The ZF 9hp transaxle has two unique clutches that I've never seen in an automatic transmission as
far as a regular planetary gearset style automatic transmission these two clutches are called dog
clutches and they pretty much act like a manual transmission as far as engaging gears two gears
that need to connect together to allow for power flow to take place for an automatic transmission
that's that's a unique thing and this 9 speed transaxle with everything also compact into one
little case uses these dog clutches and it's a it's a very interesting and unique design I
wanted to show you these two dog clutches now we've got the input shaft which is really the
only shaft of this transmission other than the idler shaft and the final drive but all
nine gears are accomplished through this shaft this we've got the splines over here
for the connection to the turbine in the torque converter and then the shaft is the rest of the
transmission well back here on the backside of this input shaft is what's called A dog clutch
so every clutch in this transmission is lettered a through E or a through F and the A clutch and
the F clutch are dog clutches the other four clutches there's two of them that are driving
clutches that cause things to rotate and there's two of them that are brakes that stop things from
rotating so the A dog clutch in the back of this trans axle on this input shaft here is
going to slide forward like this or slide back so it can go forward or back just like that but
it's controlled hydraulically and so in the back of this input shaft there's a hole and hydraulic
fluid is going to come into there and push on a piston in the center of this shaft that this dog
clutch sleeve is connected to and it'll push it forward and then on the front of this input shaft
in between these two seals right here is an oil feed hole and it feeds oil up the center of the
shaft and to the other side of this piston that the dog clutch sleeve is connected to and slides
it so I want to demonstrate that for you with just some compressed air so let me grab the air
here and get things situated where you can see it I'm going to manually slide the dog clutch sleeve
back to the released position and then I'm just going to take some compressed air come in to the
hole in the back of the input shaft and give it a little bit of air pressure so here we go
so that moves it forward I can push it back compressed air or hydraulic fluid will push it
forward so once it's pushed forward then we need to be able to push it backward also because when
it's pushed forward it engages into an internal gear or annulus gear ring gear whatever you want
to call it ZF calls it an annulus gear it engages into this annulus gear right here there are some
little teeth down inside of there that the dog clutch engages with and it will lock this gear
to the input shaft and cause it to turn the same speed and I'll show you that here in just
a moment but for now I just want to show you the releasing of the dog clutch so we've got a
hole right here I'm just going to come in with some air and release the clutch the dog clutch
so it pushes it back so I can push it forward it pushes it back so we use compressed air or
hydraulic pressurized fluid to move it forward and to move it back now as I mentioned we've got
this annulus gear here that fits onto our input shaft and all by itself it just sits up here as
a sleeve that causes it to just sit there and it is not connected to the input shaft as you
can see I'm holding the input shaft from turning this annulus gear which also it functions as a Sun
gear on the outside of it because there were four planetary gear sets in this transaxle is
not connected to the input shaft but then if I come along and take the compressed air and
simulate hydraulic fluid pressure applying that dog clutch sleeve and it has to be synchronized
just right to wear it there we go where the teeth line up so the TCM synchronizes the speed of this
annulus gear with the speed of the input shaft so that they're the same and then it engages the dog
clutch sleeve and now as you can see it rotates the entire shaft they are connected together
if I apply power from the torque converter it forces the annulus gear which is also a Sun gear
to rotate with it if I come back over here and release the dog clutch now I can spin the input
shaft and the annulus gear is not connected to it so it's a real basic connection unlike a manual
transmission there is no brass synchronizer ring or fiber synchronizer ring assembly there's just
simply a clutch pack back here that I'll show you that will lock the speed of the input shaft
to the speed of this annulus gear and then at that point it will engage the A dog clutch so
that's the A dog clutch but remember there are two dog clutches in this a transaxle so the next one
is the B dog clutch now the A dog clutch that we just got done looking at is a driving dog
clutch so when it applies it forces something to turn but the F dog clutch that we're going
to look at next is a breaking dog clutch and it will stop a Sun gear from rotating that was
rotating so let me get that set up let me just slide this out of the way and the dog cuts that
the F dog cuts that we are going to talk about is in the front of the transaxle there is a Sun gear
right here that's part of a Simpson planetary gearset in the front that all by itself when it
sits up in here it is not connected to anything it can spin freely and up inside of this stationary
housing in this housing here to cast iron it bolts to the transaxle case this is our output gear by
the way that drives the idler gear in the end the final drive here but up inside of here is a
sleeve a piston and a sleeve with teeth that are going to engage with these little teeth on the
Sun gear so this is the F dog clutch and the F dog clutch teeth and so I'm going to show you how that
applies and releases on the end of this housing here there are two hydraulic passages these two
passages one of them this one right here applies the dog clutch so it moves this piston with the
teeth forward or I'm sorry towards the the back of the transaxle this one releases it so I'm
going to demonstrate that for you here so let me get the camera positioned where you can you can
see that there we go okay so I'm going to zoom in so you can see the teeth a little bit better here
so these are the dog clutch teeth it's just dog clutch is just another name for a little
gear teeth that connect to each other we've got this the set of teeth here on the end of this
sun gear and then we have a set of dog clutch teeth down inside of the sleeve here and when
this sleeve when this piston moves forward it's going to engage with the dog clutch teeth of the
Sun gear and lock the Sun gear to this cast iron housing and prevent it from rotating so let me
grab let me get this set up to where we can see what's going on here there we go you can see the
teeth down inside here I'm going to take some compressed air and come in on the applied side
which oh by the way just a quick demonstration here little barring the Sun gear the Sun gear is
free to spin at this moment I can rotate the Sun gear but now if I come in and apply hydraulically
apply that dog clutch so here we go so do you see this sleeve right here came up it was down
about seven eight millimeters in the bore now if I put the Sun gear down in its locked solid it does
not rotate and now if I come and take that back out so you can see the sleeve right here what's
this sleeve it's going to drop drop down and hit some compressed air to it down it goes and now I
can put the Sun gear back in and it rotates freely so the purpose of this dog clutch is to when it's
applied which it's applied in first gear through seventh gear when it's applied it will hold this
Sun gear from rotating and this is a extra-tall Sun gear because the front two gear sets of this
transaxle are a Simpson gear set and a Simpson gear set is known because it has a common Sun
gear to two planetary gear set as a matter of fact these two planetary gear sets in in the front this
transaxle are absolutely identical they have the exact number of teeth on the ring or ring gear
annulus gear whatever you want to call it and the Sun gear so there are two identical gear sets that
share a common Sun gear that is a Simpson gear set now there are a lot of Simpson gears that's
out there that have a different sized Sun gear but the Sun gears are still connected together
and that's what defines a Simpson gear set while we're here looking at this F dog clutch I want
you to notice that the this gear right here that drives the idler gear and the final drive
and moves the vehicle it has little teeth on it right here and those teeth are going to connect
to a planetary carrier that will mesh on here this is not the dog clutch I've seen magazine articles
where they say this was the dog clutch from this is not the dog clutch these are just teeth
that connect the planet carrier to this output gear so if this output gear moves at all then
the vehicle is going to move obviously forward or or backwards so we have two dog clutches in
this transaxle and A dog clutch in the back that when it engages it will start a son not a son gear
it'll start a ring gear or annulus gear rotating and then the F dog clutch here in the front of the
transaxle that stops something from rotating all right now we'll take a look at some other parts