front differential setup how to and re-rebuild of genuine Subaru Remanufactured 4eat

[longassname]

SVXfiles sent me a genuine Subaru remanufactured transmission to use as a core to do a performance rebuild for one of his customers. I believe it is supposed to be slipping in 4th gear but I haven't gotten into rebuilding the actual transmission section yet. After washing it up and beginning to tear it down I didn't like the wear pattern I saw on the ring and pinion so I decided to re-setup the differential.

It's not very convenient to take pictures while setting up a differential but I set out to do so anyway. I hope the information proves useful.

ok so here's the transmission:
http://www.subiechips.com/posts/dif/DSC_1889.jpg

Here's the ring gear: What concerns me is that the contact pattern goes all the way to the outside of the ring gear (called the heel) and all the way to the edge (called the face). We'd like there to be an unworn edge around the face and the heel. We want our contact patch to start offset to the toe side (ID side of ring gear) and move to the center under load. This leaves an unworn strip all along the toe edge, the face edge, and the heel edge.
http://www.subiechips.com/posts/dif/DSC_1909.jpg

Here's the pinion: The wear pattern is nice and large but it is shinyest towards the nose of the gear. I'm suspicious this is two overlapping contact patterns from before and after the Subaru remanufacture.
http://www.subiechips.com/posts/dif/DSC_1896.jpg

[longassname]

The first thing I do is clean the mating edges of the transmission pump and the differential case. After scraping off the ultra-gray sealant and cleaning with a scotch pad surfacing disc I file down any high spots on the differential case mating edge. It turns out there are a handful of them. Anytime you dent a mating surface that metal is displaced making a high spot in the surrounding area. Low spots get filled with sealant. High spots mess up everything.


1st high spot removed:
http://www.subiechips.com/posts/dif/DSC_1922.jpg


2nd high spot removed:
http://www.subiechips.com/posts/dif/DSC_1923.jpg


3rd high spot removed:
http://www.subiechips.com/posts/dif/DSC_1926.jpg


4th high spot removed:
http://www.subiechips.com/posts/dif/DSC_1927.jpg


5th high spot removed:
http://www.subiechips.com/posts/dif/DSC_1929.jpg


Mating flange of differential case in good condition:
http://www.subiechips.com/posts/dif/DSC_1931.jpg

[longassname]

The carrier with the ring gear on it is suspended in the case between a pair of cup and cone bearings which mate into the side plates. You are squeezing the bearings that the carrier hangs in between the side plates so how far you screw in the side plates determines both the bearing preload and the ring gear's positioning left and right in the case and relative to the pinion.

There is a special Subaru tool for turning the side plates. It would be very near impossible to properly set up a Subaru front differential without this tool. You are actually putting quite a bit of torque on the side plates when you are determining the zero point (left/right placement of the ring gear) and setting the bearing pre-load.

Before touching the side plates I mark them and the case with a black marker so I can compare the current adjustment to changes that I make.
http://www.subiechips.com/posts/dif/DSC_1939.jpg
http://www.subiechips.com/posts/dif/DSC_1942.jpg


Driver's side (LH) side plate removed:
http://www.subiechips.com/posts/dif/DSC_1953.jpg


Repeat on passenger side:
http://www.subiechips.com/posts/dif/DSC_1959.jpg



You should be careful while doing this not to damage the plastic gears that drive the speedometer. I screw the first side plate back in partially while I flip the case over and loosen the other side so that I can more carefully take things apart. You don't want the carrier/ring gear banging around breaking the plastic gears while you flip the case.

[longassname]

With the side plates out you can replace the axle seals. They are pressed in from the inside so they can only be replaced when the differential is being setup.

pressing out an axle seal:
http://www.subiechips.com/posts/dif/DSC_1964.jpg


axle seal after being pressed out:
http://www.subiechips.com/posts/dif/DSC_1965.jpg


pressing in a new axle seal:
http://www.subiechips.com/posts/dif/DSC_1970.jpg

new axle seal pressed in:
http://www.subiechips.com/posts/dif/DSC_1974.jpg
http://www.subiechips.com/posts/dif/DSC_1978.jpg


At this point you remove the o-rings from the outside of the side plates. You put them back on after setting up the dif

[longassname]

Use brake cleaner to clean the oil off the ring gear and use petroleum jelly to lube the bearings and the plastic gears that drive the speedometer. Also use petroleum jelly to lubricate the side plates.
http://www.subiechips.com/posts/dif/DSC_1983.jpg


Carefully re-install the carrier assembly into the case leaving the driver's side side plate out a little further than it's previous location based upon the markings we made before taking it apart.


It's time to bolt the pump which the pinion is mounted in to the differential case. You need to actually bolt it to the case. Washers have a crown to them. Be careful to orient the washer so the crowned side faces the pump/case so the outer edges of the washers don't scratch the pump. There's a special Subaru tool for turning the pinion which you'll see in my pictures but you could get by with a big wrench for this one.
http://www.subiechips.com/posts/dif/DSC_1991.jpg


To find the left/right positioning of the ring gear we tighten the driver's side side plate until the pinion won't turn any more. That is called the zero point. Then we back the driver's side side plate out 3 notches on the side plate. I end up with the driver's side plate one half notch further in than the last rebuilder did so I have less backlash.
http://www.subiechips.com/posts/dif/DSC_1995.jpg


To set the bearing preload we tighten the passenger side side plate until it stops turning, back it off, tighten it till it stops turning again, back it off, ...repeat..repeat, tighten it till it stops turning(meaning that it stops turning using the tool with one hand)...then tighten it 1 and 3/4 notches further using both hands. I end up 3/4 notches further in than the last rebuilder did so I have more bearing pre-load.
http://www.subiechips.com/posts/dif/DSC_2002.jpg

[longassname]

Now it's time to check our contact pattern. So we unbolt the pump from the case and paint some gear matching compound onto the teeth of the pinion. The ring gear is still clean at this point.
http://www.subiechips.com/posts/dif/DSC_2011.jpg
http://www.subiechips.com/posts/dif/DSC_2012.jpg


Then we bolt the pump back to the case and give the pinion a few turns forward and a few turns backwards. Then take the pump back off to see what we have. The contact pattern on the ring gear is much better. We've moved well in from the face edge towards the center of the teeth leaving matching compound on the face edges. It's offset to the toe side now and under load will move towards the middle without making it all the way to the heel. Between removing the high spots on the mating surfaces and decreasing the backlash we've gotten to a much better place. I think I can still improve the pattern on the pinion. I'd like to move it in more in both directions and make it as big as possible.
http://www.subiechips.com/posts/dif/DSC_2016.jpg
http://www.subiechips.com/posts/dif/DSC_2017.jpg


To move the pattern from the toe side of the ring to the center (when the carrier's left to right position is set right) we want to reduce the thickness of the pinion shim/shims. Time to remove the seal retainer from the pinion/pump and then the pinion itself to pull out the existing shims and see what we have. In this case we have two shims which I measure with a micrometer. I get a measurement between in inches between the .15mm and .175mm which is the closest thicknesses they come in--so we have a dirty pair of .15mm shims. I was going to replace them with a single .2mm shim but it was rusty so I went with a .225mm shim.
http://www.subiechips.com/posts/dif/DSC_2055.jpg
http://www.subiechips.com/posts/dif/DSC_2058.jpg
http://www.subiechips.com/posts/dif/DSC_2061.jpg

[longassname]

With our new shim installed we will have to redo our side plate settings before checking the contact pattern again. We have to loosen our lh retainer before installing the pump then redo our finding our zero point setting our lh retainer then setting our bearing preload. Then we take it apart again, re-apply our matching compound, put it back together again, give it a few turns forwards, give it a few turns backwards, take it apart again, and see what we have. It's much better. It's good even. The pattern on the ring gear has shifted towards the middle and gotten bigger. We want the pattern to be a little towards the toe side like it is. Under load it will shift towards the heal. The pattern on the pinion has shifted towards the middle and gotten much bigger.
http://www.subiechips.com/posts/dif/DSC_2063.jpg
http://www.subiechips.com/posts/dif/DSC_2068.jpg
http://www.subiechips.com/posts/dif/DSC_2074.jpg

[longassname]

Double checking the setup after finishing up it looks good. We've got good size contact patterns on both the forward and reverse sides of the teeth. On the ring gear the pattern on the forward side is a little offset towards the tow edge and the pattern on the reverse side is offset a little towards the heel. Under load the contact patch will move right to the center.
http://www.subiechips.com/posts/dif/DSC_2153.jpg
http://www.subiechips.com/posts/dif/DSC_2160.jpg

[SVXRide]

Excellent write up! Shame OT didn't send you a LSD for the front diff!

[Tapani]

http://www.flatironstuning.com/p-2003-modena-front-tbd-for-the-02-07-wrx-4at-automatic.aspx

:cool:

/T

[Sean486]

Should be PDF'd and put in the how to section. Thank you for taking the time to write it up and for sharing.

[longassname]

Thanks, and thanks for sharing the link Tapani. Now someone wanting to get a front lsd can both find the part and get an understanding of how it installs.

[Tapani]

Thanks, and thanks for sharing the link Tapani. Now someone wanting to get a front lsd can both find the part and get an understanding of how it installs.

I've had mine for quite a while - three years (?), and I can assure you it's awesome in the snow :-).

I bet the effect is even greater with the MPT tranny.

/T

[SoobCrazy]

Thanks, and thanks for sharing the link Tapani. Now someone wanting to get a front lsd can both find the part and get an understanding of how it installs.

Except that all your photos are dead now... :)

[longassname]

shouldn't be Except that all your photos are dead now... :)

[ensteele]

Should be PDF'd and put in the how to section. Thank you for taking the time to write it up and for sharing.

I will do that. Thanks for sharing!

[longassname]

I should probably point out that it is unusual to find the front dif setup to be wrong from Subaru. This is the first time I've seen it be off in a genuine Subaru reman. I've had a customer come to me before after having two front dif failures on genuine Subaru reman transmissions but I never saw the failed difs. I've always assumed his failures were do to some unusual stress like putting it in park before coming to a complete stop or not using the parking brake on high hills. I've rebuilt several genuine Subaru remanufactured transmissions before and the differentials have all been perfect until now.

I can't say as much for their high clutches. I've gone through this transmission now and found that it does in fact have a bad high clutch.


Before I get into that here are a couple more tips. The front differential case makes a nice stand to hold the pump while you go through it..if you go through it. I've never found one worn out. Destroyed in a transmission with hard parts failure, yes. Worn out, no. That said if you wash the transmission before you take it apart without the converter installed (like I usually have to do) water does get in the front pump and you should make a point of immediately taking it apart. While you have it apart you might consider very slightly filing down the end of the control piston. The pump rotor has to be in just the right spot for it to line up with the lip on the pump cover. If you don't get it right the pump cover will not sit completely flat on the pump. If this happens to you you will have to take it apart and start over. Tip, push the rotor all the way, directly away from the contact point between the control piston and the cam.
http://www.subiechips.com/posts/dif/DSC_2164.jpg
http://www.subiechips.com/posts/dif/DSC_2169.jpg

[longassname]

The Subaru remanufacturer updated the high clutch hub to what I recognize as their latest style high clutch hub. It has a reasonably small number of large holes in the middle of blued/black rectangles. We've all heard this is supposed to improve cooling. Does it really make a difference? I don't know. It definitely doesn't prevent high clutch failure. This genuine Subaru remanufactured transmission, like many before it, and like almost every failed SVX transmission I have ever worked on has a failed/failing high clutch. Note in the photo that some of the frictions are worn completely smooth and the steels have clearly been running too hot.
http://www.subiechips.com/posts/dif/DSC_2173.jpg



The sure way to prevent the high clutch from slipping is to use what is called a "power pack" in transmission industry lingo. A power pack is a clutch pack with more frictions in it. A normal SVX high clutch has 5 frictions in it. I use 6 high energy graphite frictions in mine. Unfortunately there isn't a parts supplier/manufacturer that makes a power pack for phase 1 4eat transmissions but there are parts available from which I could make my own power packs after figuring it out. The black steels you see in the picture are the hard part to find. They are Alto Kolene steels made for Nissan pathfinder power packs.
http://www.subiechips.com/posts/dif/DSC_2177.jpg
http://www.subiechips.com/posts/dif/DSC_2179.jpg

[longassname]

The Subaru remanufacturer did not update the low/reverse clutch to their later style clutch pack. From other genuine Subaru remanufactured transmissions which I have rebuilt I had already learned that they do not revert back to the older style clutch packs in newer transmissions. Now we see that they do not update the older style transmissions to the newer style low/reverse clutch packs. They stick with whatever style they have.

The older style low/reverse clutch is the stronger clutch pack. It has 8 frictions. All the parts in it, including the piston, are different from the newer style. The newer style piston uses D ring seals making it much easier to install than the older style. I make the same choice as the Subaru remanufacturer when I rebuild a transmission unless it is for a supercharged car or car with a large nitrous oxide shot. I have a stock of the old style pistons, pressure plate, and steels so I can revert to the old style for race cars--otherwise I go with whatever it has. I think I've only seen 1 bad low/reverse clutch ever. It's really not a problem.
http://www.subiechips.com/posts/dif/DSC_2182.jpg


The Subaru remanufacturer did update the reverse clutch to the newer style. This requires replacing the high clutch basket. The 92 transmissions used a smaller reverse friction. The splines on the reverse frictions mate with the high clutch basket. The heat from a slipping high clutch goes right into the reverse frictions. You can see looking at the steels in this reverse clutch that is has been running hot but it has survived. The frictions in this clutch pack are still fine. If this was an early style reverse clutch it would have failed. The smaller frictions in the early style reverse clutches just don't seem to be able to disperse the heat from a slipping high clutch.
http://www.subiechips.com/posts/dif/DSC_2189.jpg


So now this transmission has the best of everything. I've upgraded all the frictions, I've put a power pack in the high clutch, it has the better reverse clutch, it has the better low/reverse clutch. I've slightly modified the control piston in the pump to increase output. Next I'll rework the valve body. This will be the last rebuild this transmission ever needs.

[longassname]

Another tip....

There is a small diameter washer that goes on the end of the pinion shaft before the drive gear (not the big washer that goes between the gear and the lock nut. It usually stays on the pinion shaft when you remove pump/pinion from the transmission but sometimes it falls into the transmission.

You must use this washer. If it happens to fall off in your case and you don't know it exists it will spell calamity for you. Without it the drive gear will be able to rub on the spring that holds the parking pawl disengaged, it will eventually wear through the spring, and then the parking brake will engage while you are driving causing the immediate destruction of the front differential.

You can just slide it on the shaft or fix it to the drive gear with petroleum jelly.

http://www.subiechips.com/posts/dif/DSC_2201.jpg
http://www.subiechips.com/posts/dif/DSC_2204.jpg
http://www.subiechips.com/posts/dif/DSC_2206.jpg