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Old 01-31-2016, 11:24 PM   #1
SergeiF
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Question Shudder/Binding from rear after tight turn - GRB STI

Hi,

I have 2008 JDM GRB STI (EJ207 with 6MT).

I noticed very interesting behaviour:

When I turn into a driveway, especially when one of the rear wheels gets some air (steep drive way), after turning in (yes, after, sometimes during) I get a shudder/binding noise/sensation from rear. Only happens on hot. Sometimes it continues through without any steering angle (front wheels are straight).
Occasionally I would get some resistance doing U-turn (like uphill start, something is holding the car up).

I know what centre diff. binding feels like, and this one is slightly different.

The oil is clean in both in diff and gearbox (replaced recently with Motul Gear 300).
This is JDM STI so rear diff is Torsen (helical).

I have checked the ABS sensors (physically, didn't check the signals). They were clean.

My suspicions are following:

a) One of the ABS sensors is "lazy" causing the drive line ECU to actuate brakes.
b) The centre diff. solenoid is sticking (but this would not explain issue happening after the turn).

The problem is very intermittent, most of the time it is fine.

Any ideas?
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Last edited by SergeiF; 01-31-2016 at 11:29 PM.
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Old 02-01-2016, 12:54 AM   #2
mrsaturn7085
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Quote:
Originally Posted by SergeiF View Post
I have 2008 JDM GRB STI (EJ207 with 6MT)...

...This is JDM STI so rear diff is Torsen (helical).
Wrong (unless you changed it) - JDM GRBA models came w/38410AA140; a clutch-pack mechanical diff. This might explain the stick-slip phenomenon I expect you are experiencing.

Quote:
Originally Posted by SergeiF View Post
...didn't check the signals...
If you suspect wheel speed sensor issues, you must check the signal. The sensitivity required for the DCCD to unlock is below the threshold to throw an ABS code.

Quote:
Originally Posted by SergeiF View Post
My suspicions are following:

a) One of the ABS sensors is "lazy" causing the drive line ECU to actuate brakes.
Nope - if you have a failing sensor, all that will happen is the c.diff will fail to unlock/open.

Quote:
Originally Posted by SergeiF View Post
b) The centre diff. solenoid is sticking (but this would not explain issue happening after the turn).
Not exactly (as you worded it) but you might have the right idea. Here is what I think is happening:

1. Stick-slip phenomenon of the rear wheels due to one leaving the ground (and the plated mechanical diff. trying to right the situation).

2. Failing wheel speed sensor causing the c.diff to remain locked.

Since you are aware of how the c.diff feels when locked, and said this is different, I'd say you're experiencing #1, which is a non-issue. The intermittent nature of the issue may be due to the r.diff temp. (plates at operating temperature will stick better), or a slightly difference geometry of the car in relation to the ground - you might only be hitting that 'sweet spot' where the wheel leaves the ground once in a while.
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Old 02-01-2016, 03:05 AM   #3
SergeiF
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Quote:
Originally Posted by mrsaturn7085 View Post
Wrong (unless you changed it) - JDM GRBA models came w/38410AA140; a clutch-pack mechanical diff. This might explain the stick-slip phenomenon I expect you are experiencing.



If you suspect wheel speed sensor issues, you must check the signal. The sensitivity required for the DCCD to unlock is below the threshold to throw an ABS code.



Nope - if you have a failing sensor, all that will happen is the c.diff will fail to unlock/open.



Not exactly (as you worded it) but you might have the right idea. Here is what I think is happening:

1. Stick-slip phenomenon of the rear wheels due to one leaving the ground (and the plated mechanical diff. trying to right the situation).

2. Failing wheel speed sensor causing the c.diff to remain locked.

Since you are aware of how the c.diff feels when locked, and said this is different, I'd say you're experiencing #1, which is a non-issue. The intermittent nature of the issue may be due to the r.diff temp. (plates at operating temperature will stick better), or a slightly difference geometry of the car in relation to the ground - you might only be hitting that 'sweet spot' where the wheel leaves the ground once in a while.
Thank you!

So, if the diff is not a Torsen, then me using straight Motul Gear 300 without LSD additive does not help?

Is there anyway to confirm differential type?
Next time I have it up I will check if there is a "lock" action (although it is not reliable). Maybe I can peek through the filler hole (I doubt, I will see anything).

My extensive research on the matter of which type of LSD without disassembly, came to conclusion I have Torsen type:

(unfortunately in Russian)
https://www.drive.net/l/8534319/
http://www.sti-club.su/advert/68929
http://www.farpost.ru/vladivostok/au...-38184484.html

In addition to that, the VDC uses the brakes to fix the open diff behaviour of the Torsen when there is no traction on one of the wheels.

Technically description "mechanical type" also covers Torsen.

I have driven cars with clutch type LSD (although they were setup for rally) and on-off action of the LSD is not the same as I am experiencing.
Normally these LSDs can be triggered easily and repeatable during a very tight turn under power. This is not my case.

I owned two cars with Torsens, one is Toyota Trueno and another is Celica GT4, Torsen behaved like it wasn't there - no noises, not a hint of it being there (except obviously it did its job).

So that leaves the failing ABS sensor.
Any ideas how to test it?

I got oscilloscope (the bench type) I could lift the car up and rotate the wheels and see if the waveform is the same, but that is a bit tedious...
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Old 02-01-2016, 09:45 AM   #4
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Quote:
Originally Posted by SergeiF View Post
Thank you!

So, if the diff is not a Torsen, then me using straight Motul Gear 300 without LSD additive does not help?

Is there anyway to confirm differential type?
I have a plate R180. I was using the gear300 ls, but was told it was for the transmission-with a plated FRONT diff. (I think MRsaturn actually was the one) He suggested Motul 90PA gear oil as the correct fluid.

I replaced it with torco SGO, and 2 oz of their friction modifier. I can definitely tell the difference. Don't use the 300 ls, to slippery.

If I jack the back up, and spin a tire, both sides turn in the same direction. I believe a helical will spin opposite direction.
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Old 02-01-2016, 09:49 AM   #5
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can you check the part/serial to see which version you have?
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Old 02-01-2016, 11:50 AM   #6
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For a rear plated diff. 90wt is the correct fluid weight; I do recommend Motul 90PA, though Castrol B373 is great as well! You'll probably need to pull the diff. cover to verify the type of diff. If it is plated (and it should be) you can see the plates through the witness holes.

FreeSSM w/your laptop was the go-to way to diagnose wheel speed sensor issues on the GD chassis, but I am unsure if the GRB and later are supported due to the addition of the CANbus. The software is free, and the required cable is around 5 USD, so even if it doesn't work, it's a cheap test.

The factory service tool, the SSM, is another way to view the raw sensor data, but you'd have to know someone at the dealership to really be able to do this - most techs will not go this in-depth into diagnosis.

Last edited by mrsaturn7085; 02-01-2016 at 12:55 PM.
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Old 02-01-2016, 02:27 PM   #7
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Quote:
Originally Posted by mrsaturn7085 View Post
For a rear plated diff. 90wt is the correct fluid weight; I do recommend Motul 90PA, though Castrol B373 is great as well! You'll probably need to pull the diff. cover to verify the type of diff. If it is plated (and it should be) you can see the plates through the witness holes.

FreeSSM w/your laptop was the go-to way to diagnose wheel speed sensor issues on the GD chassis, but I am unsure if the GRB and later are supported due to the addition of the CANbus. The software is free, and the required cable is around 5 USD, so even if it doesn't work, it's a cheap test.

The factory service tool, the SSM, is another way to view the raw sensor data, but you'd have to know someone at the dealership to really be able to do this - most techs will not go this in-depth into diagnosis.
I just checked out and FreeSSM looks great, as a bonus it is available for linux.
Do you know what type of cable do I have to get? I already have Bluetooth LM327 adapter.

Regarding the diff type, I am very convinced it is Torsen, I will do some testing and maybe get one of those inspection cameras through the filler/sensor hole.

Here is the picture of outside (I doubt it can tell any difference), when I serviced it:
http://sergei.nz/wp-content/uploads/...919_101334.jpg
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Old 02-01-2016, 03:00 PM   #8
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There's very little reason to have a temperature sensor without clutch plates... but Subaru might have just left it in, regardless.

Pull the filler bolt, shine a light through and see if the diff. case is cast or machined. A cast casing is likely plated, while the machined case is Torsen. The more I research it, the more I find conflicting images claiming to be the "AA140" part.
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Old 02-01-2016, 03:12 PM   #9
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Quote:
Originally Posted by mrsaturn7085 View Post
There's very little reason to have a temperature sensor without clutch plates... but Subaru might have just left it in, regardless.

Pull the filler bolt, shine a light through and see if the diff. case is cast or machined. A cast casing is likely plated, while the machined case is Torsen. The more I research it, the more I find conflicting images claiming to be the "AA140" part.
I have ordered an "endoscope" camera from ebay, so in 2 weeks or so I will have a definite answer.
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Old 02-01-2016, 05:23 PM   #10
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I see a couple people have already mentioned the rear diff oil..

That was my first thought as well.

I have Motul 90PA in my r180 with no issues whatsoever.
(previously was using the subaru LSD 90 gear oil in the metal can before they stopped making it)
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Old 02-02-2016, 10:32 PM   #11
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I have tried the LM327 with FreeSSM and it didn't work. Apparently LM327 can only accept AT commands (just like a modem) and not pass through "raw".

I have ordered correct cable (KKL VAG-COM 409.1), probably will get it at same time as the endoscope camera (I am in New Zealand, so a few weeks is the norm).
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Old 02-14-2016, 11:46 PM   #12
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Today I received two packages, one USB KKL VAG-COM cable and another endoscope camera.

After figuring out that freessm does not support TCM, and trying out romraider, I managed to get some data.

The ABS sensor function correctly, on straight line they are exactly the same (say I do 17km/h all of them do 17km/h). When turning they behave exactly as expected (although I haven't had the shudder in long time).

Once I have some free time I will jack up the car and take snapshots of the diff.
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Old 03-12-2016, 08:45 PM   #13
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Finally found some time probe the diff.

I can confirm now it is Torsen.

So with with sample size of 1, and multitude of examples from russian sites I can assume that JDM GRB STIs came with torsens.

Here are the craptastic pictures:





And no, you cannot see the holes from the filler/sensor hole, I had to drain the fluid and poke the camera through drain plug.
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Old 03-12-2016, 09:14 PM   #14
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I managed to do some experimenting.

I set the diff to lock and tried to turn around. The shudder was of much lower frequency and it felt more coming from front than the back.

This is very different to the problem I am having.
The problem is very difficult to replicate as well. I had it happened only once after initial thread post. It was during a tight turn on tarmac. The shudder frequency was about 5-10Hz, a lot less violent than with centre locked up.

It was definitely from the rear. The shudder was more of knocking kind (vs jerking kind for locked centre).

This happens when pretty much rear inner wheel has least speed, and can happen during right or left turn.

The diff itself is absolutely silent and there are no shavings in the fluid (it is very clear).

The intermittent nature of this suggest it is some kind of sensor problem and not mechanical problem. Or a bug in traction control logic.
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Old 03-14-2016, 12:31 PM   #15
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Quote:
Originally Posted by SergeiF View Post
After figuring out that freessm does not support TCM, and trying out romraider, I managed to get some data.

The ABS sensor function correctly, on straight line they are exactly the same (say I do 17km/h all of them do 17km/h). When turning they behave exactly as expected (although I haven't had the shudder in long time).
FreeSSM definitely works with the TCM - I use it for diagnosis of DCCD issues on a very regular basis.

The point you want to look at in the speed sensor data is 0-20 mph and 20-0 mph. Make sure all four sensors transition smoothly and do not 'skip' from 8 to 0 or something like that.
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