Baffling case of torque bind

93forestpearl · Post by **93forestpearl** » Mon Nov 09, 2009 3:28 am

This has to do with my sister's car, a '95 Legacy auto.

The tranny was rebuilt in February by Derek. A new transfer clutch was installed at that time, and he checked for the infamous wear in the extension housing, which was fine.

The car recently started shuddering around corners and barking tires when turning at full lock. I figured it was the Duty C solenoid, so we got the parts and I replaced it the other night. The new solenoid had no effect.

The kicker is, adding the "FWD" fuse releases the transfer clutch. There are no codes from the TCU that I can see. No lights on the dash or anything like that. AT Temp light does not blink. If one of the tranny's internal speed sensors was bad I would think it would throw a code. I may be wrong though.

This leads me to think the TCU itself is suspect. I don't recall TCU's going bad on people, but who knows.

Ideas?

wtdash · Post by **wtdash** » Mon Nov 09, 2009 3:46 am

If the FWD fuse works it should be mechanical - not electrical.

I presume you're referring to THIS w/the transfer clutch?

How many miles on the tranny?

Could the plates in the rear housing be bad or did those get inspected as well?

FWIW, I replaced the Duty C and filed down the grooves in the rear housing and got rid of 90% of the TB AND it got even better when I changed to a different TCU. My TCU is now the same year as my ECU '93, but not the same as the tranny, which is a '91, I believe (tag on bellhousing is gone).

93forestpearl · Post by **93forestpearl** » Mon Nov 09, 2009 4:09 am

Per my original post:

Tranny was rebuilt in February by Derek. He checked the tail housing, and the transfer clutch was replaced. The transfer clutch is what is in the rear of the tranny. He has rebuilt many of these transmissions, and does it for a living.

What tells me it is something with the TCU is that the tranfer clutch is getting plenty of pressure, and the fuse releases that pressure, via TCU. However, the clutch is getting full line pressure all the time without the fuse.

Post by **Legacy777** » Mon Nov 09, 2009 7:16 pm

Dan,

So you're saying that even with the FWD fuse installed, you're still getting torque bind?

When you install the FWD fuse, I believe you should get a warning light on the dash to come on?

I would suspect wiring before the TCU.

93forestpearl · Post by **93forestpearl** » Mon Nov 09, 2009 8:18 pm

No. No torque bind with the fuse installed, and the FWD light illuminates on the dash. Without the fuse installed, the transfer clutch is fully locked.

There are no flashing lights on the dash at startup. It seems to be an OBD2 car, as it has two oxygen sensors. No CEL's, no nothing.

I don't know enough about the TCU's operation, and how it reacts to sensors. I'm hoping Derek can make it down here in the next week or two so I can try his '95 or '96 Outback TCU to see if that fixes the problem. I don't want to throw parts at the car anymore than we already have, since my sister is unemployed.

log1call · Post by **log1call** » Tue Nov 10, 2009 4:59 am

You are right about the way the fuse works and the implications... the tcu is causing the problem.

The two speed sensors are what dictates the torque split mainly, the ratio is effected by being in first gear but
generally it will be the speed sensors.

If the first speed sensor is faulty it gives rough/abrupt shifts through the gears.

If either one of the speed sensors are faulty it causes torque bind.

If both of the sensors is fail it prevents shifts.

So, if the shifts are ok, not abrupt/rough, then it will be number two speed sensor that is faulty.

93forestpearl · Post by **93forestpearl** » Tue Nov 10, 2009 3:56 pm

The trans shifts great, especially with the basic VB upgrade.

Is the second speed sensor the one that is in the back of the trans?

A bad speed sensor wouldn't cause an error code with the tcu?

wtdash · Post by **wtdash** » Tue Nov 10, 2009 5:08 pm

Check this LINKon USMB.

OB99W mentions (pg.2) the difference between the mechanical and electrical issues. IIUC, he's saying the mechanical won't give you codes???

Here's an ENDWRENCHarticle that may help...but I didn't read it all the way thru yet.

93forestpearl · Post by **93forestpearl** » Tue Nov 10, 2009 6:39 pm

Again, the trans is in great mechanical shape. The parts that could cause a mechanical issue were checked and/or replaced. The housing is fine. The transfer clutch is new. The Duty C solenoid is new.

That endwrench article does not go into the detail I need. I need to know the failure mode of the second speed sensor, and at what point it will or will not trigger code, if at all.

log1call · Post by **log1call** » Tue Nov 10, 2009 8:23 pm

The number two sensor is in the dash. In theory it should set a code if it's faulty....

If you are sure there are no codes and the fuse stops the bind then perhaps it's something simple like tyre diameter.

Post by **Legacy777** » Tue Nov 10, 2009 8:44 pm

On the newer cars, VSS2 is the one that screws into the top side of the differential. It'd be a pretty easy swap if you can get another one to try out.

93forestpearl · Post by **93forestpearl** » Tue Nov 10, 2009 9:10 pm

The speedo works though. uuhhg. This is annoying.

Maybe I need to get a tape line out to check the tire diameters. It goes down the road just fine though. She got 30 mpg on a long trip not long ago.

jrobewesty · Post by **jrobewesty** » Tue Dec 01, 2009 7:43 am

Are the tires all the same diameter?

206er · Post by **206er** » Tue Dec 01, 2009 8:47 am

try a continuity check on the solenoid C wires?

known good TCU swap?

93forestpearl · Post by **93forestpearl** » Tue Dec 01, 2009 4:39 pm

I just put new winter tires on it. The other tires were whithin spec, barely, but were acceptable.

There continuity of the solenoid is fine. I just replaced it, and the TCU does have control over it since the fuse works.

For some reason the TCU thinks the front wheels are going faster than the rears. I'm star ting to lean towards the rear speed sensor acting up, but it isn't throwing a code. I can't really dig into it for about two weeks since it is the end of the semester for me, and am getting my ass kicked by school.

log1call · Post by **log1call** » Wed Dec 02, 2009 2:42 am

Sounds to me like the tcu is faulty. If the speed sensor code isn't set, and the fuse fixes the problem then it's wiring from the tcu or the tcu itself.

You could pull the tcu out and check it doesn't have any obvious damage like, leaking capacitors, burnt resistors, cracked circuit board, blown(exploded) transistors or water damage.

If you can borrow another tcu then that would be even better.

93forestpearl · Post by **93forestpearl** » Wed Dec 02, 2009 6:47 pm

I have Derek's TCU in there right now. Changing the TCU had no effect. His TCU worked just fine in his car. I was able to borrow it since he has the full manual VB tranny in his car at the moment.

The car shifts and drives normally on both TCU's. The A/T Temp light does not flash at all at startup. It comes on for a solid two seconds and goes off. Neither TCU has gone into limp-home mode.

I have a different cluster I could try. Unfortunately the speed sensors in the tranny are part of the harness. I would have to cut and splice to replace them.

I could really use a scope to see what is going on.

ericem · Post by **ericem** » Wed Dec 02, 2009 6:52 pm

I am pretty sure a dealership with select monitor can read the TCU and see what is going on when driving.

Post by **Legacy777** » Wed Dec 02, 2009 7:19 pm

Yup, select monitor will be able to read the TCU. I've used it on my select monitor when I was AT.

93forestpearl · Post by **93forestpearl** » Wed Dec 02, 2009 7:46 pm

I'll have to look into that. Can you still use the select monitor on OBD2 cars?

Post by **Legacy777** » Mon Dec 07, 2009 4:05 am

Yes. There are newer Select monitors than what I have. The old one you need to have the cartridge for the car you're wanting to read.

I'm not sure if the newer ones are the same or not.

93forestpearl · Post by **93forestpearl** » Mon Dec 07, 2009 4:34 am

So I would need a cartridge to read a 1995 OBD2 car?

Post by **Legacy777** » Mon Dec 07, 2009 4:37 am

Probably so, yes. At least with the older select monitor.

Without the cartridges the select monitor won't do anything.

93forestpearl · Post by **93forestpearl** » Mon Dec 07, 2009 5:00 am

A friend has a full Genesis setup, so I might just have to take the car to him to see what's going on.

Lunatech · Post by **Lunatech** » Mon Feb 22, 2010 3:30 pm

Did you ever find a resolution to this?

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Baffling case of torque bind

Baffling case of torque bind