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VSS#2 update Fri 13th


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26 replies to this topic

#1 Skip

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Posted 10 October 2006 - 08:32 AM

Okay folks first off let me say thanks for taking time to look at this post.
Second let me add that I have not driven the car in question as the engine is being swapped.

It was reported to me by the PM (Previous Mechanic) that the car was driving very poorly.
He said there was a problem with
the vehicle speed sensor and another mechanic "dummied it"
so the car could be driven ("it" meaning the engine as I found the TPS idle switch by passed)


I have read where the ECU uses VSS#2 to trigger various maps for the spark and fuel.


I will assume you know that a 4EAT uses two Vehicle Speed Sensors (VSS)
to control when to engage the clutch pack for the rear wheel drive.

One for front wheels and one for the rear. If the Transmission Control Unit (TCU)
sees a difference in the rotation RPM of the front compared to the rear, it
brings the rear drive into action.

As I understand it, VSS#1 is located in the tail shaft housing and
for years VSS#2 was located in the
speedometer head unit behind the dash.


My research shows this model tranny ( a 1997 4EAT) has VSS#2 located in the
transmission instead of the speedometer head and
VSS#1 having an external vs. internal mounting location.
Both can bee seen at
http://autorepair.ab...faqs/bl833h.htm
Posted Image


But when viewing my tranny the mounting location of VSS#2
is about ten inches in front of the location shown in the link provided above.
Posted Image

This brings me to my question
Has any one removed VSS#2 as I need to know what type of drive mechanism it
uses.

My VSS#2 looks like this
Posted Image

The sensor is said by some to be a reed switch which feeds
the ECU the road speed via digital pulses.

Mine has a square socket for a drive.
When I connect an ohm meter across the output terminals and rotate the drive
I get no evidence of a reed switch, i.e. no pulsing.

But when using a square drive bit in a cordless drill and spinning
the drive,
I see an AC voltage which varies with RPM.
I have read where a test of the VSS is to watch it's AC output volt voltage
and verify it changes with road speed.

Mine was laying loose in the mount where it picks up the signal.

Looking into the mounting hole there appears to be a brass slotted head.
(see above photo)

Does anyone know what the drive should look like?
Can I purchase just the drive?





I am going to assume that Subaru was in a state
of confusion during the 1997 campaign and may have used
a variety of configurations of the 4EAT.
This would explain
why mine seems to be in an Abby normal position.

#2 PAezb

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Posted 10 October 2006 - 09:02 AM

I don't know if you looked at this thread for any of your answers, but it may help

http://www.ultimates...read.php?t=7590

I had to replace the tranny mount VSS on my 96 OBW due to sporatic signal loss between 0 and 30mph. Above 30 it acted fine, but below 30 it "jumped around", changing the behavior of the engine and shift management. Definitely a varying voltage signaling device. The "drive" for the VSS on the 96 is a slotted bar that fits into it's female counterpart on the transmission - you will find photos in the link above. In other model years, have no idea what Subaru uses for VSS signaling and drive type.

Other than that, you've presented a good description of the basic VSS system here...

#3 johnceggleston

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Posted 10 October 2006 - 09:21 AM

i may have one off a 97 obw. i'll check today. if it's located in the same position i'll let know. i have a 4eat that went bad. i sold the clutch pack but still have the rest.

john

#4 cookie

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Posted 10 October 2006 - 04:14 PM

By the way John, i just noticed your mileage and one tow listed. That's not bad for that mileage! I should cross my fingers at 130,000 and no tows becuse the hard years are coming up!

#5 nipper

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Posted 11 October 2006 - 12:38 AM

Get a haynes manual, it explains it fully.

The VSS sensor is a hall effect type. It pulses on and off as the square tooth gear passes it. Without the VSS sensor you have no AWD, poor performance, along with a bunch of other things. The dummying of the VSS has me very worried. There is no reason in the world why that other mechanic should not have replaced the sensor. It takes longer to dummy it then to replace it. i hope he didnt damage anything.

The VSS sensor doesnt trigger anything on the AWD. It gives a speed signal to the tranny puter, and along with other inputs, the TCU decides what to do. This is also true for shift points.

Some people (pm) should not be allowed near tools. i bet the car has a few other issues too, as the bad VSS should throw a CEL. Does your CEL come on when you turn the car on?

nipper

#6 Skip

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Posted 11 October 2006 - 06:40 AM

Thanks for all the replies guys.

Esp PAezb, I did read many articles using the search function but missed that one.

Nipper, I guess my wording was not to clear. Thanks for the clarification.
There is no engine in the car now so no CEL.
PO (Previous Owner) had no money thus the dummying of the TPS not the VSS.




#7 avk

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Posted 11 October 2006 - 06:53 AM

The very first picture seems to show a manual transmission. Reed switches were only used with cable speedometers. Your sensor sits on the differential, just where it should be.

#8 johnceggleston

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Posted 11 October 2006 - 07:45 AM

By the way John, i just noticed your mileage and one tow listed. That's not bad for that mileage! I should cross my fingers at 130,000 and no tows becuse the hard years are coming up!


technically i've had 2 tows, but i don't count the second one because it wasn't the car's fault. i ran a light while dialing my cell phone.:eek: :headbang:

and it is spread out over 3 cars, all used, 93 leg - wrecked at 175K after 75K miles, 95 leg - used tranny at 170K after 100K, now at college, and 97 obw - driving now at 115K after 20K and counting.
after i got the 95 running i regretted giving it to my son. it will be interesting to see which car last longer. i told him this was his car and it would last until he graduate if he takes care of it. i'm praying it doesn't end in a wreck.

#9 Hocrest

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Posted 11 October 2006 - 08:34 AM


Does anyone know what the drive should look like?
Can I purchase just the drive?


It looks just like this.


Here is the VSS with the stem in place;
Posted Image

and the stem looks like this;
Posted Image

On the Diff, it is exactly the same whether there is a cable attached to drive the VSS in the dash, or there is a electronic VSS attached like yours. All you're missing is the stem, and maybe the seal. The seal is a rubber and metal washer that sits on the end of sensor where the shaft spins through.

I don't really want to sell this one, as it's a spare for my fleet of SVX's, but I'll ship it out if you want to try it out, to see if you need to get one.

Sorry for the crappy cell phone pics, but the battery in the camera was dead...

#10 johnceggleston

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Posted 11 October 2006 - 09:03 AM

my next question would be how does the shaft lock into the sensor, is there any chance i fell on the flooor when you removed the sensor? or are you fairly confident that the last guy removed it?

also, if the front wheels aren't turning and rear are, then the clutch pack wouild never kick in.

#11 Hocrest

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Posted 11 October 2006 - 10:04 AM

my next question would be how does the shaft lock into the sensor, is there any chance i fell on the flooor when you removed the sensor? or are you fairly confident that the last guy removed it?


It doesn't officially attach at all, just sits in there, but all of them that I've had apart, the washer is stuck at the end of the sensor and that sort of holds the stem in place.

#12 Skip

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Posted 15 October 2006 - 04:55 PM

major up date:
engine replaced car runs
speedo does not show speed

connect the VSS and spin it with a drill - speedo reads fine

The drive is now replaced and

what
the real problem appears to be

is the slotted base is not being turned by the gear in the diff.

My bet is it's nylon and part of the drive broke off (found a small portion of it in the slot). This in turn jammed the slotted drive and stripped this nylon drive gear.

Anyone know if this is feasable?
Or fixable without removing the tranny?

My luck probably not.

#13 Skip

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Posted 15 October 2006 - 07:47 PM

for got to add
installed VSS with voltmeter connected
car on stands with her feet in the air

ran in drive and got no voltage from VSS

(when VSS is turned by drill voltage varries with RPM)

#14 johnceggleston

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Posted 15 October 2006 - 08:26 PM

sounds like you are going to have to pull the differential offd the transmission. or replace the whole thing.

check these out.

http://smg.photobuck...k/Subaru/4EAT/?


major up date:
engine replaced car runs
speedo does not show speed

connect the VSS and spin it with a drill - speedo reads fine

The drive is now replaced and

what
the real problem appears to be

is the slotted base is not being turned by the gear in the diff.

My bet is it's nylon and part of the drive broke off (found a small portion of it in the slot). This in turn jammed the slotted drive and stripped this nylon drive gear.

Anyone know if this is feasable?
Or fixable without removing the tranny?

My luck probably not.



#15 avk

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Posted 15 October 2006 - 08:43 PM

Maybe somewhere along the way, someone dropped the driven gear inside the diff.

#16 ShawnW

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Posted 15 October 2006 - 09:15 PM

major up date:
engine replaced car runs
speedo does not show speed

connect the VSS and spin it with a drill - speedo reads fine

The drive is now replaced and

what
the real problem appears to be

is the slotted base is not being turned by the gear in the diff.

My bet is it's nylon and part of the drive broke off (found a small portion of it in the slot). This in turn jammed the slotted drive and stripped this nylon drive gear.

Anyone know if this is feasable?
Or fixable without removing the tranny?

My luck probably not.


You'd have to pull the trans. Youre right its a nylon gear in the ring gear section of the differential.

#17 Skip

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Posted 16 October 2006 - 07:45 AM

John thanks for the reply and the link to
the most excellent photos.
This kinda pulls a large vacuum, if you get my point?
No VSS# 2 = no AWD and worse, no pass the emission test
due to the OBD II.

Does anyone know if I can remove the output spline
cover/bearing support to gain access to this gear?

Some of John's picts make it look plausible.
My bet again is no I can't.
My Suby luv is waning.

Posted Image


#18 Skip

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Posted 16 October 2006 - 07:57 AM

Posted Image

#19 johnceggleston

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Posted 16 October 2006 - 08:48 AM

i'd like to take credit for the pictures, but i just saved the link. it looks like you have to pull the tranny, may as well open it up while it's out. you might get lucky.

the parts you need should be easy to come by, but still a PITA to get to. lots of used trannys around. so if you can't repair you can always swap trans.

john

#20 Hocrest

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Posted 16 October 2006 - 07:10 PM

I have a few "seperate" front diffs in my basement, I'll check it out later and see if theres a way. Maybe get a few photos...

#21 Hocrest

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Posted 16 October 2006 - 09:56 PM

OK, took a look. First thing, try to use a straight screw driver into the place where the speed sensor goes. If you turn it CCW I'm guessing that it won't turn at all as you'd be trying to "drive" the car with a screwdriver. When you turn it CW you should get about an 1/8 of a turn and it will float up as the gear "unthreads" itself. If the screwdriver spins freely, then you know where the problem is.

Now when I removed the passenger side bearing support, I could see the speed sensor drive gear and the little gear it drive's. But, you would have to remove the bearing to get access. And I don't see that being possible while it is in the case.

However IF?????? (hopefully) you also remove the driver side bearing support, you MAY????? be able to move the diff unit away from the pinion gear, and then have access to the small SS "driven" gear. You'll need a good set of 90* snap ring pliars to remove the snap ring holding it on the shaft. And if the SS Drive gear is also stripped, you're going to have to pull the trans to get the diff out of the case.

You have the FSM's to reference the procedure for pulling the bearing supports? IIRC (the way I did it tonight??) you need to mark the support and the case and then count how many turns it takes to unthread the support. Then rethread it the same number of turns and match up you're marks. Double check that I'm not missing anything though...

Have fun with it. Let us know.

#22 Skip

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Posted 17 October 2006 - 08:19 AM

Dave, thanks for taking all the time in this endeavor.

When I attempt to turn the slotted drive is spins freely.
I can feel it catch on some material but it is more or less free spin.
I learned yesterday that the speedo slowly died, working now and then.
No doubt as the drive gear lost more and more of it's beveled teeth.

I talked to a local tranny shop familiar with the 4EAT.
He said he has seen this multiple times. Also said postal delivery wagon have it happen,
this OB was used to deliver a free local newspaper.
(My blue wagon was used for mail,
may have had this issue dealt with before me maybe by him?)

He explained the problem as getting the driven gear up and out of the way.
Saying it must come down and out, not up and out.

He also suggested they be replaced
as a set. If I get the gear set he said he'd do it for a hundred bucks, that I don't have.

Looks like I get to smell like gear oil for a week. but as reported in another post,
the engine I put in may have head gasket problems.

So I am going to drive it for a while
as it is inspected and see if the HGs need R&R then yank the lump and tranny.

Thanks once again for the concern and the effort.



#23 fredsub

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Posted 18 March 2007 - 08:30 AM

What size spanner is required to extract the VSS? 17mm ?
I can't fit one down there, exhaust an stuf is in the way, so thinking of getting some $1 cheap spanner and cutting it in half.
Thanks

#24 Skip

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Posted 18 March 2007 - 10:39 AM

Fred you must have a turbo or manaul tranny or
thinking of a different VSS.

Possibly #1 as this shows #2
being reached from topside.

my finger is pointing at the manual tranny
location
(note: the VSS#2 has already been removed in this photo)
Posted Image

#25 Gloyale

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Posted 18 March 2007 - 10:57 AM

Fred you must have a turbo or manaul tranny or
thinking of a different VSS.

Possibly #1 as this shows #2
being reached from topside.

my finger is pointing at the manual tranny
location
(note: the VSS#2 has already been removed in this photo)
Posted Image


Totally unrelated Skip, but I'm excited. I found a stash of actual Old Latrobe RR recently. I bought 6 6packs. The guy who runs the liquor store tried to get me to buy his 12 packs, but they are from St.Louis. I am saving at least one of the sixers for my grandkids.
Notice how the new St. Louis bottles have a disclaimer about "in the tradition" and then the whole Old Latrobe stuff on back is in Quotes? Been waiting to tell ya all night




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