Fundamental Question: What is "Torque Bind" and what is it indicative of?

[Hachiroku $B%O%A%m%/(B]

I should preface with, I know what torque bind is in a S00B trans/diff. we
sold a S00B to a girl and she came back a few days later saying it 'felt
funny and made a noise going around sharp corners". We had sold the car
for a guy who fixes Ferraris and Maseraties for a living, but began as a
S00B tech and rose to the top.

His suggestion was to get some Sea Foam tranny conditioner and throw a
bottle in, which I did and never saw the girl again. When my '89 started
acting funny I did the same to it and it smoothed right out.

So, what is torque bind (as related to S00Bs), what are the causes and
what are the prescribed fixes?

 

[1 Lucky Texan]

I should preface with, I know what torque bind is in a S00B trans/diff. we
sold a S00B to a girl and she came back a few days later saying it 'felt
funny and made a noise going around sharp corners". We had sold the car
for a guy who fixes Ferraris and Maseraties for a living, but began as a
S00B tech and rose to the top.

His suggestion was to get some Sea Foam tranny conditioner and throw a
bottle in, which I did and never saw the girl again. When my '89 started
acting funny I did the same to it and it smoothed right out.

So, what is torque bind (as related to S00Bs), what are the causes and
what are the prescribed fixes?

You must be speaking about auto trannies. Someone here mentioned a
Ford additive as helping with the torque bind issue. Hadn't heard
about the Sea Foam.

the below is meant to be very general statements about the Subaru 4EAT
transmissions.

The AWD is supposed to engage automatically when slippage occurs,
then, if slippage is gone, the system returns to an 'open diffs'
condition(there isn't really a center diff, it's a 'wet clutch pack').
Anytime the system stays in the AWD condition, BUT is on dry hard
pavement, the drive train has no way to relieve stress. There's no
slippage. The TCU/computer detects slippage as a difference in signals
from the tone rings on the hubs. I think these same sensors are used
by the ABS if equipped and maybe dynamic control or w'ever. Not sure
on those last 2. If, for example, you have a larger or smaller tire on
you car, the signals from the tone rings are outside the allowable
threshold and the system reacts as if you were on snow or mud w'ever,
and begins to alter the duty cycle of the pulses sent to the Duty
Solenoid C (IIRC) that controls the clutch pack in the tail of the
tranny. The clutches begin to engage more, apply torque to the rear
diff. Depending on whether that diff is open or limited slip, one or 2
wheels in the rear will be able to apply more and more force to the
road surface Once the tone ring signals agree, the system returns to
'open diff'. Naturally, if the TCU itself were damaged, or if the Duty
Solenoid C is stuck, or perhaps damaged wheel sensors/wiring - could
all cause the clutch pack to engage when it shouldn't . It should be
pointed out that the system COULD fail in such a way that AWD never
engages even when it should. In the past, there have been issues with
a wear part in the transmission being made of aluminum causing
eventual torque bind problems (that was in the 90s IIRC - replacement
part, rebuilt trannies are steel). Also, some folks feel improper/
infrequent transmission fluid maintenance can cause the problem. If
you experience torque bind, and try troubleshooting by using the FWD
fuse in the fuse block under the hood, that can help point to where
the problem lies. If using the fuse does NOT fix the binding (as felt
by doing sharp cornering/figure 8s in a dry parking lot) then the
problem is inside the transmission or the TCU - basically, the Duty C
Solenoid is not able to respond to the FWD Only fuse's action. Some
folks have had bad U joints feel like torque bind so that should be
checked too. I think I read of someone that found a piece of steel
road debris stuck to a wheel sensor once.

I may be off on a detail or 2, but someone will no doubt correct me if
I'm misleading in any important way.

 

[Dave__67]

You must be speaking about auto trannies. Someone here mentioned a
Ford additive as helping with the torque bind issue. Hadn't heard
about the Sea Foam.

the below is meant to be very general statements about the Subaru 4EAT
transmissions.

The AWD is supposed to engage automatically when slippage occurs,
then, if slippage is gone, the system returns to an 'open diffs'
condition(there isn't really a center diff, it's a 'wet clutch pack').
Anytime the system stays in the AWD condition, BUT is on dry hard
pavement, the drive train has no way to relieve stress. There's no
slippage. The TCU/computer detects slippage as a difference in signals
from the tone rings on the hubs. I think these same sensors are used
by the ABS if equipped and maybe dynamic control or w'ever. Not sure
on those last 2. If, for example, you have a larger or smaller tire on
you car, the signals from the tone rings are outside the allowable
threshold and the system reacts as if you were on snow or mud w'ever,
and begins to alter the duty cycle of the pulses sent to the Duty
Solenoid C (IIRC) that controls the clutch pack in the tail of the
tranny. The clutches begin to engage more, apply torque to the rear
diff. Depending on whether that diff is open or limited slip, one or 2
wheels in the rear will be able to apply more and more force to the
road surface Once the tone ring signals agree, the system returns to
'open diff'. Naturally, if the TCU itself were damaged, or if the Duty
Solenoid C is stuck, or perhaps damaged wheel sensors/wiring - could
all cause the clutch pack to engage when it shouldn't . It should be
pointed out that the system COULD fail in such a way that AWD never
engages even when it should. In the past, there have been issues with
a wear part in the transmission being made of aluminum causing
eventual torque bind problems (that was in the 90s IIRC - replacement
part, rebuilt trannies are steel). Also, some folks feel improper/
infrequent transmission fluid maintenance can cause the problem. If
you experience torque bind, and try troubleshooting by using the FWD
fuse in the fuse block under the hood, that can help point to where
the problem lies. If using the fuse does NOT fix the binding (as felt
by doing sharp cornering/figure 8s in a dry parking lot) then the
problem is inside the transmission or the TCU - basically, the Duty C
Solenoid is not able to respond to the FWD Only fuse's action. Some
folks have had bad U joints feel like torque bind so that should be
checked too. I think I read of someone that found a piece of steel
road debris stuck to a wheel sensor once.

I may be off on a detail or 2, but someone will no doubt correct me if
I'm misleading in any important way.

I don't think an odd-sized tire is enough to trigger the system, but
the problem with that being the clutches are just rubbing against each
other too quickly for the heat to dissipate properly, but either way,
bad.

The additional failure mechanism is the clutch basket getting grooved
and keeping the plates engaged, or from engaging.

Dave

 

[1 Lucky Texan]

I don't think an odd-sized tire is enough to trigger the system, but
the problem with that being the clutches are just rubbing against each
other too quickly for the heat to dissipate properly, but either way,
bad.

The additional failure mechanism is the clutch basket getting grooved
and keeping the plates engaged, or from engaging.

Dave

The reason they give you the ability to force the system into FWD mode
with the fuse trick, is precisely because you NEED to if you use the
'donut' spare. Subaru used to recommend no tire more than 1/4"
difference in CIRCUMFERENCE than any other tires. That seems to work
out to a tire that is about half worn out. Now, is Subaru just being
overly cautious? Could you run a new replacement with 3 almost worn
out tires and be safe? Suppose you ran the new tire deflated 2-3 psi?
These discussions come up every 6 months or so. I'd say , it IS a risk
to mix sizes of tires. The bigger the difference in size, model, wear
w'ever - the bigger the risk to your transmission.

I run less expensive low-tread-wear tires (that are otherwise good at
traction, heat speed rating, w'ever) beacuse I knoiw I may, someday,
have to replace three 2/3rds worn tires because the sidewall got cut
on one. With cheaper tires, less wasted value if that happens. Tire
shaving can help with this issue. But it isn't easy to arrange for
most people, it costs money, AND you are shaving off part of the value
in a new tire.

(HELLO! Subaru! each dealership should offer free tire shaving!)

 

[AD]

(HELLO! Subaru! each dealership should offer free tire shaving!)

Ok, even liability in the states aside why would they want to do that
for free?

 

[Gilbert Smith]

You must be speaking about auto trannies. Someone here mentioned a
Ford additive as helping with the torque bind issue. Hadn't heard
about the Sea Foam.

the below is meant to be very general statements about the Subaru 4EAT
transmissions.

The AWD is supposed to engage automatically when slippage occurs,
then, if slippage is gone, the system returns to an 'open diffs'
condition(there isn't really a center diff, it's a 'wet clutch pack').
Anytime the system stays in the AWD condition, BUT is on dry hard
pavement, the drive train has no way to relieve stress. There's no
slippage. The TCU/computer detects slippage as a difference in signals
from the tone rings on the hubs. I think these same sensors are used
by the ABS if equipped and maybe dynamic control or w'ever. Not sure
on those last 2. If, for example, you have a larger or smaller tire on
you car, the signals from the tone rings are outside the allowable
threshold and the system reacts as if you were on snow or mud w'ever,
and begins to alter the duty cycle of the pulses sent to the Duty
Solenoid C (IIRC) that controls the clutch pack in the tail of the
tranny. The clutches begin to engage more, apply torque to the rear
diff. Depending on whether that diff is open or limited slip, one or 2
wheels in the rear will be able to apply more and more force to the
road surface Once the tone ring signals agree, the system returns to
'open diff'. Naturally, if the TCU itself were damaged, or if the Duty
Solenoid C is stuck, or perhaps damaged wheel sensors/wiring - could
all cause the clutch pack to engage when it shouldn't . It should be
pointed out that the system COULD fail in such a way that AWD never
engages even when it should. In the past, there have been issues with
a wear part in the transmission being made of aluminum causing
eventual torque bind problems (that was in the 90s IIRC - replacement
part, rebuilt trannies are steel). Also, some folks feel improper/
infrequent transmission fluid maintenance can cause the problem. If
you experience torque bind, and try troubleshooting by using the FWD
fuse in the fuse block under the hood, that can help point to where
the problem lies. If using the fuse does NOT fix the binding (as felt
by doing sharp cornering/figure 8s in a dry parking lot) then the
problem is inside the transmission or the TCU - basically, the Duty C
Solenoid is not able to respond to the FWD Only fuse's action. Some
folks have had bad U joints feel like torque bind so that should be
checked too. I think I read of someone that found a piece of steel
road debris stuck to a wheel sensor once.

I may be off on a detail or 2, but someone will no doubt correct me if
I'm misleading in any important way.

Thanks for this description of the system - the best I have read.

My 20k mile 05 Forester automatic developed the binding problem, and
neither of the two nearest "main dealers" had the slightest clue what
it was or how to fix it.

The first said it needed a new rear axle, which even I knew was
rubbish. The second thought he could fix it by driving round in
circles on full lock, one way then the other. This wrote off both
front CV joints at prohibitive cost (to me).

I took the opportunity to swap-out the whole gearbox/dry clutch assy
when offered a low milage unit at a price roughly half the cost of one
CV repair, so I never found out whether it was the gearbox or the
centre clutch. (The old unit sold too quickly to investigate, and in
any case was too big and heavy for me to work on).

The old unit had a clunk from overrun to drive, and had slight tyre
scrub on full lock from day one, whereas the replacement is completely
free of these effects (and does drive all four wheels on soft ground).

The purchaser of the old unit said it was a front diff fault, but he
didn't want to pay too much for it "as spares" so could have been
telling porkies. What do you think ?

 

[Hachiroku $B%O%A%m%/(B]

The purchaser of the old unit said it was a front diff fault, but he
didn't want to pay too much for it "as spares" so could have been telling
porkies. What do you think ?

I dunno about the problem you describe, but I like "telling porkies".

 

[1 Lucky Texan]

Thanks for this description of the system - the best I have read.

My 20k mile 05 Forester automatic developed the binding problem, and
neither of the two nearest "main dealers" had the slightest clue what
it was or how to fix it.

The first said it needed a new rear axle, which even I knew was
rubbish. The second thought he could fix it by driving round in
circles on full lock, one way then the other. This wrote off both
front CV joints at prohibitive cost (to me).

I took the opportunity to swap-out the whole gearbox/dry clutch assy
when offered a low milage unit at a price roughly half the cost of one
CV repair, so I never found out whether it was the gearbox or the
centre clutch. (The old unit sold too quickly to investigate, and in
any case was too big and heavy for me to work on).

The old unit had a clunk from overrun to drive, and had slight tyre
scrub on full lock from day one, whereas the replacement is completely
free of these effects (and does drive all four wheels on soft ground).

The purchaser of the old unit said it was a front diff fault, but he
didn't want to pay too much for it "as spares" so could have been
telling porkies. What do you think ?

I dunno really. My wife's 03 Outback has a noisy front diff and I've
read of complaints about front diffs - though it seems quite rare
compared to other drivetrain problems.

Of course, that old tranny 'could' have had more than one problem.

hard to say.

 

[Dave__67]

The reason they give you the ability to force the system into FWD mode
with the fuse trick, is precisely because you NEED to if you use the
'donut' spare. Subaru used to recommend no tire more than 1/4"
difference in CIRCUMFERENCE than any other tires. That seems to work
out to a tire that is about half worn out. Now, is Subaru just being
overly cautious? Could you run a new replacement with 3 almost worn
out tires and be safe? Suppose you ran the new tire deflated 2-3 psi?
These discussions come up every 6 months or so. I'd say , it IS a risk
to mix sizes of tires. The bigger the difference in size, model, wear
w'ever - the bigger the risk to your transmission.

I run less expensive low-tread-wear tires (that are otherwise good at
traction, heat speed rating, w'ever) beacuse I knoiw I may, someday,
have to replace three 2/3rds worn tires because the sidewall got cut
on one. With cheaper tires, less wasted value if that happens. Tire
shaving can help with this issue. But it isn't easy to arrange for
most people, it costs money, AND you are shaving off part of the value
in a new tire.

(HELLO! Subaru! each dealership should offer free tire shaving!)

I didn't say it doesn't damage the clutch, I said that the system is
not activated, and the damage occurs without the system being
activated.

The clutches are in close contact and will undergo significant
friction and generate significant heat if the system is not activated.

Tire Rack will shave-to-spec before shipping.

Dave

 

[1 Lucky Texan]

I didn't say it doesn't damage the clutch, I said that the system is
not activated, and the damage occurs without the system being
activated.

The clutches are in close contact and will undergo significant
friction and generate significant heat if the system is not activated.

Tire Rack will shave-to-spec before shipping.

Dave

That's cool that Tire rack will do that. I've done biz with them twice
and been very happy. But many people use local tire retailers that may
not offer shaving.


I don't see how the AWD 'system' can distinguish between faster tone
ring signals due to actual slippage vs faster tone ring signals from -
say - a deflated or undersized tire, but we can agree to disagree.

And I agree it's possible for components to fail or wear-out without
the system 'engaging'. (When we say 'engaging' it depends on whether
the slipping /undersized tire is on the front or rear axle. The TCU
alters the duty cycle of pulses to the Duty Solenoid C to 'direct'
torque away from the slippage and towards the non-slipping axle.)

Putting a scope on the signal to the Duty Solenoid C and letting a few
psi out of tires in various locations on the car, then doing some
sharp maneuvering on dry pavement, could be interesting.