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2009 Forester 5-speed manual
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Discussion Starter #1
Hey there.

I’m reassembling my 5 speed manual transmission with 200K km. When it was time to install the front differential, I noticed the mark I made on the right roller bearing outer race was gone so I have a 50/50 chance of confusing the left and right roller bearing outer races. :(

Based on slight visual differences in the wear patterns on the inside of the races I think I can tell left from right but I’m not 100% sure. Any dimensions I can accurately measure on the outer races are identical and the wear seems very minimal.

It clearly states in the FSM “Do not confuse the right and left roller bearing outer races.”

I don’t want to cause any premature wear or failure by confusing left and right races.

Will it make a big difference? I spoke to a couple of experienced mechanics and one said I had to inspect & adjust the hypoid gear backlash and preload on the roller bearings. Another said that the outer races are made of extremely hard material and that the wear is likely on the order of microns and so it’s likely not significant mixing left and right.

The FSM instructions for inspecting and adjusting the backlash and preload is unclear and poorly written and there are apparently some specialty tools required. I’ve called some local dealerships and they refuse to do any work on the transmission out of the car, which is bizarre, because it’s apparently ideal for the backlash and preload adjustments to be made with the transmission out of the car.

So what should I do now?

Thanks!
 

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2019 Crosstrek 2018 XT
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are the bearings in contact with each other?
Are you replacing the bearings?
 

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2009 Forester 5-speed manual
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15 Posts
Discussion Starter #3
are the bearings in contact with each other?
Are you replacing the bearings?
No they’re not in direct contact but are on opposite ends of a shaft that accepts the front drive shafts, one tapered roller bearing at each end.

No, I am not replacing the bearings; they are in excellent condition.
 

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Both the mechanics are right in my opinion.

Ideally they should go back the way they came out, not a huge issue (for the bearings) if they show little wear.

Preload is critical for bearing life, did you mark the location of the bearing retainer nuts, and count the turns out so you can set them back the same?

Backlash and contact pattern is critical for crownwheel and pinion life. Is the pinion back in with the original bearing and shims?

If the pinion is back in the original spot, when the backlash is right the contact pattern will be right.

Given the machining tolerances of a bearing cup, I’d say your backlash will be ok if you get the bearing retainers back in the same place, even if you swap the bearing cups. Ideally you’d check the backlash.

If you haven’t marked and counted the turns to put the bearing retainers back in the same spot, you need to set both the preload and backlash.
 

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2009 Forester 5-speed manual
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Discussion Starter #5
Both the mechanics are right in my opinion.

Ideally they should go back the way they came out, not a huge issue (for the bearings) if they show little wear.

Preload is critical for bearing life, did you mark the location of the bearing retainer nuts, and count the turns out so you can set them back the same?

Backlash and contact pattern is critical for crownwheel and pinion life. Is the pinion back in with the original bearing and shims?

If the pinion is back in the original spot, when the backlash is right the contact pattern will be right.

Given the machining tolerances of a bearing cup, I’d say your backlash will be ok if you get the bearing retainers back in the same place, even if you swap the bearing cups. Ideally you’d check the backlash.

If you haven’t marked and counted the turns to put the bearing retainers back in the same spot, you need to set both the preload and backlash.
thank you for that JonB,

I feel much better about the situation now. Before reading your reply, I also spoke to a local performance transmission specialist that works on a lot of Subaru transmissions and he said the same thing; ideally the outer races would go back in their original positions, however he didn't think it was critical in this situation and that if the bearings are not excessively worn, swapping the outer bearing races doesn't matter much and will not affect backlash or preload significantly. In fact, he said that he sees more problems with transmission premature wear and failures from people making incorrect adjustments deviating from the factory setup than anything else. He said, while he makes every effort to replace outer bearing races in their original positions, even he admiited that he sometimes swaps identical outer races without issue or concern. He also stated that generally speaking, unless components are changed that affect specific tolerances, it's best practice to leave it in factory adjustment.

In my situation, the bearing retainer rings have not been removed or adjusted as I split the transmission case to access everything, and the pinion bearing and shims have not been changed. I just took the front differential out and am putting it back in. Just for fun, I might check the bevel pinion gear backlash while I have everything apart.

When the transmission is put back together, as long as there's no harm in it, as an exercise, I might attempt to check the hypoid gear backlash and bearing preload just to be on the safe side. I will carefully mark the retainer rings for: 1) left and right and 2) rotary positions and note depth (number of turns out) so that I can replace the retainer rings in their original positions in case I get lost in the adjustment process. Do no harm, right? I can change the retainer ring o-rings at the same time.

The FSM is really confusing... In the FSM, they show a variety of pictures of tooth contact marks on the hypoid gear indicating proper tooth contact. They don't explicitly state it, but am I correct in assuming that if the standard hypoid gear backlash of 0.13 - 0.18 mm (0.005 - 0,007 in) for the hypoid gear is adjusted for, the toe to heel tooth contact of the hypoid gear will be correct? Also, if I understand the FSM correctly, the adjustment for tooth contact AREA has to do with the adjustment of the drive pinion to or from the hypoid gear via selection of the appropriate shims? How do you do that after everything is put back together? There must be a way to check that before assembly...

So I'm assuming that the tooth contact area can be visualized through the MTF drain plug hole? And what do you use to visualize the tooth contact surface? I've heard people mention white lithium grease and I'm assuming that there's some kind of paint or dye that can be used...
 

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That’s good news that the original pinion shims are in place, and the carrier bearing caps are as factory.

I would advise against tinkering or adjusting if the diff was quiet when you pulled it apart.
If it ain’t broke, don’t fix it...

The front diff on a Subaru must be up there with THE WORST diff to try and learn on, you can’t see contact patches easily, and you can’t measure backlash properly without specialised gear.

Diffs are really easy to get to get wrong, a bit tricky to get right.

If you really feel the urge to tinker, play with the back diff, you can see what you’re doing, you can see the contact patches, and you can measure backlash with any old garden variety dial indicator.
 

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2009 Forester 5-speed manual
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Discussion Starter #7
That’s good news that the original pinion shims are in place, and the carrier bearing caps are as factory.

I would advise against tinkering or adjusting if the diff was quiet when you pulled it apart.
If it ain’t broke, don’t fix it...

The front diff on a Subaru must be up there with THE WORST diff to try and learn on, you can’t see contact patches easily, and you can’t measure backlash properly without specialised gear.

Diffs are really easy to get to get wrong, a bit tricky to get right.

If you really feel the urge to tinker, play with the back diff, you can see what you’re doing, you can see the contact patches, and you can measure backlash with any old garden variety dial indicator.
Thanks again for your input JonB.

Okay that’s good advice regarding the front and rear differentials and although I have an accurate dial gauge indicator and i verified that it can reach the centre of the hypoid gear teeth from head to toe.

Just for fun and to use the dial gauge indicator, I checked the bevel pinion gear backlash and measured 0.0065 which is within the standard backlash range of 0.005-0.007”.

Someday I’ll check the rear differential tooth contact area as you suggest. It sounds a lot easier than the front for sure.

I’m just wondering if one can at least inspect the front differential hypoid gear backlash and tooth contact without the transmission case assembled, i.e. with the transmission case separated and just set the front differential and drive pinion assembly into the left half of the transmission case? Or is assembly required to ensure the proper preload on the bearings? I could put a weight on the right outer bearing race...

That would make the checking of the hypoid gear backlash and tooth contact easy.
 
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