DRive Train Damage from HVAC problem

[dboyte]

I am starting this thread as requested from the other post. The problem is with my truck's 4WD system being totally screwed up by jumping into 4wd hi while on the Interstate coming onto an off ramp. The problem started as the typical complaint I have seen on this board about the hvac controls not working due to the fluid drawn into vacuum system by faulty vacuum actuator on transfer case. As i was explaining in the other post,
I took the truck into the shop to have the hvac controls fixed to find out the transfer case was the problem. After spending week in the shop, I got the truck back and everything seemed okay but 7 days later on the way home, My truck decided to engage the front diff. while on the Interstate. Resulting damage was warped housing, ruined axles, and a total rebuild/replacement of the front diff. Ther is a TSB out on the fluid leak problem but it does not cover the full effect of the damage. I am currently in a legal battle with GMC over this as a safety defect. What the TSB does not say is that the fluid is caustic on all of the vacuum system components. since the front diff. and 4WD is controlled by vacuum and electrical components, the effects of this can vary. It is my understanding based on the GM certified mech. depositions that the fluid effected the front diff. controls. I Would love to be able to point you to the documentation that verifies all this but it is not public knowedge and was obtained thru my lawsuit discovery request. After the first manfunction, everytime you took your foot off the gas and hit the brakes, the front diff. engaged. Mechanic verifed this on the work order. It is due to the sudden vacuum changes in the system as far is I can tell. Has anyone else had a similar experience with their Sonoma? GMc could fix this problem if they would modify the Vacuum actuator. Based on my research and personal experience, this part can not withstand prolonged interstate runs or the higher heat ranges associated with use. My problem started after a long trip - 8 hrs. in one day. as far as redesign, It should be a simple matter of upgrading the materials in the Vacuum actuator and possibily installing a switch that removes all vacuum pressure from the 4wd until you switch the system on the dash. It appears someone did something similar to control the hot feet issue with the heater cowl. I would appreciate any additonal information or views on this matter since I am facing an uphill battle against GMC but the way they treated me requires I follow this to the end. No one should treat a loyal customer the way they did me.

[HenryJ]

You may be dealing with separate problems here. They may not all be directly related to the fluid in the HVAC system, IMO. All the pieces don't fit in this puzzle. Or at least there are pieces missing. It just doesn't add up.

The "warping" you describe, I take it was caused by heat developed under prolonged use at highway speeds, rather than a sudden engagement?

The front axle is actually engaged by a cable. It is actuated by a vacuum diaphram. If fluid enters that diaphram it could be damaged due to the incompatible composition of the materials used, as could the rest of the vacuum system , and the axle would no longer engage. The electronics will not have contact or be affected here.

I would suspect this may be more of an ABS issue if braking is involved. That can give a hard jerking action when trying to brake with the 4wd engaged. Especially on dry pavement. I don't see the front axle engaging on braking causing any issues alone. I tried braking coming off the ramp in four wheel drive and felt nothing. I did not brake hard enough to activate the ABS though.

If the transfercase vacuum switch were to fail in such a way that is inadvertently engaged the front axle, it would be all the time and not intermittent. This would be a problem. An electronically controlled vacuum switch could be incorporated, however Ford uses them in their systems and they are prone to failure. Again the front axle does not engage.

This is the first that I have heard of such a problem. It may very well be a combination of unfortunate circumstances that lead to this isolated incident.

I will ask again. What is your ultimate goal? What are you seeking to satisfy your situation?

I wish you luck on this dilemma, and share the "super secret" discovery information when you can. NHTSA will be interested , I'm sure.

[kf6kmx]

You may be dealing with separate problems here. They may not all be directly related to the fluid in the HVAC system, IMO. All the pieces don't fit in this puzzle. Or at least there are pieces missing. It just doesn't add up.

I agree.. Some of it seems opposite of what a diaphram failure in teh actuator would cause (the part that would likely deteriorate in the fluid).

The "warping" you describe, I take it was caused by heat developed under prolonged use at highway speeds, rather than a sudden engagement?

How fast was the truck moing when it engaged? I have been told by GM that you can engage the 4hi at any speed up to around 60 or 65 with no ill effects at all.. I have engaged in bad weather at up to 50 or so and not had so much as a strange noise from the system.

The front axle is actually engaged by a cable. It is actuated by a vacuum diaphram. If fluid enters that diaphram it could be damaged due to the incompatible composition of the materials used, as could the rest of the vacuum system , and the axle would no longer engage. The electronics will not have contact or be affected here.

Thats the way I understand it looking at the diagrams of the operation.. If the actuator fails, you no longer get 4x4 at all, not get it instead of 2wd.. The actuator is holding the 4x on and not holding it off.. If the actuator were to hold the system in the off position, then you would get a suggen engagement.
Like the airbrakes on a big truck.. the service brakes are held off by springs, and pulled ON by the air actuator.. The PARKING brakes are held ON by springs and pull OFF by air actuators.. If you loose air pressure in the service side you dont get brakes, loose it in the parking side and all you get it brakes..
The diagroms of the 4x operation on here is the same as the service brakes.. Its 'resting position' is off (2wd)

I would suspect this may be more of an ABS issue if braking is involved. That can give a hard jerking action when trying to brake with the 4wd engaged. Especially on dry pavement. I don't see the front axle engaging on braking causing any issues alone. I tried braking coming off the ramp in four wheel drive and felt nothing. I did not brake hard enough to activate the ABS though.

I'm leaning toward a straight ABS failure, probably one of the actuators on the front end.. My '89 Lincoln has an abs sensor failure on teh front , and when you stop hard it gets very jerky as the sensor looses track of the wheel speed.

[dboyte]

I understand you may not agree but is it not true that the front diff. is told to engage by a vacuum controlled sensor. I beleive the reason for my problem is the fact that only part of the system engaged. If the system as a whole were to engage, it would probably work okay. As far as being able to engage at any speed - on a straight run no problem - in a sharp curve - watch out at the higher speeds. The laws of physics do not change. As far as the question about what I want - left that up to the lawyer at this point. I will fill you in better later on but do not want to tip my hand since someone from GMC may be reading this.

[HenryJ]

I understand you may not agree but is it not true that the front diff. is told to engage by a vacuum controlled sensor.

You're right it is a switch

[dboyte]

Thanks, would you agree that sudden changes in the vacuum pressure could cause the system to think I engaged the 4wd.

[HenryJ]

Thanks, would you agree that sudden changes in the vacuum pressure could cause the system to think I engaged the 4wd.

Nope.

The vacuum system is controlled by the encoder motors activation of the transfercase. Therefore the activation is based upon electrical influences , not inches of vacuum.
If anything with a lack of vacuum the front axle actuator would not pull the cable and the front axle indicator switch would not be activated , signaling a lack of front axle engagement.

Also remember that there are not "sudden" changes in vacuum. The system incorporates a reservoir to retain even vacuum readings in the system.
The intake manifold does see changes obviously. Increased during deceleration and decreased during aceleration. This does not suddenly affect the accessory vacuum system dramatically like older systems with out reservoirs.

[dboyte]

I am not talking about a lack of vacuum - talking about a sudden increase in vacuum. As far there being no sudden changes in vacuum, I stated in the post that the vacuum canister was damaged (actually it was clogged up) and not operating porperly according to the gm tech that worked on the truck. I should have mentioned as well that the truck's diff. would disengage as you come to a stop and you hear it.

[HenryJ]

...I will ask again. What is your ultimate goal? What are you seeking to satisfy your situation?

[dboyte]

Well, I want to get rid of this truck. As far as what it takes to make that happen, my lawyer is asking for alot hoping to settle somewhere in the middle. I would also like an apology from the people at GMC that treated me like crap but that won't happen. What about the last post - am I right??

[F9K9]

Have you filed with the BBB/GM (maybe it is GM/BBB) online yet as mentioned in the owner's manual? Just have all your info handy such as you VIN, Dealer's name , address, ph # and dates. I so not believe you need an attorney that will get 33 to 50 percent of any award you may recieve.

[HenryJ]

Well, I want to get rid of this truck....I would also like an apology from the people at GMC...

OK, at least we now know your motivation, Thank you. It saves time knowing that you are not trying to solve the problem, but instead just gather ammunition.

What about the last post - am I right??

I am not talking about a lack of vacuum - talking about a sudden increase in vacuum. As far there being no sudden changes in vacuum, I stated in the post that the vacuum canister was damaged (actually it was clogged up) and not operating porperly according to the gm tech that worked on the truck. I should have mentioned as well that the truck's diff. would disengage as you come to a stop and you hear it.

It still doesn't add up. With an increase in vacuum , if there was vacuum to the front actuator it would engage , not disengage. No vacuum to the front actuator and it is disengaged.

If you are seeking to be rid of the truck you may need multiple problems within a specific time period. I don't know if the heat on the feet will qualify, but that one you have for sure. Check the wheel bearings and balljoints as they can fail in under 40k. Radiator caps, and Dex issues , The balance shaft noise is a good one. They put out the TSB and a fix, then when the fix doesn't work they again deny that there is a problem again. A search here will reveal information on those issues.

[dboyte]

That's why I am trying to figure it out. I know is does not all add up but it happened anyway. The only thing I can think of is when I stop - which I did as soon as it engaged, the pressures would equalize and the system would say oh what - you souldn't be engaged. As far as other issues, I already have a few. fuel gauge, bed alignment, windows, trim, truck lean, need I go on. This truck seems to have about every issue I have seen on boards. Thanks for the feedback and let me know if you think of something else.

The truck must have been built after a holiday or payday. Need to check the actual date.

[HenryJ]

Really sounds like you got the friday before a long weekend truck

I really can't say what happened from here, but obviously something happened, and maybe it was a combination of bad circumstances that lead to this failure. Bad "mojo" or luck may have played a part too.

We will keep an "ear out" for similar problems, but you may be the only lucky one to experience that specific problem.

I am sorry that your experience was not a good one. I'm sure that you will be seeking another brand, but remember that the vehicle may only be as good as the dealer you will have to work with. Build a good relationship with them and you will both be much happier.

Best of luck , and if there is any assistance that we can offer feel free to pick our brains. The pick'n may be slim sometimes though

[dboyte]

Well, I appreciate the help. I may have to go with another brand at this point even though I have been a loyal GM owner for years. As far as having a good relationship, I had one before this. I worked there several years ago in the detail shop until college and my brother was the new/used car service manager at the repairing dealer. In addition, My wife's work desk is about 15 feet from the wife of the mechanic that repaired the truck. Dealership was not the problem, It is the butt munch AVM for this region. I think one of my problems was the fact that it took so long for the dealership to find the problem. It started 6 monthes before the TSB come out. Since the vacuum system is not designed to be chemical resistant, who knows what sort of other problems this truck will have.

[HenryJ]

... Since the vacuum system is not designed to be chemical resistant, who knows what sort of other problems this truck will have.

That is true. The vacuum hoses only last about 20 years in the best environment. Usually they dry rot though. Who knows the DextronIII might keep them pliable and prevent the drying that naturally occurs? Yours might end up outlasting all of them

I don't know what the best solution would be, but perhaps Jim was on the right track with installing filters to prevent the spread of contamination and capture some of it.
I know that there are small paper element fuel filters that would trap some of the fluid. I have seen vacuum line filters as well, although they are small and designed to trap particulate matter.

I am really thinking about adding one of the small 1/4" line clear plastic fuel filters in the vacuum line at the transfercase. That way I can visually inspect it at regular service intervals.

[F9K9]

Have you filed with the BBB/GM (maybe it is GM/BBB) online yet as mentioned in the owner's manual? Just have all your info handy such as you VIN, Dealer's name , address, ph # and dates. I so not believe you need an attorney that will get 33 to 50 percent of any award you may recieve.

Will ask this once more? Have you addressed this alternative yet? I am having issues as well and this CC may be my last GM buy.

[top_sgt]

having worked at a GM dealer..... the region AVM does have a "boss"!! i saw the service manager at the dealership go above the zone reps head many-a- time for the customer!!!.........something to think about!!

[dboyte]

Tried that, I was told that I was not allowed to talk to them directly by order of the AVM. even tried to get his name and number from customer care but they would not provide it either. They probably could have saved themselves a lot of heart ache/time and money if they would have talked to me. Judges have a way of making them talk if you know what I mean.

[F9K9]

Tried that, I was told that I was not allowed to talk to them directly by order of the AVM. even tried to get his name and number from customer care but they would not provide it either. They probably could have saved themselves a lot of heart ache/time and money if they would have talked to me. Judges have a way of making them talk if you know what I mean.

Customer service in detroit advised me that I was to go there next and supplied the info.

example

another eample

[dboyte]

Sorry
I missed the question about BBB. The answer is yes I have been thru customer care and BBB arbitration. It took over 6 months. So much for 40 day rule set by feds. This has been going on for almost 2 yrs. now. Lawyer just informed me that case is on docket for April 4. Finally, this may be over. I am tired of moving this truck just to mow under it.

I was looking thru the manual a little bit more and it dawned on me why Henryj and anybody else that switched into 4WD at a decent speed did not experience what I did. Based on what I am reading, front diff. does not engage under normal conditions until the transfer case is fully engaged and spun up to speed. Since, my diff. engaged without the transfer case being active, and the fact that the gears actually did hook up. It would be like push starting a stick shift. I sure most everybody on here knows what a jolt that is when you pop the clutch to turn the engine.

Am I right or wrong.

[HenryJ]

...I was looking thru the manual a little bit more and it dawned on me why Henryj and anybody else that switched into 4WD at a decent speed did not experience what I did. Based on what I am reading, front diff. does not engage under normal conditions until the transfer case is fully engaged and spun up to speed. Since, my diff. engaged without the transfer case being active, and the fact that the gears actually did hook up. It would be like push starting a stick shift. I sure most everybody on here knows what a jolt that is when you pop the clutch to turn the engine.

Nice try , but still doesn't work.

When shifting to low range you must be stopped. The axle is then engaged from a stop. Granted you must move a little unless it is perfectly aligned, but usually it doesn't take much.

The dumping the clutch "jerk" takes place when one side is static and one has movement. The jerk is the forces equalizing rapidly.

Here both are very close to the same speed , while stopped or moving. Any differences in speed would be minimal, therefore no "jerk".

There is no reason to engage the front axle with out engaging the transfercase. That is why the front axle vacuum switch is activated there. When the T.case is shifted into gear the switch is activated and the circuit opened to send vacuum to the front axle actuator. It really is pretty simple and has been used on them for over 20 years.

[dboyte]

Didn't say anything about 4wd low. Transfer case clutches were not engaged, so how would the connecting componants between the clutches and the front diff. be at full speed and I was going into a sharp curve of an offramp when the front diff. engaged. hence the tires were moving at diff. speeds. I do understand that under normal conditions the tranfer case activates the Vacuum actuator for the cable engagement. This is not what was happening on my truck the diff. was engaging without the transfer case switching or me trying to switch it. it was doing to on is own. both the mechanic and service manager verified this on the repair order.
I am trying to figure exactly why it did it. FYI, don't know if you read the other thread where I started posting about it starting with the hvac/transfer case vacuum rupture issue.

[HenryJ]

I did read and do understand. I am only trying to make you understand the function.

The front axle can engage at any speed from zero to highway speeds. That is all I was trying to get across.

You did say that you were making a turn at higher speed. The difference in wheel speed , side to side at that speed is minimal at best.
Now if one wheel is spinning or rolling , the other is locked or sliding and then you try to engage there will be a little grinding sound and a clunk as it engages.
I have done a similar thing while engaging under full throttle in the gravel. Is this good on the components, no. Did it incur any damage, I don't think so.

I don't doubt your problem. Wish you the best in it's resolution.

I am starting to feel like we are beating a dead horse here.

[dboyte]

I agree, hopefully the horse will be at the glue factory soon.
and yes I corner a lot faster than I should but I was taught to drive by a cop and a street racer (My two brothers)

Thanks for your helpful info.