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2004 FXT 5MT
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Discussion Starter #1
Last year I had a rear differential replaced under warranty. All was OK until the other day I noticed that starting from 30MPH, I get a drone/howl noise from the rear. Since it was under one year parts/labor warranty, I took it back to the dealership for them to have a look.

Turns out one of the bolts wasn't torqued to spec, the service guy explained it to me, he said at the rear where the propeller shaft connects to the rear diff, there is a bolt that holds the crush plate (?) in place. There are two pinion bearings on each side, and since the bolt was loose, it was causing play in the joint. They took it apart and re-torqued everything.

My question, would this cause any possible damage to anything? The manager said the rear diff oil looked clean and no visible metals. I've driven about 12K miles since this was done the first time.

Also, on my drive home, everything seems to drive better, but the noise is a little worse now. Do you think it could be something else?

The noise starts at around 30MPH and is almost constant regardless of speed, in or out of gear or gas pedal. Above 40MPH I can't tell if it's there anymore since road/exhaust noise takes over.

Thanks.
 

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2009 Forester X Premium
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3,091 Posts
Id say if they were loose and there was any amount of play in there, you can bet their was some amount of wear. Id complain to Subaru about the repair and make them do it again.
 

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2008 Forester X Premium 5MT
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8,071 Posts
From what you posted it sounds as if the nut they say wasn't torqued is the pinion nut.

If this nut is left loose the pinion bearings have no preload, which can cause wear on several parts and destroy a differential.

With no preload the bearings do not mate correctly and wear prematurely, this being the least of the worries.

The big concern is with out the proper preload on the pinion bearings there is a good chance to destroy the ring and pinion gears. That nut being torqued properly is critical to setting and maintaining proper ring and pinion gear backlash and a appropriate contact pattern. With the nut being even slightly loose it can allow the pinion gear to run off center or wobble and allow it to move in and out of the pinion gear thus affecting the backlash and contact pattern.

At the very least that diff should have been pulled apart and inspected. A fluid change doesn't even begin to tell the story of what could be going on in there. If you want a second opinion I suggest finding a driveline shop and telling them what you posted here for us. I would suspect they will tell you what I just did.

http://www.scribd.com/doc/9375619/Dana-Ring-Pinion-Installation-Guide
Ring & Pinion Installation Instructions
Ring and Pinion Adjustment
Differential Repair & Installation Instructions

I agree with TC2000 make a call to Subaru customer service.
 

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2004 FXT 5MT
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Discussion Starter #4
Thanks a lot guys, I didn't know it could be this serious.

I did feel that the transmission is smoother now, would a loose pinion nut cause rough transmission feel?
 

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2008 Forester X Premium 5MT
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Thanks a lot guys, I didn't know it could be this serious.

I did feel that the transmission is smoother now, would a loose pinion nut cause rough transmission feel?
It may transmit some vibration through the driveshaft. The looser the nut the worse it would be but it is hard to say how noticeable this vibration would be.
 

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2004 FXT 5MT
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Discussion Starter #7
Thanks. I'll double check the tires, I've run it last summer no problem though.

It's not so much as vibration, but more like jerky transmission, especially in 1st and 2nd.
 

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Discussion Starter #8
I had to bring my car back to the dealership again because the noise got worse after they 'tightened' the pinion nut, and they are going to replace the rear diff this time.

Should I be concerned about possible damages to other parts of the transmission due to the loose pinion nut? Front/Center diff etc?
 

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2009 Foz
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52 Posts
I've had the same symptoms as the OP, starting at about 10,000 miles. Got the dealer tech to do a ride along with me, and he said it sounded like the rear diff. The work order says the dealer "adjusted preload on transmission bearings". Like the OP, my noise got worse after the adjustment. I took it back, and the second work order says "adjusted preload bearings in transmission". This seemed to quiet things down somewhat, but the shifting was and remains "jerky" like the OP says. Also, on occasion, when shifting from second to third (4EAT), the engine will rev up like the car is in neutral then ease into gear (i.e., it doesn't clunk into third when this happens). Also, the noise returned within about 1,000 miles. So, it looks like I'm going back to the dealer again, albeit a different dealer because we moved.

A few questions:

1. Is "adjusting preload bearings in transmission" the same as adjusting the preload on the pinion bearings?

2. If not, then do I need to be concerned about transmission wear from the problems?

3. Any idea what could be causing the weird shifting I'm seeing?

4. Do I need to push the dealer for a new rear diff?

Thanks in advance for any insight you guys can offer.
 

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2004 Forester 4EAT
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5,462 Posts
Speaking as a tech for other techs out there, sometimes you just have a bad day. That's what warranties are for. I'm surprised/impressed they owned up to it. Little weird they didn't replace it the first time you brought it back. It's common knowledge, not just for subbies, no preload will destroy a rearend.
 

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Discussion Starter #13
lawdog, sounds like you are having the same problem as I am, mine is a manual though. Sounds like you are still under warranty, hope you can get it sorted.

I'm not sure what happened the first time. The service manager and the tech both looked at the problem, and the service manager is the one that told me not to worry about it now that the pinion nut is re-tightened.
 

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2009 Foz
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Anyone out there that can share some knowledge re: these questions:

A few questions:

1. Is "adjusting preload bearings in transmission" the same as adjusting the preload on the pinion bearings?

2. If not, then do I need to be concerned about transmission wear from the problems?

3. Any idea what could be causing the weird shifting I'm seeing?

4. Do I need to push the dealer for a new rear diff?

Thanks in advance for any insight you guys can offer.
 

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Premium Member
2008 Forester X Premium 5MT
Joined
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8,071 Posts
Anyone out there that can share some knowledge re: these questions:
A few questions:

1. Is "adjusting preload bearings in transmission" the same as adjusting the preload on the pinion bearings?

2. If not, then do I need to be concerned about transmission wear from the problems?

3. Any idea what could be causing the weird shifting I'm seeing?

4. Do I need to push the dealer for a new rear diff?

Thanks in advance for any insight you guys can offer.
1. Same type of process. There is a preload adjustment for the front diff in the transmission and for a couple other items as well. Transmission and rear diff are only connected by the propeller shaft(driveshaft), the damage of one wont affect the other.

2. Yes, I would be concerned any time a tech/mechanic told me that the problem was solved by adjusting preload on a bearing. A bearing that has had improperly set preload that has been in use(driven) for any length of time develops a wear pattern and becomes noisy. Tightening it down only forces the bearing to mesh on that worn bearing surface, thus the reason the noise got louder after the first adjustment. Further tightening adding more preload can make a worn bearing quiet for a period of time until it disintegrates further down the road.

3. There is too much going on in a automatic transmission to diagnose over the internet. This needs to be done by some one who can put there hand on the problem so to speak.

4.Depends if it was the rear diff or the transmission that had the preload adjusted.
 

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2009 Foz
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1. Same type of process. There is a preload adjustment for the front diff in the transmission and for a couple other items as well. Transmission and rear diff are only connected by the propeller shaft(driveshaft), the damage of one wont affect the other.

2. Yes, I would be concerned any time a tech/mechanic told me that the problem was solved by adjusting preload on a bearing. A bearing that has had improperly set preload that has been in use(driven) for any length of time develops a wear pattern and becomes noisy. Tightening it down only forces the bearing to mesh on that worn bearing surface, thus the reason the noise got louder after the first adjustment. Further tightening adding more preload can make a worn bearing quiet for a period of time until it disintegrates further down the road.

3. There is too much going on in a automatic transmission to diagnose over the internet. This needs to be done by some one who can put there hand on the problem so to speak.

4.Depends if it was the rear diff or the transmission that had the preload adjusted.
Thanks for the info. All of what you said makes a lot of sense. The dealer tech who did a ride along with me said it sounded like the rear diff, and the service manager who returned the vehicle told me that they had made a rear diff adjustment. So, I was surprised (and somewhat confused) to see that the service receipt said bearings in the transmission were adjusted. From your answers, it sounds like there is no adjustment in the transmission that could effect the preload on the rear diff. Problems in and changes to the transmission worry me much more than the differential because, like you said, the auto trans is a complicated mechanism.
 

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2004 FXT 5MT
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Discussion Starter #18
Another question, do I need an alignment after a rear differential swap? How do they pull the axles out without messing up the alignment?
 

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2009 Foz
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Does anyone know if some measure of drivetrain howling is considered normal in a Subaru? I recently moved and my new dealership says the howling noise I'm getting (that another dealership tried twice to correct) is a normal part of the AWD system. Basically, there is a vibration in the drive train that's hitting a resonant frequency and causing the howling. I understand the description of the source of the noise, but am not convinced that such a vibration is normal. Any thoughts?
 

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2009 Forester
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2 Posts
Question

My '09 Forester is making a sound like a tablesaw when I am decelerating - from what I've read on here it sounds like a similar issue. I'm trying to figure out what exactly happened, because everything was absolutely fine until I took it through the car wash and then that night we went to sub zero temps. I'm wondering if an underwash could reach a pinion nut and consequently work it loose as the water froze and mess up the entire works? It seriously was NOT making this noise before I ran the car through that wash. Was this the most expensive wash my car will ever get?:surprise:
 
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