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Multiple threads have addressed Trailvoy fan clutches and (apparent) failure modes - I'll try to describe the history and detail of the clutch as well as I can for it being 3:00 am...

The TB fan clutch is the first electronically controlled visco clutch to be produced. Like any other cooling clutch it works with silicone fluid that is transferred between an internal reservoir to a working area and is controlled by the opening of a valve. Different from earlier clutches that were heat activated (bimetal) the valve is opened by engaging a coil (that black unit sticking out of the front of the clutch) and creates a magnetic field that attracts the valve.

Initially the distance travelled by the opening valve was controlled by the coil (EV) itself. Rubber buttons were built into the valve to reduce impact noise. If you look at the older fan clutches you'll find shims under the EV unit - that is how valve lever travel was controlled. Valve lever travel is important in maintaining controllability of the clutch. Unfortunately, the first designers (Germany) of the clutch used buttons made of fluoro-silicone and after about 2 years of contact with the silicone fluid they dissolved an fell off. :cry: Once they were floating free they would get trapped under the valve and keep it open - this led to numerous complaints of fan roar and transmissions not shifting. Now the clutch doesn't really impact the trans - but because it took a higher rpm to pump the fluid out of the working area, people thought they were stuck in first gear due to the noise they heard. The buttons got replaced with a Viton material and that particular problem was solved.

That wasn't the end of the bad news though, for a brief period there was another situation where the assembly equipment for the clutch caused some tearing of the threads where the EV mounts to the clutch - this introduced aluminum debris into the clutch and the effect was the same as the free floating rubber buttons - the valve got stuck open again. Ok, so that got fixed too - all EV units are now hand started rather than let the equipment force a cross thread.

The clutch needed work - general improvements for speed (high and low) based on requests from GM Engineering - however other groups in GM held back the release of the new design (US designers now) for almost 2 years... this means TB owners had to live with fan clutch issues for a while longer. Finally it gets released - the new valve uses a mechanical stop instead of the EV unit - this led to greater control of the clutch but, GM was fearful that the clutch would go too fast at low speeds (fuel economy) so they changed the control software that used to work at 100 pwm (pulse width modulation) to 80 pwm. They figured this would be a positive thing, what happened though was all of a sudden you could hear a ticking from the clutch when it was turning at low rpms. SO TAKE NOTE OF THIS: A ticking fan clutch is not going bad - what you are hearing is the control software opening the valve at a regular frequency - tick, tick, tick.

WTF... so why is it ticking? Because the clutch is being told to engage and most likely it is for the a/c head pressure. The inherent problem with visco clutches is the fluid used to drive the fan for speed. It is a visco-elastic fluid. It is chemically indentical to Silly Putty - if you pull it slow it stretches, if you pull it fast it snaps. This is what happens to the fluid during startup conditions - there is not enough fluid in the working area of the clutch to sustain the shear of the startup condtions. The primary input from the clutch goes from 0 rpm to ~1100 rpm in no time flat and the fluid shears. The problem becomes one of an underspeed fan - it isn't turning fast enough to pull air through the a/c condenser and the a/c cuts out to save it's own life. While the head pressure is building the software is telling the clutch to speed up by opening the valve at 80 pwm - there's that damn ticking again. The difficulty here is that at such low speeds there isn't much centripital pressure to encourage the fluid to move out of the internal reservoir - so the problem has the potential to continue beyond the time of safe a/c head pressure and may not resolve itself until you hit the road and ram air helps spin the fan up to speed.

This called for another solution. In the latest design of the clutch there is a feature that allows fluid to drain back into the clutch when it's in the off state (parked overnight kind of thing). Now when you start up there is enough fluid to spin the fan up and keep the a/c working before you get out on the road. This feature came online with the launch of the '06 TB.

Ok, so you'd think everything has been resolved - there have been the occasional leaky valves - and here comes the morning fan noise complaints again. This isn't as bad as it sounds - you can do a neutral rev disengagement of the clutch - meaning leave the truck in park and run the engine up to about 2500 rpm (you probably have a rev limiter that stops you there anyhow). The clutch will disengage (you'll hear the noise fade away) and you'll be on your way - or you can go to get a new clutch put in to solve the noise complaint. All clutches are now leak tested during assembly now to make sure this doesn't happen again.

BTW, if you want to go through the trouble - the leaky valve is a postional problem, meaning sometimes it will give you a noisy clutch and sometimes it won't. It depends on what postion the clutch stops in after shut off. If you pop the hood and examine the clutch (rotate it by hand) you'll find a 4.1 mm ball bearing stuck in the side of it (you have to look through the fan blades to see it). Put that ball bearing down - it is opposite the valve opening. What this does is put the valve up out of the fluid in the reservoir and it can't leak back. If you want to do this then make you life easier by marking the fan opposite the ball and just put the mark on top ;)

Note to aftermarket clutch buyers - some of the aftermarket clutches (made in Korea, Dorman brand) are clones - meaning they weren't designed, but copied. The design they copied was the type of clutch made with rubber buttons in the valves. The have a slightly lower top speed and slightly higher disengaged speed - meaning you could lose some performance when towing and your fuel economy will drop an mpg or two.

Common codes that relate to fan clutches:
P0526 - lost connection to clutch - you can set one of these by unplugging the harness from the tether to check for ticking noises.
P0495 - fan overspeed - got excessive fan roar? That'll do it. Fan higher than requested speed by more than ~300 rpm for longer than 120 seconds.
P0483 - fan underspeed - set when the clutch is told to engage and it doesn't hit the target fan speed within ~300 rpm within 120 seconds.
Codes have to be set twice before it turns on the SES light.

Notes about the clutch: It is attached to the water pump with a 36 mm hex shaft (factory torqued to 90 Nm). The fan bolts are 13 mm (factory torqued to 26 Nm).

With the launch of th '07 TB there was new software, and a new issue - but this time it was on the software side. A software patch fixed the issue of the fan underspeed code being set in overspeed condtions and now the latest design of the clutch is also the most reliable - figures, it will go out of production with the launch of the '08 TB.
 

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Damn thats alot of info, hmm someone must be bored. Thanks for the info though I'm sure it will help some people out. I'm hoping my 06 does better than my 02 as far as fan clutch problems.
 

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Excellent write up... Good to educate people on the "ticking" because Im sure a lot of people hear their T360/370 ticking and run out and buy a clutch fan.
 

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A bit more info about the clutch position GMT 360 talked about, where the clutch stops, the way the vehicle is tilted while parked, and the resulting effects, that a friend at a GM service dep't sent me a while back...



Operating Characteristics of the Electro-Viscous (EV) Fan Clutch

Changes to the EV fan clutch to improve the HVAC performance basically increase airflow in certain conditions. It is now possible during start up for the EV fan clutch to be engaged and match engine speed for about 1 minute depending on driving speeds (with lower speeds having a longer disengagement time) producing some noise/flare. The noise/flare will most likely be intermittent and can be dependent on the following conditions:

• Fan clutch valve orientation, with check ball at 11:00 position as viewed from front of vehicle when the engine is stopped.

• HVAC or powertrain cooling conditions when the vehicle is shut off.

• Parking incline - vehicles parked nose up on a 16% or higher incline (such as vehicles coming off transport or parked on steep driveways) may have prolonged fan noise/flare until the fluid is pumped out of the working chamber of the fan. These conditions can occur in as little as ten minutes. Once the vehicle is not parked in these conditions, it should operate as expected.

• Please note that if the vehicle is parked nose down with a 16% or more decline, the EV fan clutch may have a delayed engagement response similar to what is described in Corporate Bulletin Number 04-01-38-019A.

(Sure has been a lot of time and effort put into that damn fan clutch! :rolleyes: )
 

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GMT 360, you are our offical forum clutch fan scientist! Awesome write-up. :thumbsup::thx

Joel
 

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I'm having a hell of a time out of mine!!! I just purchased a 2002 and the 2nd day I went to drive it the fan clutch would not disengage. I read on the forums and no big deal, I will replace it. Now it will disengage if I unplug the harness. I replaced it with one from an 04 which was pulled from a wrecked TB. This one will do the same thing. It runs engaged all the time, but will not set off the SES light. Any ideas??? What would cause the PCM to want to engage the fan all the time?

Mike
 

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Thanks for the info man, clears up a couple questions Ive had (ticking in general). I think I have one of the few 02s with the stock fan clutch and stock programming...but I need to get the newest programming soon anyway.
 

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Discussion Starter #15
I'm having a hell of a time out of mine!!! I just purchased a 2002 and the 2nd day I went to drive it the fan clutch would not disengage. I read on the forums and no big deal, I will replace it. Now it will disengage if I unplug the harness. I replaced it with one from an 04 which was pulled from a wrecked TB. This one will do the same thing. It runs engaged all the time, but will not set off the SES light. Any ideas??? What would cause the PCM to want to engage the fan all the time?

Mike
I couldn't tell if the fan clutches you have are taking off again after you disengage them or if it's happening on an overnight soak situation.

The PCM shouldn't be engaging the clutch full time and it sounds like the valve is propped open on something. You can check this by running the engine and verifying you hear the clutch. Stop the engine, unplug the harness from the tether connection and pull it back clear of the fan, making sure the tether doesn't get loose in the shroud or it also will get pulled into the fan and the jet ring will cut through it. Restart the engine and run it to 2500 rpm if the valve is not forced open then the clutch should disengage in one minute or less. (There is a risk of setting a P0526 code and turning on the SES light because the PCM won't sense the clutch).

If the clutch does disengage: Turn off the engine, reconnect the harness then restart and run the engine rpm up - if the fan takes off again then you are getting a signal from the PCM, this could be due to a bad sensor somewhere else in the PTC or HVAC circuit. Make sure when you start the fan is turning normal speed and is not 'stalled'. Stalling is an underspeed condition when the fan is turning so slow (under ~450 rpm for an '05 clutch and earlier, ~350 rpm for an '06 and later) that the fluid doesn't want to come out of the reservoir right away. You can defeat some of this problem by ramping your engine rpm up slowly (say, 30 seconds) instead of just matting the pedal. If the clutch is stalled it will take slightly longer for it to take off again if the PCM is sending it a signal.

Some different things that drive the fan clutch are a/c head pressure, top tank temp, oil temp, trans oil temp. If one if these is sending a false high reading that would be the reason why the PCM is trying to run the clutch.

If the clutch does not disengage or disengages slowly (sound tapers off over the whole time instead of falling off fairly quickly): then the valve is likely being held open. The control software will see the fan is too fast and not have a reason to send a signal to it, unfortunately, this would be the cure, moving the valve would allow some time for the material to move away from under the valve.

If the clutch disengages but the next day it's running high again then the valve isn't fully open but may be partially so. You can supply some power to the EV unit manually to actuate the valve and give the offending matter time to move away from the valve and get you back to normal. OF course if the pariticle doing the dirty deed stays in the reservoir then there is always a possiblity it'll go find home under the valve again, typiclaly though it passes through into the working area and gets ground up.

Give me a day to get the wiring schematic and I can tell you what 2 pins to supply 12 V to (you can do it straight off the battery) move the valve.

If you have Mad Scientist tendencies give this a shot:

Unplug the harness from the clutch tether and check the size of the slots on the female (tether side) of the connector - you've got to get an electrical probe/lead into that or leave the harness connected and go through the insulation - you can already see the risk here...

Prep the clutch by putting the check ball pointing down for about 10 to 15 minutes (assuming the clutch is 'cold' at roughly 70º F ambient, if the clutch is hot [just came off the road] it should only take 5 minutes)

What you're doing here is letting the fluid drain away from the end of the valve so when you apply some power to the EV you may hear the valve move (tick). It's ok to keep the power to the unit, like any coil the EV wil get warm - but you'll be nowhere near it.

Go ahead and work turn the power on and off a few times to see if the ticking changes sound - if it gets more pronounced then the valve is likely clear. If the sound doesn't change then try turning the clutch 180º, the fluid will move in reaction to the valve and the motion may help wash the blocking debris clear. You can double check after a short time by bringing the valve back up and seeing if you can hear it any better. There are two 'ticks' associated with the valve the first, when it opens is the louder of the two, the second is when it closes and it's a much softer sound - this is the one that needs to change sound.


Mad Scientist, Second Level:

Supply power to the EV and turn the engine on and take the engine rpm up, the clutch should be running full blast - the difference here is the valve is full open now and the material has an opportunity to move away. Turn the engine off, then turn off the power to the EV, leave the harness off and restart your engine and see if the fan clutch disengages if so you've likely solved the problem. If not you likely have a problem and need a fan clutch.

On rare occasion the material isn't sitting under the valve but is wedged between it and the cast surface wall of the reservoir - when that happens you cannot free the valve and sorry to say, you need a new fan clutch.

Uh, any Mad Scientist activities are something you need to be comfortable with. I can supply the information but you should always work at your own level of interest and energy you want to apply to the task. Be certain to take reasonable precaution that wires are held down, hands are clear and power supplied to the EV is stable and the leads won't fall out and short or get caught in the fan. I'll get the wiring information and post what two wires you want to connect to if you want to go this route.
 

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Thanks for the info man, clears up a couple questions Ive had (ticking in general). I think I have one of the few 02s with the stock fan clutch and stock programming...but I need to get the newest programming soon anyway.

:iagree: I have the stock clutch in mine, and I have the updated software. It still ticks at start up. Its really loud and annoying on cold mornings, and non-existant on warm days. I finally understand why its ticking now.:cool:
 

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Hey, glad I checked.. the pinouts are male, that should make life easier. The two wires to connect to for engaging the valve are the black and white wires - these are located in the pins A and B portion of the connector - with the harness fixed in the shroud they become the lower two pins.

Pin A (black) is the coil ground
Pin B (white) is the +12V

additional FYI:
Pin C (gray/white) is Hall sensor ground
Pin D (dark blue) is Hall signal (output)
Pin E (gray) is hall sensor +5V
Pin F is empty

Resistance across the coil (checked via the black and white wires) is 8.3 Ohms +/- depending on temperature, usually there is no problem there, just another FYI.

Clutch Identification:

The serial number on the label is a date code/production number code that works with this format: yYMMDDPPPP

The small "y" indicates the original code that had a leading 0 for the year
Big Y = Year, next two numbers are Month followed by the two digit Date. The last 4 numbers are the actual production number.

The clutch released with the '06 model year began with serial number 505190835 (2005, May 19, clutch 0835) Any clutch number higher than that would be what you want to acquire as a replacement part. This serial number code works regardless of what the GM part number is ;)
 

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Insightful Info

Very nice and insightful information GMT 360. You sure sound like you know what you're talking about. Thanks for the good reading.
 

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Very nice and insightful information GMT 360. You sure sound like you know what you're talking about. Thanks for the good reading.
He was one of the Test Engineers on this platform... I'd say he knows what he's talking about... ;)

Mike
 
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