, the forward stroke would have acted against the existing brake spring and there probably would have been less indexing and better turnover.

Continuing this thought, indexing on the BACK stroke of a helical agitator might have actually be benificial to improving turnover as it seems there would be less push-up/push-back of the load. Anyway, I'll have to test my theory sometime. As it turns out, a Super roto-swirl will fit on the machine if I pull the drive block up about 1/2"--and its Helix just happens to be opposite that of Hotpoint.

I can tell you with certainty that locking the tub makes a BIG difference in turning large/heavy/bulky loads; a lot seems to happen at the moment the stroke reverses.

Imagine this:

Post# 115860 , Reply# 12   3/17/2006 at 11:28 (4,173 days old) by spinout ()        
Hey Austin,

Here is the anti-indexing mechanism I put on the machine:

Post# 115861 , Reply# 13   3/17/2006 at 11:34 (4,173 days old) by spinout ()        
A close up of the latch pin...

During agitate, the solenoid is pulled in, extending the pin which engages the notch on the transmission case.

Post# 115862 , Reply# 14   3/17/2006 at 11:37 (4,173 days old) by spinout ()        
another view

the bottom of the machine

Post# 115864 , Reply# 15   3/17/2006 at 12:20 (4,173 days old) by unimatic1140 (Minneapolis)        

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Hey Joseph, that is a great idea to stop the Hotpoint from indexing! My '62 Hotpoint indexes way too much, I have all the parts to repair the anti-index spring, but that means taking the whole thing apart. This fix would be much easier.

Post# 115889 , Reply# 16   3/17/2006 at 13:43 (4,173 days old) by spinout ()        


After considering several options, I chose the above design for expedience. Like you, I didn't want to take the machine apart, so I spent several evenings making the brackets and mechanism from parts on hand. And I was able to notch the transmission case using rotary and hand files.

It has been on the machine 10 years now and was well worth while--it is a much more capable machine with the tub locked. Only downside: the clunk, on what is otherwise an amazingly quite machine.

Post# 117080 , Reply# 17   3/22/2006 at 23:02 (4,167 days old) by westytoploader ()        

Wow...very cool and effective anti-indexing mechanism!! Thanks for posting! So as the tub indexes along with the solenoid energized, the notch/pin will eventually line up and "lock"? One of the things I like about my GE is when it first starts agitating on slow speed before shifting, the tub slowly indexes clockwise and then with a "CLUNK" locks into place.

Post# 117093 , Reply# 18   3/23/2006 at 00:47 (4,167 days old) by spinout ()        

Funny you should mention it, but when I was devising a way to do the anti-index, observing my GE 18# gave me the idea to use a positive latch (as opposed to a friction brake). I always kind of liked the way the tub would index for a few seconds and then lock. So I will confess to a little GE emulation. And the solenoid pull-in should make you Beam style guys happy too! Finally, at the end of the agitate period, when the latch drops out, it makes a subtle, but interesting noise and the tub indexes slightly. It's a really cool, kind of endearing idiosyncrasy not unlike those found in many of the early machines that are so etched into our memories.

Anyway, there is a plunger and spring inside the latch pin. (That pin is really the hardened end of a pushrod from a small block Chevy.) When the motor inrush current pulls the armature in, the pin contacts the transmission case and is spring loaded against the plunger until the tub indexes around to a notch and then... Clunk--tub stops just like the GE. And almost sounds the same too, if not somewhat more "polite."

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