Sol C function

[TomsSVX]

Ok I am trouble shooting a binding issue in the teal. I think i really need to understand the function of SOl. C before i go doing anything more. Now my understanding as of now is, when the solenoid does not have aprox. 12v applied to it, the valve is left open which leaves the transfer clutches engaged for a 50/50 torque split all the time. This seems unpractical for a FWD biased transmission. If I am wrong please tell me otherwise. Thank you for your response

Tom

[SVXRide]

Tom,
Okay, if my memory serves me right...

If Sol C is functioning corrrectly it will serve to control the line pressure to the transfer clutches as the TCU decides what split there should be between the front and rear diffs

If it isn't functioning correctly it will either leave the trans in 50/50 mode or you will have only FWD. This second "option" (FWD only) is what happened to my trans, resulting in having to put in a new Sol C (check my locker for pics).

-Bill

[nipper]

Hi, i'm new here but am doing research into buying an SVX, right now i have an outback. i am speaking from the Outback/legacy/imprezza point of veiw, but i think the same applies here.
The Duty C solenoid controls the AWD by cycling on and off many times a minute. The SVX transmission, like all Soobie trnasmissions, are built with AWD in mind, wether or not the car has AWD. When the solenoid is fully energized, you have only FWD. When the solenoid goes bad, you have full time 4wd, with no allowance for the difference in speed between the front axle and the rear axle. Another cause for torque bind is mismatched tires or under inflated tires. The tires must all have the same circumfrence within 1/4 inch per SOA. Subaru has the FWD fuse is only intented for emergencies (but can last years in other soobies, not sure about SVX's with thier touchy trannies). Having the solenoid as normally off, allows for a smaller solenoid.
Now if i am correct, the AWD system in the SVX is the same as in the rest of the subaru line. The first thing you do to try to cure torque bind is flush the transmission. Gunk can get in the valve seat and keep it from operating properly, and also gunk can get in between the clutch plates in the clutch pack. Before 1997 1/2, there was a design fault in the valve seat of the duty C solenoid for the rest of the soobies. The valve seat would erode with time, allowing pressure to bypass the valve. I do not know if the same applies to the svx. The fix is to replace the valve body and clutch pack. If you are not getting a flashing transmission light odds are your duty C solenoid is functioning.
You can do real damage to your car by driving with torque bind, anything from chewing up the tires, destroying your LSD, to burning out the clutch pack. If you burn out the pack, the clutches fuse together, then your in trouble.

Hope this helps.

nipper

[TomsSVX]

actually it doesn't really help me. All I need to know is if the solenoid allows the AWD to fucntion in a 50/50 split at 12v or 0v. Thats all I need to know right now

Tom

[spinn360]

no power to solenoid C 0.V makes the AWD become 50/50 or as close as possible depending who you talk to on here. power to the solenoid or 12v makes the car fwd. But if the fuse doesnt work then I would have to assume that either your solenoid has some how managed to seize in a postion allowing only 50/50 split or the wire to the solenoid has been broken probably the one in the rear of the tranny as it doesnt take much if it was put in incorrectly(it just kind of hangs in there). I dont think but am not sure that the 92's have a code for the solenoid c maybe all the way up to 95(I think I read that somewhere) mine never gave a code.


Nipper you seem to know alot about the auto subie trannies.

[nipper]

Dirvetrain mechnaics, electrics and brakes i'm really good at, Engine mgmt im ok at (i havent kept up with it), i can usually steer you in the right direction.... thanks.

nipper

[Trevor]

Originally Posted by nipper

Dirvetrain mechnaics, electrics and brakes i'm really good at, Engine mgmt im ok at (i havent kept up with it), i can usually steer you in the right direction.... thanks.

nipper

Can you please advise:-

(1) Is PWM pressure control solenoid valve "c", a normally open or a normally closed device?

(2) Is control achieved with the valve in line, or as a bypass?

My subaru manuals are not clear on either of these two important points.

Thanks in anticipation, Trevor.

Tom, when it comes to things like this, you have to think about it from a worst case scenario perspective. If the solenoid fails, which would be the better situation? 50/50 or 100/0? 50/50, as you would be in better shape for poor driving conditions. Having the solenoid fail would be the same as 0v to the solenoid, so 0v would be 50/50. It's the same for other solenoids, Solenoid A fails, no lock up, Solenoid B fails full line pressure, etc.

[TomsSVX]

Ok, I replaced the transfer clutches and I had to put a new clip on the sol. c wiring after I swapped it out for one I was told to work well. The wire is either broken somewhere going from the TCU all the way to the trans. The other option is that the solenoid C I installed is not no good. Now I am trying to figure out it's full function so I can tell whether it is an electrical problem or purely a faulty solenoid. I don't want to go buying a new solenoid to find out it was only wiring.

Tom

[spinn360]

Heres something else that might have something to do with your problem. This is what Harvey told me about. Although not the prob with my car might have something to do with yours. Not sure though.

some of what he say's has nothing to do with your prob, but still could be a sticking transfer valve.
Because my car's AWD wasnt working making it FWD. But I believe that this might be of some use to you.

Originally Posted by oab_au

You are overlooking the section between the C solenoid and the transfer clutch. The C solenoid does not control the transfer clutch directly. The C solenoid controls the Pilot pressure, which operates the transfer valve, that applies line pressure to the clutch.

As you say the rear does kick in with a delayed action, binding is felt. These are the symptoms of a sticking transfer valve, not a C solenoid problem. Switching the C solenoid, won't fix the problem, as it is doing what it is suppose to. The transfer valve is not reacting to the changes in the Pilot pressure.

The rear of the trans has to come off to replace the C solenoid/transfer valve assemble, shown below.


Harvey.

[TomsSVX]

Originally Posted by TomsSVX

All I need to know is if the solenoid allows the AWD to fucntion in a 50/50 split at 12v or 0v. Thats all I need to know right now

Tom

Still need a definate answer to this. Some of you had said this MIGHT be the case but weren't sure. I need to know for sure if this is how it operates.

Tom

[NikFu S.]

Originally Posted by TomsSVX

Still need a definate answer to this. Some of you had said this MIGHT be the case but weren't sure. I need to know for sure if this is how it operates.

Tom

0v from what I gather from the above posts.

According to memory, models outside the US it is 12v.

[spinn360]

Tom did you even read any of the posts they pretty much all say



0.0Vfor the AWD 50/50 split

This is definate

[TomsSVX]

yes but everyone was not sure. People kept saying, "if my memory serves me right, or I think, or I believe." My car doesn't run on memories and I thinks, it runs of facts. So I need to know facts not thoughts. Sorry to get snippy but thats what I needed to know. Are you saying that you are 100% sure that it is how it functions? Would you care to lay down the $100+ it is going to take to replace my solenoid if you are wrong? Listen, I needed to know what it was for sure.

Tom

I'm 100% sure that's the way it functions, and I would put down the money IF THAT IS THE ACTUAL PROBLEM.